* Patch deployment. `download.pl' (intended to be used in the

substitute mechanism) creates a store path by downloading full NAR
  archives and/or patches specified in the available manifests.

  Any combination of present paths, full downloads, and patches can be
  used to construct the target path.  In particular, patches can be
  chained in sequence; and full NAR archives of the target path can be
  omitted (i.e., patch-only deployment is possible).  A shortest path
  algorithm is used to find the smallest set of files to be downloaded
  (the edge weights are currently file sizes, but one can imagine
  taking the network speed to the various source into account).

  Patches are binary deltas between two store paths.  To be precise,
  they are the output of the `bsdiff' program applied to the NAR
  archives obtained by dumping (`nix-store --dump') the two store
  paths.  The advantage of diff'ing NAR archives (and not, say, doing
  file-by-file diffs) is that file renames/moves are handled
  automatically.  The disadvantage is that we cannot optimise creation
  of unchanged files (by hard-linking).

corepkgs/nix-pull/download.pl

@@ -0,0 +1,218 @@
+#! /usr/bin/perl -w -I/home/eelco/Dev/nix/scripts
+
+use strict;
+use readmanifest;
+
+my $manifestDir = "/home/eelco/Dev/nix/patch/test";
+
+
+# Check the arguments.
+die unless scalar @ARGV == 1;
+my $targetPath = $ARGV[0];
+
+
+# Load all manifests.
+my %narFiles;
+my %patches;
+my %successors;
+
+for my $manifest (glob "$manifestDir/*.nixmanifest") {
+    print STDERR "reading $manifest\n";
+    readManifest $manifest, \%narFiles, \%patches, \%successors;
+}
+
+
+# Build a graph of all store paths that might contribute to the
+# construction of $targetPath, and the special node "start".  The
+# edges are either patch operations, or downloads of full NAR files.
+# The latter edges only occur between "start" and a store path.
+
+my %graph;
+
+$graph{"start"} = {d => 0, pred => undef, edges => []};
+
+my @queue = ();
+my $queueFront = 0;
+my %done;
+
+sub addToQueue {
+    my $v = shift;
+    return if defined $done{$v};
+    $done{$v} = 1;
+    push @queue, $v;
+}
+
+sub addNode {
+    my $u = shift;
+    $graph{$u} = {d => 999999999999, pred => undef, edges => []}
+        unless defined $graph{$u};
+}
+
+sub addEdge {
+    my $u = shift;
+    my $v = shift;
+    my $w = shift;
+    my $type = shift;
+    my $info = shift;
+    addNode $u;
+    push @{$graph{$u}->{edges}},
+        {weight => $w, start => $u, end => $v, type => $type, info => $info};
+    my $n = scalar @{$graph{$u}->{edges}};
+}
+
+addToQueue $targetPath;
+
+while ($queueFront < scalar @queue) {
+    my $u = $queue[$queueFront++];
+    print "$u\n";
+
+    addNode $u;
+
+    # If the path already exists, it has distance 0 from the "start"
+    # node.
+    system "nix-store --isvalid '$u' 2> /dev/null";
+    if ($? == 0) {
+        addEdge "start", $u, 0, "present", undef;
+    }
+
+    else {
+
+        # Add patch edges.
+        my $patchList = $patches{$u};
+        foreach my $patch (@{$patchList}) {
+            # !!! this should be cached
+            my $hash = `nix-hash "$patch->{basePath}"`;
+            chomp $hash;
+            print "  MY HASH is $hash\n";
+            if ($hash ne $patch->{baseHash}) {
+                print "  REJECTING PATCH from $patch->{basePath}\n";
+                next;
+            }
+            print "  PATCH from $patch->{basePath}\n";
+            addToQueue $patch->{basePath};
+            addEdge $patch->{basePath}, $u, $patch->{size}, "patch", $patch;
+        }
+
+        # Add NAR file edges to the start node.
+        my $narFileList = $narFiles{$u};
+        foreach my $narFile (@{$narFileList}) {
+            print "  NAR from $narFile->{url}\n";
+            addEdge "start", $u, $narFile->{size}, "narfile", $narFile;
+        }
+
+    }
+}
+
+
+# Run Dijkstra's shortest path algorithm to determine the shortest
+# sequence of download and/or patch actions that will produce
+# $targetPath.
+
+sub byDistance { # sort by distance, reversed
+    return -($graph{$a}->{d} <=> $graph{$b}->{d});
+}
+
+my @todo = keys %graph;
+
+while (scalar @todo > 0) {
+
+    # Remove the closest element from the todo list.
+    @todo = sort byDistance @todo;
+    my $u = pop @todo;
+
+    my $u_ = $graph{$u};
+
+    print "IN $u $u_->{d}\n";
+
+    foreach my $edge (@{$u_->{edges}}) {
+        my $v_ = $graph{$edge->{end}};
+        if ($v_->{d} > $u_->{d} + $edge->{weight}) {
+            $v_->{d} = $u_->{d} + $edge->{weight};
+            # Store the edge; to edge->start is actually the
+            # predecessor.
+            $v_->{pred} = $edge; 
+            print "  RELAX $edge->{end} $v_->{d}\n";
+        }
+    }
+}
+
+
+# Retrieve the shortest path from "start" to $targetPath.
+my @path = ();
+my $cur = $targetPath;
+die "don't know how to produce $targetPath\n"
+    unless defined $graph{$targetPath}->{pred};
+while ($cur ne "start") {
+    push @path, $graph{$cur}->{pred};
+    $cur = $graph{$cur}->{pred}->{start};
+}
+
+
+# Traverse the shortest path, perform the actions described by the
+# edges.
+my $curStep = 1;
+my $maxStep = scalar @path;
+
+sub downloadFile {
+    my $url = shift;
+    my $hash = shift;
+    $ENV{"PRINT_PATH"} = 1;
+    $ENV{"QUIET"} = 1;
+    my ($hash2, $path) = `nix-prefetch-url '$url' '$hash'`;
+    chomp $hash2;
+    chomp $path;
+    die "hash mismatch" if $hash ne $hash2;
+    return $path;
+}
+
+while (scalar @path > 0) {
+    my $edge = pop @path;
+    my $u = $edge->{start};
+    my $v = $edge->{end};
+
+    print "\n*** Step $curStep/$maxStep: ";
+    $curStep++;
+
+    if ($edge->{type} eq "present") {
+        print "using already present path `$v'\n";
+    }
+
+    elsif ($edge->{type} eq "patch") {
+        my $patch = $edge->{info};
+        print "applying patch `$patch->{url}' to `$u' to create `$v'\n";
+
+        # Download the patch.
+        print "  downloading patch...\n";
+        my $patchPath = downloadFile "$patch->{url}", "$patch->{hash}";
+
+        # Turn the base path into a NAR archive, to which we can
+        # actually apply the patch.
+        print "  packing base path...\n";
+        system "nix-store --dump $patch->{basePath} > /tmp/nar";
+        die "cannot dump `$patch->{basePath}'" if ($? != 0);
+
+        # Apply the patch.
+        print "  applying patch...\n";
+        system "bspatch /tmp/nar /tmp/nar2 $patchPath";
+        die "cannot apply patch `$patchPath' to /tmp/nar" if ($? != 0);
+
+        # Unpack the resulting NAR archive into the target path.
+        print "  unpacking patched archive...\n";
+        system "nix-store --restore $targetPath < /tmp/nar2";
+        die "cannot unpack /tmp/nar2 into `$targetPath'" if ($? != 0);
+    }
+
+    elsif ($edge->{type} eq "narfile") {
+        my $narFile = $edge->{info};
+        print "downloading `$narFile->{url}' into `$v'\n";
+
+        # Download the archive.
+        print "  downloading archive...\n";
+        my $narFilePath = downloadFile "$narFile->{url}", "$narFile->{hash}";
+
+        # Unpack the archive into the target path.
+        print "  unpacking archive...\n";
+        system "bunzip2 < '$narFilePath' | nix-store --restore '$targetPath'";
+        die "cannot unpack `$narFilePath' into `$targetPath'" if ($? != 0);
+    }
+}

scripts/nix-pull.in

@@ -19,14 +19,24 @@ my $confFile = "@sysconfdir@/nix/prebuilts.conf";
 my %storePaths2urls;
 my %urls2hashes;
 my %successors;
-sub doURL {
+
+sub processURL {
     my $url = shift;
-    processURL $manifest, $url, \%storePaths2urls, \%urls2hashes, \%successors;
+
+    $url =~ s/\/$//;
+    print "obtaining list of Nix archives at $url...\n";
+
+    system("@curl@ --fail --silent --show-error --location --max-redirs 20 " .
+           "'$url' > '$manifest'") == 0
+           or die "curl failed: $?";
+    
+    readManifest $manifest, \%storePaths2urls, \%urls2hashes, \%successors;
 }
+
 if (scalar @ARGV > 0) {
     while (@ARGV) {
         my $url = shift @ARGV;
-	doURL $url;
+	processURL $url;
     }
 } else {
     open CONFFILE, "<$confFile";
@@ -34,7 +44,7 @@ if (scalar @ARGV > 0) {
         chomp;
         if (/^\s*(\S+)\s*(\#.*)?$/) {
             my $url = $1;
-	    doURL $url;
+	    processURL $url;
         }
     }
     close CONFFILE;

scripts/readmanifest.pm.in

@@ -1,27 +1,24 @@
 use strict;
 
-sub processURL {
+sub readManifest {
     my $manifest = shift;
-    my $url = shift;
+    my $narFiles = shift;
-    my $storePaths2urls = shift;
+    my $patches = shift;
-    my $urls2hashes = shift;
     my $successors = shift;
 
-    $url =~ s/\/$//;
-    print "obtaining list of Nix archives at $url...\n";
-
-    system("@curl@ --fail --silent --show-error --location --max-redirs 20 " .
-           "'$url' > '$manifest'") == 0
-           or die "curl failed: $?";
-        
     open MANIFEST, "<$manifest";
 
     my $inside = 0;
+    my $type;
 
     my $storePath;
-    my $narurl;
+    my $url;
     my $hash;
+    my $size;
     my @preds;
+    my $basePath;
+    my $baseHash;
+    my $patchType;
 
     while (<MANIFEST>) {
         chomp;
@@ -30,37 +27,101 @@ sub processURL {
 
         if (!$inside) {
             if (/^\{$/) {
+                $type = "narfile";
                 $inside = 1;
                 undef $storePath;
-                undef $narurl;
+                undef $url;
                 undef $hash;
+                $size = 999999999;
                 @preds = ();
 	    }
+            elsif (/^patch \{$/) {
+                $type = "patch";
+                $inside = 1;
+                undef $url;
+                undef $hash;
+                undef $size;
+                undef $basePath;
+                undef $baseHash;
+                undef $patchType;
+            }
             else { die "bad line: $_"; }
         } else {
+            
             if (/^\}$/) {
                 $inside = 0;
 
-		$$storePaths2urls{$storePath} = $narurl;
+                if ($type eq "narfile") {
-		$$urls2hashes{$narurl} = $hash;
+
+                    $$narFiles{$storePath} = []
+                        unless defined $$narFiles{$storePath};
+
+                    my $narFileList = $$narFiles{$storePath};
+
+                    my $found = 0;
+                    foreach my $narFile (@{$narFileList}) {
+                        if ($narFile->{url} eq $url) {
+                            if ($narFile->{hash} eq $hash) {
+                                $found = 1;
+                            } else {
+                                die "conflicting hashes for URL $url, " .
+                                    "namely $narFile->{hash} and $hash";
+                            }
+                        }
+                    }
+                    if (!$found) {
+                        push @{$narFileList},
+                            {url => $url, hash => $hash, size => $size};
+                    }
                 
                     foreach my $p (@preds) {
                         $$successors{$p} = $storePath;
                     }
 
                 }
-            elsif (/^\s*StorePath:\s*(\/\S+)\s*$/) {
+
-                $storePath = $1;
+                elsif ($type eq "patch") {
+
+                    $$patches{$storePath} = []
+                        unless defined $$patches{$storePath};
+
+                    my $patchList = $$patches{$storePath};
+
+                    my $found = 0;
+                    foreach my $patch (@{$patchList}) {
+                        if ($patch->{url} eq $url) {
+                            if ($patch->{hash} eq $hash) {
+                                $found = 1 if ($patch->{basePath} eq $basePath);
+                            } else {
+                                die "conflicting hashes for URL $url, " .
+                                    "namely $patch->{hash} and $hash";
                             }
-            elsif (/^\s*NarURL:\s*(\S+)\s*$/) {
-                $narurl = $1;
                         }
-            elsif (/^\s*MD5:\s*(\S+)\s*$/) {
-                $hash = $1;
                     }
-            elsif (/^\s*SuccOf:\s*(\/\S+)\s*$/) {
+                    if (!$found) {
-                push @preds, $1;
+                        push @{$patchList},
+                            { url => $url, hash => $hash, size => $size
+                            , basePath => $basePath, baseHash => $baseHash
+                            };
                     }
+                    
+                }
+
+            }
+            
+            elsif (/^\s*StorePath:\s*(\/\S+)\s*$/) { $storePath = $1; }
+            elsif (/^\s*Hash:\s*(\S+)\s*$/) { $hash = $1; }
+            elsif (/^\s*URL:\s*(\S+)\s*$/) { $url = $1; }
+            elsif (/^\s*Size:\s*(\d+)\s*$/) { $size = $1; }
+            elsif (/^\s*SuccOf:\s*(\/\S+)\s*$/) { push @preds, $1; }
+            elsif (/^\s*BasePath:\s*(\/\S+)\s*$/) { $basePath = $1; }
+            elsif (/^\s*BaseHash:\s*(\S+)\s*$/) { $baseHash = $1; }
+            elsif (/^\s*Type:\s*(\S+)\s*$/) { $patchType = $1; }
+
+            # Compatibility;
+            elsif (/^\s*NarURL:\s*(\S+)\s*$/) { $url = $1; }
+            elsif (/^\s*MD5:\s*(\S+)\s*$/) { $hash = $1; }
+            
             else { die "bad line: $_"; }
         }
     }