fix: harden high-fanout delivery under load

loadtest/im-pressure/wsclient.go

@@ -35,6 +35,11 @@ type dataPacket struct {
 	Content   json.RawMessage `json:"content"`
 }
 
+type queuedDataPacket struct {
+	packet   dataPacket
+	queuedAt time.Time
+}
+
 type ctrlError struct {
 	Code int
 	Text string
@@ -52,18 +57,19 @@ type WSClient struct {
 	commandTimeout time.Duration
 	onData         func(AccountRecord, dataPacket)
 	onDisconnect   func(AccountRecord, error)
+	callbackQueue  *callbackQueueMetrics
 
 	sendMu sync.Mutex
 	mu     sync.Mutex
 	seq    uint64
 	waits  map[string]chan ctrlPacket
 	done   chan struct{}
-	data   chan dataPacket
+	data   chan queuedDataPacket
 	closed atomic.Bool
 }
 
 func connectWSClient(ctx context.Context, cfg *Config, account AccountRecord, apiKey, password string,
-	onData func(AccountRecord, dataPacket), onDisconnect func(AccountRecord, error)) (*WSClient, error) {
+	onData func(AccountRecord, dataPacket), onDisconnect func(AccountRecord, error), callbackQueue *callbackQueueMetrics) (*WSClient, error) {
 	timeout, err := configDuration(cfg.CommandTimeout)
 	if err != nil {
 		return nil, err
@@ -85,7 +91,8 @@ func connectWSClient(ctx context.Context, cfg *Config, account AccountRecord, ap
 	}
 	client := &WSClient{
 		account: account, conn: conn, commandTimeout: timeout, onData: onData, onDisconnect: onDisconnect,
-		waits: make(map[string]chan ctrlPacket), done: make(chan struct{}),
+		callbackQueue: callbackQueue,
+		waits:         make(map[string]chan ctrlPacket), done: make(chan struct{}),
 	}
 	client.startDataProcessor()
 	go client.readLoop()
@@ -382,7 +389,9 @@ func (c *WSClient) readLoop() {
 				if c.data == nil {
 					c.onData(c.account, data)
 				} else {
-					c.data <- data
+					queued := queuedDataPacket{packet: data, queuedAt: time.Now()}
+					c.callbackQueue.enqueue()
+					c.data <- queued
 				}
 			}
 		}
@@ -393,10 +402,12 @@ func (c *WSClient) startDataProcessor() {
 	if c.onData == nil || c.data != nil {
 		return
 	}
-	c.data = make(chan dataPacket, dataCallbackQueueSize)
+	c.data = make(chan queuedDataPacket, dataCallbackQueueSize)
 	go func() {
 		for data := range c.data {
-			c.onData(c.account, data)
+			c.callbackQueue.startCallback(data.queuedAt)
+			c.onData(c.account, data.packet)
+			c.callbackQueue.finishCallback()
 		}
 	}()
 }