Introduce mkBinaryCache function

2 files changed, 83 insertions, 0 deletions

diff --git a/pkgs/build-support/binary-cache/default.nix b/pkgs/build-support/binary-cache/default.nix
new file mode 100644
index 00000000000..577328cad92
--- /dev/null
+++ b/pkgs/build-support/binary-cache/default.nix
@@ -0,0 +1,40 @@
+{ stdenv, buildPackages }:
+
+# This function is for creating a flat-file binary cache, i.e. the kind created by
+# nix copy --to file:///some/path and usable as a substituter (with the file:// prefix).
+
+# For example, in the Nixpkgs repo:
+# nix-build -E 'with import ./. {}; mkBinaryCache { rootPaths = [hello]; }'
+
+{ name ? "binary-cache"
+, rootPaths
+}:
+
+stdenv.mkDerivation {
+  inherit name;
+
+  __structuredAttrs = true;
+
+  exportReferencesGraph.closure = rootPaths;
+
+  preferLocalBuild = true;
+
+  PATH = "${buildPackages.coreutils}/bin:${buildPackages.jq}/bin:${buildPackages.python3}/bin:${buildPackages.nix}/bin:${buildPackages.xz}/bin";
+
+  builder = builtins.toFile "builder" ''
+    . .attrs.sh
+
+    export out=''${outputs[out]}
+
+    mkdir $out
+    mkdir $out/nar
+
+    python ${./make-binary-cache.py}
+
+    # These directories must exist, or Nix might try to create them in LocalBinaryCacheStore::init(),
+    # which fails if mounted read-only
+    mkdir $out/realisations
+    mkdir $out/debuginfo
+    mkdir $out/log
+  '';
+}
diff --git a/pkgs/build-support/binary-cache/make-binary-cache.py b/pkgs/build-support/binary-cache/make-binary-cache.py
new file mode 100644
index 00000000000..16dd8a7e96b
--- /dev/null
+++ b/pkgs/build-support/binary-cache/make-binary-cache.py
@@ -0,0 +1,43 @@
+
+import json
+import os
+import subprocess
+
+with open(".attrs.json", "r") as f:
+  closures = json.load(f)["closure"]
+
+os.chdir(os.environ["out"])
+
+nixPrefix = os.environ["NIX_STORE"] # Usually /nix/store
+
+with open("nix-cache-info", "w") as f:
+  f.write("StoreDir: " + nixPrefix + "\n")
+
+def dropPrefix(path):
+  return path[len(nixPrefix + "/"):]
+
+for item in closures:
+  narInfoHash = dropPrefix(item["path"]).split("-")[0]
+
+  xzFile = "nar/" + narInfoHash + ".nar.xz"
+  with open(xzFile, "w") as f:
+    subprocess.run("nix-store --dump %s | xz -c" % item["path"], stdout=f, shell=True)
+
+  fileHash = subprocess.run(["nix-hash", "--base32", "--type", "sha256", item["path"]], capture_output=True).stdout.decode().strip()
+  fileSize = os.path.getsize(xzFile)
+
+  # Rename the .nar.xz file to its own hash to match "nix copy" behavior
+  finalXzFile = "nar/" + fileHash + ".nar.xz"
+  os.rename(xzFile, finalXzFile)
+
+  with open(narInfoHash + ".narinfo", "w") as f:
+    f.writelines((x + "\n" for x in [
+      "StorePath: " + item["path"],
+      "URL: " + finalXzFile,
+      "Compression: xz",
+      "FileHash: sha256:" + fileHash,
+      "FileSize: " + str(fileSize),
+      "NarHash: " + item["narHash"],
+      "NarSize: " + str(item["narSize"]),
+      "References: " + " ".join(dropPrefix(ref) for ref in item["references"]),
+    ]))