fix: supply mtree file for determinism

bazel-contrib · Oct 4, 2023 · 85e619c · 85e619c
1 parent e1a871e
commit 85e619c
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Showing 2 changed files with 21 additions and 8 deletions.
diff --git a/oci/private/tarball.bzl b/oci/private/tarball.bzl
@@ -51,13 +51,14 @@ def _tarball_impl(ctx):
     yq_bin = ctx.toolchains["@aspect_bazel_lib//lib:yq_toolchain_type"].yqinfo.bin
     bsdtar = ctx.toolchains["@aspect_bazel_lib//lib:tar_toolchain_type"]
     executable = ctx.actions.declare_file("{}/tarball.sh".format(ctx.label.name))
+    mtree = ctx.actions.declare_file("_{}.mtree".format(ctx.label.name))
     repo_tags = ctx.file.repo_tags
 
     substitutions = {
         "{{yq}}": yq_bin.path,
         "{{tar}}": bsdtar.tarinfo.binary.path,
         "{{image_dir}}": image.path,
-        "{{tarball_path}}": tarball.path,
+        "{{mtree_out}}": mtree.path,
     }
 
     if ctx.attr.repo_tags:
@@ -72,16 +73,24 @@ def _tarball_impl(ctx):
 
     ctx.actions.run(
         executable = util.maybe_wrap_launcher_for_windows(ctx, executable),
-        inputs = depset(
-            direct = [image, repo_tags, executable],
-            transitive = [bsdtar.default.files],
-        ),
-        outputs = [tarball],
+        inputs = [image, repo_tags, executable],
+        outputs = [mtree],
         tools = [yq_bin],
         mnemonic = "OCITarball",
         progress_message = "OCI Tarball %{label}",
     )
 
+    # TODO(2.0): this oci_tarball rule should just produce an mtree manifest instead,
+    # and then the tar rule can be composed in the oci_tarball macro in defs.bzl.
+    # To make it a non-breaking change, call the tar action ourselves instead.
+    ctx.actions.run(
+        executable = bsdtar.tarinfo.binary,
+        inputs = depset(direct = [mtree], transitive = [bsdtar.default.files]),
+        outputs = [tarball],
+        arguments = ["--create", "--file", tarball.path, "@" + mtree.path],
+        mnemonic = "Tar",
+    )
+
     exe = ctx.actions.declare_file(ctx.label.name + ".sh")
 
     ctx.actions.expand_template(

diff --git a/oci/private/tarball.sh.tpl b/oci/private/tarball.sh.tpl
@@ -6,7 +6,7 @@ readonly YQ="{{yq}}"
 readonly TAR="{{tar}}"
 readonly IMAGE_DIR="{{image_dir}}"
 readonly BLOBS_DIR="${STAGING_DIR}/blobs"
-readonly TARBALL_PATH="{{tarball_path}}"
+readonly OUT="{{mtree_out}}"
 readonly TAGS_FILE="{{tags}}"
 
 MANIFEST_DIGEST=$(${YQ} eval '.manifests[0].digest | sub(":"; "/")' "${IMAGE_DIR}/index.json" | tr  -d '"')
@@ -35,4 +35,8 @@ layers="${LAYERS}" \
         --null-input '.[0] = {"Config": env(config), "RepoTags": "${repo_tags}" | envsubst | split("%") | map(select(. != "")) , "Layers": env(layers) | map( "blobs/" + . + ".tar.gz") }' \
         --output-format json > "${STAGING_DIR}/manifest.json"
 
-${TAR} -C "${STAGING_DIR}" -cf "${TARBALL_PATH}" manifest.json blobs
+# Write output in mtree format
+# https://man.freebsd.org/cgi/man.cgi?mtree(8)
+# so that tar produces a deterministic output.
+echo "manifest.json uid=0 gid=0 mode=0755 type=file content=${STAGING_DIR}/manifest.json">>${OUT}
+echo "blobs uid=0 gid=0 mode=0755 type=dir">>${OUT}