Add flusher check to utils.WriteFlusher.

That way we can know when the stream has been flushed.

Signed-off-by: David Calavera <david.calavera@gmail.com>

api/server/server.go

@@ -1285,9 +1285,6 @@ func (s *Server) postBuild(eng *engine.Engine, version version.Version, w http.R
 		}
 	}
 
-	stdout := engine.NewOutput()
-	stdout.Set(utils.NewWriteFlusher(w))
-
 	if version.GreaterThanOrEqualTo("1.8") {
 		w.Header().Set("Content-Type", "application/json")
 		buildConfig.JSONFormat = true
@@ -1304,7 +1301,8 @@ func (s *Server) postBuild(eng *engine.Engine, version version.Version, w http.R
 		buildConfig.Pull = true
 	}
 
-	buildConfig.Stdout = stdout
+	output := utils.NewWriteFlusher(w)
+	buildConfig.Stdout = output
 	buildConfig.Context = r.Body
 
 	buildConfig.RemoteURL = r.FormValue("remote")
@@ -1336,7 +1334,9 @@ func (s *Server) postBuild(eng *engine.Engine, version version.Version, w http.R
 	}
 
 	if err := builder.Build(s.daemon, eng, buildConfig); err != nil {
-		if !stdout.Used() {
+		// Do not write the error in the http output if it's still empty.
+		// This prevents from writing a 200(OK) when there is an interal error.
+		if !output.Flushed() {
 			return err
 		}
 		sf := streamformatter.NewStreamFormatter(version.GreaterThanOrEqualTo("1.8"))

utils/utils.go

@@ -128,12 +128,14 @@ type WriteFlusher struct {
 	sync.Mutex
 	w       io.Writer
 	flusher http.Flusher
+	flushed bool
 }
 
 func (wf *WriteFlusher) Write(b []byte) (n int, err error) {
 	wf.Lock()
 	defer wf.Unlock()
 	n, err = wf.w.Write(b)
+	wf.flushed = true
 	wf.flusher.Flush()
 	return n, err
 }
@@ -142,9 +144,16 @@ func (wf *WriteFlusher) Write(b []byte) (n int, err error) {
 func (wf *WriteFlusher) Flush() {
 	wf.Lock()
 	defer wf.Unlock()
+	wf.flushed = true
 	wf.flusher.Flush()
 }
 
+func (wf *WriteFlusher) Flushed() bool {
+	wf.Lock()
+	defer wf.Unlock()
+	return wf.flushed
+}
+
 func NewWriteFlusher(w io.Writer) *WriteFlusher {
 	var flusher http.Flusher
 	if f, ok := w.(http.Flusher); ok {