Squashed 'third_party/git/' content from commit cb71568594

git-subtree-dir: third_party/git
git-subtree-split: cb715685942260375e1eb8153b0768a376e4ece7

1 files changed, 4346 insertions, 0 deletions

diff --git a/contrib/hooks/multimail/git_multimail.py b/contrib/hooks/multimail/git_multimail.py
new file mode 100755
index 000000000000..8823399e7522
--- /dev/null
+++ b/contrib/hooks/multimail/git_multimail.py
@@ -0,0 +1,4346 @@
+#! /usr/bin/env python
+
+__version__ = '1.5.0'
+
+# Copyright (c) 2015-2016 Matthieu Moy and others
+# Copyright (c) 2012-2014 Michael Haggerty and others
+# Derived from contrib/hooks/post-receive-email, which is
+# Copyright (c) 2007 Andy Parkins
+# and also includes contributions by other authors.
+#
+# This file is part of git-multimail.
+#
+# git-multimail is free software: you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version
+# 2 as published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see
+# <http://www.gnu.org/licenses/>.
+
+"""Generate notification emails for pushes to a git repository.
+
+This hook sends emails describing changes introduced by pushes to a
+git repository.  For each reference that was changed, it emits one
+ReferenceChange email summarizing how the reference was changed,
+followed by one Revision email for each new commit that was introduced
+by the reference change.
+
+Each commit is announced in exactly one Revision email.  If the same
+commit is merged into another branch in the same or a later push, then
+the ReferenceChange email will list the commit's SHA1 and its one-line
+summary, but no new Revision email will be generated.
+
+This script is designed to be used as a "post-receive" hook in a git
+repository (see githooks(5)).  It can also be used as an "update"
+script, but this usage is not completely reliable and is deprecated.
+
+To help with debugging, this script accepts a --stdout option, which
+causes the emails to be written to standard output rather than sent
+using sendmail.
+
+See the accompanying README file for the complete documentation.
+
+"""
+
+import sys
+import os
+import re
+import bisect
+import socket
+import subprocess
+import shlex
+import optparse
+import logging
+import smtplib
+try:
+    import ssl
+except ImportError:
+    # Python < 2.6 do not have ssl, but that's OK if we don't use it.
+    pass
+import time
+
+import uuid
+import base64
+
+PYTHON3 = sys.version_info >= (3, 0)
+
+if sys.version_info <= (2, 5):
+    def all(iterable):
+        for element in iterable:
+            if not element:
+                return False
+        return True
+
+
+def is_ascii(s):
+    return all(ord(c) < 128 and ord(c) > 0 for c in s)
+
+
+if PYTHON3:
+    def is_string(s):
+        return isinstance(s, str)
+
+    def str_to_bytes(s):
+        return s.encode(ENCODING)
+
+    def bytes_to_str(s, errors='strict'):
+        return s.decode(ENCODING, errors)
+
+    unicode = str
+
+    def write_str(f, msg):
+        # Try outputing with the default encoding. If it fails,
+        # try UTF-8.
+        try:
+            f.buffer.write(msg.encode(sys.getdefaultencoding()))
+        except UnicodeEncodeError:
+            f.buffer.write(msg.encode(ENCODING))
+
+    def read_line(f):
+        # Try reading with the default encoding. If it fails,
+        # try UTF-8.
+        out = f.buffer.readline()
+        try:
+            return out.decode(sys.getdefaultencoding())
+        except UnicodeEncodeError:
+            return out.decode(ENCODING)
+
+    import html
+
+    def html_escape(s):
+        return html.escape(s)
+
+else:
+    def is_string(s):
+        try:
+            return isinstance(s, basestring)
+        except NameError:  # Silence Pyflakes warning
+            raise
+
+    def str_to_bytes(s):
+        return s
+
+    def bytes_to_str(s, errors='strict'):
+        return s
+
+    def write_str(f, msg):
+        f.write(msg)
+
+    def read_line(f):
+        return f.readline()
+
+    def next(it):
+        return it.next()
+
+    import cgi
+
+    def html_escape(s):
+        return cgi.escape(s, True)
+
+try:
+    from email.charset import Charset
+    from email.utils import make_msgid
+    from email.utils import getaddresses
+    from email.utils import formataddr
+    from email.utils import formatdate
+    from email.header import Header
+except ImportError:
+    # Prior to Python 2.5, the email module used different names:
+    from email.Charset import Charset
+    from email.Utils import make_msgid
+    from email.Utils import getaddresses
+    from email.Utils import formataddr
+    from email.Utils import formatdate
+    from email.Header import Header
+
+
+DEBUG = False
+
+ZEROS = '0' * 40
+LOGBEGIN = '- Log -----------------------------------------------------------------\n'
+LOGEND = '-----------------------------------------------------------------------\n'
+
+ADDR_HEADERS = set(['from', 'to', 'cc', 'bcc', 'reply-to', 'sender'])
+
+# It is assumed in many places that the encoding is uniformly UTF-8,
+# so changing these constants is unsupported.  But define them here
+# anyway, to make it easier to find (at least most of) the places
+# where the encoding is important.
+(ENCODING, CHARSET) = ('UTF-8', 'utf-8')
+
+
+REF_CREATED_SUBJECT_TEMPLATE = (
+    '%(emailprefix)s%(refname_type)s %(short_refname)s created'
+    ' (now %(newrev_short)s)'
+    )
+REF_UPDATED_SUBJECT_TEMPLATE = (
+    '%(emailprefix)s%(refname_type)s %(short_refname)s updated'
+    ' (%(oldrev_short)s -> %(newrev_short)s)'
+    )
+REF_DELETED_SUBJECT_TEMPLATE = (
+    '%(emailprefix)s%(refname_type)s %(short_refname)s deleted'
+    ' (was %(oldrev_short)s)'
+    )
+
+COMBINED_REFCHANGE_REVISION_SUBJECT_TEMPLATE = (
+    '%(emailprefix)s%(refname_type)s %(short_refname)s updated: %(oneline)s'
+    )
+
+REFCHANGE_HEADER_TEMPLATE = """\
+Date: %(send_date)s
+To: %(recipients)s
+Subject: %(subject)s
+MIME-Version: 1.0
+Content-Type: text/%(contenttype)s; charset=%(charset)s
+Content-Transfer-Encoding: 8bit
+Message-ID: %(msgid)s
+From: %(fromaddr)s
+Reply-To: %(reply_to)s
+Thread-Index: %(thread_index)s
+X-Git-Host: %(fqdn)s
+X-Git-Repo: %(repo_shortname)s
+X-Git-Refname: %(refname)s
+X-Git-Reftype: %(refname_type)s
+X-Git-Oldrev: %(oldrev)s
+X-Git-Newrev: %(newrev)s
+X-Git-NotificationType: ref_changed
+X-Git-Multimail-Version: %(multimail_version)s
+Auto-Submitted: auto-generated
+"""
+
+REFCHANGE_INTRO_TEMPLATE = """\
+This is an automated email from the git hooks/post-receive script.
+
+%(pusher)s pushed a change to %(refname_type)s %(short_refname)s
+in repository %(repo_shortname)s.
+
+"""
+
+
+FOOTER_TEMPLATE = """\
+
+-- \n\
+To stop receiving notification emails like this one, please contact
+%(administrator)s.
+"""
+
+
+REWIND_ONLY_TEMPLATE = """\
+This update removed existing revisions from the reference, leaving the
+reference pointing at a previous point in the repository history.
+
+ * -- * -- N   %(refname)s (%(newrev_short)s)
+            \\
+             O -- O -- O   (%(oldrev_short)s)
+
+Any revisions marked "omit" are not gone; other references still
+refer to them.  Any revisions marked "discard" are gone forever.
+"""
+
+
+NON_FF_TEMPLATE = """\
+This update added new revisions after undoing existing revisions.
+That is to say, some revisions that were in the old version of the
+%(refname_type)s are not in the new version.  This situation occurs
+when a user --force pushes a change and generates a repository
+containing something like this:
+
+ * -- * -- B -- O -- O -- O   (%(oldrev_short)s)
+            \\
+             N -- N -- N   %(refname)s (%(newrev_short)s)
+
+You should already have received notification emails for all of the O
+revisions, and so the following emails describe only the N revisions
+from the common base, B.
+
+Any revisions marked "omit" are not gone; other references still
+refer to them.  Any revisions marked "discard" are gone forever.
+"""
+
+
+NO_NEW_REVISIONS_TEMPLATE = """\
+No new revisions were added by this update.
+"""
+
+
+DISCARDED_REVISIONS_TEMPLATE = """\
+This change permanently discards the following revisions:
+"""
+
+
+NO_DISCARDED_REVISIONS_TEMPLATE = """\
+The revisions that were on this %(refname_type)s are still contained in
+other references; therefore, this change does not discard any commits
+from the repository.
+"""
+
+
+NEW_REVISIONS_TEMPLATE = """\
+The %(tot)s revisions listed above as "new" are entirely new to this
+repository and will be described in separate emails.  The revisions
+listed as "add" were already present in the repository and have only
+been added to this reference.
+
+"""
+
+
+TAG_CREATED_TEMPLATE = """\
+      at %(newrev_short)-8s (%(newrev_type)s)
+"""
+
+
+TAG_UPDATED_TEMPLATE = """\
+*** WARNING: tag %(short_refname)s was modified! ***
+
+    from %(oldrev_short)-8s (%(oldrev_type)s)
+      to %(newrev_short)-8s (%(newrev_type)s)
+"""
+
+
+TAG_DELETED_TEMPLATE = """\
+*** WARNING: tag %(short_refname)s was deleted! ***
+
+"""
+
+
+# The template used in summary tables.  It looks best if this uses the
+# same alignment as TAG_CREATED_TEMPLATE and TAG_UPDATED_TEMPLATE.
+BRIEF_SUMMARY_TEMPLATE = """\
+%(action)8s %(rev_short)-8s %(text)s
+"""
+
+
+NON_COMMIT_UPDATE_TEMPLATE = """\
+This is an unusual reference change because the reference did not
+refer to a commit either before or after the change.  We do not know
+how to provide full information about this reference change.
+"""
+
+
+REVISION_HEADER_TEMPLATE = """\
+Date: %(send_date)s
+To: %(recipients)s
+Cc: %(cc_recipients)s
+Subject: %(emailprefix)s%(num)02d/%(tot)02d: %(oneline)s
+MIME-Version: 1.0
+Content-Type: text/%(contenttype)s; charset=%(charset)s
+Content-Transfer-Encoding: 8bit
+From: %(fromaddr)s
+Reply-To: %(reply_to)s
+In-Reply-To: %(reply_to_msgid)s
+References: %(reply_to_msgid)s
+Thread-Index: %(thread_index)s
+X-Git-Host: %(fqdn)s
+X-Git-Repo: %(repo_shortname)s
+X-Git-Refname: %(refname)s
+X-Git-Reftype: %(refname_type)s
+X-Git-Rev: %(rev)s
+X-Git-NotificationType: diff
+X-Git-Multimail-Version: %(multimail_version)s
+Auto-Submitted: auto-generated
+"""
+
+REVISION_INTRO_TEMPLATE = """\
+This is an automated email from the git hooks/post-receive script.
+
+%(pusher)s pushed a commit to %(refname_type)s %(short_refname)s
+in repository %(repo_shortname)s.
+
+"""
+
+LINK_TEXT_TEMPLATE = """\
+View the commit online:
+%(browse_url)s
+
+"""
+
+LINK_HTML_TEMPLATE = """\
+<p><a href="%(browse_url)s">View the commit online</a>.</p>
+"""
+
+
+REVISION_FOOTER_TEMPLATE = FOOTER_TEMPLATE
+
+
+# Combined, meaning refchange+revision email (for single-commit additions)
+COMBINED_HEADER_TEMPLATE = """\
+Date: %(send_date)s
+To: %(recipients)s
+Subject: %(subject)s
+MIME-Version: 1.0
+Content-Type: text/%(contenttype)s; charset=%(charset)s
+Content-Transfer-Encoding: 8bit
+Message-ID: %(msgid)s
+From: %(fromaddr)s
+Reply-To: %(reply_to)s
+X-Git-Host: %(fqdn)s
+X-Git-Repo: %(repo_shortname)s
+X-Git-Refname: %(refname)s
+X-Git-Reftype: %(refname_type)s
+X-Git-Oldrev: %(oldrev)s
+X-Git-Newrev: %(newrev)s
+X-Git-Rev: %(rev)s
+X-Git-NotificationType: ref_changed_plus_diff
+X-Git-Multimail-Version: %(multimail_version)s
+Auto-Submitted: auto-generated
+"""
+
+COMBINED_INTRO_TEMPLATE = """\
+This is an automated email from the git hooks/post-receive script.
+
+%(pusher)s pushed a commit to %(refname_type)s %(short_refname)s
+in repository %(repo_shortname)s.
+
+"""
+
+COMBINED_FOOTER_TEMPLATE = FOOTER_TEMPLATE
+
+
+class CommandError(Exception):
+    def __init__(self, cmd, retcode):
+        self.cmd = cmd
+        self.retcode = retcode
+        Exception.__init__(
+            self,
+            'Command "%s" failed with retcode %s' % (' '.join(cmd), retcode,)
+            )
+
+
+class ConfigurationException(Exception):
+    pass
+
+
+# The "git" program (this could be changed to include a full path):
+GIT_EXECUTABLE = 'git'
+
+
+# How "git" should be invoked (including global arguments), as a list
+# of words.  This variable is usually initialized automatically by
+# read_git_output() via choose_git_command(), but if a value is set
+# here then it will be used unconditionally.
+GIT_CMD = None
+
+
+def choose_git_command():
+    """Decide how to invoke git, and record the choice in GIT_CMD."""
+
+    global GIT_CMD
+
+    if GIT_CMD is None:
+        try:
+            # Check to see whether the "-c" option is accepted (it was
+            # only added in Git 1.7.2).  We don't actually use the
+            # output of "git --version", though if we needed more
+            # specific version information this would be the place to
+            # do it.
+            cmd = [GIT_EXECUTABLE, '-c', 'foo.bar=baz', '--version']
+            read_output(cmd)
+            GIT_CMD = [GIT_EXECUTABLE, '-c', 'i18n.logoutputencoding=%s' % (ENCODING,)]
+        except CommandError:
+            GIT_CMD = [GIT_EXECUTABLE]
+
+
+def read_git_output(args, input=None, keepends=False, **kw):
+    """Read the output of a Git command."""
+
+    if GIT_CMD is None:
+        choose_git_command()
+
+    return read_output(GIT_CMD + args, input=input, keepends=keepends, **kw)
+
+
+def read_output(cmd, input=None, keepends=False, **kw):
+    if input:
+        stdin = subprocess.PIPE
+        input = str_to_bytes(input)
+    else:
+        stdin = None
+    errors = 'strict'
+    if 'errors' in kw:
+        errors = kw['errors']
+        del kw['errors']
+    p = subprocess.Popen(
+        tuple(str_to_bytes(w) for w in cmd),
+        stdin=stdin, stdout=subprocess.PIPE, stderr=subprocess.PIPE, **kw
+        )
+    (out, err) = p.communicate(input)
+    out = bytes_to_str(out, errors=errors)
+    retcode = p.wait()
+    if retcode:
+        raise CommandError(cmd, retcode)
+    if not keepends:
+        out = out.rstrip('\n\r')
+    return out
+
+
+def read_git_lines(args, keepends=False, **kw):
+    """Return the lines output by Git command.
+
+    Return as single lines, with newlines stripped off."""
+
+    return read_git_output(args, keepends=True, **kw).splitlines(keepends)
+
+
+def git_rev_list_ish(cmd, spec, args=None, **kw):
+    """Common functionality for invoking a 'git rev-list'-like command.
+
+    Parameters:
+      * cmd is the Git command to run, e.g., 'rev-list' or 'log'.
+      * spec is a list of revision arguments to pass to the named
+        command.  If None, this function returns an empty list.
+      * args is a list of extra arguments passed to the named command.
+      * All other keyword arguments (if any) are passed to the
+        underlying read_git_lines() function.
+
+    Return the output of the Git command in the form of a list, one
+    entry per output line.
+    """
+    if spec is None:
+        return []
+    if args is None:
+        args = []
+    args = [cmd, '--stdin'] + args
+    spec_stdin = ''.join(s + '\n' for s in spec)
+    return read_git_lines(args, input=spec_stdin, **kw)
+
+
+def git_rev_list(spec, **kw):
+    """Run 'git rev-list' with the given list of revision arguments.
+
+    See git_rev_list_ish() for parameter and return value
+    documentation.
+    """
+    return git_rev_list_ish('rev-list', spec, **kw)
+
+
+def git_log(spec, **kw):
+    """Run 'git log' with the given list of revision arguments.
+
+    See git_rev_list_ish() for parameter and return value
+    documentation.
+    """
+    return git_rev_list_ish('log', spec, **kw)
+
+
+def header_encode(text, header_name=None):
+    """Encode and line-wrap the value of an email header field."""
+
+    # Convert to unicode, if required.
+    if not isinstance(text, unicode):
+        text = unicode(text, 'utf-8')
+
+    if is_ascii(text):
+        charset = 'ascii'
+    else:
+        charset = 'utf-8'
+
+    return Header(text, header_name=header_name, charset=Charset(charset)).encode()
+
+
+def addr_header_encode(text, header_name=None):
+    """Encode and line-wrap the value of an email header field containing
+    email addresses."""
+
+    # Convert to unicode, if required.
+    if not isinstance(text, unicode):
+        text = unicode(text, 'utf-8')
+
+    text = ', '.join(
+        formataddr((header_encode(name), emailaddr))
+        for name, emailaddr in getaddresses([text])
+        )
+
+    if is_ascii(text):
+        charset = 'ascii'
+    else:
+        charset = 'utf-8'
+
+    return Header(text, header_name=header_name, charset=Charset(charset)).encode()
+
+
+class Config(object):
+    def __init__(self, section, git_config=None):
+        """Represent a section of the git configuration.
+
+        If git_config is specified, it is passed to "git config" in
+        the GIT_CONFIG environment variable, meaning that "git config"
+        will read the specified path rather than the Git default
+        config paths."""
+
+        self.section = section
+        if git_config:
+            self.env = os.environ.copy()
+            self.env['GIT_CONFIG'] = git_config
+        else:
+            self.env = None
+
+    @staticmethod
+    def _split(s):
+        """Split NUL-terminated values."""
+
+        words = s.split('\0')
+        assert words[-1] == ''
+        return words[:-1]
+
+    @staticmethod
+    def add_config_parameters(c):
+        """Add configuration parameters to Git.
+
+        c is either an str or a list of str, each element being of the
+        form 'var=val' or 'var', with the same syntax and meaning as
+        the argument of 'git -c var=val'.
+        """
+        if isinstance(c, str):
+            c = (c,)
+        parameters = os.environ.get('GIT_CONFIG_PARAMETERS', '')
+        if parameters:
+            parameters += ' '
+        # git expects GIT_CONFIG_PARAMETERS to be of the form
+        #    "'name1=value1' 'name2=value2' 'name3=value3'"
+        # including everything inside the double quotes (but not the double
+        # quotes themselves).  Spacing is critical.  Also, if a value contains
+        # a literal single quote that quote must be represented using the
+        # four character sequence: '\''
+        parameters += ' '.join("'" + x.replace("'", "'\\''") + "'" for x in c)
+        os.environ['GIT_CONFIG_PARAMETERS'] = parameters
+
+    def get(self, name, default=None):
+        try:
+            values = self._split(read_git_output(
+                ['config', '--get', '--null', '%s.%s' % (self.section, name)],
+                env=self.env, keepends=True,
+                ))
+            assert len(values) == 1
+            return values[0]
+        except CommandError:
+            return default
+
+    def get_bool(self, name, default=None):
+        try:
+            value = read_git_output(
+                ['config', '--get', '--bool', '%s.%s' % (self.section, name)],
+                env=self.env,
+                )
+        except CommandError:
+            return default
+        return value == 'true'
+
+    def get_all(self, name, default=None):
+        """Read a (possibly multivalued) setting from the configuration.
+
+        Return the result as a list of values, or default if the name
+        is unset."""
+
+        try:
+            return self._split(read_git_output(
+                ['config', '--get-all', '--null', '%s.%s' % (self.section, name)],
+                env=self.env, keepends=True,
+                ))
+        except CommandError:
+            t, e, traceback = sys.exc_info()
+            if e.retcode == 1:
+                # "the section or key is invalid"; i.e., there is no
+                # value for the specified key.
+                return default
+            else:
+                raise
+
+    def set(self, name, value):
+        read_git_output(
+            ['config', '%s.%s' % (self.section, name), value],
+            env=self.env,
+            )
+
+    def add(self, name, value):
+        read_git_output(
+            ['config', '--add', '%s.%s' % (self.section, name), value],
+            env=self.env,
+            )
+
+    def __contains__(self, name):
+        return self.get_all(name, default=None) is not None
+
+    # We don't use this method anymore internally, but keep it here in
+    # case somebody is calling it from their own code:
+    def has_key(self, name):
+        return name in self
+
+    def unset_all(self, name):
+        try:
+            read_git_output(
+                ['config', '--unset-all', '%s.%s' % (self.section, name)],
+                env=self.env,
+                )
+        except CommandError:
+            t, e, traceback = sys.exc_info()
+            if e.retcode == 5:
+                # The name doesn't exist, which is what we wanted anyway...
+                pass
+            else:
+                raise
+
+    def set_recipients(self, name, value):
+        self.unset_all(name)
+        for pair in getaddresses([value]):
+            self.add(name, formataddr(pair))
+
+
+def generate_summaries(*log_args):
+    """Generate a brief summary for each revision requested.
+
+    log_args are strings that will be passed directly to "git log" as
+    revision selectors.  Iterate over (sha1_short, subject) for each
+    commit specified by log_args (subject is the first line of the
+    commit message as a string without EOLs)."""
+
+    cmd = [
+        'log', '--abbrev', '--format=%h %s',
+        ] + list(log_args) + ['--']
+    for line in read_git_lines(cmd):
+        yield tuple(line.split(' ', 1))
+
+
+def limit_lines(lines, max_lines):
+    for (index, line) in enumerate(lines):
+        if index < max_lines:
+            yield line
+
+    if index >= max_lines:
+        yield '... %d lines suppressed ...\n' % (index + 1 - max_lines,)
+
+
+def limit_linelength(lines, max_linelength):
+    for line in lines:
+        # Don't forget that lines always include a trailing newline.
+        if len(line) > max_linelength + 1:
+            line = line[:max_linelength - 7] + ' [...]\n'
+        yield line
+
+
+class CommitSet(object):
+    """A (constant) set of object names.
+
+    The set should be initialized with full SHA1 object names.  The
+    __contains__() method returns True iff its argument is an
+    abbreviation of any the names in the set."""
+
+    def __init__(self, names):
+        self._names = sorted(names)
+
+    def __len__(self):
+        return len(self._names)
+
+    def __contains__(self, sha1_abbrev):
+        """Return True iff this set contains sha1_abbrev (which might be abbreviated)."""
+
+        i = bisect.bisect_left(self._names, sha1_abbrev)
+        return i < len(self) and self._names[i].startswith(sha1_abbrev)
+
+
+class GitObject(object):
+    def __init__(self, sha1, type=None):
+        if sha1 == ZEROS:
+            self.sha1 = self.type = self.commit_sha1 = None
+        else:
+            self.sha1 = sha1
+            self.type = type or read_git_output(['cat-file', '-t', self.sha1])
+
+            if self.type == 'commit':
+                self.commit_sha1 = self.sha1
+            elif self.type == 'tag':
+                try:
+                    self.commit_sha1 = read_git_output(
+                        ['rev-parse', '--verify', '%s^0' % (self.sha1,)]
+                        )
+                except CommandError:
+                    # Cannot deref tag to determine commit_sha1
+                    self.commit_sha1 = None
+            else:
+                self.commit_sha1 = None
+
+        self.short = read_git_output(['rev-parse', '--short', sha1])
+
+    def get_summary(self):
+        """Return (sha1_short, subject) for this commit."""
+
+        if not self.sha1:
+            raise ValueError('Empty commit has no summary')
+
+        return next(iter(generate_summaries('--no-walk', self.sha1)))
+
+    def __eq__(self, other):
+        return isinstance(other, GitObject) and self.sha1 == other.sha1
+
+    def __ne__(self, other):
+        return not self == other
+
+    def __hash__(self):
+        return hash(self.sha1)
+
+    def __nonzero__(self):
+        return bool(self.sha1)
+
+    def __bool__(self):
+        """Python 2 backward compatibility"""
+        return self.__nonzero__()
+
+    def __str__(self):
+        return self.sha1 or ZEROS
+
+
+class Change(object):
+    """A Change that has been made to the Git repository.
+
+    Abstract class from which both Revisions and ReferenceChanges are
+    derived.  A Change knows how to generate a notification email
+    describing itself."""
+
+    def __init__(self, environment):
+        self.environment = environment
+        self._values = None
+        self._contains_html_diff = False
+
+    def _contains_diff(self):
+        # We do contain a diff, should it be rendered in HTML?
+        if self.environment.commit_email_format == "html":
+            self._contains_html_diff = True
+
+    def _compute_values(self):
+        """Return a dictionary {keyword: expansion} for this Change.
+
+        Derived classes overload this method to add more entries to
+        the return value.  This method is used internally by
+        get_values().  The return value should always be a new
+        dictionary."""
+
+        values = self.environment.get_values()
+        fromaddr = self.environment.get_fromaddr(change=self)
+        if fromaddr is not None:
+            values['fromaddr'] = fromaddr
+        values['multimail_version'] = get_version()
+        return values
+
+    # Aliases usable in template strings. Tuple of pairs (destination,
+    # source).
+    VALUES_ALIAS = (
+        ("id", "newrev"),
+        )
+
+    def get_values(self, **extra_values):
+        """Return a dictionary {keyword: expansion} for this Change.
+
+        Return a dictionary mapping keywords to the values that they
+        should be expanded to for this Change (used when interpolating
+        template strings).  If any keyword arguments are supplied, add
+        those to the return value as well.  The return value is always
+        a new dictionary."""
+
+        if self._values is None:
+            self._values = self._compute_values()
+
+        values = self._values.copy()
+        if extra_values:
+            values.update(extra_values)
+
+        for alias, val in self.VALUES_ALIAS:
+            values[alias] = values[val]
+        return values
+
+    def expand(self, template, **extra_values):
+        """Expand template.
+
+        Expand the template (which should be a string) using string
+        interpolation of the values for this Change.  If any keyword
+        arguments are provided, also include those in the keywords
+        available for interpolation."""
+
+        return template % self.get_values(**extra_values)
+
+    def expand_lines(self, template, html_escape_val=False, **extra_values):
+        """Break template into lines and expand each line."""
+
+        values = self.get_values(**extra_values)
+        if html_escape_val:
+            for k in values:
+                if is_string(values[k]):
+                    values[k] = html_escape(values[k])
+        for line in template.splitlines(True):
+            yield line % values
+
+    def expand_header_lines(self, template, **extra_values):
+        """Break template into lines and expand each line as an RFC 2822 header.
+
+        Encode values and split up lines that are too long.  Silently
+        skip lines that contain references to unknown variables."""
+
+        values = self.get_values(**extra_values)
+        if self._contains_html_diff:
+            self._content_type = 'html'
+        else:
+            self._content_type = 'plain'
+        values['contenttype'] = self._content_type
+
+        for line in template.splitlines():
+            (name, value) = line.split(': ', 1)
+
+            try:
+                value = value % values
+            except KeyError:
+                t, e, traceback = sys.exc_info()
+                if DEBUG:
+                    self.environment.log_warning(
+                        'Warning: unknown variable %r in the following line; line skipped:\n'
+                        '    %s\n'
+                        % (e.args[0], line,)
+                        )
+            else:
+                if name.lower() in ADDR_HEADERS:
+                    value = addr_header_encode(value, name)
+                else:
+                    value = header_encode(value, name)
+                for splitline in ('%s: %s\n' % (name, value)).splitlines(True):
+                    yield splitline
+
+    def generate_email_header(self):
+        """Generate the RFC 2822 email headers for this Change, a line at a time.
+
+        The output should not include the trailing blank line."""
+
+        raise NotImplementedError()
+
+    def generate_browse_link(self, base_url):
+        """Generate a link to an online repository browser."""
+        return iter(())
+
+    def generate_email_intro(self, html_escape_val=False):
+        """Generate the email intro for this Change, a line at a time.
+
+        The output will be used as the standard boilerplate at the top
+        of the email body."""
+
+        raise NotImplementedError()
+
+    def generate_email_body(self, push):
+        """Generate the main part of the email body, a line at a time.
+
+        The text in the body might be truncated after a specified
+        number of lines (see multimailhook.emailmaxlines)."""
+
+        raise NotImplementedError()
+
+    def generate_email_footer(self, html_escape_val):
+        """Generate the footer of the email, a line at a time.
+
+        The footer is always included, irrespective of
+        multimailhook.emailmaxlines."""
+
+        raise NotImplementedError()
+
+    def _wrap_for_html(self, lines):
+        """Wrap the lines in HTML <pre> tag when using HTML format.
+
+        Escape special HTML characters and add <pre> and </pre> tags around
+        the given lines if we should be generating HTML as indicated by
+        self._contains_html_diff being set to true.
+        """
+        if self._contains_html_diff:
+            yield "<pre style='margin:0'>\n"
+
+            for line in lines:
+                yield html_escape(line)
+
+            yield '</pre>\n'
+        else:
+            for line in lines:
+                yield line
+
+    def generate_email(self, push, body_filter=None, extra_header_values={}):
+        """Generate an email describing this change.
+
+        Iterate over the lines (including the header lines) of an
+        email describing this change.  If body_filter is not None,
+        then use it to filter the lines that are intended for the
+        email body.
+
+        The extra_header_values field is received as a dict and not as
+        **kwargs, to allow passing other keyword arguments in the
+        future (e.g. passing extra values to generate_email_intro()"""
+
+        for line in self.generate_email_header(**extra_header_values):
+            yield line
+        yield '\n'
+        html_escape_val = (self.environment.html_in_intro and
+                           self._contains_html_diff)
+        intro = self.generate_email_intro(html_escape_val)
+        if not self.environment.html_in_intro:
+            intro = self._wrap_for_html(intro)
+        for line in intro:
+            yield line
+
+        if self.environment.commitBrowseURL:
+            for line in self.generate_browse_link(self.environment.commitBrowseURL):
+                yield line
+
+        body = self.generate_email_body(push)
+        if body_filter is not None:
+            body = body_filter(body)
+
+        diff_started = False
+        if self._contains_html_diff:
+            # "white-space: pre" is the default, but we need to
+            # specify it again in case the message is viewed in a
+            # webmail which wraps it in an element setting white-space
+            # to something else (Zimbra does this and sets
+            # white-space: pre-line).
+            yield '<pre style="white-space: pre; background: #F8F8F8">'
+        for line in body:
+            if self._contains_html_diff:
+                # This is very, very naive. It would be much better to really
+                # parse the diff, i.e. look at how many lines do we have in
+                # the hunk headers instead of blindly highlighting everything
+                # that looks like it might be part of a diff.
+                bgcolor = ''
+                fgcolor = ''
+                if line.startswith('--- a/'):
+                    diff_started = True
+                    bgcolor = 'e0e0ff'
+                elif line.startswith('diff ') or line.startswith('index '):
+                    diff_started = True
+                    fgcolor = '808080'
+                elif diff_started:
+                    if line.startswith('+++ '):
+                        bgcolor = 'e0e0ff'
+                    elif line.startswith('@@'):
+                        bgcolor = 'e0e0e0'
+                    elif line.startswith('+'):
+                        bgcolor = 'e0ffe0'
+                    elif line.startswith('-'):
+                        bgcolor = 'ffe0e0'
+                elif line.startswith('commit '):
+                    fgcolor = '808000'
+                elif line.startswith('    '):
+                    fgcolor = '404040'
+
+                # Chop the trailing LF, we don't want it inside <pre>.
+                line = html_escape(line[:-1])
+
+                if bgcolor or fgcolor:
+                    style = 'display:block; white-space:pre;'
+                    if bgcolor:
+                        style += 'background:#' + bgcolor + ';'
+                    if fgcolor:
+                        style += 'color:#' + fgcolor + ';'
+                    # Use a <span style='display:block> to color the
+                    # whole line. The newline must be inside the span
+                    # to display properly both in Firefox and in
+                    # text-based browser.
+                    line = "<span style='%s'>%s\n</span>" % (style, line)
+                else:
+                    line = line + '\n'
+
+            yield line
+        if self._contains_html_diff:
+            yield '</pre>'
+        html_escape_val = (self.environment.html_in_footer and
+                           self._contains_html_diff)
+        footer = self.generate_email_footer(html_escape_val)
+        if not self.environment.html_in_footer:
+            footer = self._wrap_for_html(footer)
+        for line in footer:
+            yield line
+
+    def get_specific_fromaddr(self):
+        """For kinds of Changes which specify it, return the kind-specific
+        From address to use."""
+        return None
+
+
+class Revision(Change):
+    """A Change consisting of a single git commit."""
+
+    CC_RE = re.compile(r'^\s*C[Cc]:\s*(?P<to>[^#]+@[^\s#]*)\s*(#.*)?$')
+
+    def __init__(self, reference_change, rev, num, tot):
+        Change.__init__(self, reference_change.environment)
+        self.reference_change = reference_change
+        self.rev = rev
+        self.change_type = self.reference_change.change_type
+        self.refname = self.reference_change.refname
+        self.num = num
+        self.tot = tot
+        self.author = read_git_output(['log', '--no-walk', '--format=%aN <%aE>', self.rev.sha1])
+        self.recipients = self.environment.get_revision_recipients(self)
+
+        # -s is short for --no-patch, but -s works on older git's (e.g. 1.7)
+        self.parents = read_git_lines(['show', '-s', '--format=%P',
+                                      self.rev.sha1])[0].split()
+
+        self.cc_recipients = ''
+        if self.environment.get_scancommitforcc():
+            self.cc_recipients = ', '.join(to.strip() for to in self._cc_recipients())
+            if self.cc_recipients:
+                self.environment.log_msg(
+                    'Add %s to CC for %s' % (self.cc_recipients, self.rev.sha1))
+
+    def _cc_recipients(self):
+        cc_recipients = []
+        message = read_git_output(['log', '--no-walk', '--format=%b', self.rev.sha1])
+        lines = message.strip().split('\n')
+        for line in lines:
+            m = re.match(self.CC_RE, line)
+            if m:
+                cc_recipients.append(m.group('to'))
+
+        return cc_recipients
+
+    def _compute_values(self):
+        values = Change._compute_values(self)
+
+        oneline = read_git_output(
+            ['log', '--format=%s', '--no-walk', self.rev.sha1]
+            )
+
+        max_subject_length = self.environment.get_max_subject_length()
+        if max_subject_length > 0 and len(oneline) > max_subject_length:
+            oneline = oneline[:max_subject_length - 6] + ' [...]'
+
+        values['rev'] = self.rev.sha1
+        values['parents'] = ' '.join(self.parents)
+        values['rev_short'] = self.rev.short
+        values['change_type'] = self.change_type
+        values['refname'] = self.refname
+        values['newrev'] = self.rev.sha1
+        values['short_refname'] = self.reference_change.short_refname
+        values['refname_type'] = self.reference_change.refname_type
+        values['reply_to_msgid'] = self.reference_change.msgid
+        values['thread_index'] = self.reference_change.thread_index
+        values['num'] = self.num
+        values['tot'] = self.tot
+        values['recipients'] = self.recipients
+        if self.cc_recipients:
+            values['cc_recipients'] = self.cc_recipients
+        values['oneline'] = oneline
+        values['author'] = self.author
+
+        reply_to = self.environment.get_reply_to_commit(self)
+        if reply_to:
+            values['reply_to'] = reply_to
+
+        return values
+
+    def generate_email_header(self, **extra_values):
+        for line in self.expand_header_lines(
+                REVISION_HEADER_TEMPLATE, **extra_values
+                ):
+            yield line
+
+    def generate_browse_link(self, base_url):
+        if '%(' not in base_url:
+            base_url += '%(id)s'
+        url = "".join(self.expand_lines(base_url))
+        if self._content_type == 'html':
+            for line in self.expand_lines(LINK_HTML_TEMPLATE,
+                                          html_escape_val=True,
+                                          browse_url=url):
+                yield line
+        elif self._content_type == 'plain':
+            for line in self.expand_lines(LINK_TEXT_TEMPLATE,
+                                          html_escape_val=False,
+                                          browse_url=url):
+                yield line
+        else:
+            raise NotImplementedError("Content-type %s unsupported. Please report it as a bug.")
+
+    def generate_email_intro(self, html_escape_val=False):
+        for line in self.expand_lines(REVISION_INTRO_TEMPLATE,
+                                      html_escape_val=html_escape_val):
+            yield line
+
+    def generate_email_body(self, push):
+        """Show this revision."""
+
+        for line in read_git_lines(
+                ['log'] + self.environment.commitlogopts + ['-1', self.rev.sha1],
+                keepends=True,
+                errors='replace'):
+            if line.startswith('Date:   ') and self.environment.date_substitute:
+                yield self.environment.date_substitute + line[len('Date:   '):]
+            else:
+                yield line
+
+    def generate_email_footer(self, html_escape_val):
+        return self.expand_lines(REVISION_FOOTER_TEMPLATE,
+                                 html_escape_val=html_escape_val)
+
+    def generate_email(self, push, body_filter=None, extra_header_values={}):
+        self._contains_diff()
+        return Change.generate_email(self, push, body_filter, extra_header_values)
+
+    def get_specific_fromaddr(self):
+        return self.environment.from_commit
+
+
+class ReferenceChange(Change):
+    """A Change to a Git reference.
+
+    An abstract class representing a create, update, or delete of a
+    Git reference.  Derived classes handle specific types of reference
+    (e.g., tags vs. branches).  These classes generate the main
+    reference change email summarizing the reference change and
+    whether it caused any any commits to be added or removed.
+
+    ReferenceChange objects are usually created using the static
+    create() method, which has the logic to decide which derived class
+    to instantiate."""
+
+    REF_RE = re.compile(r'^refs\/(?P<area>[^\/]+)\/(?P<shortname>.*)$')
+
+    @staticmethod
+    def create(environment, oldrev, newrev, refname):
+        """Return a ReferenceChange object representing the change.
+
+        Return an object that represents the type of change that is being
+        made. oldrev and newrev should be SHA1s or ZEROS."""
+
+        old = GitObject(oldrev)
+        new = GitObject(newrev)
+        rev = new or old
+
+        # The revision type tells us what type the commit is, combined with
+        # the location of the ref we can decide between
+        #  - working branch
+        #  - tracking branch
+        #  - unannotated tag
+        #  - annotated tag
+        m = ReferenceChange.REF_RE.match(refname)
+        if m:
+            area = m.group('area')
+            short_refname = m.group('shortname')
+        else:
+            area = ''
+            short_refname = refname
+
+        if rev.type == 'tag':
+            # Annotated tag:
+            klass = AnnotatedTagChange
+        elif rev.type == 'commit':
+            if area == 'tags':
+                # Non-annotated tag:
+                klass = NonAnnotatedTagChange
+            elif area == 'heads':
+                # Branch:
+                klass = BranchChange
+            elif area == 'remotes':
+                # Tracking branch:
+                environment.log_warning(
+                    '*** Push-update of tracking branch %r\n'
+                    '***  - incomplete email generated.'
+                    % (refname,)
+                    )
+                klass = OtherReferenceChange
+            else:
+                # Some other reference namespace:
+                environment.log_warning(
+                    '*** Push-update of strange reference %r\n'
+                    '***  - incomplete email generated.'
+                    % (refname,)
+                    )
+                klass = OtherReferenceChange
+        else:
+            # Anything else (is there anything else?)
+            environment.log_warning(
+                '*** Unknown type of update to %r (%s)\n'
+                '***  - incomplete email generated.'
+                % (refname, rev.type,)
+                )
+            klass = OtherReferenceChange
+
+        return klass(
+            environment,
+            refname=refname, short_refname=short_refname,
+            old=old, new=new, rev=rev,
+            )
+
+    @staticmethod
+    def make_thread_index():
+        """Return a string appropriate for the Thread-Index header,
+        needed by MS Outlook to get threading right.
+
+        The format is (base64-encoded):
+        - 1 byte must be 1
+        - 5 bytes encode a date (hardcoded here)
+        - 16 bytes for a globally unique identifier
+
+        FIXME: Unfortunately, even with the Thread-Index field, MS
+        Outlook doesn't seem to do the threading reliably (see
+        https://github.com/git-multimail/git-multimail/pull/194).
+        """
+        thread_index = b'\x01\x00\x00\x12\x34\x56' + uuid.uuid4().bytes
+        return base64.standard_b64encode(thread_index).decode('ascii')
+
+    def __init__(self, environment, refname, short_refname, old, new, rev):
+        Change.__init__(self, environment)
+        self.change_type = {
+            (False, True): 'create',
+            (True, True): 'update',
+            (True, False): 'delete',
+            }[bool(old), bool(new)]
+        self.refname = refname
+        self.short_refname = short_refname
+        self.old = old
+        self.new = new
+        self.rev = rev
+        self.msgid = make_msgid()
+        self.thread_index = self.make_thread_index()
+        self.diffopts = environment.diffopts
+        self.graphopts = environment.graphopts
+        self.logopts = environment.logopts
+        self.commitlogopts = environment.commitlogopts
+        self.showgraph = environment.refchange_showgraph
+        self.showlog = environment.refchange_showlog
+
+        self.header_template = REFCHANGE_HEADER_TEMPLATE
+        self.intro_template = REFCHANGE_INTRO_TEMPLATE
+        self.footer_template = FOOTER_TEMPLATE
+
+    def _compute_values(self):
+        values = Change._compute_values(self)
+
+        values['change_type'] = self.change_type
+        values['refname_type'] = self.refname_type
+        values['refname'] = self.refname
+        values['short_refname'] = self.short_refname
+        values['msgid'] = self.msgid
+        values['thread_index'] = self.thread_index
+        values['recipients'] = self.recipients
+        values['oldrev'] = str(self.old)
+        values['oldrev_short'] = self.old.short
+        values['newrev'] = str(self.new)
+        values['newrev_short'] = self.new.short
+
+        if self.old:
+            values['oldrev_type'] = self.old.type
+        if self.new:
+            values['newrev_type'] = self.new.type
+
+        reply_to = self.environment.get_reply_to_refchange(self)
+        if reply_to:
+            values['reply_to'] = reply_to
+
+        return values
+
+    def send_single_combined_email(self, known_added_sha1s):
+        """Determine if a combined refchange/revision email should be sent
+
+        If there is only a single new (non-merge) commit added by a
+        change, it is useful to combine the ReferenceChange and
+        Revision emails into one.  In such a case, return the single
+        revision; otherwise, return None.
+
+        This method is overridden in BranchChange."""
+
+        return None
+
+    def generate_combined_email(self, push, revision, body_filter=None, extra_header_values={}):
+        """Generate an email describing this change AND specified revision.
+
+        Iterate over the lines (including the header lines) of an
+        email describing this change.  If body_filter is not None,
+        then use it to filter the lines that are intended for the
+        email body.
+
+        The extra_header_values field is received as a dict and not as
+        **kwargs, to allow passing other keyword arguments in the
+        future (e.g. passing extra values to generate_email_intro()
+
+        This method is overridden in BranchChange."""
+
+        raise NotImplementedError
+
+    def get_subject(self):
+        template = {
+            'create': REF_CREATED_SUBJECT_TEMPLATE,
+            'update': REF_UPDATED_SUBJECT_TEMPLATE,
+            'delete': REF_DELETED_SUBJECT_TEMPLATE,
+            }[self.change_type]
+        return self.expand(template)
+
+    def generate_email_header(self, **extra_values):
+        if 'subject' not in extra_values:
+            extra_values['subject'] = self.get_subject()
+
+        for line in self.expand_header_lines(
+                self.header_template, **extra_values
+                ):
+            yield line
+
+    def generate_email_intro(self, html_escape_val=False):
+        for line in self.expand_lines(self.intro_template,
+                                      html_escape_val=html_escape_val):
+            yield line
+
+    def generate_email_body(self, push):
+        """Call the appropriate body-generation routine.
+
+        Call one of generate_create_summary() /
+        generate_update_summary() / generate_delete_summary()."""
+
+        change_summary = {
+            'create': self.generate_create_summary,
+            'delete': self.generate_delete_summary,
+            'update': self.generate_update_summary,
+            }[self.change_type](push)
+        for line in change_summary:
+            yield line
+
+        for line in self.generate_revision_change_summary(push):
+            yield line
+
+    def generate_email_footer(self, html_escape_val):
+        return self.expand_lines(self.footer_template,
+                                 html_escape_val=html_escape_val)
+
+    def generate_revision_change_graph(self, push):
+        if self.showgraph:
+            args = ['--graph'] + self.graphopts
+            for newold in ('new', 'old'):
+                has_newold = False
+                spec = push.get_commits_spec(newold, self)
+                for line in git_log(spec, args=args, keepends=True):
+                    if not has_newold:
+                        has_newold = True
+                        yield '\n'
+                        yield 'Graph of %s commits:\n\n' % (
+                            {'new': 'new', 'old': 'discarded'}[newold],)
+                    yield '  ' + line
+                if has_newold:
+                    yield '\n'
+
+    def generate_revision_change_log(self, new_commits_list):
+        if self.showlog:
+            yield '\n'
+            yield 'Detailed log of new commits:\n\n'
+            for line in read_git_lines(
+                    ['log', '--no-walk'] +
+                    self.logopts +
+                    new_commits_list +
+                    ['--'],
+                    keepends=True,
+                    ):
+                yield line
+
+    def generate_new_revision_summary(self, tot, new_commits_list, push):
+        for line in self.expand_lines(NEW_REVISIONS_TEMPLATE, tot=tot):
+            yield line
+        for line in self.generate_revision_change_graph(push):
+            yield line
+        for line in self.generate_revision_change_log(new_commits_list):
+            yield line
+
+    def generate_revision_change_summary(self, push):
+        """Generate a summary of the revisions added/removed by this change."""
+
+        if self.new.commit_sha1 and not self.old.commit_sha1:
+            # A new reference was created.  List the new revisions
+            # brought by the new reference (i.e., those revisions that
+            # were not in the repository before this reference
+            # change).
+            sha1s = list(push.get_new_commits(self))
+            sha1s.reverse()
+            tot = len(sha1s)
+            new_revisions = [
+                Revision(self, GitObject(sha1), num=i + 1, tot=tot)
+                for (i, sha1) in enumerate(sha1s)
+                ]
+
+            if new_revisions:
+                yield self.expand('This %(refname_type)s includes the following new commits:\n')
+                yield '\n'
+                for r in new_revisions:
+                    (sha1, subject) = r.rev.get_summary()
+                    yield r.expand(
+                        BRIEF_SUMMARY_TEMPLATE, action='new', text=subject,
+                        )
+                yield '\n'
+                for line in self.generate_new_revision_summary(
+                        tot, [r.rev.sha1 for r in new_revisions], push):
+                    yield line
+            else:
+                for line in self.expand_lines(NO_NEW_REVISIONS_TEMPLATE):
+                    yield line
+
+        elif self.new.commit_sha1 and self.old.commit_sha1:
+            # A reference was changed to point at a different commit.
+            # List the revisions that were removed and/or added *from
+            # that reference* by this reference change, along with a
+            # diff between the trees for its old and new values.
+
+            # List of the revisions that were added to the branch by
+            # this update.  Note this list can include revisions that
+            # have already had notification emails; we want such
+            # revisions in the summary even though we will not send
+            # new notification emails for them.
+            adds = list(generate_summaries(
+                '--topo-order', '--reverse', '%s..%s'
+                % (self.old.commit_sha1, self.new.commit_sha1,)
+                ))
+
+            # List of the revisions that were removed from the branch
+            # by this update.  This will be empty except for
+            # non-fast-forward updates.
+            discards = list(generate_summaries(
+                '%s..%s' % (self.new.commit_sha1, self.old.commit_sha1,)
+                ))
+
+            if adds:
+                new_commits_list = push.get_new_commits(self)
+            else:
+                new_commits_list = []
+            new_commits = CommitSet(new_commits_list)
+
+            if discards:
+                discarded_commits = CommitSet(push.get_discarded_commits(self))
+            else:
+                discarded_commits = CommitSet([])
+
+            if discards and adds:
+                for (sha1, subject) in discards:
+                    if sha1 in discarded_commits:
+                        action = 'discard'
+                    else:
+                        action = 'omit'
+                    yield self.expand(
+                        BRIEF_SUMMARY_TEMPLATE, action=action,
+                        rev_short=sha1, text=subject,
+                        )
+                for (sha1, subject) in adds:
+                    if sha1 in new_commits:
+                        action = 'new'
+                    else:
+                        action = 'add'
+                    yield self.expand(
+                        BRIEF_SUMMARY_TEMPLATE, action=action,
+                        rev_short=sha1, text=subject,
+                        )
+                yield '\n'
+                for line in self.expand_lines(NON_FF_TEMPLATE):
+                    yield line
+
+            elif discards:
+                for (sha1, subject) in discards:
+                    if sha1 in discarded_commits:
+                        action = 'discard'
+                    else:
+                        action = 'omit'
+                    yield self.expand(
+                        BRIEF_SUMMARY_TEMPLATE, action=action,
+                        rev_short=sha1, text=subject,
+                        )
+                yield '\n'
+                for line in self.expand_lines(REWIND_ONLY_TEMPLATE):
+                    yield line
+
+            elif adds:
+                (sha1, subject) = self.old.get_summary()
+                yield self.expand(
+                    BRIEF_SUMMARY_TEMPLATE, action='from',
+                    rev_short=sha1, text=subject,
+                    )
+                for (sha1, subject) in adds:
+                    if sha1 in new_commits:
+                        action = 'new'
+                    else:
+                        action = 'add'
+                    yield self.expand(
+                        BRIEF_SUMMARY_TEMPLATE, action=action,
+                        rev_short=sha1, text=subject,
+                        )
+
+            yield '\n'
+
+            if new_commits:
+                for line in self.generate_new_revision_summary(
+                        len(new_commits), new_commits_list, push):
+                    yield line
+            else:
+                for line in self.expand_lines(NO_NEW_REVISIONS_TEMPLATE):
+                    yield line
+                for line in self.generate_revision_change_graph(push):
+                    yield line
+
+            # The diffstat is shown from the old revision to the new
+            # revision.  This is to show the truth of what happened in
+            # this change.  There's no point showing the stat from the
+            # base to the new revision because the base is effectively a
+            # random revision at this point - the user will be interested
+            # in what this revision changed - including the undoing of
+            # previous revisions in the case of non-fast-forward updates.
+            yield '\n'
+            yield 'Summary of changes:\n'
+            for line in read_git_lines(
+                    ['diff-tree'] +
+                    self.diffopts +
+                    ['%s..%s' % (self.old.commit_sha1, self.new.commit_sha1,)],
+                    keepends=True,
+                    ):
+                yield line
+
+        elif self.old.commit_sha1 and not self.new.commit_sha1:
+            # A reference was deleted.  List the revisions that were
+            # removed from the repository by this reference change.
+
+            sha1s = list(push.get_discarded_commits(self))
+            tot = len(sha1s)
+            discarded_revisions = [
+                Revision(self, GitObject(sha1), num=i + 1, tot=tot)
+                for (i, sha1) in enumerate(sha1s)
+                ]
+
+            if discarded_revisions:
+                for line in self.expand_lines(DISCARDED_REVISIONS_TEMPLATE):
+                    yield line
+                yield '\n'
+                for r in discarded_revisions:
+                    (sha1, subject) = r.rev.get_summary()
+                    yield r.expand(
+                        BRIEF_SUMMARY_TEMPLATE, action='discard', text=subject,
+                        )
+                for line in self.generate_revision_change_graph(push):
+                    yield line
+            else:
+                for line in self.expand_lines(NO_DISCARDED_REVISIONS_TEMPLATE):
+                    yield line
+
+        elif not self.old.commit_sha1 and not self.new.commit_sha1:
+            for line in self.expand_lines(NON_COMMIT_UPDATE_TEMPLATE):
+                yield line
+
+    def generate_create_summary(self, push):
+        """Called for the creation of a reference."""
+
+        # This is a new reference and so oldrev is not valid
+        (sha1, subject) = self.new.get_summary()
+        yield self.expand(
+            BRIEF_SUMMARY_TEMPLATE, action='at',
+            rev_short=sha1, text=subject,
+            )
+        yield '\n'
+
+    def generate_update_summary(self, push):
+        """Called for the change of a pre-existing branch."""
+
+        return iter([])
+
+    def generate_delete_summary(self, push):
+        """Called for the deletion of any type of reference."""
+
+        (sha1, subject) = self.old.get_summary()
+        yield self.expand(
+            BRIEF_SUMMARY_TEMPLATE, action='was',
+            rev_short=sha1, text=subject,
+            )
+        yield '\n'
+
+    def get_specific_fromaddr(self):
+        return self.environment.from_refchange
+
+
+class BranchChange(ReferenceChange):
+    refname_type = 'branch'
+
+    def __init__(self, environment, refname, short_refname, old, new, rev):
+        ReferenceChange.__init__(
+            self, environment,
+            refname=refname, short_refname=short_refname,
+            old=old, new=new, rev=rev,
+            )
+        self.recipients = environment.get_refchange_recipients(self)
+        self._single_revision = None
+
+    def send_single_combined_email(self, known_added_sha1s):
+        if not self.environment.combine_when_single_commit:
+            return None
+
+        # In the sadly-all-too-frequent usecase of people pushing only
+        # one of their commits at a time to a repository, users feel
+        # the reference change summary emails are noise rather than
+        # important signal.  This is because, in this particular
+        # usecase, there is a reference change summary email for each
+        # new commit, and all these summaries do is point out that
+        # there is one new commit (which can readily be inferred by
+        # the existence of the individual revision email that is also
+        # sent).  In such cases, our users prefer there to be a combined
+        # reference change summary/new revision email.
+        #
+        # So, if the change is an update and it doesn't discard any
+        # commits, and it adds exactly one non-merge commit (gerrit
+        # forces a workflow where every commit is individually merged
+        # and the git-multimail hook fired off for just this one
+        # change), then we send a combined refchange/revision email.
+        try:
+            # If this change is a reference update that doesn't discard
+            # any commits...
+            if self.change_type != 'update':
+                return None
+
+            if read_git_lines(
+                    ['merge-base', self.old.sha1, self.new.sha1]
+                    ) != [self.old.sha1]:
+                return None
+
+            # Check if this update introduced exactly one non-merge
+            # commit:
+
+            def split_line(line):
+                """Split line into (sha1, [parent,...])."""
+
+                words = line.split()
+                return (words[0], words[1:])
+
+            # Get the new commits introduced by the push as a list of
+            # (sha1, [parent,...])
+            new_commits = [
+                split_line(line)
+                for line in read_git_lines(
+                    [
+                        'log', '-3', '--format=%H %P',
+                        '%s..%s' % (self.old.sha1, self.new.sha1),
+                        ]
+                    )
+                ]
+
+            if not new_commits:
+                return None
+
+            # If the newest commit is a merge, save it for a later check
+            # but otherwise ignore it
+            merge = None
+            tot = len(new_commits)
+            if len(new_commits[0][1]) > 1:
+                merge = new_commits[0][0]
+                del new_commits[0]
+
+            # Our primary check: we can't combine if more than one commit
+            # is introduced.  We also currently only combine if the new
+            # commit is a non-merge commit, though it may make sense to
+            # combine if it is a merge as well.
+            if not (
+                    len(new_commits) == 1 and
+                    len(new_commits[0][1]) == 1 and
+                    new_commits[0][0] in known_added_sha1s
+                    ):
+                return None
+
+            # We do not want to combine revision and refchange emails if
+            # those go to separate locations.
+            rev = Revision(self, GitObject(new_commits[0][0]), 1, tot)
+            if rev.recipients != self.recipients:
+                return None
+
+            # We ignored the newest commit if it was just a merge of the one
+            # commit being introduced.  But we don't want to ignore that
+            # merge commit it it involved conflict resolutions.  Check that.
+            if merge and merge != read_git_output(['diff-tree', '--cc', merge]):
+                return None
+
+            # We can combine the refchange and one new revision emails
+            # into one.  Return the Revision that a combined email should
+            # be sent about.
+            return rev
+        except CommandError:
+            # Cannot determine number of commits in old..new or new..old;
+            # don't combine reference/revision emails:
+            return None
+
+    def generate_combined_email(self, push, revision, body_filter=None, extra_header_values={}):
+        values = revision.get_values()
+        if extra_header_values:
+            values.update(extra_header_values)
+        if 'subject' not in extra_header_values:
+            values['subject'] = self.expand(COMBINED_REFCHANGE_REVISION_SUBJECT_TEMPLATE, **values)
+
+        self._single_revision = revision
+        self._contains_diff()
+        self.header_template = COMBINED_HEADER_TEMPLATE
+        self.intro_template = COMBINED_INTRO_TEMPLATE
+        self.footer_template = COMBINED_FOOTER_TEMPLATE
+
+        def revision_gen_link(base_url):
+            # revision is used only to generate the body, and
+            # _content_type is set while generating headers. Get it
+            # from the BranchChange object.
+            revision._content_type = self._content_type
+            return revision.generate_browse_link(base_url)
+        self.generate_browse_link = revision_gen_link
+        for line in self.generate_email(push, body_filter, values):
+            yield line
+
+    def generate_email_body(self, push):
+        '''Call the appropriate body generation routine.
+
+        If this is a combined refchange/revision email, the special logic
+        for handling this combined email comes from this function.  For
+        other cases, we just use the normal handling.'''
+
+        # If self._single_revision isn't set; don't override
+        if not self._single_revision:
+            for line in super(BranchChange, self).generate_email_body(push):
+                yield line
+            return
+
+        # This is a combined refchange/revision email; we first provide
+        # some info from the refchange portion, and then call the revision
+        # generate_email_body function to handle the revision portion.
+        adds = list(generate_summaries(
+            '--topo-order', '--reverse', '%s..%s'
+            % (self.old.commit_sha1, self.new.commit_sha1,)
+            ))
+
+        yield self.expand("The following commit(s) were added to %(refname)s by this push:\n")
+        for (sha1, subject) in adds:
+            yield self.expand(
+                BRIEF_SUMMARY_TEMPLATE, action='new',
+                rev_short=sha1, text=subject,
+                )
+
+        yield self._single_revision.rev.short + " is described below\n"
+        yield '\n'
+
+        for line in self._single_revision.generate_email_body(push):
+            yield line
+
+
+class AnnotatedTagChange(ReferenceChange):
+    refname_type = 'annotated tag'
+
+    def __init__(self, environment, refname, short_refname, old, new, rev):
+        ReferenceChange.__init__(
+            self, environment,
+            refname=refname, short_refname=short_refname,
+            old=old, new=new, rev=rev,
+            )
+        self.recipients = environment.get_announce_recipients(self)
+        self.show_shortlog = environment.announce_show_shortlog
+
+    ANNOTATED_TAG_FORMAT = (
+        '%(*objectname)\n'
+        '%(*objecttype)\n'
+        '%(taggername)\n'
+        '%(taggerdate)'
+        )
+
+    def describe_tag(self, push):
+        """Describe the new value of an annotated tag."""
+
+        # Use git for-each-ref to pull out the individual fields from
+        # the tag
+        [tagobject, tagtype, tagger, tagged] = read_git_lines(
+            ['for-each-ref', '--format=%s' % (self.ANNOTATED_TAG_FORMAT,), self.refname],
+            )
+
+        yield self.expand(
+            BRIEF_SUMMARY_TEMPLATE, action='tagging',
+            rev_short=tagobject, text='(%s)' % (tagtype,),
+            )
+        if tagtype == 'commit':
+            # If the tagged object is a commit, then we assume this is a
+            # release, and so we calculate which tag this tag is
+            # replacing
+            try:
+                prevtag = read_git_output(['describe', '--abbrev=0', '%s^' % (self.new,)])
+            except CommandError:
+                prevtag = None
+            if prevtag:
+                yield ' replaces %s\n' % (prevtag,)
+        else:
+            prevtag = None
+            yield '  length %s bytes\n' % (read_git_output(['cat-file', '-s', tagobject]),)
+
+        yield '      by %s\n' % (tagger,)
+        yield '      on %s\n' % (tagged,)
+        yield '\n'
+
+        # Show the content of the tag message; this might contain a
+        # change log or release notes so is worth displaying.
+        yield LOGBEGIN
+        contents = list(read_git_lines(['cat-file', 'tag', self.new.sha1], keepends=True))
+        contents = contents[contents.index('\n') + 1:]
+        if contents and contents[-1][-1:] != '\n':
+            contents.append('\n')
+        for line in contents:
+            yield line
+
+        if self.show_shortlog and tagtype == 'commit':
+            # Only commit tags make sense to have rev-list operations
+            # performed on them
+            yield '\n'
+            if prevtag:
+                # Show changes since the previous release
+                revlist = read_git_output(
+                    ['rev-list', '--pretty=short', '%s..%s' % (prevtag, self.new,)],
+                    keepends=True,
+                    )
+            else:
+                # No previous tag, show all the changes since time
+                # began
+                revlist = read_git_output(
+                    ['rev-list', '--pretty=short', '%s' % (self.new,)],
+                    keepends=True,
+                    )
+            for line in read_git_lines(['shortlog'], input=revlist, keepends=True):
+                yield line
+
+        yield LOGEND
+        yield '\n'
+
+    def generate_create_summary(self, push):
+        """Called for the creation of an annotated tag."""
+
+        for line in self.expand_lines(TAG_CREATED_TEMPLATE):
+            yield line
+
+        for line in self.describe_tag(push):
+            yield line
+
+    def generate_update_summary(self, push):
+        """Called for the update of an annotated tag.
+
+        This is probably a rare event and may not even be allowed."""
+
+        for line in self.expand_lines(TAG_UPDATED_TEMPLATE):
+            yield line
+
+        for line in self.describe_tag(push):
+            yield line
+
+    def generate_delete_summary(self, push):
+        """Called when a non-annotated reference is updated."""
+
+        for line in self.expand_lines(TAG_DELETED_TEMPLATE):
+            yield line
+
+        yield self.expand('   tag was  %(oldrev_short)s\n')
+        yield '\n'
+
+
+class NonAnnotatedTagChange(ReferenceChange):
+    refname_type = 'tag'
+
+    def __init__(self, environment, refname, short_refname, old, new, rev):
+        ReferenceChange.__init__(
+            self, environment,
+            refname=refname, short_refname=short_refname,
+            old=old, new=new, rev=rev,
+            )
+        self.recipients = environment.get_refchange_recipients(self)
+
+    def generate_create_summary(self, push):
+        """Called for the creation of an annotated tag."""
+
+        for line in self.expand_lines(TAG_CREATED_TEMPLATE):
+            yield line
+
+    def generate_update_summary(self, push):
+        """Called when a non-annotated reference is updated."""
+
+        for line in self.expand_lines(TAG_UPDATED_TEMPLATE):
+            yield line
+
+    def generate_delete_summary(self, push):
+        """Called when a non-annotated reference is updated."""
+
+        for line in self.expand_lines(TAG_DELETED_TEMPLATE):
+            yield line
+
+        for line in ReferenceChange.generate_delete_summary(self, push):
+            yield line
+
+
+class OtherReferenceChange(ReferenceChange):
+    refname_type = 'reference'
+
+    def __init__(self, environment, refname, short_refname, old, new, rev):
+        # We use the full refname as short_refname, because otherwise
+        # the full name of the reference would not be obvious from the
+        # text of the email.
+        ReferenceChange.__init__(
+            self, environment,
+            refname=refname, short_refname=refname,
+            old=old, new=new, rev=rev,
+            )
+        self.recipients = environment.get_refchange_recipients(self)
+
+
+class Mailer(object):
+    """An object that can send emails."""
+
+    def __init__(self, environment):
+        self.environment = environment
+
+    def close(self):
+        pass
+
+    def send(self, lines, to_addrs):
+        """Send an email consisting of lines.
+
+        lines must be an iterable over the lines constituting the
+        header and body of the email.  to_addrs is a list of recipient
+        addresses (can be needed even if lines already contains a
+        "To:" field).  It can be either a string (comma-separated list
+        of email addresses) or a Python list of individual email
+        addresses.
+
+        """
+
+        raise NotImplementedError()
+
+
+class SendMailer(Mailer):
+    """Send emails using 'sendmail -oi -t'."""
+
+    SENDMAIL_CANDIDATES = [
+        '/usr/sbin/sendmail',
+        '/usr/lib/sendmail',
+        ]
+
+    @staticmethod
+    def find_sendmail():
+        for path in SendMailer.SENDMAIL_CANDIDATES:
+            if os.access(path, os.X_OK):
+                return path
+        else:
+            raise ConfigurationException(
+                'No sendmail executable found.  '
+                'Try setting multimailhook.sendmailCommand.'
+                )
+
+    def __init__(self, environment, command=None, envelopesender=None):
+        """Construct a SendMailer instance.
+
+        command should be the command and arguments used to invoke
+        sendmail, as a list of strings.  If an envelopesender is
+        provided, it will also be passed to the command, via '-f
+        envelopesender'."""
+        super(SendMailer, self).__init__(environment)
+        if command:
+            self.command = command[:]
+        else:
+            self.command = [self.find_sendmail(), '-oi', '-t']
+
+        if envelopesender:
+            self.command.extend(['-f', envelopesender])
+
+    def send(self, lines, to_addrs):
+        try:
+            p = subprocess.Popen(self.command, stdin=subprocess.PIPE)
+        except OSError:
+            self.environment.get_logger().error(
+                '*** Cannot execute command: %s\n' % ' '.join(self.command) +
+                '*** %s\n' % sys.exc_info()[1] +
+                '*** Try setting multimailhook.mailer to "smtp"\n' +
+                '*** to send emails without using the sendmail command.\n'
+                )
+            sys.exit(1)
+        try:
+            lines = (str_to_bytes(line) for line in lines)
+            p.stdin.writelines(lines)
+        except Exception:
+            self.environment.get_logger().error(
+                '*** Error while generating commit email\n'
+                '***  - mail sending aborted.\n'
+                )
+            if hasattr(p, 'terminate'):
+                # subprocess.terminate() is not available in Python 2.4
+                p.terminate()
+            else:
+                import signal
+                os.kill(p.pid, signal.SIGTERM)
+            raise
+        else:
+            p.stdin.close()
+            retcode = p.wait()
+            if retcode:
+                raise CommandError(self.command, retcode)
+
+
+class SMTPMailer(Mailer):
+    """Send emails using Python's smtplib."""
+
+    def __init__(self, environment,
+                 envelopesender, smtpserver,
+                 smtpservertimeout=10.0, smtpserverdebuglevel=0,
+                 smtpencryption='none',
+                 smtpuser='', smtppass='',
+                 smtpcacerts=''
+                 ):
+        super(SMTPMailer, self).__init__(environment)
+        if not envelopesender:
+            self.environment.get_logger().error(
+                'fatal: git_multimail: cannot use SMTPMailer without a sender address.\n'
+                'please set either multimailhook.envelopeSender or user.email\n'
+                )
+            sys.exit(1)
+        if smtpencryption == 'ssl' and not (smtpuser and smtppass):
+            raise ConfigurationException(
+                'Cannot use SMTPMailer with security option ssl '
+                'without options username and password.'
+                )
+        self.envelopesender = envelopesender
+        self.smtpserver = smtpserver
+        self.smtpservertimeout = smtpservertimeout
+        self.smtpserverdebuglevel = smtpserverdebuglevel
+        self.security = smtpencryption
+        self.username = smtpuser
+        self.password = smtppass
+        self.smtpcacerts = smtpcacerts
+        self.loggedin = False
+        try:
+            def call(klass, server, timeout):
+                try:
+                    return klass(server, timeout=timeout)
+                except TypeError:
+                    # Old Python versions do not have timeout= argument.
+                    return klass(server)
+            if self.security == 'none':
+                self.smtp = call(smtplib.SMTP, self.smtpserver, timeout=self.smtpservertimeout)
+            elif self.security == 'ssl':
+                if self.smtpcacerts:
+                    raise smtplib.SMTPException(
+                        "Checking certificate is not supported for ssl, prefer starttls"
+                        )
+                self.smtp = call(smtplib.SMTP_SSL, self.smtpserver, timeout=self.smtpservertimeout)
+            elif self.security == 'tls':
+                if 'ssl' not in sys.modules:
+                    self.environment.get_logger().error(
+                        '*** Your Python version does not have the ssl library installed\n'
+                        '*** smtpEncryption=tls is not available.\n'
+                        '*** Either upgrade Python to 2.6 or later\n'
+                        '    or use git_multimail.py version 1.2.\n')
+                if ':' not in self.smtpserver:
+                    self.smtpserver += ':587'  # default port for TLS
+                self.smtp = call(smtplib.SMTP, self.smtpserver, timeout=self.smtpservertimeout)
+                # start: ehlo + starttls
+                # equivalent to
+                #     self.smtp.ehlo()
+                #     self.smtp.starttls()
+                # with acces to the ssl layer
+                self.smtp.ehlo()
+                if not self.smtp.has_extn("starttls"):
+                    raise smtplib.SMTPException("STARTTLS extension not supported by server")
+                resp, reply = self.smtp.docmd("STARTTLS")
+                if resp != 220:
+                    raise smtplib.SMTPException("Wrong answer to the STARTTLS command")
+                if self.smtpcacerts:
+                    self.smtp.sock = ssl.wrap_socket(
+                        self.smtp.sock,
+                        ca_certs=self.smtpcacerts,
+                        cert_reqs=ssl.CERT_REQUIRED
+                        )
+                else:
+                    self.smtp.sock = ssl.wrap_socket(
+                        self.smtp.sock,
+                        cert_reqs=ssl.CERT_NONE
+                        )
+                    self.environment.get_logger().error(
+                        '*** Warning, the server certificat is not verified (smtp) ***\n'
+                        '***          set the option smtpCACerts                   ***\n'
+                        )
+                if not hasattr(self.smtp.sock, "read"):
+                    # using httplib.FakeSocket with Python 2.5.x or earlier
+                    self.smtp.sock.read = self.smtp.sock.recv
+                self.smtp.file = smtplib.SSLFakeFile(self.smtp.sock)
+                self.smtp.helo_resp = None
+                self.smtp.ehlo_resp = None
+                self.smtp.esmtp_features = {}
+                self.smtp.does_esmtp = 0
+                # end:   ehlo + starttls
+                self.smtp.ehlo()
+            else:
+                sys.stdout.write('*** Error: Control reached an invalid option. ***')
+                sys.exit(1)
+            if self.smtpserverdebuglevel > 0:
+                sys.stdout.write(
+                    "*** Setting debug on for SMTP server connection (%s) ***\n"
+                    % self.smtpserverdebuglevel)
+                self.smtp.set_debuglevel(self.smtpserverdebuglevel)
+        except Exception:
+            self.environment.get_logger().error(
+                '*** Error establishing SMTP connection to %s ***\n'
+                '*** %s\n'
+                % (self.smtpserver, sys.exc_info()[1]))
+            sys.exit(1)
+
+    def close(self):
+        if hasattr(self, 'smtp'):
+            self.smtp.quit()
+            del self.smtp
+
+    def __del__(self):
+        self.close()
+
+    def send(self, lines, to_addrs):
+        try:
+            if self.username or self.password:
+                if not self.loggedin:
+                    self.smtp.login(self.username, self.password)
+                    self.loggedin = True
+            msg = ''.join(lines)
+            # turn comma-separated list into Python list if needed.
+            if is_string(to_addrs):
+                to_addrs = [email for (name, email) in getaddresses([to_addrs])]
+            self.smtp.sendmail(self.envelopesender, to_addrs, msg)
+        except socket.timeout:
+            self.environment.get_logger().error(
+                '*** Error sending email ***\n'
+                '*** SMTP server timed out (timeout is %s)\n'
+                % self.smtpservertimeout)
+        except smtplib.SMTPResponseException:
+            err = sys.exc_info()[1]
+            self.environment.get_logger().error(
+                '*** Error sending email ***\n'
+                '*** Error %d: %s\n'
+                % (err.smtp_code, bytes_to_str(err.smtp_error)))
+            try:
+                smtp = self.smtp
+                # delete the field before quit() so that in case of
+                # error, self.smtp is deleted anyway.
+                del self.smtp
+                smtp.quit()
+            except:
+                self.environment.get_logger().error(
+                    '*** Error closing the SMTP connection ***\n'
+                    '*** Exiting anyway ... ***\n'
+                    '*** %s\n' % sys.exc_info()[1])
+            sys.exit(1)
+
+
+class OutputMailer(Mailer):
+    """Write emails to an output stream, bracketed by lines of '=' characters.
+
+    This is intended for debugging purposes."""
+
+    SEPARATOR = '=' * 75 + '\n'
+
+    def __init__(self, f, environment=None):
+        super(OutputMailer, self).__init__(environment=environment)
+        self.f = f
+
+    def send(self, lines, to_addrs):
+        write_str(self.f, self.SEPARATOR)
+        for line in lines:
+            write_str(self.f, line)
+        write_str(self.f, self.SEPARATOR)
+
+
+def get_git_dir():
+    """Determine GIT_DIR.
+
+    Determine GIT_DIR either from the GIT_DIR environment variable or
+    from the working directory, using Git's usual rules."""
+
+    try:
+        return read_git_output(['rev-parse', '--git-dir'])
+    except CommandError:
+        sys.stderr.write('fatal: git_multimail: not in a git directory\n')
+        sys.exit(1)
+
+
+class Environment(object):
+    """Describes the environment in which the push is occurring.
+
+    An Environment object encapsulates information about the local
+    environment.  For example, it knows how to determine:
+
+    * the name of the repository to which the push occurred
+
+    * what user did the push
+
+    * what users want to be informed about various types of changes.
+
+    An Environment object is expected to have the following methods:
+
+        get_repo_shortname()
+
+            Return a short name for the repository, for display
+            purposes.
+
+        get_repo_path()
+
+            Return the absolute path to the Git repository.
+
+        get_emailprefix()
+
+            Return a string that will be prefixed to every email's
+            subject.
+
+        get_pusher()
+
+            Return the username of the person who pushed the changes.
+            This value is used in the email body to indicate who
+            pushed the change.
+
+        get_pusher_email() (may return None)
+
+            Return the email address of the person who pushed the
+            changes.  The value should be a single RFC 2822 email
+            address as a string; e.g., "Joe User <user@example.com>"
+            if available, otherwise "user@example.com".  If set, the
+            value is used as the Reply-To address for refchange
+            emails.  If it is impossible to determine the pusher's
+            email, this attribute should be set to None (in which case
+            no Reply-To header will be output).
+
+        get_sender()
+
+            Return the address to be used as the 'From' email address
+            in the email envelope.
+
+        get_fromaddr(change=None)
+
+            Return the 'From' email address used in the email 'From:'
+            headers.  If the change is known when this function is
+            called, it is passed in as the 'change' parameter.  (May
+            be a full RFC 2822 email address like 'Joe User
+            <user@example.com>'.)
+
+        get_administrator()
+
+            Return the name and/or email of the repository
+            administrator.  This value is used in the footer as the
+            person to whom requests to be removed from the
+            notification list should be sent.  Ideally, it should
+            include a valid email address.
+
+        get_reply_to_refchange()
+        get_reply_to_commit()
+
+            Return the address to use in the email "Reply-To" header,
+            as a string.  These can be an RFC 2822 email address, or
+            None to omit the "Reply-To" header.
+            get_reply_to_refchange() is used for refchange emails;
+            get_reply_to_commit() is used for individual commit
+            emails.
+
+        get_ref_filter_regex()
+
+            Return a tuple -- a compiled regex, and a boolean indicating
+            whether the regex picks refs to include (if False, the regex
+            matches on refs to exclude).
+
+        get_default_ref_ignore_regex()
+
+            Return a regex that should be ignored for both what emails
+            to send and when computing what commits are considered new
+            to the repository.  Default is "^refs/notes/".
+
+        get_max_subject_length()
+
+            Return an int giving the maximal length for the subject
+            (git log --oneline).
+
+    They should also define the following attributes:
+
+        announce_show_shortlog (bool)
+
+            True iff announce emails should include a shortlog.
+
+        commit_email_format (string)
+
+            If "html", generate commit emails in HTML instead of plain text
+            used by default.
+
+        html_in_intro (bool)
+        html_in_footer (bool)
+
+            When generating HTML emails, the introduction (respectively,
+            the footer) will be HTML-escaped iff html_in_intro (respectively,
+            the footer) is true. When false, only the values used to expand
+            the template are escaped.
+
+        refchange_showgraph (bool)
+
+            True iff refchanges emails should include a detailed graph.
+
+        refchange_showlog (bool)
+
+            True iff refchanges emails should include a detailed log.
+
+        diffopts (list of strings)
+
+            The options that should be passed to 'git diff' for the
+            summary email.  The value should be a list of strings
+            representing words to be passed to the command.
+
+        graphopts (list of strings)
+
+            Analogous to diffopts, but contains options passed to
+            'git log --graph' when generating the detailed graph for
+            a set of commits (see refchange_showgraph)
+
+        logopts (list of strings)
+
+            Analogous to diffopts, but contains options passed to
+            'git log' when generating the detailed log for a set of
+            commits (see refchange_showlog)
+
+        commitlogopts (list of strings)
+
+            The options that should be passed to 'git log' for each
+            commit mail.  The value should be a list of strings
+            representing words to be passed to the command.
+
+        date_substitute (string)
+
+            String to be used in substitution for 'Date:' at start of
+            line in the output of 'git log'.
+
+        quiet (bool)
+            On success do not write to stderr
+
+        stdout (bool)
+            Write email to stdout rather than emailing. Useful for debugging
+
+        combine_when_single_commit (bool)
+
+            True if a combined email should be produced when a single
+            new commit is pushed to a branch, False otherwise.
+
+        from_refchange, from_commit (strings)
+
+            Addresses to use for the From: field for refchange emails
+            and commit emails respectively.  Set from
+            multimailhook.fromRefchange and multimailhook.fromCommit
+            by ConfigEnvironmentMixin.
+
+        log_file, error_log_file, debug_log_file (string)
+
+            Name of a file to which logs should be sent.
+
+        verbose (int)
+
+            How verbose the system should be.
+            - 0 (default): show info, errors, ...
+            - 1 : show basic debug info
+    """
+
+    REPO_NAME_RE = re.compile(r'^(?P<name>.+?)(?:\.git)$')
+
+    def __init__(self, osenv=None):
+        self.osenv = osenv or os.environ
+        self.announce_show_shortlog = False
+        self.commit_email_format = "text"
+        self.html_in_intro = False
+        self.html_in_footer = False
+        self.commitBrowseURL = None
+        self.maxcommitemails = 500
+        self.excludemergerevisions = False
+        self.diffopts = ['--stat', '--summary', '--find-copies-harder']
+        self.graphopts = ['--oneline', '--decorate']
+        self.logopts = []
+        self.refchange_showgraph = False
+        self.refchange_showlog = False
+        self.commitlogopts = ['-C', '--stat', '-p', '--cc']
+        self.date_substitute = 'AuthorDate: '
+        self.quiet = False
+        self.stdout = False
+        self.combine_when_single_commit = True
+        self.logger = None
+
+        self.COMPUTED_KEYS = [
+            'administrator',
+            'charset',
+            'emailprefix',
+            'pusher',
+            'pusher_email',
+            'repo_path',
+            'repo_shortname',
+            'sender',
+            ]
+
+        self._values = None
+
+    def get_logger(self):
+        """Get (possibly creates) the logger associated to this environment."""
+        if self.logger is None:
+            self.logger = Logger(self)
+        return self.logger
+
+    def get_repo_shortname(self):
+        """Use the last part of the repo path, with ".git" stripped off if present."""
+
+        basename = os.path.basename(os.path.abspath(self.get_repo_path()))
+        m = self.REPO_NAME_RE.match(basename)
+        if m:
+            return m.group('name')
+        else:
+            return basename
+
+    def get_pusher(self):
+        raise NotImplementedError()
+
+    def get_pusher_email(self):
+        return None
+
+    def get_fromaddr(self, change=None):
+        config = Config('user')
+        fromname = config.get('name', default='')
+        fromemail = config.get('email', default='')
+        if fromemail:
+            return formataddr([fromname, fromemail])
+        return self.get_sender()
+
+    def get_administrator(self):
+        return 'the administrator of this repository'
+
+    def get_emailprefix(self):
+        return ''
+
+    def get_repo_path(self):
+        if read_git_output(['rev-parse', '--is-bare-repository']) == 'true':
+            path = get_git_dir()
+        else:
+            path = read_git_output(['rev-parse', '--show-toplevel'])
+        return os.path.abspath(path)
+
+    def get_charset(self):
+        return CHARSET
+
+    def get_values(self):
+        """Return a dictionary {keyword: expansion} for this Environment.
+
+        This method is called by Change._compute_values().  The keys
+        in the returned dictionary are available to be used in any of
+        the templates.  The dictionary is created by calling
+        self.get_NAME() for each of the attributes named in
+        COMPUTED_KEYS and recording those that do not return None.
+        The return value is always a new dictionary."""
+
+        if self._values is None:
+            values = {'': ''}  # %()s expands to the empty string.
+
+            for key in self.COMPUTED_KEYS:
+                value = getattr(self, 'get_%s' % (key,))()
+                if value is not None:
+                    values[key] = value
+
+            self._values = values
+
+        return self._values.copy()
+
+    def get_refchange_recipients(self, refchange):
+        """Return the recipients for notifications about refchange.
+
+        Return the list of email addresses to which notifications
+        about the specified ReferenceChange should be sent."""
+
+        raise NotImplementedError()
+
+    def get_announce_recipients(self, annotated_tag_change):
+        """Return the recipients for notifications about annotated_tag_change.
+
+        Return the list of email addresses to which notifications
+        about the specified AnnotatedTagChange should be sent."""
+
+        raise NotImplementedError()
+
+    def get_reply_to_refchange(self, refchange):
+        return self.get_pusher_email()
+
+    def get_revision_recipients(self, revision):
+        """Return the recipients for messages about revision.
+
+        Return the list of email addresses to which notifications
+        about the specified Revision should be sent.  This method
+        could be overridden, for example, to take into account the
+        contents of the revision when deciding whom to notify about
+        it.  For example, there could be a scheme for users to express
+        interest in particular files or subdirectories, and only
+        receive notification emails for revisions that affecting those
+        files."""
+
+        raise NotImplementedError()
+
+    def get_reply_to_commit(self, revision):
+        return revision.author
+
+    def get_default_ref_ignore_regex(self):
+        # The commit messages of git notes are essentially meaningless
+        # and "filenames" in git notes commits are an implementational
+        # detail that might surprise users at first.  As such, we
+        # would need a completely different method for handling emails
+        # of git notes in order for them to be of benefit for users,
+        # which we simply do not have right now.
+        return "^refs/notes/"
+
+    def get_max_subject_length(self):
+        """Return the maximal subject line (git log --oneline) length.
+        Longer subject lines will be truncated."""
+        raise NotImplementedError()
+
+    def filter_body(self, lines):
+        """Filter the lines intended for an email body.
+
+        lines is an iterable over the lines that would go into the
+        email body.  Filter it (e.g., limit the number of lines, the
+        line length, character set, etc.), returning another iterable.
+        See FilterLinesEnvironmentMixin and MaxlinesEnvironmentMixin
+        for classes implementing this functionality."""
+
+        return lines
+
+    def log_msg(self, msg):
+        """Write the string msg on a log file or on stderr.
+
+        Sends the text to stderr by default, override to change the behavior."""
+        self.get_logger().info(msg)
+
+    def log_warning(self, msg):
+        """Write the string msg on a log file or on stderr.
+
+        Sends the text to stderr by default, override to change the behavior."""
+        self.get_logger().warning(msg)
+
+    def log_error(self, msg):
+        """Write the string msg on a log file or on stderr.
+
+        Sends the text to stderr by default, override to change the behavior."""
+        self.get_logger().error(msg)
+
+    def check(self):
+        pass
+
+
+class ConfigEnvironmentMixin(Environment):
+    """A mixin that sets self.config to its constructor's config argument.
+
+    This class's constructor consumes the "config" argument.
+
+    Mixins that need to inspect the config should inherit from this
+    class (1) to make sure that "config" is still in the constructor
+    arguments with its own constructor runs and/or (2) to be sure that
+    self.config is set after construction."""
+
+    def __init__(self, config, **kw):
+        super(ConfigEnvironmentMixin, self).__init__(**kw)
+        self.config = config
+
+
+class ConfigOptionsEnvironmentMixin(ConfigEnvironmentMixin):
+    """An Environment that reads most of its information from "git config"."""
+
+    @staticmethod
+    def forbid_field_values(name, value, forbidden):
+        for forbidden_val in forbidden:
+            if value is not None and value.lower() == forbidden:
+                raise ConfigurationException(
+                    '"%s" is not an allowed setting for %s' % (value, name)
+                    )
+
+    def __init__(self, config, **kw):
+        super(ConfigOptionsEnvironmentMixin, self).__init__(
+            config=config, **kw
+            )
+
+        for var, cfg in (
+                ('announce_show_shortlog', 'announceshortlog'),
+                ('refchange_showgraph', 'refchangeShowGraph'),
+                ('refchange_showlog', 'refchangeshowlog'),
+                ('quiet', 'quiet'),
+                ('stdout', 'stdout'),
+                ):
+            val = config.get_bool(cfg)
+            if val is not None:
+                setattr(self, var, val)
+
+        commit_email_format = config.get('commitEmailFormat')
+        if commit_email_format is not None:
+            if commit_email_format != "html" and commit_email_format != "text":
+                self.log_warning(
+                    '*** Unknown value for multimailhook.commitEmailFormat: %s\n' %
+                    commit_email_format +
+                    '*** Expected either "text" or "html".  Ignoring.\n'
+                    )
+            else:
+                self.commit_email_format = commit_email_format
+
+        html_in_intro = config.get_bool('htmlInIntro')
+        if html_in_intro is not None:
+            self.html_in_intro = html_in_intro
+
+        html_in_footer = config.get_bool('htmlInFooter')
+        if html_in_footer is not None:
+            self.html_in_footer = html_in_footer
+
+        self.commitBrowseURL = config.get('commitBrowseURL')
+
+        self.excludemergerevisions = config.get('excludeMergeRevisions')
+
+        maxcommitemails = config.get('maxcommitemails')
+        if maxcommitemails is not None:
+            try:
+                self.maxcommitemails = int(maxcommitemails)
+            except ValueError:
+                self.log_warning(
+                    '*** Malformed value for multimailhook.maxCommitEmails: %s\n'
+                    % maxcommitemails +
+                    '*** Expected a number.  Ignoring.\n'
+                    )
+
+        diffopts = config.get('diffopts')
+        if diffopts is not None:
+            self.diffopts = shlex.split(diffopts)
+
+        graphopts = config.get('graphOpts')
+        if graphopts is not None:
+            self.graphopts = shlex.split(graphopts)
+
+        logopts = config.get('logopts')
+        if logopts is not None:
+            self.logopts = shlex.split(logopts)
+
+        commitlogopts = config.get('commitlogopts')
+        if commitlogopts is not None:
+            self.commitlogopts = shlex.split(commitlogopts)
+
+        date_substitute = config.get('dateSubstitute')
+        if date_substitute == 'none':
+            self.date_substitute = None
+        elif date_substitute is not None:
+            self.date_substitute = date_substitute
+
+        reply_to = config.get('replyTo')
+        self.__reply_to_refchange = config.get('replyToRefchange', default=reply_to)
+        self.forbid_field_values('replyToRefchange',
+                                 self.__reply_to_refchange,
+                                 ['author'])
+        self.__reply_to_commit = config.get('replyToCommit', default=reply_to)
+
+        self.from_refchange = config.get('fromRefchange')
+        self.forbid_field_values('fromRefchange',
+                                 self.from_refchange,
+                                 ['author', 'none'])
+        self.from_commit = config.get('fromCommit')
+        self.forbid_field_values('fromCommit',
+                                 self.from_commit,
+                                 ['none'])
+
+        combine = config.get_bool('combineWhenSingleCommit')
+        if combine is not None:
+            self.combine_when_single_commit = combine
+
+        self.log_file = config.get('logFile', default=None)
+        self.error_log_file = config.get('errorLogFile', default=None)
+        self.debug_log_file = config.get('debugLogFile', default=None)
+        if config.get_bool('Verbose', default=False):
+            self.verbose = 1
+        else:
+            self.verbose = 0
+
+    def get_administrator(self):
+        return (
+            self.config.get('administrator') or
+            self.get_sender() or
+            super(ConfigOptionsEnvironmentMixin, self).get_administrator()
+            )
+
+    def get_repo_shortname(self):
+        return (
+            self.config.get('reponame') or
+            super(ConfigOptionsEnvironmentMixin, self).get_repo_shortname()
+            )
+
+    def get_emailprefix(self):
+        emailprefix = self.config.get('emailprefix')
+        if emailprefix is not None:
+            emailprefix = emailprefix.strip()
+            if emailprefix:
+                emailprefix += ' '
+        else:
+            emailprefix = '[%(repo_shortname)s] '
+        short_name = self.get_repo_shortname()
+        try:
+            return emailprefix % {'repo_shortname': short_name}
+        except:
+            self.get_logger().error(
+                '*** Invalid multimailhook.emailPrefix: %s\n' % emailprefix +
+                '*** %s\n' % sys.exc_info()[1] +
+                "*** Only the '%(repo_shortname)s' placeholder is allowed\n"
+                )
+            raise ConfigurationException(
+                '"%s" is not an allowed setting for emailPrefix' % emailprefix
+                )
+
+    def get_sender(self):
+        return self.config.get('envelopesender')
+
+    def process_addr(self, addr, change):
+        if addr.lower() == 'author':
+            if hasattr(change, 'author'):
+                return change.author
+            else:
+                return None
+        elif addr.lower() == 'pusher':
+            return self.get_pusher_email()
+        elif addr.lower() == 'none':
+            return None
+        else:
+            return addr
+
+    def get_fromaddr(self, change=None):
+        fromaddr = self.config.get('from')
+        if change:
+            specific_fromaddr = change.get_specific_fromaddr()
+            if specific_fromaddr:
+                fromaddr = specific_fromaddr
+        if fromaddr:
+            fromaddr = self.process_addr(fromaddr, change)
+        if fromaddr:
+            return fromaddr
+        return super(ConfigOptionsEnvironmentMixin, self).get_fromaddr(change)
+
+    def get_reply_to_refchange(self, refchange):
+        if self.__reply_to_refchange is None:
+            return super(ConfigOptionsEnvironmentMixin, self).get_reply_to_refchange(refchange)
+        else:
+            return self.process_addr(self.__reply_to_refchange, refchange)
+
+    def get_reply_to_commit(self, revision):
+        if self.__reply_to_commit is None:
+            return super(ConfigOptionsEnvironmentMixin, self).get_reply_to_commit(revision)
+        else:
+            return self.process_addr(self.__reply_to_commit, revision)
+
+    def get_scancommitforcc(self):
+        return self.config.get('scancommitforcc')
+
+
+class FilterLinesEnvironmentMixin(Environment):
+    """Handle encoding and maximum line length of body lines.
+
+        email_max_line_length (int or None)
+
+            The maximum length of any single line in the email body.
+            Longer lines are truncated at that length with ' [...]'
+            appended.
+
+        strict_utf8 (bool)
+
+            If this field is set to True, then the email body text is
+            expected to be UTF-8.  Any invalid characters are
+            converted to U+FFFD, the Unicode replacement character
+            (encoded as UTF-8, of course).
+
+    """
+
+    def __init__(self, strict_utf8=True,
+                 email_max_line_length=500, max_subject_length=500,
+                 **kw):
+        super(FilterLinesEnvironmentMixin, self).__init__(**kw)
+        self.__strict_utf8 = strict_utf8
+        self.__email_max_line_length = email_max_line_length
+        self.__max_subject_length = max_subject_length
+
+    def filter_body(self, lines):
+        lines = super(FilterLinesEnvironmentMixin, self).filter_body(lines)
+        if self.__strict_utf8:
+            if not PYTHON3:
+                lines = (line.decode(ENCODING, 'replace') for line in lines)
+            # Limit the line length in Unicode-space to avoid
+            # splitting characters:
+            if self.__email_max_line_length > 0:
+                lines = limit_linelength(lines, self.__email_max_line_length)
+            if not PYTHON3:
+                lines = (line.encode(ENCODING, 'replace') for line in lines)
+        elif self.__email_max_line_length:
+            lines = limit_linelength(lines, self.__email_max_line_length)
+
+        return lines
+
+    def get_max_subject_length(self):
+        return self.__max_subject_length
+
+
+class ConfigFilterLinesEnvironmentMixin(
+        ConfigEnvironmentMixin,
+        FilterLinesEnvironmentMixin,
+        ):
+    """Handle encoding and maximum line length based on config."""
+
+    def __init__(self, config, **kw):
+        strict_utf8 = config.get_bool('emailstrictutf8', default=None)
+        if strict_utf8 is not None:
+            kw['strict_utf8'] = strict_utf8
+
+        email_max_line_length = config.get('emailmaxlinelength')
+        if email_max_line_length is not None:
+            kw['email_max_line_length'] = int(email_max_line_length)
+
+        max_subject_length = config.get('subjectMaxLength', default=email_max_line_length)
+        if max_subject_length is not None:
+            kw['max_subject_length'] = int(max_subject_length)
+
+        super(ConfigFilterLinesEnvironmentMixin, self).__init__(
+            config=config, **kw
+            )
+
+
+class MaxlinesEnvironmentMixin(Environment):
+    """Limit the email body to a specified number of lines."""
+
+    def __init__(self, emailmaxlines, **kw):
+        super(MaxlinesEnvironmentMixin, self).__init__(**kw)
+        self.__emailmaxlines = emailmaxlines
+
+    def filter_body(self, lines):
+        lines = super(MaxlinesEnvironmentMixin, self).filter_body(lines)
+        if self.__emailmaxlines > 0:
+            lines = limit_lines(lines, self.__emailmaxlines)
+        return lines
+
+
+class ConfigMaxlinesEnvironmentMixin(
+        ConfigEnvironmentMixin,
+        MaxlinesEnvironmentMixin,
+        ):
+    """Limit the email body to the number of lines specified in config."""
+
+    def __init__(self, config, **kw):
+        emailmaxlines = int(config.get('emailmaxlines', default='0'))
+        super(ConfigMaxlinesEnvironmentMixin, self).__init__(
+            config=config,
+            emailmaxlines=emailmaxlines,
+            **kw
+            )
+
+
+class FQDNEnvironmentMixin(Environment):
+    """A mixin that sets the host's FQDN to its constructor argument."""
+
+    def __init__(self, fqdn, **kw):
+        super(FQDNEnvironmentMixin, self).__init__(**kw)
+        self.COMPUTED_KEYS += ['fqdn']
+        self.__fqdn = fqdn
+
+    def get_fqdn(self):
+        """Return the fully-qualified domain name for this host.
+
+        Return None if it is unavailable or unwanted."""
+
+        return self.__fqdn
+
+
+class ConfigFQDNEnvironmentMixin(
+        ConfigEnvironmentMixin,
+        FQDNEnvironmentMixin,
+        ):
+    """Read the FQDN from the config."""
+
+    def __init__(self, config, **kw):
+        fqdn = config.get('fqdn')
+        super(ConfigFQDNEnvironmentMixin, self).__init__(
+            config=config,
+            fqdn=fqdn,
+            **kw
+            )
+
+
+class ComputeFQDNEnvironmentMixin(FQDNEnvironmentMixin):
+    """Get the FQDN by calling socket.getfqdn()."""
+
+    def __init__(self, **kw):
+        super(ComputeFQDNEnvironmentMixin, self).__init__(
+            fqdn=socket.getfqdn(),
+            **kw
+            )
+
+
+class PusherDomainEnvironmentMixin(ConfigEnvironmentMixin):
+    """Deduce pusher_email from pusher by appending an emaildomain."""
+
+    def __init__(self, **kw):
+        super(PusherDomainEnvironmentMixin, self).__init__(**kw)
+        self.__emaildomain = self.config.get('emaildomain')
+
+    def get_pusher_email(self):
+        if self.__emaildomain:
+            # Derive the pusher's full email address in the default way:
+            return '%s@%s' % (self.get_pusher(), self.__emaildomain)
+        else:
+            return super(PusherDomainEnvironmentMixin, self).get_pusher_email()
+
+
+class StaticRecipientsEnvironmentMixin(Environment):
+    """Set recipients statically based on constructor parameters."""
+
+    def __init__(
+            self,
+            refchange_recipients, announce_recipients, revision_recipients, scancommitforcc,
+            **kw
+            ):
+        super(StaticRecipientsEnvironmentMixin, self).__init__(**kw)
+
+        # The recipients for various types of notification emails, as
+        # RFC 2822 email addresses separated by commas (or the empty
+        # string if no recipients are configured).  Although there is
+        # a mechanism to choose the recipient lists based on on the
+        # actual *contents* of the change being reported, we only
+        # choose based on the *type* of the change.  Therefore we can
+        # compute them once and for all:
+        self.__refchange_recipients = refchange_recipients
+        self.__announce_recipients = announce_recipients
+        self.__revision_recipients = revision_recipients
+
+    def check(self):
+        if not (self.get_refchange_recipients(None) or
+                self.get_announce_recipients(None) or
+                self.get_revision_recipients(None) or
+                self.get_scancommitforcc()):
+            raise ConfigurationException('No email recipients configured!')
+        super(StaticRecipientsEnvironmentMixin, self).check()
+
+    def get_refchange_recipients(self, refchange):
+        if self.__refchange_recipients is None:
+            return super(StaticRecipientsEnvironmentMixin,
+                         self).get_refchange_recipients(refchange)
+        return self.__refchange_recipients
+
+    def get_announce_recipients(self, annotated_tag_change):
+        if self.__announce_recipients is None:
+            return super(StaticRecipientsEnvironmentMixin,
+                         self).get_refchange_recipients(annotated_tag_change)
+        return self.__announce_recipients
+
+    def get_revision_recipients(self, revision):
+        if self.__revision_recipients is None:
+            return super(StaticRecipientsEnvironmentMixin,
+                         self).get_refchange_recipients(revision)
+        return self.__revision_recipients
+
+
+class CLIRecipientsEnvironmentMixin(Environment):
+    """Mixin storing recipients information coming from the
+    command-line."""
+
+    def __init__(self, cli_recipients=None, **kw):
+        super(CLIRecipientsEnvironmentMixin, self).__init__(**kw)
+        self.__cli_recipients = cli_recipients
+
+    def get_refchange_recipients(self, refchange):
+        if self.__cli_recipients is None:
+            return super(CLIRecipientsEnvironmentMixin,
+                         self).get_refchange_recipients(refchange)
+        return self.__cli_recipients
+
+    def get_announce_recipients(self, annotated_tag_change):
+        if self.__cli_recipients is None:
+            return super(CLIRecipientsEnvironmentMixin,
+                         self).get_announce_recipients(annotated_tag_change)
+        return self.__cli_recipients
+
+    def get_revision_recipients(self, revision):
+        if self.__cli_recipients is None:
+            return super(CLIRecipientsEnvironmentMixin,
+                         self).get_revision_recipients(revision)
+        return self.__cli_recipients
+
+
+class ConfigRecipientsEnvironmentMixin(
+        ConfigEnvironmentMixin,
+        StaticRecipientsEnvironmentMixin
+        ):
+    """Determine recipients statically based on config."""
+
+    def __init__(self, config, **kw):
+        super(ConfigRecipientsEnvironmentMixin, self).__init__(
+            config=config,
+            refchange_recipients=self._get_recipients(
+                config, 'refchangelist', 'mailinglist',
+                ),
+            announce_recipients=self._get_recipients(
+                config, 'announcelist', 'refchangelist', 'mailinglist',
+                ),
+            revision_recipients=self._get_recipients(
+                config, 'commitlist', 'mailinglist',
+                ),
+            scancommitforcc=config.get('scancommitforcc'),
+            **kw
+            )
+
+    def _get_recipients(self, config, *names):
+        """Return the recipients for a particular type of message.
+
+        Return the list of email addresses to which a particular type
+        of notification email should be sent, by looking at the config
+        value for "multimailhook.$name" for each of names.  Use the
+        value from the first name that is configured.  The return
+        value is a (possibly empty) string containing RFC 2822 email
+        addresses separated by commas.  If no configuration could be
+        found, raise a ConfigurationException."""
+
+        for name in names:
+            lines = config.get_all(name)
+            if lines is not None:
+                lines = [line.strip() for line in lines]
+                # Single "none" is a special value equivalen to empty string.
+                if lines == ['none']:
+                    lines = ['']
+                return ', '.join(lines)
+        else:
+            return ''
+
+
+class StaticRefFilterEnvironmentMixin(Environment):
+    """Set branch filter statically based on constructor parameters."""
+
+    def __init__(self, ref_filter_incl_regex, ref_filter_excl_regex,
+                 ref_filter_do_send_regex, ref_filter_dont_send_regex,
+                 **kw):
+        super(StaticRefFilterEnvironmentMixin, self).__init__(**kw)
+
+        if ref_filter_incl_regex and ref_filter_excl_regex:
+            raise ConfigurationException(
+                "Cannot specify both a ref inclusion and exclusion regex.")
+        self.__is_inclusion_filter = bool(ref_filter_incl_regex)
+        default_exclude = self.get_default_ref_ignore_regex()
+        if ref_filter_incl_regex:
+            ref_filter_regex = ref_filter_incl_regex
+        elif ref_filter_excl_regex:
+            ref_filter_regex = ref_filter_excl_regex + '|' + default_exclude
+        else:
+            ref_filter_regex = default_exclude
+        try:
+            self.__compiled_regex = re.compile(ref_filter_regex)
+        except Exception:
+            raise ConfigurationException(
+                'Invalid Ref Filter Regex "%s": %s' % (ref_filter_regex, sys.exc_info()[1]))
+
+        if ref_filter_do_send_regex and ref_filter_dont_send_regex:
+            raise ConfigurationException(
+                "Cannot specify both a ref doSend and dontSend regex.")
+        self.__is_do_send_filter = bool(ref_filter_do_send_regex)
+        if ref_filter_do_send_regex:
+            ref_filter_send_regex = ref_filter_do_send_regex
+        elif ref_filter_dont_send_regex:
+            ref_filter_send_regex = ref_filter_dont_send_regex
+        else:
+            ref_filter_send_regex = '.*'
+            self.__is_do_send_filter = True
+        try:
+            self.__send_compiled_regex = re.compile(ref_filter_send_regex)
+        except Exception:
+            raise ConfigurationException(
+                'Invalid Ref Filter Regex "%s": %s' %
+                (ref_filter_send_regex, sys.exc_info()[1]))
+
+    def get_ref_filter_regex(self, send_filter=False):
+        if send_filter:
+            return self.__send_compiled_regex, self.__is_do_send_filter
+        else:
+            return self.__compiled_regex, self.__is_inclusion_filter
+
+
+class ConfigRefFilterEnvironmentMixin(
+        ConfigEnvironmentMixin,
+        StaticRefFilterEnvironmentMixin
+        ):
+    """Determine branch filtering statically based on config."""
+
+    def _get_regex(self, config, key):
+        """Get a list of whitespace-separated regex. The refFilter* config
+        variables are multivalued (hence the use of get_all), and we
+        allow each entry to be a whitespace-separated list (hence the
+        split on each line). The whole thing is glued into a single regex."""
+        values = config.get_all(key)
+        if values is None:
+            return values
+        items = []
+        for line in values:
+            for i in line.split():
+                items.append(i)
+        if items == []:
+            return None
+        return '|'.join(items)
+
+    def __init__(self, config, **kw):
+        super(ConfigRefFilterEnvironmentMixin, self).__init__(
+            config=config,
+            ref_filter_incl_regex=self._get_regex(config, 'refFilterInclusionRegex'),
+            ref_filter_excl_regex=self._get_regex(config, 'refFilterExclusionRegex'),
+            ref_filter_do_send_regex=self._get_regex(config, 'refFilterDoSendRegex'),
+            ref_filter_dont_send_regex=self._get_regex(config, 'refFilterDontSendRegex'),
+            **kw
+            )
+
+
+class ProjectdescEnvironmentMixin(Environment):
+    """Make a "projectdesc" value available for templates.
+
+    By default, it is set to the first line of $GIT_DIR/description
+    (if that file is present and appears to be set meaningfully)."""
+
+    def __init__(self, **kw):
+        super(ProjectdescEnvironmentMixin, self).__init__(**kw)
+        self.COMPUTED_KEYS += ['projectdesc']
+
+    def get_projectdesc(self):
+        """Return a one-line descripition of the project."""
+
+        git_dir = get_git_dir()
+        try:
+            projectdesc = open(os.path.join(git_dir, 'description')).readline().strip()
+            if projectdesc and not projectdesc.startswith('Unnamed repository'):
+                return projectdesc
+        except IOError:
+            pass
+
+        return 'UNNAMED PROJECT'
+
+
+class GenericEnvironmentMixin(Environment):
+    def get_pusher(self):
+        return self.osenv.get('USER', self.osenv.get('USERNAME', 'unknown user'))
+
+
+class GitoliteEnvironmentHighPrecMixin(Environment):
+    def get_pusher(self):
+        return self.osenv.get('GL_USER', 'unknown user')
+
+
+class GitoliteEnvironmentLowPrecMixin(
+        ConfigEnvironmentMixin,
+        Environment):
+
+    def get_repo_shortname(self):
+        # The gitolite environment variable $GL_REPO is a pretty good
+        # repo_shortname (though it's probably not as good as a value
+        # the user might have explicitly put in his config).
+        return (
+            self.osenv.get('GL_REPO', None) or
+            super(GitoliteEnvironmentLowPrecMixin, self).get_repo_shortname()
+            )
+
+    @staticmethod
+    def _compile_regex(re_template):
+        return (
+            re.compile(re_template % x)
+            for x in (
+                r'BEGIN\s+USER\s+EMAILS',
+                r'([^\s]+)\s+(.*)',
+                r'END\s+USER\s+EMAILS',
+                ))
+
+    def get_fromaddr(self, change=None):
+        GL_USER = self.osenv.get('GL_USER')
+        if GL_USER is not None:
+            # Find the path to gitolite.conf.  Note that gitolite v3
+            # did away with the GL_ADMINDIR and GL_CONF environment
+            # variables (they are now hard-coded).
+            GL_ADMINDIR = self.osenv.get(
+                'GL_ADMINDIR',
+                os.path.expanduser(os.path.join('~', '.gitolite')))
+            GL_CONF = self.osenv.get(
+                'GL_CONF',
+                os.path.join(GL_ADMINDIR, 'conf', 'gitolite.conf'))
+
+            mailaddress_map = self.config.get('MailaddressMap')
+            # If relative, consider relative to GL_CONF:
+            if mailaddress_map:
+                mailaddress_map = os.path.join(os.path.dirname(GL_CONF),
+                                               mailaddress_map)
+                if os.path.isfile(mailaddress_map):
+                    f = open(mailaddress_map, 'rU')
+                    try:
+                        # Leading '#' is optional
+                        re_begin, re_user, re_end = self._compile_regex(
+                            r'^(?:\s*#)?\s*%s\s*$')
+                        for l in f:
+                            l = l.rstrip('\n')
+                            if re_begin.match(l) or re_end.match(l):
+                                continue  # Ignore these lines
+                            m = re_user.match(l)
+                            if m:
+                                if m.group(1) == GL_USER:
+                                    return m.group(2)
+                                else:
+                                    continue  # Not this user, but not an error
+                            raise ConfigurationException(
+                                "Syntax error in mail address map.\n"
+                                "Check file {}.\n"
+                                "Line: {}".format(mailaddress_map, l))
+
+                    finally:
+                        f.close()
+
+            if os.path.isfile(GL_CONF):
+                f = open(GL_CONF, 'rU')
+                try:
+                    in_user_emails_section = False
+                    re_begin, re_user, re_end = self._compile_regex(
+                        r'^\s*#\s*%s\s*$')
+                    for l in f:
+                        l = l.rstrip('\n')
+                        if not in_user_emails_section:
+                            if re_begin.match(l):
+                                in_user_emails_section = True
+                            continue
+                        if re_end.match(l):
+                            break
+                        m = re_user.match(l)
+                        if m and m.group(1) == GL_USER:
+                            return m.group(2)
+                finally:
+                    f.close()
+        return super(GitoliteEnvironmentLowPrecMixin, self).get_fromaddr(change)
+
+
+class IncrementalDateTime(object):
+    """Simple wrapper to give incremental date/times.
+
+    Each call will result in a date/time a second later than the
+    previous call.  This can be used to falsify email headers, to
+    increase the likelihood that email clients sort the emails
+    correctly."""
+
+    def __init__(self):
+        self.time = time.time()
+        self.next = self.__next__  # Python 2 backward compatibility
+
+    def __next__(self):
+        formatted = formatdate(self.time, True)
+        self.time += 1
+        return formatted
+
+
+class StashEnvironmentHighPrecMixin(Environment):
+    def __init__(self, user=None, repo=None, **kw):
+        super(StashEnvironmentHighPrecMixin,
+              self).__init__(user=user, repo=repo, **kw)
+        self.__user = user
+        self.__repo = repo
+
+    def get_pusher(self):
+        return re.match(r'(.*?)\s*<', self.__user).group(1)
+
+    def get_pusher_email(self):
+        return self.__user
+
+
+class StashEnvironmentLowPrecMixin(Environment):
+    def __init__(self, user=None, repo=None, **kw):
+        super(StashEnvironmentLowPrecMixin, self).__init__(**kw)
+        self.__repo = repo
+        self.__user = user
+
+    def get_repo_shortname(self):
+        return self.__repo
+
+    def get_fromaddr(self, change=None):
+        return self.__user
+
+
+class GerritEnvironmentHighPrecMixin(Environment):
+    def __init__(self, project=None, submitter=None, update_method=None, **kw):
+        super(GerritEnvironmentHighPrecMixin,
+              self).__init__(submitter=submitter, project=project, **kw)
+        self.__project = project
+        self.__submitter = submitter
+        self.__update_method = update_method
+        "Make an 'update_method' value available for templates."
+        self.COMPUTED_KEYS += ['update_method']
+
+    def get_pusher(self):
+        if self.__submitter:
+            if self.__submitter.find('<') != -1:
+                # Submitter has a configured email, we transformed
+                # __submitter into an RFC 2822 string already.
+                return re.match(r'(.*?)\s*<', self.__submitter).group(1)
+            else:
+                # Submitter has no configured email, it's just his name.
+                return self.__submitter
+        else:
+            # If we arrive here, this means someone pushed "Submit" from
+            # the gerrit web UI for the CR (or used one of the programmatic
+            # APIs to do the same, such as gerrit review) and the
+            # merge/push was done by the Gerrit user.  It was technically
+            # triggered by someone else, but sadly we have no way of
+            # determining who that someone else is at this point.
+            return 'Gerrit'  # 'unknown user'?
+
+    def get_pusher_email(self):
+        if self.__submitter:
+            return self.__submitter
+        else:
+            return super(GerritEnvironmentHighPrecMixin, self).get_pusher_email()
+
+    def get_default_ref_ignore_regex(self):
+        default = super(GerritEnvironmentHighPrecMixin, self).get_default_ref_ignore_regex()
+        return default + '|^refs/changes/|^refs/cache-automerge/|^refs/meta/'
+
+    def get_revision_recipients(self, revision):
+        # Merge commits created by Gerrit when users hit "Submit this patchset"
+        # in the Web UI (or do equivalently with REST APIs or the gerrit review
+        # command) are not something users want to see an individual email for.
+        # Filter them out.
+        committer = read_git_output(['log', '--no-walk', '--format=%cN',
+                                     revision.rev.sha1])
+        if committer == 'Gerrit Code Review':
+            return []
+        else:
+            return super(GerritEnvironmentHighPrecMixin, self).get_revision_recipients(revision)
+
+    def get_update_method(self):
+        return self.__update_method
+
+
+class GerritEnvironmentLowPrecMixin(Environment):
+    def __init__(self, project=None, submitter=None, **kw):
+        super(GerritEnvironmentLowPrecMixin, self).__init__(**kw)
+        self.__project = project
+        self.__submitter = submitter
+
+    def get_repo_shortname(self):
+        return self.__project
+
+    def get_fromaddr(self, change=None):
+        if self.__submitter and self.__submitter.find('<') != -1:
+            return self.__submitter
+        else:
+            return super(GerritEnvironmentLowPrecMixin, self).get_fromaddr(change)
+
+
+class Push(object):
+    """Represent an entire push (i.e., a group of ReferenceChanges).
+
+    It is easy to figure out what commits were added to a *branch* by
+    a Reference change:
+
+        git rev-list change.old..change.new
+
+    or removed from a *branch*:
+
+        git rev-list change.new..change.old
+
+    But it is not quite so trivial to determine which entirely new
+    commits were added to the *repository* by a push and which old
+    commits were discarded by a push.  A big part of the job of this
+    class is to figure out these things, and to make sure that new
+    commits are only detailed once even if they were added to multiple
+    references.
+
+    The first step is to determine the "other" references--those
+    unaffected by the current push.  They are computed by listing all
+    references then removing any affected by this push.  The results
+    are stored in Push._other_ref_sha1s.
+
+    The commits contained in the repository before this push were
+
+        git rev-list other1 other2 other3 ... change1.old change2.old ...
+
+    Where "changeN.old" is the old value of one of the references
+    affected by this push.
+
+    The commits contained in the repository after this push are
+
+        git rev-list other1 other2 other3 ... change1.new change2.new ...
+
+    The commits added by this push are the difference between these
+    two sets, which can be written
+
+        git rev-list \
+            ^other1 ^other2 ... \
+            ^change1.old ^change2.old ... \
+            change1.new change2.new ...
+
+    The commits removed by this push can be computed by
+
+        git rev-list \
+            ^other1 ^other2 ... \
+            ^change1.new ^change2.new ... \
+            change1.old change2.old ...
+
+    The last point is that it is possible that other pushes are
+    occurring simultaneously to this one, so reference values can
+    change at any time.  It is impossible to eliminate all race
+    conditions, but we reduce the window of time during which problems
+    can occur by translating reference names to SHA1s as soon as
+    possible and working with SHA1s thereafter (because SHA1s are
+    immutable)."""
+
+    # A map {(changeclass, changetype): integer} specifying the order
+    # that reference changes will be processed if multiple reference
+    # changes are included in a single push.  The order is significant
+    # mostly because new commit notifications are threaded together
+    # with the first reference change that includes the commit.  The
+    # following order thus causes commits to be grouped with branch
+    # changes (as opposed to tag changes) if possible.
+    SORT_ORDER = dict(
+        (value, i) for (i, value) in enumerate([
+            (BranchChange, 'update'),
+            (BranchChange, 'create'),
+            (AnnotatedTagChange, 'update'),
+            (AnnotatedTagChange, 'create'),
+            (NonAnnotatedTagChange, 'update'),
+            (NonAnnotatedTagChange, 'create'),
+            (BranchChange, 'delete'),
+            (AnnotatedTagChange, 'delete'),
+            (NonAnnotatedTagChange, 'delete'),
+            (OtherReferenceChange, 'update'),
+            (OtherReferenceChange, 'create'),
+            (OtherReferenceChange, 'delete'),
+            ])
+        )
+
+    def __init__(self, environment, changes, ignore_other_refs=False):
+        self.changes = sorted(changes, key=self._sort_key)
+        self.__other_ref_sha1s = None
+        self.__cached_commits_spec = {}
+        self.environment = environment
+
+        if ignore_other_refs:
+            self.__other_ref_sha1s = set()
+
+    @classmethod
+    def _sort_key(klass, change):
+        return (klass.SORT_ORDER[change.__class__, change.change_type], change.refname,)
+
+    @property
+    def _other_ref_sha1s(self):
+        """The GitObjects referred to by references unaffected by this push.
+        """
+        if self.__other_ref_sha1s is None:
+            # The refnames being changed by this push:
+            updated_refs = set(
+                change.refname
+                for change in self.changes
+                )
+
+            # The SHA-1s of commits referred to by all references in this
+            # repository *except* updated_refs:
+            sha1s = set()
+            fmt = (
+                '%(objectname) %(objecttype) %(refname)\n'
+                '%(*objectname) %(*objecttype) %(refname)'
+                )
+            ref_filter_regex, is_inclusion_filter = \
+                self.environment.get_ref_filter_regex()
+            for line in read_git_lines(
+                    ['for-each-ref', '--format=%s' % (fmt,)]):
+                (sha1, type, name) = line.split(' ', 2)
+                if (sha1 and type == 'commit' and
+                        name not in updated_refs and
+                        include_ref(name, ref_filter_regex, is_inclusion_filter)):
+                    sha1s.add(sha1)
+
+            self.__other_ref_sha1s = sha1s
+
+        return self.__other_ref_sha1s
+
+    def _get_commits_spec_incl(self, new_or_old, reference_change=None):
+        """Get new or old SHA-1 from one or each of the changed refs.
+
+        Return a list of SHA-1 commit identifier strings suitable as
+        arguments to 'git rev-list' (or 'git log' or ...).  The
+        returned identifiers are either the old or new values from one
+        or all of the changed references, depending on the values of
+        new_or_old and reference_change.
+
+        new_or_old is either the string 'new' or the string 'old'.  If
+        'new', the returned SHA-1 identifiers are the new values from
+        each changed reference.  If 'old', the SHA-1 identifiers are
+        the old values from each changed reference.
+
+        If reference_change is specified and not None, only the new or
+        old reference from the specified reference is included in the
+        return value.
+
+        This function returns None if there are no matching revisions
+        (e.g., because a branch was deleted and new_or_old is 'new').
+        """
+
+        if not reference_change:
+            incl_spec = sorted(
+                getattr(change, new_or_old).sha1
+                for change in self.changes
+                if getattr(change, new_or_old)
+                )
+            if not incl_spec:
+                incl_spec = None
+        elif not getattr(reference_change, new_or_old).commit_sha1:
+            incl_spec = None
+        else:
+            incl_spec = [getattr(reference_change, new_or_old).commit_sha1]
+        return incl_spec
+
+    def _get_commits_spec_excl(self, new_or_old):
+        """Get exclusion revisions for determining new or discarded commits.
+
+        Return a list of strings suitable as arguments to 'git
+        rev-list' (or 'git log' or ...) that will exclude all
+        commits that, depending on the value of new_or_old, were
+        either previously in the repository (useful for determining
+        which commits are new to the repository) or currently in the
+        repository (useful for determining which commits were
+        discarded from the repository).
+
+        new_or_old is either the string 'new' or the string 'old'.  If
+        'new', the commits to be excluded are those that were in the
+        repository before the push.  If 'old', the commits to be
+        excluded are those that are currently in the repository.  """
+
+        old_or_new = {'old': 'new', 'new': 'old'}[new_or_old]
+        excl_revs = self._other_ref_sha1s.union(
+            getattr(change, old_or_new).sha1
+            for change in self.changes
+            if getattr(change, old_or_new).type in ['commit', 'tag']
+            )
+        return ['^' + sha1 for sha1 in sorted(excl_revs)]
+
+    def get_commits_spec(self, new_or_old, reference_change=None):
+        """Get rev-list arguments for added or discarded commits.
+
+        Return a list of strings suitable as arguments to 'git
+        rev-list' (or 'git log' or ...) that select those commits
+        that, depending on the value of new_or_old, are either new to
+        the repository or were discarded from the repository.
+
+        new_or_old is either the string 'new' or the string 'old'.  If
+        'new', the returned list is used to select commits that are
+        new to the repository.  If 'old', the returned value is used
+        to select the commits that have been discarded from the
+        repository.
+
+        If reference_change is specified and not None, the new or
+        discarded commits are limited to those that are reachable from
+        the new or old value of the specified reference.
+
+        This function returns None if there are no added (or discarded)
+        revisions.
+        """
+        key = (new_or_old, reference_change)
+        if key not in self.__cached_commits_spec:
+            ret = self._get_commits_spec_incl(new_or_old, reference_change)
+            if ret is not None:
+                ret.extend(self._get_commits_spec_excl(new_or_old))
+            self.__cached_commits_spec[key] = ret
+        return self.__cached_commits_spec[key]
+
+    def get_new_commits(self, reference_change=None):
+        """Return a list of commits added by this push.
+
+        Return a list of the object names of commits that were added
+        by the part of this push represented by reference_change.  If
+        reference_change is None, then return a list of *all* commits
+        added by this push."""
+
+        spec = self.get_commits_spec('new', reference_change)
+        return git_rev_list(spec)
+
+    def get_discarded_commits(self, reference_change):
+        """Return a list of commits discarded by this push.
+
+        Return a list of the object names of commits that were
+        entirely discarded from the repository by the part of this
+        push represented by reference_change."""
+
+        spec = self.get_commits_spec('old', reference_change)
+        return git_rev_list(spec)
+
+    def send_emails(self, mailer, body_filter=None):
+        """Use send all of the notification emails needed for this push.
+
+        Use send all of the notification emails (including reference
+        change emails and commit emails) needed for this push.  Send
+        the emails using mailer.  If body_filter is not None, then use
+        it to filter the lines that are intended for the email
+        body."""
+
+        # The sha1s of commits that were introduced by this push.
+        # They will be removed from this set as they are processed, to
+        # guarantee that one (and only one) email is generated for
+        # each new commit.
+        unhandled_sha1s = set(self.get_new_commits())
+        send_date = IncrementalDateTime()
+        for change in self.changes:
+            sha1s = []
+            for sha1 in reversed(list(self.get_new_commits(change))):
+                if sha1 in unhandled_sha1s:
+                    sha1s.append(sha1)
+                    unhandled_sha1s.remove(sha1)
+
+            # Check if we've got anyone to send to
+            if not change.recipients:
+                change.environment.log_warning(
+                    '*** no recipients configured so no email will be sent\n'
+                    '*** for %r update %s->%s'
+                    % (change.refname, change.old.sha1, change.new.sha1,)
+                    )
+            else:
+                if not change.environment.quiet:
+                    change.environment.log_msg(
+                        'Sending notification emails to: %s' % (change.recipients,))
+                extra_values = {'send_date': next(send_date)}
+
+                rev = change.send_single_combined_email(sha1s)
+                if rev:
+                    mailer.send(
+                        change.generate_combined_email(self, rev, body_filter, extra_values),
+                        rev.recipients,
+                        )
+                    # This change is now fully handled; no need to handle
+                    # individual revisions any further.
+                    continue
+                else:
+                    mailer.send(
+                        change.generate_email(self, body_filter, extra_values),
+                        change.recipients,
+                        )
+
+            max_emails = change.environment.maxcommitemails
+            if max_emails and len(sha1s) > max_emails:
+                change.environment.log_warning(
+                    '*** Too many new commits (%d), not sending commit emails.\n' % len(sha1s) +
+                    '*** Try setting multimailhook.maxCommitEmails to a greater value\n' +
+                    '*** Currently, multimailhook.maxCommitEmails=%d' % max_emails
+                    )
+                return
+
+            for (num, sha1) in enumerate(sha1s):
+                rev = Revision(change, GitObject(sha1), num=num + 1, tot=len(sha1s))
+                if len(rev.parents) > 1 and change.environment.excludemergerevisions:
+                    # skipping a merge commit
+                    continue
+                if not rev.recipients and rev.cc_recipients:
+                    change.environment.log_msg('*** Replacing Cc: with To:')
+                    rev.recipients = rev.cc_recipients
+                    rev.cc_recipients = None
+                if rev.recipients:
+                    extra_values = {'send_date': next(send_date)}
+                    mailer.send(
+                        rev.generate_email(self, body_filter, extra_values),
+                        rev.recipients,
+                        )
+
+        # Consistency check:
+        if unhandled_sha1s:
+            change.environment.log_error(
+                'ERROR: No emails were sent for the following new commits:\n'
+                '    %s'
+                % ('\n    '.join(sorted(unhandled_sha1s)),)
+                )
+
+
+def include_ref(refname, ref_filter_regex, is_inclusion_filter):
+    does_match = bool(ref_filter_regex.search(refname))
+    if is_inclusion_filter:
+        return does_match
+    else:  # exclusion filter -- we include the ref if the regex doesn't match
+        return not does_match
+
+
+def run_as_post_receive_hook(environment, mailer):
+    environment.check()
+    send_filter_regex, send_is_inclusion_filter = environment.get_ref_filter_regex(True)
+    ref_filter_regex, is_inclusion_filter = environment.get_ref_filter_regex(False)
+    changes = []
+    while True:
+        line = read_line(sys.stdin)
+        if line == '':
+            break
+        (oldrev, newrev, refname) = line.strip().split(' ', 2)
+        environment.get_logger().debug(
+            "run_as_post_receive_hook: oldrev=%s, newrev=%s, refname=%s" %
+            (oldrev, newrev, refname))
+
+        if not include_ref(refname, ref_filter_regex, is_inclusion_filter):
+            continue
+        if not include_ref(refname, send_filter_regex, send_is_inclusion_filter):
+            continue
+        changes.append(
+            ReferenceChange.create(environment, oldrev, newrev, refname)
+            )
+    if not changes:
+        mailer.close()
+        return
+    push = Push(environment, changes)
+    try:
+        push.send_emails(mailer, body_filter=environment.filter_body)
+    finally:
+        mailer.close()
+
+
+def run_as_update_hook(environment, mailer, refname, oldrev, newrev, force_send=False):
+    environment.check()
+    send_filter_regex, send_is_inclusion_filter = environment.get_ref_filter_regex(True)
+    ref_filter_regex, is_inclusion_filter = environment.get_ref_filter_regex(False)
+    if not include_ref(refname, ref_filter_regex, is_inclusion_filter):
+        return
+    if not include_ref(refname, send_filter_regex, send_is_inclusion_filter):
+        return
+    changes = [
+        ReferenceChange.create(
+            environment,
+            read_git_output(['rev-parse', '--verify', oldrev]),
+            read_git_output(['rev-parse', '--verify', newrev]),
+            refname,
+            ),
+        ]
+    if not changes:
+        mailer.close()
+        return
+    push = Push(environment, changes, force_send)
+    try:
+        push.send_emails(mailer, body_filter=environment.filter_body)
+    finally:
+        mailer.close()
+
+
+def check_ref_filter(environment):
+    send_filter_regex, send_is_inclusion = environment.get_ref_filter_regex(True)
+    ref_filter_regex, ref_is_inclusion = environment.get_ref_filter_regex(False)
+
+    def inc_exc_lusion(b):
+        if b:
+            return 'inclusion'
+        else:
+            return 'exclusion'
+
+    if send_filter_regex:
+        sys.stdout.write("DoSend/DontSend filter regex (" +
+                         (inc_exc_lusion(send_is_inclusion)) +
+                         '): ' + send_filter_regex.pattern +
+                         '\n')
+    if send_filter_regex:
+        sys.stdout.write("Include/Exclude filter regex (" +
+                         (inc_exc_lusion(ref_is_inclusion)) +
+                         '): ' + ref_filter_regex.pattern +
+                         '\n')
+    sys.stdout.write(os.linesep)
+
+    sys.stdout.write(
+        "Refs marked as EXCLUDE are excluded by either refFilterInclusionRegex\n"
+        "or refFilterExclusionRegex. No emails will be sent for commits included\n"
+        "in these refs.\n"
+        "Refs marked as DONT-SEND are excluded by either refFilterDoSendRegex or\n"
+        "refFilterDontSendRegex, but not by either refFilterInclusionRegex or\n"
+        "refFilterExclusionRegex. Emails will be sent for commits included in these\n"
+        "refs only when the commit reaches a ref which isn't excluded.\n"
+        "Refs marked as DO-SEND are not excluded by any filter. Emails will\n"
+        "be sent normally for commits included in these refs.\n")
+
+    sys.stdout.write(os.linesep)
+
+    for refname in read_git_lines(['for-each-ref', '--format', '%(refname)']):
+        sys.stdout.write(refname)
+        if not include_ref(refname, ref_filter_regex, ref_is_inclusion):
+            sys.stdout.write(' EXCLUDE')
+        elif not include_ref(refname, send_filter_regex, send_is_inclusion):
+            sys.stdout.write(' DONT-SEND')
+        else:
+            sys.stdout.write(' DO-SEND')
+
+        sys.stdout.write(os.linesep)
+
+
+def show_env(environment, out):
+    out.write('Environment values:\n')
+    for (k, v) in sorted(environment.get_values().items()):
+        if k:  # Don't show the {'' : ''} pair.
+            out.write('    %s : %r\n' % (k, v))
+    out.write('\n')
+    # Flush to avoid interleaving with further log output
+    out.flush()
+
+
+def check_setup(environment):
+    environment.check()
+    show_env(environment, sys.stdout)
+    sys.stdout.write("Now, checking that git-multimail's standard input "
+                     "is properly set ..." + os.linesep)
+    sys.stdout.write("Please type some text and then press Return" + os.linesep)
+    stdin = sys.stdin.readline()
+    sys.stdout.write("You have just entered:" + os.linesep)
+    sys.stdout.write(stdin)
+    sys.stdout.write("git-multimail seems properly set up." + os.linesep)
+
+
+def choose_mailer(config, environment):
+    mailer = config.get('mailer', default='sendmail')
+
+    if mailer == 'smtp':
+        smtpserver = config.get('smtpserver', default='localhost')
+        smtpservertimeout = float(config.get('smtpservertimeout', default=10.0))
+        smtpserverdebuglevel = int(config.get('smtpserverdebuglevel', default=0))
+        smtpencryption = config.get('smtpencryption', default='none')
+        smtpuser = config.get('smtpuser', default='')
+        smtppass = config.get('smtppass', default='')
+        smtpcacerts = config.get('smtpcacerts', default='')
+        mailer = SMTPMailer(
+            environment,
+            envelopesender=(environment.get_sender() or environment.get_fromaddr()),
+            smtpserver=smtpserver, smtpservertimeout=smtpservertimeout,
+            smtpserverdebuglevel=smtpserverdebuglevel,
+            smtpencryption=smtpencryption,
+            smtpuser=smtpuser,
+            smtppass=smtppass,
+            smtpcacerts=smtpcacerts
+            )
+    elif mailer == 'sendmail':
+        command = config.get('sendmailcommand')
+        if command:
+            command = shlex.split(command)
+        mailer = SendMailer(environment,
+                            command=command, envelopesender=environment.get_sender())
+    else:
+        environment.log_error(
+            'fatal: multimailhook.mailer is set to an incorrect value: "%s"\n' % mailer +
+            'please use one of "smtp" or "sendmail".'
+            )
+        sys.exit(1)
+    return mailer
+
+
+KNOWN_ENVIRONMENTS = {
+    'generic': {'highprec': GenericEnvironmentMixin},
+    'gitolite': {'highprec': GitoliteEnvironmentHighPrecMixin,
+                 'lowprec': GitoliteEnvironmentLowPrecMixin},
+    'stash': {'highprec': StashEnvironmentHighPrecMixin,
+              'lowprec': StashEnvironmentLowPrecMixin},
+    'gerrit': {'highprec': GerritEnvironmentHighPrecMixin,
+               'lowprec': GerritEnvironmentLowPrecMixin},
+    }
+
+
+def choose_environment(config, osenv=None, env=None, recipients=None,
+                       hook_info=None):
+    env_name = choose_environment_name(config, env, osenv)
+    environment_klass = build_environment_klass(env_name)
+    env = build_environment(environment_klass, env_name, config,
+                            osenv, recipients, hook_info)
+    return env
+
+
+def choose_environment_name(config, env, osenv):
+    if not osenv:
+        osenv = os.environ
+
+    if not env:
+        env = config.get('environment')
+
+    if not env:
+        if 'GL_USER' in osenv and 'GL_REPO' in osenv:
+            env = 'gitolite'
+        else:
+            env = 'generic'
+    return env
+
+
+COMMON_ENVIRONMENT_MIXINS = [
+    ConfigRecipientsEnvironmentMixin,
+    CLIRecipientsEnvironmentMixin,
+    ConfigRefFilterEnvironmentMixin,
+    ProjectdescEnvironmentMixin,
+    ConfigMaxlinesEnvironmentMixin,
+    ComputeFQDNEnvironmentMixin,
+    ConfigFilterLinesEnvironmentMixin,
+    PusherDomainEnvironmentMixin,
+    ConfigOptionsEnvironmentMixin,
+    ]
+
+
+def build_environment_klass(env_name):
+    if 'class' in KNOWN_ENVIRONMENTS[env_name]:
+        return KNOWN_ENVIRONMENTS[env_name]['class']
+
+    environment_mixins = []
+    known_env = KNOWN_ENVIRONMENTS[env_name]
+    if 'highprec' in known_env:
+        high_prec_mixin = known_env['highprec']
+        environment_mixins.append(high_prec_mixin)
+    environment_mixins = environment_mixins + COMMON_ENVIRONMENT_MIXINS
+    if 'lowprec' in known_env:
+        low_prec_mixin = known_env['lowprec']
+        environment_mixins.append(low_prec_mixin)
+    environment_mixins.append(Environment)
+    klass_name = env_name.capitalize() + 'Environment'
+    environment_klass = type(
+        klass_name,
+        tuple(environment_mixins),
+        {},
+        )
+    KNOWN_ENVIRONMENTS[env_name]['class'] = environment_klass
+    return environment_klass
+
+
+GerritEnvironment = build_environment_klass('gerrit')
+StashEnvironment = build_environment_klass('stash')
+GitoliteEnvironment = build_environment_klass('gitolite')
+GenericEnvironment = build_environment_klass('generic')
+
+
+def build_environment(environment_klass, env, config,
+                      osenv, recipients, hook_info):
+    environment_kw = {
+        'osenv': osenv,
+        'config': config,
+        }
+
+    if env == 'stash':
+        environment_kw['user'] = hook_info['stash_user']
+        environment_kw['repo'] = hook_info['stash_repo']
+    elif env == 'gerrit':
+        environment_kw['project'] = hook_info['project']
+        environment_kw['submitter'] = hook_info['submitter']
+        environment_kw['update_method'] = hook_info['update_method']
+
+    environment_kw['cli_recipients'] = recipients
+
+    return environment_klass(**environment_kw)
+
+
+def get_version():
+    oldcwd = os.getcwd()
+    try:
+        try:
+            os.chdir(os.path.dirname(os.path.realpath(__file__)))
+            git_version = read_git_output(['describe', '--tags', 'HEAD'])
+            if git_version == __version__:
+                return git_version
+            else:
+                return '%s (%s)' % (__version__, git_version)
+        except:
+            pass
+    finally:
+        os.chdir(oldcwd)
+    return __version__
+
+
+def compute_gerrit_options(options, args, required_gerrit_options,
+                           raw_refname):
+    if None in required_gerrit_options:
+        raise SystemExit("Error: Specify all of --oldrev, --newrev, --refname, "
+                         "and --project; or none of them.")
+
+    if options.environment not in (None, 'gerrit'):
+        raise SystemExit("Non-gerrit environments incompatible with --oldrev, "
+                         "--newrev, --refname, and --project")
+    options.environment = 'gerrit'
+
+    if args:
+        raise SystemExit("Error: Positional parameters not allowed with "
+                         "--oldrev, --newrev, and --refname.")
+
+    # Gerrit oddly omits 'refs/heads/' in the refname when calling
+    # ref-updated hook; put it back.
+    git_dir = get_git_dir()
+    if (not os.path.exists(os.path.join(git_dir, raw_refname)) and
+        os.path.exists(os.path.join(git_dir, 'refs', 'heads',
+                                    raw_refname))):
+        options.refname = 'refs/heads/' + options.refname
+
+    # New revisions can appear in a gerrit repository either due to someone
+    # pushing directly (in which case options.submitter will be set), or they
+    # can press "Submit this patchset" in the web UI for some CR (in which
+    # case options.submitter will not be set and gerrit will not have provided
+    # us the information about who pressed the button).
+    #
+    # Note for the nit-picky: I'm lumping in REST API calls and the ssh
+    # gerrit review command in with "Submit this patchset" button, since they
+    # have the same effect.
+    if options.submitter:
+        update_method = 'pushed'
+        # The submitter argument is almost an RFC 2822 email address; change it
+        # from 'User Name (email@domain)' to 'User Name <email@domain>' so it is
+        options.submitter = options.submitter.replace('(', '<').replace(')', '>')
+    else:
+        update_method = 'submitted'
+        # Gerrit knew who submitted this patchset, but threw that information
+        # away when it invoked this hook.  However, *IF* Gerrit created a
+        # merge to bring the patchset in (project 'Submit Type' is either
+        # "Always Merge", or is "Merge if Necessary" and happens to be
+        # necessary for this particular CR), then it will have the committer
+        # of that merge be 'Gerrit Code Review' and the author will be the
+        # person who requested the submission of the CR.  Since this is fairly
+        # likely for most gerrit installations (of a reasonable size), it's
+        # worth the extra effort to try to determine the actual submitter.
+        rev_info = read_git_lines(['log', '--no-walk', '--merges',
+                                   '--format=%cN%n%aN <%aE>', options.newrev])
+        if rev_info and rev_info[0] == 'Gerrit Code Review':
+            options.submitter = rev_info[1]
+
+    # We pass back refname, oldrev, newrev as args because then the
+    # gerrit ref-updated hook is much like the git update hook
+    return (options,
+            [options.refname, options.oldrev, options.newrev],
+            {'project': options.project, 'submitter': options.submitter,
+             'update_method': update_method})
+
+
+def check_hook_specific_args(options, args):
+    raw_refname = options.refname
+    # Convert each string option unicode for Python3.
+    if PYTHON3:
+        opts = ['environment', 'recipients', 'oldrev', 'newrev', 'refname',
+                'project', 'submitter', 'stash_user', 'stash_repo']
+        for opt in opts:
+            if not hasattr(options, opt):
+                continue
+            obj = getattr(options, opt)
+            if obj:
+                enc = obj.encode('utf-8', 'surrogateescape')
+                dec = enc.decode('utf-8', 'replace')
+                setattr(options, opt, dec)
+
+    # First check for stash arguments
+    if (options.stash_user is None) != (options.stash_repo is None):
+        raise SystemExit("Error: Specify both of --stash-user and "
+                         "--stash-repo or neither.")
+    if options.stash_user:
+        options.environment = 'stash'
+        return options, args, {'stash_user': options.stash_user,
+                               'stash_repo': options.stash_repo}
+
+    # Finally, check for gerrit specific arguments
+    required_gerrit_options = (options.oldrev, options.newrev, options.refname,
+                               options.project)
+    if required_gerrit_options != (None,) * 4:
+        return compute_gerrit_options(options, args, required_gerrit_options,
+                                      raw_refname)
+
+    # No special options in use, just return what we started with
+    return options, args, {}
+
+
+class Logger(object):
+    def parse_verbose(self, verbose):
+        if verbose > 0:
+            return logging.DEBUG
+        else:
+            return logging.INFO
+
+    def create_log_file(self, environment, name, path, verbosity):
+        log_file = logging.getLogger(name)
+        file_handler = logging.FileHandler(path)
+        log_fmt = logging.Formatter("%(asctime)s [%(levelname)-5.5s]  %(message)s")
+        file_handler.setFormatter(log_fmt)
+        log_file.addHandler(file_handler)
+        log_file.setLevel(verbosity)
+        return log_file
+
+    def __init__(self, environment):
+        self.environment = environment
+        self.loggers = []
+        stderr_log = logging.getLogger('git_multimail.stderr')
+
+        class EncodedStderr(object):
+            def write(self, x):
+                write_str(sys.stderr, x)
+
+            def flush(self):
+                sys.stderr.flush()
+
+        stderr_handler = logging.StreamHandler(EncodedStderr())
+        stderr_log.addHandler(stderr_handler)
+        stderr_log.setLevel(self.parse_verbose(environment.verbose))
+        self.loggers.append(stderr_log)
+
+        if environment.debug_log_file is not None:
+            debug_log_file = self.create_log_file(
+                environment, 'git_multimail.debug', environment.debug_log_file, logging.DEBUG)
+            self.loggers.append(debug_log_file)
+
+        if environment.log_file is not None:
+            log_file = self.create_log_file(
+                environment, 'git_multimail.file', environment.log_file, logging.INFO)
+            self.loggers.append(log_file)
+
+        if environment.error_log_file is not None:
+            error_log_file = self.create_log_file(
+                environment, 'git_multimail.error', environment.error_log_file, logging.ERROR)
+            self.loggers.append(error_log_file)
+
+    def info(self, msg, *args, **kwargs):
+        for l in self.loggers:
+            l.info(msg, *args, **kwargs)
+
+    def debug(self, msg, *args, **kwargs):
+        for l in self.loggers:
+            l.debug(msg, *args, **kwargs)
+
+    def warning(self, msg, *args, **kwargs):
+        for l in self.loggers:
+            l.warning(msg, *args, **kwargs)
+
+    def error(self, msg, *args, **kwargs):
+        for l in self.loggers:
+            l.error(msg, *args, **kwargs)
+
+
+def main(args):
+    parser = optparse.OptionParser(
+        description=__doc__,
+        usage='%prog [OPTIONS]\n   or: %prog [OPTIONS] REFNAME OLDREV NEWREV',
+        )
+
+    parser.add_option(
+        '--environment', '--env', action='store', type='choice',
+        choices=list(KNOWN_ENVIRONMENTS.keys()), default=None,
+        help=(
+            'Choose type of environment is in use.  Default is taken from '
+            'multimailhook.environment if set; otherwise "generic".'
+            ),
+        )
+    parser.add_option(
+        '--stdout', action='store_true', default=False,
+        help='Output emails to stdout rather than sending them.',
+        )
+    parser.add_option(
+        '--recipients', action='store', default=None,
+        help='Set list of email recipients for all types of emails.',
+        )
+    parser.add_option(
+        '--show-env', action='store_true', default=False,
+        help=(
+            'Write to stderr the values determined for the environment '
+            '(intended for debugging purposes), then proceed normally.'
+            ),
+        )
+    parser.add_option(
+        '--force-send', action='store_true', default=False,
+        help=(
+            'Force sending refchange email when using as an update hook. '
+            'This is useful to work around the unreliable new commits '
+            'detection in this mode.'
+            ),
+        )
+    parser.add_option(
+        '-c', metavar="<name>=<value>", action='append',
+        help=(
+            'Pass a configuration parameter through to git.  The value given '
+            'will override values from configuration files.  See the -c option '
+            'of git(1) for more details.  (Only works with git >= 1.7.3)'
+            ),
+        )
+    parser.add_option(
+        '--version', '-v', action='store_true', default=False,
+        help=(
+            "Display git-multimail's version"
+            ),
+        )
+
+    parser.add_option(
+        '--python-version', action='store_true', default=False,
+        help=(
+            "Display the version of Python used by git-multimail"
+            ),
+        )
+
+    parser.add_option(
+        '--check-ref-filter', action='store_true', default=False,
+        help=(
+            'List refs and show information on how git-multimail '
+            'will process them.'
+            )
+        )
+
+    # The following options permit this script to be run as a gerrit
+    # ref-updated hook.  See e.g.
+    # code.google.com/p/gerrit/source/browse/Documentation/config-hooks.txt
+    # We suppress help for these items, since these are specific to gerrit,
+    # and we don't want users directly using them any way other than how the
+    # gerrit ref-updated hook is called.
+    parser.add_option('--oldrev', action='store', help=optparse.SUPPRESS_HELP)
+    parser.add_option('--newrev', action='store', help=optparse.SUPPRESS_HELP)
+    parser.add_option('--refname', action='store', help=optparse.SUPPRESS_HELP)
+    parser.add_option('--project', action='store', help=optparse.SUPPRESS_HELP)
+    parser.add_option('--submitter', action='store', help=optparse.SUPPRESS_HELP)
+
+    # The following allow this to be run as a stash asynchronous post-receive
+    # hook (almost identical to a git post-receive hook but triggered also for
+    # merges of pull requests from the UI).  We suppress help for these items,
+    # since these are specific to stash.
+    parser.add_option('--stash-user', action='store', help=optparse.SUPPRESS_HELP)
+    parser.add_option('--stash-repo', action='store', help=optparse.SUPPRESS_HELP)
+
+    (options, args) = parser.parse_args(args)
+    (options, args, hook_info) = check_hook_specific_args(options, args)
+
+    if options.version:
+        sys.stdout.write('git-multimail version ' + get_version() + '\n')
+        return
+
+    if options.python_version:
+        sys.stdout.write('Python version ' + sys.version + '\n')
+        return
+
+    if options.c:
+        Config.add_config_parameters(options.c)
+
+    config = Config('multimailhook')
+
+    environment = None
+    try:
+        environment = choose_environment(
+            config, osenv=os.environ,
+            env=options.environment,
+            recipients=options.recipients,
+            hook_info=hook_info,
+            )
+
+        if options.show_env:
+            show_env(environment, sys.stderr)
+
+        if options.stdout or environment.stdout:
+            mailer = OutputMailer(sys.stdout, environment)
+        else:
+            mailer = choose_mailer(config, environment)
+
+        must_check_setup = os.environ.get('GIT_MULTIMAIL_CHECK_SETUP')
+        if must_check_setup == '':
+            must_check_setup = False
+        if options.check_ref_filter:
+            check_ref_filter(environment)
+        elif must_check_setup:
+            check_setup(environment)
+        # Dual mode: if arguments were specified on the command line, run
+        # like an update hook; otherwise, run as a post-receive hook.
+        elif args:
+            if len(args) != 3:
+                parser.error('Need zero or three non-option arguments')
+            (refname, oldrev, newrev) = args
+            environment.get_logger().debug(
+                "run_as_update_hook: refname=%s, oldrev=%s, newrev=%s, force_send=%s" %
+                (refname, oldrev, newrev, options.force_send))
+            run_as_update_hook(environment, mailer, refname, oldrev, newrev, options.force_send)
+        else:
+            run_as_post_receive_hook(environment, mailer)
+    except ConfigurationException:
+        sys.exit(sys.exc_info()[1])
+    except SystemExit:
+        raise
+    except Exception:
+        t, e, tb = sys.exc_info()
+        import traceback
+        sys.stderr.write('\n')  # Avoid mixing message with previous output
+        msg = (
+            'Exception \'' + t.__name__ +
+            '\' raised. Please report this as a bug to\n'
+            'https://github.com/git-multimail/git-multimail/issues\n'
+            'with the information below:\n\n'
+            'git-multimail version ' + get_version() + '\n'
+            'Python version ' + sys.version + '\n' +
+            traceback.format_exc())
+        try:
+            environment.get_logger().error(msg)
+        except:
+            sys.stderr.write(msg)
+        sys.exit(1)
+
+
+if __name__ == '__main__':
+    main(sys.argv[1:])