include image name in errors

The go docker client's ErrNoSuchImage does not include the image
name. However, it is imperative that this name appears in error
messages sent to clients, since the docker client, as of version
1.7.0, only automatically pulls images when their name is present in
the error.

Fixes #967.

proxy/create_container_interceptor.go

@@ -21,6 +21,17 @@ type createContainerRequestBody struct {
 	MacAddress string             `json:"MacAddress,omitempty" yaml:"MacAddress,omitempty"`
 }
 
+// Replacement for docker.NoSuchImage, which does not contain the
+// image name, which in turn breaks docker clients post 1.7.0 since
+// they expect the image name to be present in errors.
+type ErrNoSuchImage struct {
+	Name string
+}
+
+func (err *ErrNoSuchImage) Error() string {
+	return "No such image: " + err.Name
+}
+
 func (i *createContainerInterceptor) InterceptRequest(r *http.Request) error {
 	body, err := ioutil.ReadAll(r.Body)
 	if err != nil {
@@ -63,7 +74,9 @@ func (i *createContainerInterceptor) InterceptRequest(r *http.Request) error {
 func (i *createContainerInterceptor) setWeaveWaitEntrypoint(container *docker.Config) error {
 	if len(container.Entrypoint) == 0 {
 		image, err := i.proxy.client.InspectImage(container.Image)
-		if err != nil {
+		if err == docker.ErrNoSuchImage {
+			return &ErrNoSuchImage{container.Image}
+		} else if err != nil {
 			return err
 		}
 

proxy/proxy_intercept.go

@@ -16,11 +16,10 @@ import (
 
 func (proxy *Proxy) Intercept(i interceptor, w http.ResponseWriter, r *http.Request) {
 	if err := i.InterceptRequest(r); err != nil {
-		_, isNoSuchContainer := err.(*docker.NoSuchContainer)
-		switch {
-		case isNoSuchContainer:
+		switch err.(type) {
+		case *docker.NoSuchContainer:
 			http.Error(w, err.Error(), http.StatusNotFound)
-		case err == docker.ErrNoSuchImage:
+		case *ErrNoSuchImage:
 			http.Error(w, err.Error(), http.StatusNotFound)
 		default:
 			http.Error(w, err.Error(), http.StatusInternalServerError)