* The policy-free derivate sharing now *almost* works. :-) For any

  hash for which no local expansion is available, Nix can execute a
  `substitute' which should produce a path with such a hash.

  This is policy-free since Nix does not in any way specify how the
  substitute should work, i.e., it's an arbitrary (unnormalised)
  fstate expression.  For example, `nix-pull' registers substitutes
  that fetch Nix archives from the network (through `wget') and unpack
  them, but any other method is possible as well.  This is an
  improvement over the old Nix sharing scheme, which had a policy
  (fetching through `wget') built in.

  The sharing scheme doesn't work completely yet because successors
  from fstate rewriting have to be registered on the receiving side.
  Probably the whole successor stuff can be folded up into the
  substitute mechanism; this would be a nice simplification.

1 files changed, 65 insertions, 0 deletions

diff --git a/scripts/nix-pull b/scripts/nix-pull
index 0b09c8e00a1b..59773a2bad17 100644
--- a/scripts/nix-pull
+++ b/scripts/nix-pull
@@ -1,2 +1,67 @@
 #! /usr/bin/perl -w
 
+my $prefix = $ENV{"NIX"} || "/tmp/nix"; # !!! use prefix
+my $etcdir = "$prefix/etc/nix";
+my $tmpfile = "$prefix/var/nix/pull.tmp";
+
+my $conffile = "$etcdir/prebuilts.conf";
+
+open CONFFILE, "<$conffile";
+
+while (<CONFFILE>) {
+
+    chomp;
+    if (/^\s*(\S+)\s*(\#.*)?$/) {
+        my $url = $1;
+
+        print "obtaining list of Nix archives at $url...\n";
+
+	system "wget '$url' -O '$tmpfile' 2> /dev/null"; # !!! escape
+	if ($?) { die "`wget' failed"; }
+	
+	open INDEX, "<$tmpfile";
+
+	while (<INDEX>) {
+	    # Get all links to prebuilts, that is, file names of the
+	    # form foo-HASH-HASH.tar.bz2.
+	    next unless (/HREF=\"([^\"]*)\"/);
+	    my $fn = $1;
+	    next if $fn =~ /\.\./;
+	    next if $fn =~ /\//;
+	    next unless $fn =~ /([0-9a-z]{32})-([0-9a-z]{32})\.nar/;
+	    my $hash = $2;
+
+	    print "registering $hash -> $url/$fn\n";
+
+	    # Construct a Fix expression that fetches and unpacks a
+	    # Nix archive from the network.
+	    my $fetch =
+              "App(IncludeFix(\"fetchurl/fetchurl.fix\"), " .
+              "[(\"url\", \"$url/$fn\"), (\"hash\", \"\")])";
+	    my $fixexpr = 
+		"App(IncludeFix(\"nar/unnar.fix\"), " .
+		"[ (\"nar\", $fetch)" .
+		", (\"name\", \"fetched-$hash\")" .
+		"])";
+	    
+	    my $fixfile = "/tmp/nix-pull-tmp.fix";
+	    open FIX, ">$fixfile";
+	    print FIX $fixexpr;
+	    close FIX;
+
+	    # Instantiate a Nix expression from the Fix expression.
+	    my $nhash = `fix $fixfile`;
+	    $? and die "instantiating Nix archive expression";
+	    chomp $nhash;
+	    die unless $nhash =~ /^([0-9a-z]{32})$/;
+
+	    system "nix --substitute $hash $nhash";
+	    if ($?) { die "`nix --substitute' failed"; }
+	}
+
+	close INDEX;
+
+	unlink $tmpfile;
+    }
+
+}