1 files changed, 49 insertions, 0 deletions
diff --git a/corepkgs/nar.nix b/corepkgs/nar.nix
new file mode 100644
index 000000000000..04be17fb0ce2
--- /dev/null
+++ b/corepkgs/nar.nix
@@ -0,0 +1,49 @@
+with import <nix/config.nix>;
+
+let
+
+  builder = builtins.toFile "nar.sh"
+    ''
+      export PATH=${nixBinDir}:${coreutils}
+
+      if [ $compressionType = xz ]; then
+        ext=.xz
+        compressor="| ${xz} -7"
+      elif [ $compressionType = bzip2 ]; then
+        ext=.bz2
+        compressor="| ${bzip2}"
+      else
+        ext=
+        compressor=
+      fi
+
+      echo "packing ‘$storePath’..."
+      mkdir $out
+      dst=$out/tmp.nar$ext
+
+      set -o pipefail
+      eval "nix-store --dump \"$storePath\" $compressor > $dst"
+
+      hash=$(nix-hash --flat --type $hashAlgo --base32 $dst)
+      echo -n $hash > $out/nar-compressed-hash
+
+      mv $dst $out/$hash.nar$ext
+    '';
+
+in
+
+{ storePath, hashAlgo, compressionType }:
+
+derivation {
+  name = "nar";
+  system = builtins.currentSystem;
+  builder = shell;
+  args = [ "-e" builder ];
+  inherit storePath hashAlgo compressionType;
+
+  # Don't build in a chroot because Nix's dependencies may not be there.
+  __noChroot = true;
+
+  # Remote machines may not have ${nixBinDir} or ${coreutils} in the same prefixes
+  preferLocalBuild = true;
+}