add support for user-specified annotations

build.go

@@ -219,6 +219,11 @@ func (b *Builder) updateOCIConfigForOutput(sf *types.Stackerfile, s types.Storag
 		return err
 	}
 
+	// add user-defined annotations
+	for k, v := range l.Annotations {
+		annotations[k] = v
+	}
+
 	// compute the git version for the directory that the stacker file is
 	// in. we don't care if it's not a git directory, because in that case
 	// we'll fall back to putting the whole stacker file contents in the

cache_test.go

@@ -126,5 +126,5 @@ func TestCacheEntryChanged(t *testing.T) {
 	// This test works because the type information is included in the
 	// hashstructure hash above, so using a zero valued CacheEntry is
 	// enough to capture changes in types.
-	assert.Equal(uint64(0x99dd94c023d7ccc6), h)
+	assert.Equal(uint64(0x98ab47c70ff0b70), h)
 }

doc/stacker_yaml.md

@@ -218,3 +218,16 @@ In this particular case the parent folder of the current folder, let's call it
 When `stacker build -f parent/folder1/stacker.yaml` is invoked, stacker would search
 for the other two stacker.yaml files and build them first, before building
 the stacker.yaml specified in the command line.
+
+##### `annotations`
+
+`annotations` is a user-specified key value map that will be included in the final OCI image.
+
+    annotations:
+      a.b.c.key: abc_val
+      p.q.r.key: pqr_val
+
+While `config` section supports a similar `labels`, it is more pertitent to the
+image runtime. On the other hand, `annotations` is intended to be
+image-specific metadata aligned with the
+[annotations in the image spec](https://github.com/opencontainers/image-spec/blob/main/annotations.md).

test/annotations.bats

@@ -0,0 +1,31 @@
+load helpers
+
+function setup() {
+    stacker_setup
+}
+
+function teardown() {
+    cleanup
+}
+
+@test "annotations work" {
+    cat > stacker.yaml <<EOF
+thing:
+    from:
+        type: oci
+        url: $CENTOS_OCI
+    run: ls
+    annotations:
+      a.b.c.key: val
+EOF
+    stacker build 
+    [ "$status" -eq 0 ]
+    manifest=$(cat oci/index.json | jq -r .manifests[0].digest | cut -f2 -d:)
+    cat oci/blobs/sha256/$manifest | jq .
+    key=$(cat oci/blobs/sha256/$manifest | jq -r .annotations | cut -f1 -d:)
+    echo $key
+    val=$(cat oci/blobs/sha256/$manifest | jq -r .annotations | cut -f2 -d:)
+    echo $val
+    [[ "$key" == *"a.b.c.key"* ]]
+    [[ "$val" == *"val"* ]]
+}

types/layer.go

@@ -191,6 +191,7 @@ type Layer struct {
 	BuildOnly      bool              `yaml:"build_only"`
 	Binds          Binds             `yaml:"binds"`
 	RuntimeUser    string            `yaml:"runtime_user"`
+	Annotations    map[string]string `yaml:"annotations"`
 }
 
 func parseLayers(referenceDirectory string, lms yaml.MapSlice, requireHash bool) (map[string]Layer, error) {