Add WithTransport to gcrane (#1022)

Also add some silly tests for coverage.

pkg/gcrane/options.go

@@ -16,6 +16,7 @@ package gcrane
 
 import (
 	"context"
+	"net/http"
 	"runtime"
 
 	"github.com/google/go-containerregistry/pkg/authn"
@@ -64,6 +65,16 @@ func WithJobs(jobs int) Option {
 	}
 }
 
+// WithTransport is a functional option for overriding the default transport
+// for remote operations.
+func WithTransport(t http.RoundTripper) Option {
+	return func(o *options) {
+		o.remote = append(o.remote, remote.WithTransport(t))
+		o.google = append(o.google, google.WithTransport(t))
+		o.crane = append(o.crane, crane.WithTransport(t))
+	}
+}
+
 // WithUserAgent adds the given string to the User-Agent header for any HTTP
 // requests.
 func WithUserAgent(ua string) Option {

pkg/gcrane/options_test.go

@@ -0,0 +1,58 @@
+// 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 gcrane
+
+import (
+	"context"
+	"net/http"
+	"testing"
+
+	"github.com/google/go-containerregistry/pkg/authn"
+)
+
+func TestOptions(t *testing.T) {
+	o := makeOptions()
+	if len(o.remote) != 1 {
+		t.Errorf("remote should default to Keychain")
+	}
+	if len(o.crane) != 1 {
+		t.Errorf("crane should default to Keychain")
+	}
+	if len(o.google) != 1 {
+		t.Errorf("google should default to Keychain")
+	}
+
+	o = makeOptions(WithAuth(authn.Anonymous), WithKeychain(authn.DefaultKeychain))
+	if len(o.remote) != 1 {
+		t.Errorf("WithKeychain should replace remote[0]")
+	}
+	if len(o.crane) != 1 {
+		t.Errorf("WithKeychain should replace crane[0]")
+	}
+	if len(o.google) != 1 {
+		t.Errorf("WithKeychain should replace google[0]")
+	}
+
+	o = makeOptions(WithTransport(http.DefaultTransport), WithUserAgent("hi"), WithContext(context.TODO()))
+	if len(o.remote) != 4 {
+		t.Errorf("wrong number of options: %d", len(o.remote))
+	}
+	if len(o.crane) != 4 {
+		t.Errorf("wrong number of options: %d", len(o.crane))
+	}
+	if len(o.google) != 4 {
+		t.Errorf("wrong number of options: %d", len(o.google))
+	}
+}