fix: stop the first Close from returning net.ErrClosed

close.go

@@ -96,7 +96,18 @@ func CloseStatus(err error) StatusCode {
 //
 // Close will unblock all goroutines interacting with the connection once
 // complete.
-func (c *Conn) Close(code StatusCode, reason string) (err error) {
+func (c *Conn) Close(code StatusCode, reason string) error {
+	firstCall := !c.closeCalled.Swap(true)
+	err := c.closeWithHandshake(code, reason)
+	if firstCall && errors.Is(err, net.ErrClosed) {
+		return nil
+	}
+	return err
+}
+
+// closeWithHandshake implements Close for library code, which must not set
+// closeCalled.
+func (c *Conn) closeWithHandshake(code StatusCode, reason string) (err error) {
 	defer errd.Wrap(&err, "failed to close WebSocket")
 
 	if c.casClosing() {
@@ -129,7 +140,16 @@ func (c *Conn) Close(code StatusCode, reason string) (err error) {
 
 // CloseNow closes the WebSocket connection without attempting a close handshake.
 // Use when you do not want the overhead of the close handshake.
-func (c *Conn) CloseNow() (err error) {
+func (c *Conn) CloseNow() error {
+	firstCall := !c.closeCalled.Swap(true)
+	err := c.closeWithoutHandshake()
+	if firstCall && errors.Is(err, net.ErrClosed) {
+		return nil
+	}
+	return err
+}
+
+func (c *Conn) closeWithoutHandshake() (err error) {
 	defer errd.Wrap(&err, "failed to immediately close WebSocket")
 
 	if c.casClosing() {

conn.go

@@ -77,9 +77,13 @@ type Conn struct {
 	closeReadCtx  context.Context
 	closeReadDone chan struct{}
 
-	closing atomic.Bool
-	closeMu sync.Mutex // Protects following.
-	closed  chan struct{}
+	// closeCalled is set by the first Close or CloseNow call. Library code
+	// closes the connection without setting it, so the user's first Close
+	// does not report net.ErrClosed when the library closed first.
+	closeCalled atomic.Bool
+	closing     atomic.Bool
+	closeMu     sync.Mutex // Protects following.
+	closed      chan struct{}
 
 	pingCounter    atomic.Int64
 	activePingsMu  sync.Mutex

conn_test.go

@@ -401,6 +401,71 @@ func TestConn(t *testing.T) {
 		assert.ErrorIs(t, websocket.ErrClosed, err2)
 	})
 
+	t.Run("firstCloseAfterLibraryClose", func(t *testing.T) {
+		t.Parallel()
+
+		closers := []struct {
+			name  string
+			close func(*websocket.Conn) error
+		}{
+			{"Close", func(c *websocket.Conn) error { return c.Close(websocket.StatusNormalClosure, "") }},
+			{"CloseNow", (*websocket.Conn).CloseNow},
+		}
+		for _, closer := range closers {
+			t.Run(closer.name, func(t *testing.T) {
+				t.Parallel()
+
+				t.Run("peerClose", func(t *testing.T) {
+					tt, c1, c2 := newConnTest(t, nil, nil)
+
+					readErr := xsync.Go(func() error {
+						_, _, err := c1.Read(tt.ctx)
+						return err
+					})
+					assert.Success(t, c2.Close(websocket.StatusNormalClosure, ""))
+					assert.Success(t, assertCloseStatus(websocket.StatusNormalClosure, <-readErr))
+
+					assert.Success(t, closer.close(c1))
+				})
+
+				t.Run("closeReadDataMessage", func(t *testing.T) {
+					tt, c1, c2 := newConnTest(t, nil, nil)
+
+					closeReadCtx := c1.CloseRead(tt.ctx)
+					readErr := xsync.Go(func() error {
+						_, _, err := c2.Read(tt.ctx)
+						return err
+					})
+					assert.Success(t, c2.Write(tt.ctx, websocket.MessageText, []byte("x")))
+					assert.Success(t, assertCloseStatus(websocket.StatusPolicyViolation, <-readErr))
+					<-closeReadCtx.Done()
+
+					assert.Success(t, closer.close(c1))
+				})
+
+				t.Run("netConnUnexpectedType", func(t *testing.T) {
+					tt, c1, c2 := newConnTest(t, nil, nil)
+
+					nc := websocket.NetConn(tt.ctx, c1, websocket.MessageBinary)
+					readErr := xsync.Go(func() error {
+						_, _, err := c2.Read(tt.ctx)
+						return err
+					})
+					// net.Pipe writes block until nc.Read reads them.
+					writeErr := xsync.Go(func() error {
+						return c2.Write(tt.ctx, websocket.MessageText, []byte("x"))
+					})
+					_, err := nc.Read(make([]byte, 1))
+					assert.Contains(t, err, "unexpected frame type")
+					assert.Success(t, <-writeErr)
+					assert.Success(t, assertCloseStatus(websocket.StatusUnsupportedData, <-readErr))
+
+					assert.Success(t, closer.close(c1))
+				})
+			})
+		}
+	})
+
 	t.Run("MidReadClose", func(t *testing.T) {
 		tt, c1, c2 := newConnTest(t, nil, nil)
 
@@ -449,6 +514,21 @@ func TestWasm(t *testing.T) {
 	}
 
 	s := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Header.Get("Sec-WebSocket-Protocol") == "close" {
+			// Closes first so the client's Close runs after the browser
+			// closed the connection.
+			c, err := websocket.Accept(w, r, &websocket.AcceptOptions{
+				Subprotocols:       []string{"close"},
+				InsecureSkipVerify: true,
+			})
+			if err == nil {
+				err = c.Close(websocket.StatusNormalClosure, "")
+			}
+			if err != nil {
+				t.Error(err)
+			}
+			return
+		}
 		err := echoServer(w, r, &websocket.AcceptOptions{
 			Subprotocols:       []string{"echo"},
 			InsecureSkipVerify: true,

netconn.go

@@ -174,7 +174,7 @@ func (nc *netConn) read(p []byte) (int, error) {
 		}
 		if typ != nc.msgType {
 			err := fmt.Errorf("unexpected frame type read (expected %v): %v", nc.msgType, typ)
-			nc.c.Close(StatusUnsupportedData, err.Error())
+			nc.c.closeWithHandshake(StatusUnsupportedData, err.Error())
 			return 0, err
 		}
 		nc.reader = r

read.go

@@ -79,7 +79,7 @@ func (c *Conn) CloseRead(ctx context.Context) context.Context {
 		defer c.close()
 		_, _, err := c.Reader(ctx)
 		if err == nil {
-			c.Close(StatusPolicyViolation, "unexpected data message")
+			c.closeWithHandshake(StatusPolicyViolation, "unexpected data message")
 		}
 	}()
 	return ctx

ws_js.go

@@ -56,6 +56,10 @@ type Conn struct {
 	closeErrOnce  sync.Once
 	closeErr      error
 	closeWasClean bool
+	// closeCalled is set by the first Close or CloseNow call. Library code
+	// and the browser close the connection without setting it, so the user's
+	// first Close does not report net.ErrClosed after either closed it.
+	closeCalled atomic.Bool
 
 	releaseOnClose   func()
 	releaseOnError   func()
@@ -125,7 +129,7 @@ func (c *Conn) init() {
 }
 
 func (c *Conn) closeWithInternal() {
-	c.Close(StatusInternalError, "something went wrong")
+	c.closeWithHandshake(StatusInternalError, "something went wrong")
 }
 
 // Read attempts to read a message from the connection.
@@ -145,7 +149,7 @@ func (c *Conn) Read(ctx context.Context) (MessageType, []byte, error) {
 	readLimit := c.msgReadLimit.Load()
 	if readLimit >= 0 && int64(len(p)) > readLimit {
 		reason := fmt.Errorf("read limited at %d bytes", c.msgReadLimit.Load())
-		c.Close(StatusMessageTooBig, reason.Error())
+		c.closeWithHandshake(StatusMessageTooBig, reason.Error())
 		return 0, nil, fmt.Errorf("%w: %v", ErrMessageTooBig, reason)
 	}
 	return typ, p, nil
@@ -154,7 +158,7 @@ func (c *Conn) Read(ctx context.Context) (MessageType, []byte, error) {
 func (c *Conn) read(ctx context.Context) (MessageType, []byte, error) {
 	select {
 	case <-ctx.Done():
-		c.Close(StatusPolicyViolation, "read timed out")
+		c.closeWithHandshake(StatusPolicyViolation, "read timed out")
 		return 0, nil, ctx.Err()
 	case <-c.readSignal:
 	case <-c.closed:
@@ -229,6 +233,17 @@ func (c *Conn) write(typ MessageType, p []byte) error {
 // or the connection is closed.
 // It thus performs the full WebSocket close handshake.
 func (c *Conn) Close(code StatusCode, reason string) error {
+	firstCall := !c.closeCalled.Swap(true)
+	err := c.closeWithHandshake(code, reason)
+	if firstCall && errors.Is(err, net.ErrClosed) {
+		return nil
+	}
+	return err
+}
+
+// closeWithHandshake implements Close for library code, which must not set
+// closeCalled.
+func (c *Conn) closeWithHandshake(code StatusCode, reason string) error {
 	err := c.exportedClose(code, reason)
 	if err != nil {
 		return fmt.Errorf("failed to close WebSocket: %w", err)
@@ -403,10 +418,10 @@ func (c *Conn) CloseRead(ctx context.Context) context.Context {
 
 	go func() {
 		defer cancel()
-		defer c.CloseNow()
+		defer c.closeWithHandshake(StatusGoingAway, "")
 		_, _, err := c.read(ctx)
 		if err != nil {
-			c.Close(StatusPolicyViolation, "unexpected data message")
+			c.closeWithHandshake(StatusPolicyViolation, "unexpected data message")
 		}
 	}()
 	return ctx

ws_js_test.go

@@ -2,6 +2,7 @@ package websocket_test
 
 import (
 	"context"
+	"net"
 	"net/http"
 	"os"
 	"testing"
@@ -37,6 +38,25 @@ func TestWasm(t *testing.T) {
 	assert.Success(t, err)
 }
 
+func TestWasmFirstCloseAfterPeerClose(t *testing.T) {
+	t.Parallel()
+
+	ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
+	defer cancel()
+
+	c, _, err := websocket.Dial(ctx, os.Getenv("WS_ECHO_SERVER_URL"), &websocket.DialOptions{
+		Subprotocols: []string{"close"},
+	})
+	assert.Success(t, err)
+
+	_, _, err = c.Read(ctx)
+	// Read returns once the browser has closed the connection.
+	assert.ErrorIs(t, net.ErrClosed, err)
+
+	err = c.Close(websocket.StatusNormalClosure, "")
+	assert.Success(t, err)
+}
+
 func TestWasmDialTimeout(t *testing.T) {
 	t.Parallel()