return write error

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)
Upstream-commit: c65de2c0207ac67e5023ada8709490ef4627bd01
Component: engine

components/engine/api/server/server.go

@@ -978,8 +978,8 @@ func writeCorsHeaders(w http.ResponseWriter, r *http.Request) {
 }
 
 func ping(eng *engine.Engine, version version.Version, w http.ResponseWriter, r *http.Request, vars map[string]string) error {
-	w.Write([]byte{'O', 'K'})
-	return nil
+	_, err := w.Write([]byte{'O', 'K'})
+	return err
 }
 
 func makeHttpHandler(eng *engine.Engine, logging bool, localMethod string, localRoute string, handlerFunc HttpApiFunc, enableCors bool, dockerVersion version.Version) http.HandlerFunc {

components/engine/docs/sources/reference/api/docker_remote_api_v1.11.md

@@ -1181,6 +1181,7 @@ Ping the docker server
     Status Codes:
 
     -   **200** - no error
+    -   **500** - server error
 
 ### Create a new image from a container's changes