Fix chunk encoding issue (#93)

Root cause: The .Flush() was called after releasing the write mutex lock (since defers are called in reverse order). This allowed concurrent writes to the http.ResponseWriter, which in turn caused stdlib's chunk encoder to produce invalid sequence of data. The JavaScript client then failed with ERR_INVALID_CHUNKED_ENCODING error (stream lost) in the browser.

Author: kalalannn

server.go.tmpl

@@ -206,11 +206,15 @@ func (s *{{$serviceName}}) serve{{firstLetterToUpper $method.Name}}JSONStream(ct
 
 	// Call service method implementation.
 	if err {{if or (eq (len $method.Inputs) 0) (gt (len $method.Outputs) 0)}}:{{end}}= s.{{$name}}.{{$method.Name}}(ctx{{range $i, $_ := $method.Inputs}}, reqPayload.Arg{{$i}}{{end}}, streamWriter); err != nil {
+		cancel()
 		rpcErr, ok := err.(WebRPCError)
 		if !ok {
 			rpcErr = ErrWebrpcEndpoint.WithCause(err)
 		}
+		streamWriter.mu.Lock()
 		streamWriter.sendError(w, r, rpcErr)
+		streamWriter.f.Flush()
+		streamWriter.mu.Unlock()
 		return
 	}
 }

types.go.tmpl

@@ -150,22 +150,21 @@ func (w *streamWriter) keepAlive(ctx context.Context) {
 }
 
 func (w *streamWriter) ping() error {
-	defer w.f.Flush()
-
 	w.mu.Lock()
-	defer w.mu.Unlock()
-
 	_, err := w.w.Write([]byte("\n"))
+	w.f.Flush()
+	w.mu.Unlock()
+
 	return err
 }
 
 func (w *streamWriter) write(respPayload interface{}) error {
-	defer w.f.Flush()
-
 	w.mu.Lock()
-	defer w.mu.Unlock()
+	err := w.e.Encode(respPayload)
+	w.f.Flush()
+	w.mu.Unlock()
 
-	return w.e.Encode(respPayload)
+	return err
 }
 {{- end }}