Add static.NewLayer (#1093)

* Add static.NewLayer

* Document that static layer contents aren't compressed

* remove unnecessary comment

* update copyright year

Author: imjasonh

Diff for: pkg/v1/static/layer.go

@@ -0,0 +1,69 @@
+// Copyright 2021 Google LLC All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package static
+
+import (
+	"bytes"
+	"io"
+	"io/ioutil"
+	"sync"
+
+	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/types"
+)
+
+// NewLayer returns a layer containing the given bytes, with the given mediaType.
+//
+// Contents will not be compressed.
+func NewLayer(b []byte, mt types.MediaType) v1.Layer {
+	return &staticLayer{b: b, mt: mt}
+}
+
+type staticLayer struct {
+	b  []byte
+	mt types.MediaType
+
+	once sync.Once
+	h    v1.Hash
+}
+
+func (l *staticLayer) Digest() (v1.Hash, error) {
+	var err error
+	// Only calculate digest the first time we're asked.
+	l.once.Do(func() {
+		l.h, _, err = v1.SHA256(bytes.NewReader(l.b))
+	})
+	return l.h, err
+}
+
+func (l *staticLayer) DiffID() (v1.Hash, error) {
+	return l.Digest()
+}
+
+func (l *staticLayer) Compressed() (io.ReadCloser, error) {
+	return ioutil.NopCloser(bytes.NewReader(l.b)), nil
+}
+
+func (l *staticLayer) Uncompressed() (io.ReadCloser, error) {
+	return ioutil.NopCloser(bytes.NewReader(l.b)), nil
+}
+
+func (l *staticLayer) Size() (int64, error) {
+	return int64(len(l.b)), nil
+}
+
+func (l *staticLayer) MediaType() (types.MediaType, error) {
+	return l.mt, nil
+}

Diff for: pkg/v1/static/static_test.go

@@ -0,0 +1,83 @@
+// Copyright 2021 Google LLC All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package static
+
+import (
+	"io/ioutil"
+	"strings"
+	"testing"
+
+	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/types"
+	"github.com/google/go-containerregistry/pkg/v1/validate"
+)
+
+func TestNewLayer(t *testing.T) {
+	b := []byte(strings.Repeat(".", 10))
+	l := NewLayer(b, types.OCILayer)
+
+	// This does basically nothing.
+	if err := validate.Layer(l, validate.Fast); err != nil {
+		t.Fatal(err)
+	}
+
+	// Digest and DiffID match, and match expectations.
+	h, err := l.Digest()
+	if err != nil {
+		t.Fatal(err)
+	}
+	h2, err := l.DiffID()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if h != h2 {
+		t.Errorf("Digest != DiffID; digest is %v, diffid is %v", h, h2)
+	}
+	wantDigest, err := v1.NewHash("sha256:537f3fb69ba01fc388a3a5c920c485b2873d5f327305c3dd2004d6a04451659b")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if h != wantDigest {
+		t.Errorf("Digest mismatch; got %v, want %v", h, wantDigest)
+	}
+
+	sz, err := l.Size()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if sz != 10 {
+		t.Errorf("Size mismatch; got %d, want %d", sz, 10)
+	}
+
+	mt, err := l.MediaType()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if mt != types.OCILayer {
+		t.Errorf("MediaType mismatch; got %v, want %v", mt, types.OCILayer)
+	}
+
+	r, err := l.Uncompressed()
+	if err != nil {
+		t.Fatal(err)
+	}
+	got, err := ioutil.ReadAll(r)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(got) != string(b) {
+		t.Errorf("Contents mismatch: got %q, want %q", string(got), string(b))
+	}
+}