load authConfig only when needed and fix useless WARNING

auth/auth.go

@@ -76,7 +76,7 @@ func LoadConfig(rootPath string) (*ConfigFile, error) {
 	configFile := ConfigFile{Configs: make(map[string]AuthConfig), rootPath: rootPath}
 	confFile := path.Join(rootPath, CONFIGFILE)
 	if _, err := os.Stat(confFile); err != nil {
-		return &configFile, ErrConfigFileMissing
+		return &configFile, nil //missing file is not an error
 	}
 	b, err := ioutil.ReadFile(confFile)
 	if err != nil {
@@ -86,13 +86,13 @@ func LoadConfig(rootPath string) (*ConfigFile, error) {
 	if err := json.Unmarshal(b, &configFile.Configs); err != nil {
 		arr := strings.Split(string(b), "\n")
 		if len(arr) < 2 {
-			return nil, fmt.Errorf("The Auth config file is empty")
+			return &configFile, fmt.Errorf("The Auth config file is empty")
 		}
 		authConfig := AuthConfig{}
 		origAuth := strings.Split(arr[0], " = ")
 		authConfig.Username, authConfig.Password, err = decodeAuth(origAuth[1])
 		if err != nil {
-			return nil, err
+			return &configFile, err
 		}
 		origEmail := strings.Split(arr[1], " = ")
 		authConfig.Email = origEmail[1]
@@ -101,7 +101,7 @@ func LoadConfig(rootPath string) (*ConfigFile, error) {
 		for k, authConfig := range configFile.Configs {
 			authConfig.Username, authConfig.Password, err = decodeAuth(authConfig.Auth)
 			if err != nil {
-				return nil, err
+				return &configFile, err
 			}
 			authConfig.Auth = ""
 			configFile.Configs[k] = authConfig

commands.go

@@ -303,6 +303,8 @@ func (cli *DockerCli) CmdLogin(args ...string) error {
 		return nil
 	}
 
+	cli.LoadConfigFile()
+
 	var oldState *term.State
 	if *flUsername == "" || *flPassword == "" || *flEmail == "" {
 		oldState, err = term.SetRawTerminal(cli.terminalFd)
@@ -498,6 +500,7 @@ func (cli *DockerCli) CmdInfo(args ...string) error {
 	}
 
 	if len(out.IndexServerAddress) != 0 {
+		cli.LoadConfigFile()
 		u := cli.configFile.Configs[out.IndexServerAddress].Username
 		if len(u) > 0 {
 			fmt.Fprintf(cli.out, "Username: %v\n", u)
@@ -838,12 +841,18 @@ func (cli *DockerCli) CmdPush(args ...string) error {
 		return nil
 	}
 
+	cli.LoadConfigFile()
+
 	// If we're not using a custom registry, we know the restrictions
 	// applied to repository names and can warn the user in advance.
 	// Custom repositories can have different rules, and we must also
 	// allow pushing by image ID.
 	if len(strings.SplitN(name, "/", 2)) == 1 {
-		return fmt.Errorf("Impossible to push a \"root\" repository. Please rename your repository in <user>/<repo> (ex: %s/%s)", cli.configFile.Configs[auth.IndexServerAddress()].Username, name)
+		username := cli.configFile.Configs[auth.IndexServerAddress()].Username
+		if username == "" {
+			username = "<user>"
+		}
+		return fmt.Errorf("Impossible to push a \"root\" repository. Please rename your repository in <user>/<repo> (ex: %s/%s)", username, name)
 	}
 
 	v := url.Values{}
@@ -1745,6 +1754,14 @@ func Subcmd(name, signature, description string) *flag.FlagSet {
 	return flags
 }
 
+func (cli *DockerCli) LoadConfigFile() (err error) {
+	cli.configFile, err = auth.LoadConfig(os.Getenv("HOME"))
+	if err != nil {
+		fmt.Fprintf(cli.err, "WARNING: %s\n", err)
+	}
+	return err
+}
+
 func NewDockerCli(in io.ReadCloser, out, err io.Writer, proto, addr string) *DockerCli {
 	var (
 		isTerminal = false
@@ -1761,15 +1778,9 @@ func NewDockerCli(in io.ReadCloser, out, err io.Writer, proto, addr string) *Doc
 	if err == nil {
 		err = out
 	}
-
-	configFile, e := auth.LoadConfig(os.Getenv("HOME"))
-	if e != nil {
-		fmt.Fprintf(err, "WARNING: %s\n", e)
-	}
 	return &DockerCli{
 		proto:      proto,
 		addr:       addr,
-		configFile: configFile,
 		in:         in,
 		out:        out,
 		err:        err,