* Prebuilt package sharing. We allow transparent binary deployment by

sharing package directories (i.e., the result of building a Nix
  descriptor).

  `nix-pull-prebuilts' obtains a list of all known prebuilts by
  consulting the paths and URLs specified in
  $prefix/etc/nix/prebuilts.conf.  The mappings ($pkghash,
  $prebuilthash) and ($prebuilthash, $location) are registered with
  Nix so that it can use the prebuilt with hash $prebuilthash when
  installing a package with hash $pkghash by downloading and unpacking
  $location.

  `nix-push-prebuilts' creates prebuilts for all packages for which no
  prebuilt is known to exist.  It can then optionally upload these
  to the network through rsync.

  `nix-[pull|push]-prebuilts' just provide a policy.  Nix provides the
  mechanism through the `nix [export|regprebuilt|regurl]' commands.

scripts/Makefile.am

@@ -1,5 +1,9 @@
-bin_SCRIPTS = nix-generate-regscript nix-switch nix-collect-garbage
+bin_SCRIPTS = nix-generate-regscript nix-switch nix-collect-garbage \
+ nix-pull-prebuilts nix-push-prebuilts
 
 install-exec-local:
 	$(INSTALL) -d $(sysconfdir)/profile.d
 	$(INSTALL_PROGRAM) nix-profile.sh $(sysconfdir)/profile.d/nix.sh
+	$(INSTALL) -d $(sysconfdir)/nix
+    # !!! don't overwrite local modifications
+	$(INSTALL_PROGRAM) prebuilts.conf $(sysconfdir)/nix/prebuilts.conf

scripts/nix-generate-regscript

@@ -1,20 +0,0 @@
-#! /usr/bin/perl -w
-
-my $dir = shift @ARGV;
-$dir || die "missing directory";
-my $url = shift @ARGV;
-$url || die "missing base url";
-
-chdir $dir || die "cannot chdir to $dir";
-
-foreach my $prebuilt (glob("*.tar.bz2")) {
-
-    $prebuilt =~ /-([a-z0-9]+)-([a-z0-9]+).tar.bz2$/
-	|| die "invalid file name: $prebuilt";
-
-    my $pkgHash = $1;
-    my $prebuiltHash = $2;
-
-    print "regprebuilt $pkgHash $prebuiltHash\n";
-    print "regurl $prebuiltHash $url/$prebuilt\n";
-}

scripts/nix-pull-prebuilts

@@ -0,0 +1,69 @@
+#! /usr/bin/perl -w
+
+my $prefix = $ENV{"NIX"} || "/nix"; # !!! use prefix
+my $etcdir = "$prefix/etc/nix";
+my $knowns = "$prefix/var/nix/known-prebuilts";
+my $tmpfile = "$prefix/var/nix/prebuilts.tmp";
+
+my $conffile = "$etcdir/prebuilts.conf";
+
+sub register {
+    my $fn = shift;
+    return unless $fn =~ /([^\/]*)-([0-9a-z]{32})-([0-9a-z]{32})\.tar\.bz2/;
+    my $id = $1;
+    my $pkghash = $2;
+    my $prebuilthash = $3;
+    print "$pkghash => $prebuilthash ($id)\n";
+    system "nix regprebuilt $pkghash $prebuilthash";
+    if ($?) { die "`nix regprebuilt' failed"; }
+    print KNOWNS "$pkghash\n";
+}
+
+open KNOWNS, ">$knowns";
+
+open CONFFILE, "<$conffile";
+
+while (<CONFFILE>) {
+    chomp;
+    if (/^\s*(\S+)\s*(\#.*)?$/) {
+        my $url = $1;
+
+        print "obtaining prebuilt list from $url...\n";
+
+        if ($url =~ /^\//) {
+
+            # It's a local path.
+
+            foreach my $fn (glob "$url/*") {
+                register $fn;
+            }
+
+        } else {
+
+            # It's a URL.
+
+            system "wget '$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 =~ /\//;
+                register $fn;
+            }
+
+            close INDEX;
+
+            unlink $tmpfile;
+        }
+    }
+}
+
+close CONFFILE;
+
+close KNOWNS;

scripts/nix-push-prebuilts

@@ -0,0 +1,40 @@
+#! /usr/bin/perl -w
+
+my $prefix = $ENV{"NIX"} || "/nix"; # !!! use prefix
+my $etcdir = "$prefix/etc/nix";
+my $exportdir = "$prefix/var/nix/prebuilts/exports";
+my $knowns = "$prefix/var/nix/known-prebuilts";
+
+# For performance, put the known hashes in an associative array.
+my %knowns = ();
+open KNOWNS, "<$knowns";
+while (<KNOWNS>) {
+    next unless /([0-9a-z]{32})/;
+    $knowns{$1} = 1;
+}
+close KNOWNS;
+
+# For each installed package, check whether a prebuilt is known.
+
+open PKGS, "nix listinst|";
+open KNOWNS, ">>$knowns";
+
+while (<PKGS>) {
+    chomp;
+    next unless /([0-9a-z]{32})/;
+    my $pkghash = $1;
+    if (!defined $knowns{$1}) {
+        # No known prebuilt exists for this package; so export it.
+        print "exporting $pkghash...\n";
+        system "nix export '$exportdir' $pkghash";
+        if ($?) { die "`nix export' failed"; }
+        print KNOWNS "$pkghash\n";
+    }
+}
+
+close KNOWNS;
+close PKGS;
+
+# Push the prebuilts to the server. !!! FIXME
+
+system "rsync -av -e ssh '$exportdir' losser:/home/eelco/public_html/nix-prebuilts/";

scripts/prebuilts.conf

@@ -0,0 +1,4 @@
+# A list of URLs or local paths from where we obtain prebuilts.
+/nix/var/nix/prebuilts/imports
+/nix/var/nix/prebuilts/exports
+http://losser.st-lab.cs.uu.nl/~eelco/nix-prebuilts/