@@ -12,20 +12,26 @@ func (i imageNotFoundError) Error() string {

 	return fmt.Sprintf("Image not found: %s", i.imageID)

 }

-// ImageNotFound returns the ID of the image not found on the docker host.

-func (i imageNotFoundError) ImageIDNotFound() string {

-	return i.imageID

+// IsImageNotFound returns true if the error is caused

+// when an image is not found in the docker host.

+func IsErrImageNotFound(err error) bool {

+	_, ok := err.(imageNotFoundError)

+	return ok

 }

-// ImageNotFound is an interface that describes errors caused

-// when an image is not found in the docker host.

-type ImageNotFound interface {

-	ImageIDNotFound() string

+// unauthorizedError represents an authorization error in a remote registry.

+type unauthorizedError struct {

+	cause error

 }

-// IsImageNotFound returns true when the error is caused

-// when an image is not found in the docker host.

-func IsErrImageNotFound(err error) bool {

-	_, ok := err.(ImageNotFound)

+// Error returns a string representation of an unauthorizedError

+func (u unauthorizedError) Error() string {

+	return u.cause.Error()

+}

+

+// IsUnauthorized returns true if the error is caused

+// when an the remote registry authentication fails

+func IsErrUnauthorized(err error) bool {

+	_, ok := err.(unauthorizedError)

 	return ok

 }

new file mode 100644

@@ -0,0 +1,28 @@

+package lib

+

+import (

+	"encoding/json"

+	"net/http"

+	"net/url"

+

+	"github.com/docker/docker/api/types"

+	"github.com/docker/docker/cliconfig"

+)

+

+// RegistryLogin authenticates the docker server with a given docker registry.

+// It returns UnauthorizerError when the authentication fails.

+func (cli *Client) RegistryLogin(auth cliconfig.AuthConfig) (types.AuthResponse, error) {

+	resp, err := cli.POST("/auth", url.Values{}, auth, nil)

+

+	if resp != nil && resp.statusCode == http.StatusUnauthorized {

+		return types.AuthResponse{}, unauthorizedError{err}

+	}

+	if err != nil {

+		return types.AuthResponse{}, err

+	}

+	defer resp.body.Close()

+

+	var response types.AuthResponse

+	err = json.NewDecoder(resp.body).Decode(&response)

+	return response, err

+}

@@ -2,14 +2,13 @@ package client

 import (

 	"bufio"

-	"encoding/json"

 	"fmt"

 	"io"

 	"os"

 	"runtime"

 	"strings"

-	"github.com/docker/docker/api/types"

+	"github.com/docker/docker/api/client/lib"

 	Cli "github.com/docker/docker/cli"

 	"github.com/docker/docker/cliconfig"

 	flag "github.com/docker/docker/pkg/mflag"

@@ -120,24 +119,15 @@ func (cli *DockerCli) CmdLogin(args ...string) error {

 	authconfig.ServerAddress = serverAddress

 	cli.configFile.AuthConfigs[serverAddress] = authconfig

-	serverResp, err := cli.call("POST", "/auth", cli.configFile.AuthConfigs[serverAddress], nil)

-	if serverResp.statusCode == 401 {

-		delete(cli.configFile.AuthConfigs, serverAddress)

-		if err2 := cli.configFile.Save(); err2 != nil {

-			fmt.Fprintf(cli.out, "WARNING: could not save config file: %v\n", err2)

-		}

-		return err

-	}

+	auth := cli.configFile.AuthConfigs[serverAddress]

+	response, err := cli.client.RegistryLogin(auth)

 	if err != nil {

-		return err

-	}

-

-	defer serverResp.body.Close()

-

-	var response types.AuthResponse

-	if err := json.NewDecoder(serverResp.body).Decode(&response); err != nil {

-		// Upon error, remove entry

-		delete(cli.configFile.AuthConfigs, serverAddress)

+		if lib.IsErrUnauthorized(err) {

+			delete(cli.configFile.AuthConfigs, serverAddress)

+			if err2 := cli.configFile.Save(); err2 != nil {

+				fmt.Fprintf(cli.out, "WARNING: could not save config file: %v\n", err2)

+			}

+		}

 		return err

 	}