Cope with client sending a HostConfig named HostConfig

proxy/start_container_interceptor.go

@@ -15,11 +15,22 @@ func (i *startContainerInterceptor) InterceptRequest(r *http.Request) error {
 	// If the client has sent some JSON which might be a HostConfig, add our
 	// parameters back into it, otherwise Docker will consider them overwritten
 	if containerShouldAttach(container) && r.Header.Get("Content-Type") == "application/json" {
-		hostConfig := map[string]interface{}{}
-		if err := unmarshalRequestBody(r, &hostConfig); err != nil {
+		params := map[string]interface{}{}
+		if err := unmarshalRequestBody(r, &params); err != nil {
 			return err
 		}
-		if len(hostConfig) > 0 {
+		// HostConfig can be sent either as a struct named HostConfig, or unnamed at top level
+		var hostConfig map[string]interface{}
+		if subParam, found := params["HostConfig"]; found {
+			if typecast, ok := subParam.(map[string]interface{}); ok {
+				hostConfig = typecast
+			}
+			// We can't reliably detect what Docker will see as a top-level HostConfig,
+			// so just assume any parameter at top level indicates there is one.
+		} else if len(params) > 0 {
+			hostConfig = params
+		}
+		if hostConfig != nil {
 			i.proxy.addWeaveWaitVolume(hostConfig)
 			if dnsDomain := i.proxy.getDNSDomain(); dnsDomain != "" {
 				if err := i.proxy.setWeaveDNS(hostConfig, container.Config.Hostname, dnsDomain); err != nil {
@@ -27,7 +38,8 @@ func (i *startContainerInterceptor) InterceptRequest(r *http.Request) error {
 				}
 			}
 
-			if err := marshalRequestBody(r, hostConfig); err != nil {
+			// Note we marshal the original top-level dictionary to avoid disturbing anything else
+			if err := marshalRequestBody(r, params); err != nil {
 				return err
 			}
 		}