adds a lock on writeClose. closes #448

close.go

@@ -169,6 +169,12 @@ func (c *Conn) closeHandshake(code StatusCode, reason string) error {
 }
 
 func (c *Conn) writeClose(code StatusCode, reason string) error {
+	c.closeMu.Lock()
+	defer c.closeMu.Unlock()
+	if c.closeWritten {
+		return nil
+	}
+
 	ce := CloseError{
 		Code:   code,
 		Reason: reason,
@@ -193,6 +199,7 @@ func (c *Conn) writeClose(code StatusCode, reason string) error {
 	if err != nil && !errors.Is(err, net.ErrClosed) {
 		return err
 	}
+	c.closeWritten = true
 	return nil
 }
 

conn.go

@@ -73,9 +73,10 @@ type Conn struct {
 	closeReadCtx  context.Context
 	closeReadDone chan struct{}
 
-	closed  chan struct{}
-	closeMu sync.Mutex
-	closing bool
+	closed       chan struct{}
+	closeMu      sync.Mutex
+	closing      bool
+	closeWritten bool
 
 	pingCounter   atomic.Int64
 	activePingsMu sync.Mutex