feat: support all hash algorithms (#433)

oci/private/pull.bzl

@@ -216,12 +216,10 @@ _SUPPORTED_MEDIA_TYPES = {
 def _is_tag(str):
     return str.find(":") == -1
 
-def _trim_hash_algorithm(identifier):
-    "Optionally remove the sha256: prefix from identifier, if present"
-    parts = identifier.split(":", 1)
-    if len(parts) != 2:
-        return identifier
-    return parts[1]
+def _digest_into_blob_path(digest):
+    "convert sha256:deadbeef into sha256/deadbeef"
+    digest_path = digest.replace(":", "/", 1)
+    return "blobs/{}".format(digest_path)
 
 def _download(rctx, state, identifier, output, resource, download_fn = download.bazel, headers = {}, allow_fail = False):
     "Use the Bazel Downloader to fetch from the remote registry"
@@ -325,31 +323,9 @@ def _create_downloader(rctx):
     )
 
 _BUILD_FILE_TMPL = """\
-"Generated by oci_pull"
+"Generated by oci_pull. DO NOT EDIT!"
 
 load("@aspect_bazel_lib//lib:copy_to_directory.bzl", "copy_to_directory")
-load("@aspect_bazel_lib//lib:copy_file.bzl", "copy_file")
-load("@aspect_bazel_lib//lib:jq.bzl", "jq")
-load("@bazel_skylib//rules:write_file.bzl", "write_file")
-
-package(default_visibility = ["//visibility:public"])
-
-copy_file(
-    name = "manifest",
-    src = "manifest.json",
-    out = "{image_digest}"
-)
-
-copy_to_directory(
-    name = "blobs",
-    # TODO(https://github.com/bazel-contrib/rules_oci/issues/73): other hash algorithms
-    out = "blobs/sha256",
-    include_external_repositories = ["*"],
-    srcs = {tars} + [
-        ":{image_digest}",
-        ":{config_file}",
-    ],
-)
 
 copy_to_directory(
     name = "{target_name}",
@@ -360,6 +336,7 @@ copy_to_directory(
         "oci-layout",
         "index.json",
     ],
+    visibility = ["//visibility:public"]
 )
 """
 
@@ -385,7 +362,7 @@ def _oci_pull_impl(rctx):
     if manifest["mediaType"] in _SUPPORTED_MEDIA_TYPES["manifest"]:
         if rctx.attr.platform:
             fail("{}/{} is a single-architecture image, so attribute 'platforms' should not be set.".format(rctx.attr.registry, rctx.attr.repository))
-            
+
     elif manifest["mediaType"] in _SUPPORTED_MEDIA_TYPES["index"]:
         if not rctx.attr.platform:
             fail("{}/{} is a multi-architecture image, so attribute 'platforms' is required.".format(rctx.attr.registry, rctx.attr.repository))
@@ -398,34 +375,29 @@ def _oci_pull_impl(rctx):
         manifest, size, digest = downloader.download_manifest(matching_manifest["digest"], "manifest.json")
     else:
         fail("Unrecognized mediaType {} in manifest file".format(manifest["mediaType"]))
+
+    # symlink manifest.json to blobs with it's digest. 
+    # it is okay to use symlink here as copy_to_directory will dereference it when creating the TreeArtifact.
+    rctx.symlink("manifest.json", _digest_into_blob_path(digest))
 
     # download the image config
-    config_file = _trim_hash_algorithm(manifest["config"]["digest"])
-    downloader.download_blob(manifest["config"]["digest"], config_file)
+    downloader.download_blob(manifest["config"]["digest"], _digest_into_blob_path(manifest["config"]["digest"]))
 
     # download all layers
     # TODO: we should avoid eager-download of the layers ("shallow pull")
-    tars = []
     for layer in manifest["layers"]:
-        blob_digest = _trim_hash_algorithm(layer["digest"])
-        downloader.download_blob(layer["digest"], blob_digest)
-
-        if blob_digest not in tars:
-            tars.append(blob_digest)
+        downloader.download_blob(layer["digest"], _digest_into_blob_path(layer["digest"]))
 
     rctx.file("index.json", util.build_manifest_json(
         media_type = manifest["mediaType"],
         size = size,
         digest = digest,
-        platform = rctx.attr.platform
+        platform = rctx.attr.platform,
     ))
     rctx.file("oci-layout", json.encode_indent({"imageLayoutVersion": "1.0.0"}, indent = "    "))
-    
+
     rctx.file("BUILD.bazel", content = _BUILD_FILE_TMPL.format(
-        target_name = rctx.attr.target_name,
-        tars = tars,
-        image_digest = _trim_hash_algorithm(digest),
-        config_file = config_file,
+        target_name = rctx.attr.target_name
     ))
 
 oci_pull = repository_rule(