working epics ioc and tested

internal/server/ws.go

@@ -115,7 +115,7 @@ func (h *wsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	wg.Add(3)
 	go func() { defer wg.Done(); c.readLoop(ctx, cancel) }()
 	go func() { defer wg.Done(); c.dispatchLoop(ctx) }()
-	go func() { defer wg.Done(); c.writeLoop(ctx) }()
+	go func() { defer wg.Done(); c.writeLoop(ctx, cancel) }()
 	wg.Wait()
 
 	// Cancel all subscriptions on disconnect.
@@ -193,7 +193,10 @@ func (c *wsClient) dispatchLoop(ctx context.Context) {
 }
 
 // writeLoop sends queued messages over the WebSocket connection.
-func (c *wsClient) writeLoop(ctx context.Context) {
+// It cancels ctx on any write error so that readLoop and dispatchLoop exit
+// promptly rather than blocking forever waiting for outCh to drain.
+func (c *wsClient) writeLoop(ctx context.Context, cancel context.CancelFunc) {
+	defer cancel()
 	for {
 		select {
 		case msg := <-c.outCh:
@@ -251,8 +254,11 @@ func (c *wsClient) handleSubscribe(ctx context.Context, refs []sigRef) {
 		c.subs[ref] = cancelSub
 		c.subsMu.Unlock()
 
-		// Send metadata once on subscribe.
-		c.sendMeta(ctx, ref)
+		// Send metadata in a goroutine: for EPICS signals GetMetadata may block
+		// for several seconds waiting for the CA channel to connect and for
+		// ca_pend_io to complete. Running it inline would stall readLoop and
+		// prevent any further messages from this client from being processed.
+		go c.sendMeta(ctx, ref)
 	}
 }
 
@@ -341,7 +347,7 @@ func (c *wsClient) handleHistory(ctx context.Context, msg inMsg) {
 	b, _ := json.Marshal(resp)
 	select {
 	case c.outCh <- b:
-	default:
+	case <-ctx.Done():
 	}
 }