* Removed the `id' attribute hack.

* Formalise the notion of fixed-output derivations, i.e., derivations
  for which a cryptographic hash of the output is known in advance.
  Changes to such derivations should not propagate upwards through the
  dependency graph.  Previously this was done by specifying the hash
  component of the output path through the `id' attribute, but this is
  insecure since you can lie about it (i.e., you can specify any hash
  and then produce a completely different output).  Now the
  responsibility for checking the output is moved from the builder to
  Nix itself.

  A fixed-output derivation can be created by specifying the
  `outputHash' and `outputHashAlgo' attributes, the latter taking
  values `md5', `sha1', and `sha256', and the former specifying the
  actual hash in hexadecimal or in base-32 (auto-detected by looking
  at the length of the attribute value).  MD5 is included for
  compatibility but should be considered deprecated.

* Removed the `drvPath' pseudo-attribute in derivation results.  It's
  no longer necessary.

* Cleaned up the support for multiple output paths in derivation store
  expressions.  Each output now has a unique identifier (e.g., `out',
  `devel', `docs').  Previously there was no way to tell output paths
  apart at the store expression level.

* `nix-hash' now has a flag `--base32' to specify that the hash should
  be printed in base-32 notation.

* `fetchurl' accepts parameters `sha256' and `sha1' in addition to
  `md5'.

* `nix-prefetch-url' now prints out a SHA-1 hash in base-32.  (TODO: a
  flag to specify the hash.)

2 files changed, 18 insertions, 9 deletions

diff --git a/corepkgs/fetchurl/builder.sh.in b/corepkgs/fetchurl/builder.sh.in
index c1a735d68f..aaba65d6d2 100644
--- a/corepkgs/fetchurl/builder.sh.in
+++ b/corepkgs/fetchurl/builder.sh.in
@@ -4,16 +4,10 @@ export PATH=/bin:/usr/bin
 
 echo "downloading $url into $out"
 
-prefetch=@storedir@/nix-prefetch-url-$md5
+prefetch=@storedir@/nix-prefetch-url-$outputHash
 if test -f "$prefetch"; then
     echo "using prefetched $prefetch";
     mv $prefetch $out
 else
     @curl@ --fail --location --max-redirs 20 "$url" > "$out"
 fi
-
-actual=$(@bindir@/nix-hash --flat $out)
-if test "$actual" != "$md5"; then
-    echo "hash is $actual, expected $md5"
-    exit 1
-fi
diff --git a/corepkgs/fetchurl/default.nix b/corepkgs/fetchurl/default.nix
index 8957662ecc..37f01b55ee 100644
--- a/corepkgs/fetchurl/default.nix
+++ b/corepkgs/fetchurl/default.nix
@@ -1,8 +1,23 @@
-{system, url, md5}:
+# Argh, this thing is duplicated (more-or-less) in Nixpkgs.  Need to
+# find a way to combine them.
+
+{system, url, outputHash ? "", outputHashAlgo ? "", md5 ? "", sha1 ? "", sha256 ? ""}:
+
+assert (outputHash != "" && outputHashAlgo != "")
+    || md5 != "" || sha1 != "" || sha256 != "";
 
 derivation {
   name = baseNameOf (toString url);
   builder = ./builder.sh;
+
+  # Compatibility with Nix <= 0.7.
   id = md5;
-  inherit system url md5;
+
+  # New-style output content requirements.
+  outputHashAlgo = if outputHashAlgo != "" then outputHashAlgo else
+      if sha256 != "" then "sha256" else if sha1 != "" then "sha1" else "md5";
+  outputHash = if outputHash != "" then outputHash else
+      if sha256 != "" then sha256 else if sha1 != "" then sha1 else md5;
+  
+  inherit system url;
 }