* Channels. These allow you to stay current with an evolving set of

Nix expressions.

  To subscribe to a channel (needs to be done only once):

    nix-channel --add \
      http://catamaran.labs.cs.uu.nl/dist/nix/channels/nixpkgs-unstable

  This just adds the given URL to ~/.nix-channels (which can also be
  edited manually).

  To update from all channels:

    nix-channel --update

  This fetches the latest expressions and pulls cache manifests.  The
  default Nix expression (~/.nix-defexpr) is made to point to the
  conjunction of the expressions downloaded from all channels.

  So to update all installed derivations in the current user
  environment:

    nix-channel --update
    nix-env --upgrade '*'

  If you are really courageous, you can put this in a cronjob or
  something.

  You can subscribe to multiple channels.  It is not entirely clear
  what happens when there are name clashes between derivations from
  different channels.  From nix-env/main.cc it appears that the one
  with the lowest (highest?) hash will be used, which is pretty
  meaningless.

configure.ac

@@ -140,6 +140,7 @@ AC_CONFIG_FILES([Makefile
    corepkgs/fetchurl/Makefile
    corepkgs/nar/Makefile
    corepkgs/buildenv/Makefile
+   corepkgs/channels/Makefile
    doc/Makefile
    doc/manual/Makefile
   ])

corepkgs/Makefile.am

@@ -1 +1 @@
-SUBDIRS = fetchurl nar buildenv
+SUBDIRS = fetchurl nar buildenv channels

corepkgs/channels/Makefile.am

@@ -0,0 +1,11 @@
+all-local: unpack.sh
+
+install-exec-local:
+	$(INSTALL) -d $(DESTDIR)$(datadir)/nix/corepkgs
+	$(INSTALL) -d $(DESTDIR)$(datadir)/nix/corepkgs/channels
+	$(INSTALL_DATA) unpack.nix $(DESTDIR)$(datadir)/nix/corepkgs/channels
+	$(INSTALL_PROGRAM) unpack.sh $(DESTDIR)$(datadir)/nix/corepkgs/channels
+
+include ../../substitute.mk
+
+EXTRA_DIST = default.nix unpack.sh.in

corepkgs/channels/unpack.nix

@@ -0,0 +1,7 @@
+{system, inputs}:
+
+derivation {
+  name = "channels";
+  builder = ./unpack.sh;
+  inherit system inputs;
+}

corepkgs/channels/unpack.sh.in

@@ -0,0 +1,24 @@
+#! @shell@ -e
+
+export PATH=/bin:/usr/bin # !!! impure
+
+mkdir $out
+mkdir $out/tmp
+cd $out/tmp
+
+expr=$out/default.nix
+echo '[' > $expr
+
+nr=0
+for i in $inputs; do
+    echo "unpacking $i"
+    @bunzip2@ < $i | tar xvf -
+    mv * ../$nr # !!! hacky
+    echo "(import ./$nr)" >> $expr
+    nr=$(($nr + 1))
+done
+
+echo ']' >> $expr
+
+cd ..
+rmdir tmp

corepkgs/fetchurl/default.nix

@@ -1,8 +1,8 @@
-{system, url, md5}: derivation {
+{system, url, md5}:
+
+derivation {
   name = baseNameOf (toString url);
-  system = system;
   builder = ./builder.sh;
-  url = url;
-  md5 = md5;
   id = md5;
+  inherit system url md5;
 }

scripts/Makefile.am

@@ -1,6 +1,6 @@
 bin_SCRIPTS = nix-collect-garbage \
  nix-pull nix-push nix-prefetch-url \
- nix-install-package
+ nix-install-package nix-channel
 
 noinst_SCRIPTS = nix-profile.sh
 
@@ -20,4 +20,5 @@ include ../substitute.mk
 EXTRA_DIST = nix-collect-garbage.in \
  nix-pull.in nix-push.in nix-profile.sh.in \
  nix-prefetch-url.in nix-install-package.in \
+ nix-channel.in \
  prebuilts.conf readmanifest.pm.in

scripts/nix-channel.in

@@ -0,0 +1,115 @@
+#! @perl@ -w
+
+use strict;
+
+
+# Figure out the name of the `.nix-channels' file to use.
+my $home = $ENV{"HOME"};
+die '$HOME not set' unless defined $home;
+my $channelsList = "$home/.nix-channels";
+    
+
+my @channels;
+
+
+# Reads the list of channels from the file $channelsList;
+sub readChannels {
+    return if (!-f $channelsList);
+    open CHANNELS, "<$channelsList" or die "cannot open `$channelsList'";
+    while (<CHANNELS>) {
+        chomp;
+        push @channels, $_;
+    }
+    close CHANNELS;
+}
+
+
+# Writes the list of channels to the file $channelsList;
+sub writeChannels {
+    open CHANNELS, ">$channelsList" or die "cannot open `$channelsList'";
+    foreach my $url (@channels) {
+        print CHANNELS "$url\n";
+    }
+    close CHANNELS;
+}
+
+
+# Adds a channel to the file $channelsList;
+sub addChannel {
+    my $url = shift;
+    readChannels;
+    foreach my $url2 (@channels) {
+        return if $url eq $url2;
+    }
+    push @channels, $url;
+    writeChannels;
+}
+
+
+# Fetch Nix expressions and pull cache manifests from the subscribed
+# channels.
+sub update {
+    readChannels;
+
+    # Pull cache manifests.
+    foreach my $url (@channels) {
+        print "pulling cache manifest from `$url'\n";
+        system "@bindir@/nix-pull '$url'/MANIFEST";
+        die "cannot pull cache manifest from `$url'" if ($? != 0);
+    }
+
+    # Create a Nix expression that fetches and unpacks the channel Nix
+    # expressions.
+
+    my $nixExpr = "[";
+    
+    foreach my $url (@channels) {
+        my $fullURL = "$url/nixexprs.tar.bz2";
+        my $hash = `@bindir@/nix-prefetch-url '$fullURL' 2> /dev/null`
+            or die "cannot fetch `$fullURL'";
+        chomp $hash;
+        # !!! escaping
+        $nixExpr .= "((import @datadir@/nix/corepkgs/fetchurl) " .
+            "{url = $fullURL; md5 = \"$hash\"; system = \"@system@\";}) "
+    }
+
+    $nixExpr .= "]";
+
+    $nixExpr =
+        "(import @datadir@/nix/corepkgs/channels/unpack.nix) " .
+        "{inputs = $nixExpr; system = \"@system@\";}";
+
+    # Instantiate and realise it.
+    my $storeExpr = `echo '$nixExpr' | @bindir@/nix-instantiate -`
+        or die "cannot instantiate Nix expression";
+    chomp $storeExpr;
+
+    my $outPath = `nix-store -qnfB '$storeExpr'`
+        or die "cannot realise store expression";
+    chomp $outPath;
+
+    # Make it the default Nix expression for `nix-env'.
+    system "@bindir@/nix-env --import '$outPath'";
+    die "cannot pull set default Nix expression to `$outPath'" if ($? != 0);
+}
+
+
+while (scalar @ARGV) {
+    my $arg = shift @ARGV;
+
+    if ($arg eq "--add") {
+        die "syntax: nix-channel --add URL" if (scalar @ARGV != 1);
+        addChannel (shift @ARGV);
+        last;
+    }
+
+    elsif ($arg eq "--update") {
+        die "syntax: nix-channel --update" if (scalar @ARGV != 0);
+        update;
+        last;
+    }
+
+    else {
+        die "unknown argument `$arg'";
+    }
+}

scripts/nix-prefetch-url.in

@@ -1,56 +1,37 @@
-#! @perl@ -w
+#! @shell@ -e
 
-use strict;
-use IPC::Open2;
+url=$1
 
-my $url = shift @ARGV;
-defined $url or die;
+if test -z "$url"; then
+    echo "syntax: nix-prefetch-url URL" >&2
+    exit 1
+fi
 
-print "fetching $url...\n";
+# !!! race? should be relatively safe, `svn export' barfs if $tmpPath exists.
+tmpPath1=@storedir@/nix-prefetch-url-$$
 
-my $out = "@storedir@/nix-prefetch-url-$$";
+# Perform the checkout.
+@curl@ --fail --location --max-redirs 20 "$url" > $tmpPath1
 
-system "@curl@ --fail --location --max-redirs 20 \"$url\" > \"$out\"";
-$? == 0 or die "unable to fetch $url";
+# Compute the hash.
+hash=$(@bindir@/nix-hash --flat $tmpPath1)
+echo "hash is $hash" >&2
 
-my $hash=`@bindir@/nix-hash --flat $out`;
-$? == 0 or die "unable to hash $out";
-chomp $hash;
+# Rename it so that the fetchsvn builder can find it.
+tmpPath2=@storedir@/nix-prefetch-url-$hash
+test -e $tmpPath2 || mv $tmpPath1 $tmpPath2 # !!! race
 
-print "file has hash $hash\n";
+# Create a Nix expression that does a fetchsvn.
+storeExpr=$( \
+  echo "(import @datadir@/nix/corepkgs/fetchurl) \
+        {url = $url; md5 = \"$hash\"; system = \"@system@\";}" \
+  | nix-instantiate -)
 
-my $out2 = "@storedir@/nix-prefetch-url-$hash";
-rename $out, $out2;
+# Realise it.
+finalPath=$(nix-store -qnB --force-realise $storeExpr)
 
-# Create a Nix expression.
-my $nixexpr =
-    "(import @datadir@/nix/corepkgs/fetchurl) " .
-    "{url = $url; md5 = \"$hash\"; system = \"@system@\";}";
+echo "path is $finalPath" >&2
 
-#print STDERR "expr: $nixexpr\n";
+rm -rf $tmpPath2 || true
 
-# Instantiate a Nix expression.
-#print STDERR "instantiating Nix expression...\n";
-my $pid = open2(\*READ, \*WRITE, "@bindir@/nix-instantiate -")
-    or die "cannot run nix-instantiate";
-
-print WRITE $nixexpr;
-close WRITE;
-
-my $drvpath = <READ>;
-chomp $drvpath;
-
-waitpid $pid, 0;
-$? == 0 or die "nix-instantiate failed";
-
-# Run Nix.
-#print STDERR "realising store expression $drvpath...\n";
-system "@bindir@/nix-store --realise $drvpath > /dev/null";
-$? == 0 or die "realisation failed";
-
-my $path = `@bindir@/nix-store -qn $drvpath`;
-$? == 0 or die "query failed";
-
-print "path is $path";
-
-unlink $out2;
+echo $hash

scripts/nix-push.in

@@ -12,7 +12,9 @@ my $manifest = "$tmpdir/MANIFEST";
 
 END { unlink $manifest; unlink $nixfile; rmdir $tmpdir; }
 
-my $curl = "@curl@ --fail --silent ${ENV{'CURL_FLAGS'}}";
+my $curl = "@curl@ --fail --silent";
+my $extraCurlFlags = ${ENV{'CURL_FLAGS'}};
+$curl = "$curl $extraCurlFlags" if defined $extraCurlFlags;
 
 
 # Parse the command line.