resume pulling the layer on disconnect

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)

docs/registry.go

@@ -256,12 +256,43 @@ func (r *Registry) GetRemoteImageJSON(imgID, registry string, token []string) ([
 	return jsonString, imageSize, nil
 }
 
-func (r *Registry) GetRemoteImageLayer(imgID, registry string, token []string) (io.ReadCloser, error) {
+func (r *Registry) GetRemoteImageLayer(imgID, registry string, token []string, imgSize int64) (io.ReadCloser, error) {
-	req, err := r.reqFactory.NewRequest("GET", registry+"images/"+imgID+"/layer", nil)
+	var (
+		retries   = 5
+		headRes   *http.Response
+		hasResume bool = false
+		imageURL       = fmt.Sprintf("%simages/%s/layer", registry, imgID)
+	)
+	headReq, err := r.reqFactory.NewRequest("HEAD", imageURL, nil)
+	if err != nil {
+		return nil, fmt.Errorf("Error while getting from the server: %s\n", err)
+	}
+	setTokenAuth(headReq, token)
+	for i := 1; i <= retries; i++ {
+		headRes, err = r.client.Do(headReq)
+		if err != nil && i == retries {
+			return nil, fmt.Errorf("Eror while making head request: %s\n", err)
+		} else if err != nil {
+			time.Sleep(time.Duration(i) * 5 * time.Second)
+			continue
+		}
+		break
+	}
+
+	if headRes.Header.Get("Accept-Ranges") == "bytes" && imgSize > 0 {
+		hasResume = true
+	}
+
+	req, err := r.reqFactory.NewRequest("GET", imageURL, nil)
 	if err != nil {
 		return nil, fmt.Errorf("Error while getting from the server: %s\n", err)
 	}
 	setTokenAuth(req, token)
+	if hasResume {
+		utils.Debugf("server supports resume")
+		return utils.ResumableRequestReader(r.client, req, 5, imgSize), nil
+	}
+	utils.Debugf("server doesn't support resume")
 	res, err := r.client.Do(req)
 	if err != nil {
 		return nil, err
@@ -725,6 +756,13 @@ type Registry struct {
 	indexEndpoint string
 }
 
+func AddRequiredHeadersToRedirectedRequests(req *http.Request, via []*http.Request) error {
+	if via != nil && via[0] != nil {
+		req.Header = via[0].Header
+	}
+	return nil
+}
+
 func NewRegistry(authConfig *AuthConfig, factory *utils.HTTPRequestFactory, indexEndpoint string) (r *Registry, err error) {
 	httpDial := func(proto string, addr string) (net.Conn, error) {
 		conn, err := net.Dial(proto, addr)
@@ -744,7 +782,8 @@ func NewRegistry(authConfig *AuthConfig, factory *utils.HTTPRequestFactory, inde
 	r = &Registry{
 		authConfig: authConfig,
 		client: &http.Client{
-			Transport: httpTransport,
+			Transport:     httpTransport,
+			CheckRedirect: AddRequiredHeadersToRedirectedRequests,
 		},
 		indexEndpoint: indexEndpoint,
 	}

docs/registry_test.go

@@ -70,7 +70,7 @@ func TestGetRemoteImageJSON(t *testing.T) {
 
 func TestGetRemoteImageLayer(t *testing.T) {
 	r := spawnTestRegistry(t)
-	data, err := r.GetRemoteImageLayer(IMAGE_ID, makeURL("/v1/"), TOKEN)
+	data, err := r.GetRemoteImageLayer(IMAGE_ID, makeURL("/v1/"), TOKEN, 0)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -78,7 +78,7 @@ func TestGetRemoteImageLayer(t *testing.T) {
 		t.Fatal("Expected non-nil data result")
 	}
 
-	_, err = r.GetRemoteImageLayer("abcdef", makeURL("/v1/"), TOKEN)
+	_, err = r.GetRemoteImageLayer("abcdef", makeURL("/v1/"), TOKEN, 0)
 	if err == nil {
 		t.Fatal("Expected image not found error")
 	}