Generate *.narinfo files on the fly to support the binary cache substituter

src/lib/Hydra/Controller/Root.pm

@@ -195,9 +195,28 @@ sub nar :Local :Args(1) {
 }
 
 
-sub narinfo :Path('*.narinfo') {
+sub hashToPath {
+    my ($c, $hash) = @_;
+    die if length($hash) != 32;
+    # FIXME: doing a glob is very inefficient.  Should do a database
+    # lookup.
+    my @glob = glob("/nix/store/$hash*");
+    foreach my $storePath (@glob) {
+	if (isValidPath($storePath)) {
+	    print STDERR "FOUND: $hash -> $storePath\n";
+	    return $storePath;
+	}
+	#return $storePath if isValidPath($storePath);
+    }
+    notFound($c, "Store path with hash ‘$hash’ does not exist.");
+}
+
+
+sub narinfo :LocalRegex('^([a-z0-9]+).narinfo$') :Args(0) {
     my ($self, $c) = @_;
-    $c->stash->{current_view} = 'NixInfo';
+    my $hash = $c->req->captures->[0];
+    $c->stash->{storePath} = hashToPath($c, $hash);
+    $c->stash->{current_view} = 'NARInfo';
 }
 
 

src/lib/Hydra/View/NARInfo.pm

@@ -0,0 +1,39 @@
+package Hydra::View::NARInfo;
+
+use strict;
+use base qw/Catalyst::View/;
+use File::Basename;
+use Nix::Store;
+
+sub process {
+    my ($self, $c) = @_;
+
+    my $storePath = $c->stash->{storePath};
+    
+    $c->response->content_type('text/x-nix-narinfo'); # !!! check MIME type
+
+    my ($deriver, $narHash, $time, $narSize, $refs) = queryPathInfo($storePath);
+
+    my $info;
+    $info .= "StorePath: $storePath\n";
+    $info .= "URL: nar/" . basename $storePath. "\n";
+    $info .= "Compression: bzip2\n";
+    #$info .= "FileHash: sha256:$compressedHash\n";
+    #$info .= "FileSize: $compressedSize\n";
+    $info .= "NarHash: $narHash\n";
+    $info .= "NarSize: $narSize\n";
+    $info .= "References: " . join(" ", map { basename $_ } @{$refs}) . "\n";
+    if (defined $deriver) {
+        $info .= "Deriver: " . basename $deriver . "\n";
+        if (isValidPath($deriver)) {
+            my $drv = derivationFromPath($deriver);
+            $info .= "System: $drv->{platform}\n";
+        }
+    }
+
+    $c->response->body($info);
+
+    return 1;
+}
+
+1;