Enable proxying registries to downgrade fetched manifests to Schema 1.

Ensure Accept headers are sent with TagService.Get (which hits manifest
endpoints).  Add support for remote Get and Put for the proxied blobstore.

Signed-off-by: Richard Scothern <richard.scothern@gmail.com>

docs/client/repository.go

@@ -292,9 +292,18 @@ func (t *tags) Get(ctx context.Context, tag string) (distribution.Descriptor, er
 	if err != nil {
 		return distribution.Descriptor{}, err
 	}
-	var attempts int
-	resp, err := t.client.Head(u)
 
+	req, err := http.NewRequest("HEAD", u, nil)
+	if err != nil {
+		return distribution.Descriptor{}, err
+	}
+
+	for _, t := range distribution.ManifestMediaTypes() {
+		req.Header.Add("Accept", t)
+	}
+
+	var attempts int
+	resp, err := t.client.Do(req)
 check:
 	if err != nil {
 		return distribution.Descriptor{}, err
@@ -304,7 +313,16 @@ check:
 	case resp.StatusCode >= 200 && resp.StatusCode < 400:
 		return descriptorFromResponse(resp)
 	case resp.StatusCode == http.StatusMethodNotAllowed:
-		resp, err = t.client.Get(u)
+		req, err = http.NewRequest("GET", u, nil)
+		if err != nil {
+			return distribution.Descriptor{}, err
+		}
+
+		for _, t := range distribution.ManifestMediaTypes() {
+			req.Header.Add("Accept", t)
+		}
+
+		resp, err = t.client.Do(req)
 		attempts++
 		if attempts > 1 {
 			return distribution.Descriptor{}, err

docs/proxy/proxyblobstore.go

@@ -174,6 +174,28 @@ func (pbs *proxyBlobStore) Stat(ctx context.Context, dgst digest.Digest) (distri
 	return pbs.remoteStore.Stat(ctx, dgst)
 }
 
+func (pbs *proxyBlobStore) Get(ctx context.Context, dgst digest.Digest) ([]byte, error) {
+	blob, err := pbs.localStore.Get(ctx, dgst)
+	if err == nil {
+		return blob, nil
+	}
+
+	if err := pbs.authChallenger.tryEstablishChallenges(ctx); err != nil {
+		return []byte{}, err
+	}
+
+	blob, err = pbs.remoteStore.Get(ctx, dgst)
+	if err != nil {
+		return []byte{}, err
+	}
+
+	_, err = pbs.localStore.Put(ctx, "", blob)
+	if err != nil {
+		return []byte{}, err
+	}
+	return blob, nil
+}
+
 // Unsupported functions
 func (pbs *proxyBlobStore) Put(ctx context.Context, mediaType string, p []byte) (distribution.Descriptor, error) {
 	return distribution.Descriptor{}, distribution.ErrUnsupported
@@ -195,10 +217,6 @@ func (pbs *proxyBlobStore) Open(ctx context.Context, dgst digest.Digest) (distri
 	return nil, distribution.ErrUnsupported
 }
 
-func (pbs *proxyBlobStore) Get(ctx context.Context, dgst digest.Digest) ([]byte, error) {
-	return nil, distribution.ErrUnsupported
-}
-
 func (pbs *proxyBlobStore) Delete(ctx context.Context, dgst digest.Digest) error {
 	return distribution.ErrUnsupported
 }

docs/proxy/proxyblobstore_test.go

@@ -218,6 +218,40 @@ func populate(t *testing.T, te *testEnv, blobCount, size, numUnique int) {
 	te.inRemote = inRemote
 	te.numUnique = numUnique
 }
+func TestProxyStoreGet(t *testing.T) {
+	te := makeTestEnv(t, "foo/bar")
+
+	localStats := te.LocalStats()
+	remoteStats := te.RemoteStats()
+
+	populate(t, te, 1, 10, 1)
+	_, err := te.store.Get(te.ctx, te.inRemote[0].Digest)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if (*localStats)["get"] != 1 && (*localStats)["put"] != 1 {
+		t.Errorf("Unexpected local counts")
+	}
+
+	if (*remoteStats)["get"] != 1 {
+		t.Errorf("Unexpected remote get count")
+	}
+
+	_, err = te.store.Get(te.ctx, te.inRemote[0].Digest)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if (*localStats)["get"] != 2 && (*localStats)["put"] != 1 {
+		t.Errorf("Unexpected local counts")
+	}
+
+	if (*remoteStats)["get"] != 1 {
+		t.Errorf("Unexpected remote get count")
+	}
+
+}
 
 func TestProxyStoreStat(t *testing.T) {
 	te := makeTestEnv(t, "foo/bar")