improve yamux logging (#4952)

client/connector.go

@@ -17,7 +17,6 @@ package client
 import (
 	"context"
 	"crypto/tls"
-	"io"
 	"net"
 	"strconv"
 	"strings"
@@ -115,7 +114,8 @@ func (c *defaultConnectorImpl) Open() error {
 
 	fmuxCfg := fmux.DefaultConfig()
 	fmuxCfg.KeepAliveInterval = time.Duration(c.cfg.Transport.TCPMuxKeepaliveInterval) * time.Second
-	fmuxCfg.LogOutput = io.Discard
+	// Use trace level for yamux logs
+	fmuxCfg.LogOutput = xlog.NewTraceWriter(xl)
 	fmuxCfg.MaxStreamWindowSize = 6 * 1024 * 1024
 	session, err := fmux.Client(conn, fmuxCfg)
 	if err != nil {

client/control.go

@@ -276,10 +276,12 @@ func (ctl *Control) heartbeatWorker() {
 }
 
 func (ctl *Control) worker() {
+	xl := ctl.xl
 	go ctl.heartbeatWorker()
 	go ctl.msgDispatcher.Run()
 
 	<-ctl.msgDispatcher.Done()
+	xl.Debugf("control message dispatcher exited")
 	ctl.closeSession()
 
 	ctl.pm.Close()