Etags must be quoted according to http spec

Signed-off-by: Stephen J Day <stephen.day@docker.com>

docs/client/repository.go

@@ -254,13 +254,14 @@ func (ms *manifests) Get(dgst digest.Digest) (*manifest.SignedManifest, error) {
 	return ms.GetByTag(dgst.String())
 }
 
-// AddEtagToTag allows a client to supply an eTag to GetByTag which will
-// be used for a conditional HTTP request.  If the eTag matches, a nil
-// manifest and nil error will be returned.
-func AddEtagToTag(tagName, dgst string) distribution.ManifestServiceOption {
+// AddEtagToTag allows a client to supply an eTag to GetByTag which will be
+// used for a conditional HTTP request.  If the eTag matches, a nil manifest
+// and nil error will be returned. etag is automatically quoted when added to
+// this map.
+func AddEtagToTag(tag, etag string) distribution.ManifestServiceOption {
 	return func(ms distribution.ManifestService) error {
 		if ms, ok := ms.(*manifests); ok {
-			ms.etags[tagName] = dgst
+			ms.etags[tag] = fmt.Sprintf(`"%s"`, etag)
 			return nil
 		}
 		return fmt.Errorf("etag options is a client-only option")

docs/client/repository_test.go

@@ -430,7 +430,7 @@ func addTestManifestWithEtag(repo, reference string, content []byte, m *testutil
 		Method: "GET",
 		Route:  "/v2/" + repo + "/manifests/" + reference,
 		Headers: http.Header(map[string][]string{
-			"Etag": {dgst},
+			"Etag": {fmt.Sprintf(`"%s"`, dgst)},
 		}),
 	}