nix-copy-closure: Add flag ‘--use-substitutes’

doc/manual/nix-copy-closure.xml

@@ -28,6 +28,8 @@
     <arg><option>--xz</option></arg>
     <arg><option>--show-progress</option></arg>
     <arg><option>--include-outputs</option></arg>
+    <arg><option>--use-substitutes</option></arg>
+    <arg><option>-s</option></arg>
     <arg choice='plain'>
       <replaceable>user@</replaceable><replaceable>machine</replaceable>
     </arg>
@@ -120,8 +122,20 @@ those paths.  If this bothers you, use
 
   <varlistentry><term><option>--include-outputs</option></term>
 
-  <listitem><para>Also copy the outputs of store derivations included
+    <listitem><para>Also copy the outputs of store derivations
-  in the closure.</para></listitem>
+    included in the closure.</para></listitem>
+
+  </varlistentry>
+
+  <varlistentry><term><option>--use-substitutes</option> / <option>-s</option></term>
+
+    <listitem><para>Attempt to download missing paths on the target
+    machine using Nix’s substitute mechanism.  Any paths that cannot
+    be substituted on the target are still copied normally from the
+    source.  This is useful, for instance, if the connection between
+    the source and target machine is slow, but the connection between
+    the target machine and <literal>nixos.org</literal> (the default
+    binary cache server) is fast.</para></listitem>
 
   </varlistentry>
 

doc/manual/release-notes.xml

@@ -81,6 +81,13 @@ $ mount -o remount,ro,bind /nix/store
     modifications.</para>
   </listitem>
 
+  <listitem>
+    <para>The command <command>nix-copy-closure</command> has a new
+    flag <option>--use-substitutes</option> (<option>-s</option>) to
+    download missing paths on the target machine using the substitute
+    mechanism.</para>
+  </listitem>
+
   <listitem>
     <para>The command <command>nix-worker</command> has been renamed
     to <command>nix-daemon</command>.  Support for running the Nix

perl/lib/Nix/CopyClosure.pm

@@ -6,7 +6,8 @@ use Nix::Store;
 
 
 sub copyTo {
-    my ($sshHost, $sshOpts, $storePaths, $compressor, $decompressor, $includeOutputs, $dryRun, $sign, $progressViewer) = @_;
+    my ($sshHost, $sshOpts, $storePaths, $compressor, $decompressor,
+        $includeOutputs, $dryRun, $sign, $progressViewer, $useSubstitutes) = @_;
 
     $compressor = "$compressor |" if $compressor ne "";
     $decompressor = "$decompressor |" if $decompressor ne "";
@@ -16,6 +17,12 @@ sub copyTo {
     my @closure = reverse(topoSortPaths(computeFSClosure(0, $includeOutputs,
         map { followLinksToStorePath $_ } @{$storePaths})));
 
+    # Optionally use substitutes on the remote host.
+    if (!$dryRun && $useSubstitutes) {
+        system "ssh $sshHost @{$sshOpts} nix-store -r --ignore-unknown @closure";
+        # Ignore exit status because this is just an optimisation.
+    }
+
     # 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

scripts/nix-copy-closure.in

@@ -17,19 +17,14 @@ EOF
 
 # Get the target host.
 my $sshHost;
-
 my $sign = 0;
-
 my $compressor = "";
 my $decompressor = "";
-
 my $progressViewer = "";
-
 my $toMode = 1;
-
 my $includeOutputs = 0;
-
 my $dryRun = 0;
+my $useSubstitutes = 0;
 
 
 # !!! Copied from nix-pack-closure, should put this in a module.
@@ -71,6 +66,9 @@ while (@ARGV) {
     elsif ($arg eq "--dry-run") {
         $dryRun = 1;
     }
+    elsif ($arg eq "--use-substitutes" || $arg eq "-s") {
+        $useSubstitutes = 1;
+    }
     elsif (!defined $sshHost) {
         $sshHost = $arg;
     }
@@ -84,7 +82,9 @@ openSSHConnection $sshHost or die "$0: unable to start SSH\n";
 
 
 if ($toMode) { # Copy TO the remote machine.
-    Nix::CopyClosure::copyTo($sshHost, [ @sshOpts ], [ @storePaths ], $compressor, $decompressor, $includeOutputs, $dryRun, $sign, $progressViewer);
+    Nix::CopyClosure::copyTo(
+        $sshHost, [ @sshOpts ], [ @storePaths ], $compressor, $decompressor,
+        $includeOutputs, $dryRun, $sign, $progressViewer, $useSubstitutes);
 }
 
 else { # Copy FROM the remote machine.
@@ -107,10 +107,13 @@ else { # Copy FROM the remote machine.
     # Export the store paths on the remote machine and import them locally.
     if (scalar @missing > 0) {
         print STDERR "copying ", scalar @missing, " missing paths from ‘$sshHost’...\n";
+        unless ($dryRun) {
+            if ($useSubstitutes) {
+                system "$Nix::Config::binDir/nix-store -r --ignore-unknown @missing";
+            }
             $compressor = "| $compressor" if $compressor ne "";
             $decompressor = "$decompressor |" if $decompressor ne "";
             $progressViewer = "$progressViewer |" if $progressViewer ne "";
-        unless ($dryRun) {
             my $extraOpts = $sign ? "--sign" : "";
             system("set -f; ssh $sshHost @sshOpts 'nix-store --export $extraOpts @missing $compressor' | $progressViewer $decompressor $Nix::Config::binDir/nix-store --import > /dev/null") == 0
                 or die "copying store paths from remote machine `$sshHost' failed: $?";