return resp error message

follow containers#709
return and wrap http response message to show server-side error message.

Signed-off-by: Qi Wang <[email protected]>

docker/docker_client.go

@@ -591,7 +591,7 @@ func (c *dockerClient) getBearerToken(ctx context.Context, challenge challenge,
 	case http.StatusUnauthorized:
 		err := clientLib.HandleErrorResponse(res)
 		logrus.Debugf("Server response when trying to obtain an access token: \n%q", err.Error())
-		return nil, ErrUnauthorizedForCredentials
+		return nil, ErrUnauthorizedForCredentials{Err: err}
 	case http.StatusOK:
 		break
 	default:

docker/errors.go

@@ -2,21 +2,30 @@ package docker
 
 import (
 	"errors"
+	"fmt"
 	"net/http"
 
+	"github.com/docker/distribution/registry/client"
 	perrors "github.com/pkg/errors"
 )
 
 var (
 	// ErrV1NotSupported is returned when we're trying to talk to a
 	// docker V1 registry.
 	ErrV1NotSupported = errors.New("can't talk to a V1 docker registry")
-	// ErrUnauthorizedForCredentials is returned when the status code returned is 401
-	ErrUnauthorizedForCredentials = errors.New("unable to retrieve auth token: invalid username/password")
 	// ErrTooManyRequests is returned when the status code returned is 429
 	ErrTooManyRequests = errors.New("too many request to registry")
 )
 
+// ErrUnauthorizedForCredentials is returned when the status code returned is 401
+type ErrUnauthorizedForCredentials struct { // We only use a struct to allow a type assertion, without limiting the contents of the error otherwise.
+	Err error
+}
+
+func (e ErrUnauthorizedForCredentials) Error() string {
+	return fmt.Sprintf("unable to retrieve auth token: invalid username/password: %s", e.Err.Error())
+}
+
 // httpResponseToError translates the https.Response into an error. It returns
 // nil if the response is not considered an error.
 func httpResponseToError(res *http.Response) error {
@@ -26,7 +35,8 @@ func httpResponseToError(res *http.Response) error {
 	case http.StatusTooManyRequests:
 		return ErrTooManyRequests
 	case http.StatusUnauthorized:
-		return ErrUnauthorizedForCredentials
+		err := client.HandleErrorResponse(res)
+		return ErrUnauthorizedForCredentials{Err: err}
 	default:
 		return perrors.Errorf("invalid status code from registry %d (%s)", res.StatusCode, http.StatusText(res.StatusCode))
 	}