Made the digest exporter report image digest if there is only one image.

cmd/imagedigestexporter/digest.go

@@ -0,0 +1,18 @@
+package main
+
+import (
+ v1 "github.com/google/go-containerregistry/pkg/v1"
+)
+
+// GetDigest returns the digest of an OCI image index. If there is only one image in the index, the
+// digest of the image is returned; otherwise, the digest of the whole index is returned.
+func GetDigest(ii v1.ImageIndex) (v1.Hash, error) {
+ im, err := ii.IndexManifest()
+ if err != nil {
+ return v1.Hash{}, err
+ }
+ if len(im.Manifests) == 1 {
+ return im.Manifests[0].Digest, nil
+ }
+ return ii.Digest()
+}

cmd/imagedigestexporter/digest_test.go

@@ -0,0 +1,65 @@
+package main
+
+import (
+ "testing"
+
+ "github.com/google/go-cmp/cmp"
+ v1 "github.com/google/go-containerregistry/pkg/v1"
+ "github.com/google/go-containerregistry/pkg/v1/empty"
+ "github.com/google/go-containerregistry/pkg/v1/random"
+)
+
+func TestGetDigest(t *testing.T) {
+ mustGetIndex := func(ii v1.ImageIndex, err error) v1.ImageIndex {
+ if err != nil {
+ t.Fatalf("must get image: %s", err)
+ }
+ return ii
+ }
+ mustGetManifest := func(im *v1.IndexManifest, err error) *v1.IndexManifest {
+ if err != nil {
+ t.Fatalf("must get manifest: %s", err)
+ }
+ return im
+ }
+ mustGetDigest := func(h v1.Hash, err error) v1.Hash {
+ if err != nil {
+ t.Fatalf("must get digest: %s", err)
+ }
+ return h
+ }
+ indexSingleImage := mustGetIndex(random.Index(1024, 4, 1))
+ indexMultipleImages := mustGetIndex(random.Index(1024, 4, 4))
+ tests := []struct {
+ name string
+ index v1.ImageIndex
+ expected v1.Hash
+ }{
+ {
+ name: "empty index",
+ index: empty.Index,
+ expected: mustGetDigest(empty.Index.Digest()),
+ },
+ {
+ name: "index with single image",
+ index: indexSingleImage,
+ expected: mustGetManifest(indexSingleImage.IndexManifest()).Manifests[0].Digest,
+ },
+ {
+ name: "index with multiple images",
+ index: indexMultipleImages,
+ expected: mustGetDigest(indexMultipleImages.Digest()),
+ },
+ }
+ for _, test := range tests {
+ t.Run(test.name, func(t *testing.T) {
+ digest, err := GetDigest(test.index)
+ if err != nil {
+ t.Fatalf("cannot get digest: %s", err)
+ }
+ if diff := cmp.Diff(digest, test.expected); diff != "" {
+ t.Errorf("get digest: -want +got: %s", diff)
+ }
+ })
+ }
+}

cmd/imagedigestexporter/main.go

@@ -55,9 +55,9 @@ func main() {
  log.Printf("ImageResource %s doesn't have an index.json file: %s", imageResource.Name, err)
  continue
  }
- digest, err := ii.Digest()
+ digest, err := GetDigest(ii)
  if err != nil {
- log.Fatalf("Unexpected error getting image digest %v: %v", imageResource, err)
+ log.Fatalf("Unexpected error getting image digest for %s: %v", imageResource.Name, err)
  }
  output = append(output, v1alpha1.PipelineResourceResult{Name: imageResource.Name, Digest: digest.String()})
  }

docs/resources.md

@@ -289,9 +289,9 @@ To surface the image digest in the output of the `taskRun` the builder tool
 should produce this information in a
 [OCI Image Spec](https://github.com/opencontainers/image-spec/blob/master/image-layout.md)
 `index.json` file. This file should be placed on a location as specified in the
-task definition under the resource `outputImageDir`. Annotations in `index.json`
-will be ignored, and if there are multiple versions of the image, the latest
-will be used.
+task definition under the resource `outputImageDir`. If there is only one image
+in the `index.json` file, the digest of that image is exported; otherwise, the
+digest of the whole image index would be exported.
 
 For example this build-push task defines the `outputImageDir` for the
 `builtImage` resource in `/workspace/buildImage`

examples/taskruns/task-multiple-output-image.yaml

@@ -104,7 +104,7 @@ spec:
  }
  ]
  }
- EOF 
+ EOF
 ---
 apiVersion: tekton.dev/v1alpha1
 kind: TaskRun

examples/taskruns/taskrun-cloud-event.yaml

@@ -112,7 +112,7 @@ spec:
  {
  "mediaType": "application/vnd.oci.image.index.v1+json",
  "size": 314,
- "digest": "sha256:NOTAREALDIGEST"
+ "digest": "sha256:deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef"
  }
  ]
  }