cipd: Implement local cache for ResolveVersion(...) call with tags.

go/src/infra/tools/cipd/internal/checksum_test.go

Index: go/src/infra/tools/cipd/internal/checksum_test.go
diff --git a/go/src/infra/tools/cipd/internal/checksum_test.go b/go/src/infra/tools/cipd/internal/checksum_test.go
new file mode 100644
index 0000000000000000000000000000000000000000..3b307c0def2090889d0580a7fbf0aa40e9275b27
--- /dev/null
+++ b/go/src/infra/tools/cipd/internal/checksum_test.go
@@ -0,0 +1,45 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package internal
+
+import (
+	"testing"
+
+	"infra/tools/cipd/internal/messages"
+
+	. "github.com/smartystreets/goconvey/convey"
+)
+
+func TestChecksumCheckingWorks(t *testing.T) {
+	msg := messages.TagCache{
+		Entries: []*messages.TagCache_Entry{
+			&messages.TagCache_Entry{
+				Package:    strPtr("package"),
+				Tag:        strPtr("tag"),
+				InstanceId: strPtr("instance_id"),
+			},
+		},
+	}
+
+	Convey("Works", t, func(c C) {
+		buf, err := MarshalWithSHA1(&msg)
+		So(err, ShouldBeNil)
+		out := messages.TagCache{}
+		So(UnmarshalWithSHA1(buf, &out), ShouldBeNil)
+		So(out, ShouldResemble, msg)
+	})
+
+	Convey("Rejects bad msg", t, func(c C) {
+		buf, err := MarshalWithSHA1(&msg)
+		So(err, ShouldBeNil)
+		buf[10] = 0
+		out := messages.TagCache{}
+		So(UnmarshalWithSHA1(buf, &out), ShouldNotBeNil)
+	})
+}
+
+func strPtr(s string) *string {
+	return &s
+}