Add download-via-ssh substituter

This substituter connects to a remote host, runs nix-store --serve
there, and then forwards substituter commands on to the remote host and
sends their results to the calling program. The ssh-substituter-hosts
option can be specified as a list of hosts to try.

This is an initial implementation and, while it works, it has some
limitations:

* Only the first host is used
* There is no caching of query results (all queries are sent to the
  remote machine)
* There is no informative output (such as progress bars)
* Some failure modes may cause unhelpful error messages
* There is no concept of trusted-ssh-substituter-hosts

Signed-off-by: Shea Levy <shea@shealevy.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index 9300edbe96..5e7cfda9a1 100644
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -25,6 +25,8 @@ struct Settings {
 
     string pack();
 
+    void unpack(string pack);
+
     SettingsMap getOverrides();
 
     /* The directory where we store sources and derived files. */
@@ -144,6 +146,9 @@ struct Settings {
        chroot. */
     StringSet dirsInChroot;
 
+    /* Set of ssh connection strings for the ssh substituter */
+    Strings sshSubstituterHosts;
+
     /* Whether to impersonate a Linux 2.6 machine on newer kernels. */
     bool impersonateLinux26;
 
@@ -195,6 +200,7 @@ private:
     void get(string & res, const string & name);
     void get(bool & res, const string & name);
     void get(StringSet & res, const string & name);
+    void get(Strings & res, const string & name);
     template<class N> void get(N & res, const string & name);
 };