feat: Output the image id of an oci_load target.

oci/private/image_id.sh.tpl

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+# Read the configuration json sha256 digest from the manifest.json file passed
+# as the first positional argument. Output that sha256 to the
+# file provided as the second positional argument.
+set -o pipefail -o errexit -o nounset
+
+readonly JQ="{{jq_path}}"
+
+CONFIG_PATH=$("$JQ" -r '.[0].Config' "$1")
+# CONFIG_PATH will be blobs/sha256/<digest>
+SHA256_OF_CONFIG="${CONFIG_PATH#blobs/sha256/}"
+
+if [[ "$SHA256_OF_CONFIG" == "$CONFIG_PATH" ]]; then
+  echo "Error: Failed to extract SHA256 digest from CONFIG_PATH" >&2
+  exit 1
+fi
+
+echo "$SHA256_OF_CONFIG" > "$2"

oci/private/load.bzl

@@ -129,6 +129,7 @@ attrs = {
         allow_single_file = True,
     ),
     "_tarball_sh": attr.label(allow_single_file = True, default = "//oci/private:tarball.sh.tpl"),
+    "_image_id_sh": attr.label(allow_single_file = True, default = "//oci/private:image_id.sh.tpl"),
     "_runfiles": attr.label(default = "@bazel_tools//tools/bash/runfiles"),
     "_windows_constraint": attr.label(default = "@platforms//os:windows"),
 }
@@ -143,6 +144,7 @@ def _load_impl(ctx):
 
     mtree_spec = ctx.actions.declare_file("{}/tarball.spec".format(ctx.label.name))
     executable = ctx.actions.declare_file("{}/load.sh".format(ctx.label.name))
+    image_id_sh = ctx.actions.declare_file("{}/image_id.sh".format(ctx.label.name))
     manifest_json = ctx.actions.declare_file("{}/manifest.json".format(ctx.label.name))
 
     # Represents either manifest.json or index.json depending on the image format
@@ -181,6 +183,32 @@ def _load_impl(ctx):
         ],
         mnemonic = "OCITarballManifest",
     )
+    ctx.actions.expand_template(
+        template = ctx.file._image_id_sh,
+        output = image_id_sh,
+        is_executable = True,
+        substitutions = {
+            "{{jq_path}}": jq.jqinfo.bin.path,
+        },
+    )
+    image_id = ctx.actions.declare_file("{}/image_id.txt".format(ctx.label.name))
+    image_id_args = ctx.actions.args()
+    image_id_args.add(manifest_json)
+    image_id_args.add(image_id)
+    ctx.actions.run(
+        executable = image_id_sh,
+        inputs = [manifest_json],
+        outputs = [image_id],
+        arguments = [image_id_args],
+        tools = [
+            jq.jqinfo.bin,
+        ],
+        env = {
+            "MANIFEST_JSON_PATH": manifest_json.path,
+            "OUTPUT_PATH": image_id.path,
+        },
+        mnemonic = "ImageId",
+    )
 
     # This action produces a large output and should rarely be used as it puts load on the cache.
     # It will only run if the "tarball" output_group is explicitly requested
@@ -228,6 +256,7 @@ def _load_impl(ctx):
         DefaultInfo(
             runfiles = runfiles,
             executable = runnable_loader,
+            files = depset([image_id]),
         ),
         OutputGroupInfo(tarball = depset([tarball])),
     ]

oci/private/load.sh.tpl

@@ -8,6 +8,7 @@ runfiles_export_envvars
 readonly TAR="$(rlocation "{{tar}}")"
 readonly MTREE="$(rlocation "{{mtree_path}}")"
 readonly LOADER="$(rlocation "{{loader}}")"
+readonly JQ="$(rlocation "{{jq_path}}")"
 
 if [ -f "$LOADER" ]; then
     CONTAINER_CLI="$LOADER"