* Add an API function exportPaths() that provides the functionality of

‘nix-store --export’.
* Add a Perl module that provides the functionality of
  ‘nix-copy-closure --to’.  This is used by build-remote.pl so it no
  longer needs to start a separate nix-copy-closure process.  Also, it
  uses the Perl API to do the export, so it doesn't need to start a
  separate nix-store process either.  As a result, nix-copy-closure
  and build-remote.pl should no longer fail on very large closures due
  to an "Argument list too long" error.  (Note that having very many
  dependencies in a single derivation can still fail because the
  environment can become too large.  Can't be helped though.)

perl/lib/Nix/CopyClosure.pm

@@ -0,0 +1,46 @@
+package Nix::CopyClosure;
+
+use strict;
+use Nix::Config;
+use Nix::Store;
+
+
+sub copyTo {
+    my ($sshHost, $sshOpts, $storePaths, $compressor, $decompressor, $includeOutputs, $dryRun, $sign) = @_;
+
+    $compressor = "$compressor |" if $compressor ne "";
+    $decompressor = "$decompressor |" if $decompressor ne "";
+    
+    # Get the closure of this path.
+    my @closure = reverse(topoSortPaths(computeFSClosure(0, $includeOutputs,
+        map { followLinksToStorePath $_ } @{$storePaths})));
+
+    # Ask the remote host which paths are invalid.  Because of limits
+    # to the command line length, do this in chunks.  Eventually,
+    # we'll want to use ‘--from-stdin’, but we can't rely on the
+    # target having this option yet.
+    my @missing = ();
+    while (scalar(@closure) > 0) {
+        my @ps = splice(@closure, 0, 1500);
+        open(READ, "set -f; ssh $sshHost @{$sshOpts} nix-store --check-validity --print-invalid @ps|");
+        while (<READ>) {
+            chomp;
+            push @missing, $_;
+        }
+        close READ or die;
+    }
+
+    # Export the store paths and import them on the remote machine.
+    if (scalar @missing > 0) {
+        print STDERR "copying ", scalar @missing, " missing paths to ‘$sshHost’...\n";
+        #print STDERR "  $_\n" foreach @missing;
+        unless ($dryRun) {
+            open SSH, "| $compressor ssh $sshHost @{$sshOpts} '$decompressor nix-store --import'" or die;
+            exportPaths(fileno(SSH), $sign, @missing);
+            close SSH or die "copying store paths to remote machine `$sshHost' failed: $?";
+        }
+    }
+}
+
+
+1;

perl/lib/Nix/Store.pm

@@ -12,7 +12,7 @@ our %EXPORT_TAGS = ( 'all' => [ qw( ) ] );
 
 our @EXPORT_OK = ( @{ $EXPORT_TAGS{'all'} } );
 
-our @EXPORT = qw(isValidPath topoSortPaths computeFSClosure followLinksToStorePath);
+our @EXPORT = qw(isValidPath topoSortPaths computeFSClosure followLinksToStorePath exportPaths);
 
 our $VERSION = '0.15';
 

perl/lib/Nix/Store.xs

@@ -146,3 +146,16 @@ SV * followLinksToStorePath(char * path)
         }
     OUTPUT:
         RETVAL
+
+
+void exportPaths(int fd, int sign, ...)
+    PPCODE:
+        try {
+            doInit();
+            Paths paths;
+            for (int n = 2; n < items; ++n) paths.push_back(SvPV_nolen(ST(n)));
+            FdSink sink(fd);
+            exportPaths(*store, paths, sign, sink);
+        } catch (Error & e) {
+            croak(e.what());
+        }