Add support for dialing with context to websockets

Right now there is no way to pass context.Context to websocket.Dial. In
addition, this method can block indefinitely in the `NewClient` call.

Fixes golang/go#57953

Author: Cyberax

websocket/client.go

@@ -6,10 +6,12 @@ package websocket
 
 import (
 	"bufio"
+	"context"
 	"io"
 	"net"
 	"net/http"
 	"net/url"
+	"time"
 )
 
 // DialError is an error that occurs while dialling a websocket server.
@@ -77,30 +79,60 @@ func parseAuthority(location *url.URL) string {
 	return location.Host
 }
 
-// DialConfig opens a new client connection to a WebSocket with a config.
 func DialConfig(config *Config) (ws *Conn, err error) {
-	var client net.Conn
+	return config.DialContext(context.Background())
+}
+
+// DialContext opens a new client connection to a WebSocket, with context support for timeouts/cancellation.
+func (config *Config) DialContext(ctx context.Context) (*Conn, error) {
 	if config.Location == nil {
 		return nil, &DialError{config, ErrBadWebSocketLocation}
 	}
 	if config.Origin == nil {
 		return nil, &DialError{config, ErrBadWebSocketOrigin}
 	}
+
 	dialer := config.Dialer
 	if dialer == nil {
 		dialer = &net.Dialer{}
 	}
-	client, err = dialWithDialer(dialer, config)
-	if err != nil {
-		goto Error
-	}
-	ws, err = NewClient(config, client)
+
+	client, err := dialWithDialer(ctx, dialer, config)
 	if err != nil {
-		client.Close()
-		goto Error
+		return nil, &DialError{config, err}
 	}
-	return
 
-Error:
-	return nil, &DialError{config, err}
+	// Cleanup the connection if we fail to create the websocket successfully
+	success := false
+	defer func() {
+		if !success {
+			_ = client.Close()
+		}
+	}()
+
+	var ws *Conn
+	var wsErr error
+	doneConnecting := make(chan struct{})
+	go func() {
+		defer close(doneConnecting)
+		ws, err = NewClient(config, client)
+		if err != nil {
+			wsErr = &DialError{config, err}
+		}
+	}()
+
+	// The websocket.NewClient() function can block indefinitely, make sure that we
+	// respect the deadlines specified by the context.
+	select {
+	case <-ctx.Done():
+		// Force the pending operations to fail, terminating the pending connection attempt
+		_ = client.SetDeadline(time.Now())
+		<-doneConnecting // Wait for the goroutine that tries to establish the connection to finish
+		return nil, &DialError{config, ctx.Err()}
+	case <-doneConnecting:
+		if wsErr == nil {
+			success = true // Disarm the deferred connection cleanup
+		}
+		return ws, wsErr
+	}
 }

websocket/dial.go

@@ -5,18 +5,23 @@
 package websocket
 
 import (
+	"context"
 	"crypto/tls"
 	"net"
 )
 
-func dialWithDialer(dialer *net.Dialer, config *Config) (conn net.Conn, err error) {
+func dialWithDialer(ctx context.Context, dialer *net.Dialer, config *Config) (conn net.Conn, err error) {
 	switch config.Location.Scheme {
 	case "ws":
-		conn, err = dialer.Dial("tcp", parseAuthority(config.Location))
+		conn, err = dialer.DialContext(ctx, "tcp", parseAuthority(config.Location))
 
 	case "wss":
-		conn, err = tls.DialWithDialer(dialer, "tcp", parseAuthority(config.Location), config.TlsConfig)
+		tlsDialer := &tls.Dialer{
+			NetDialer: dialer,
+			Config:    config.TlsConfig,
+		}
 
+		conn, err = tlsDialer.DialContext(ctx, "tcp", parseAuthority(config.Location))
 	default:
 		err = ErrBadScheme
 	}

websocket/dial_test.go

@@ -5,10 +5,13 @@
 package websocket
 
 import (
+	"context"
 	"crypto/tls"
+	"errors"
 	"fmt"
 	"log"
 	"net"
+	"net/http"
 	"net/http/httptest"
 	"testing"
 	"time"
@@ -41,3 +44,37 @@ func TestDialConfigTLSWithDialer(t *testing.T) {
 		t.Fatalf("expected timeout error, got %#v", neterr)
 	}
 }
+
+func TestDialConfigTLSWithTimeouts(t *testing.T) {
+	t.Parallel()
+
+	finishedRequest := make(chan bool)
+
+	// Context for cancellation
+	ctx, cancel := context.WithCancel(context.Background())
+
+	// This is a TLS server that blocks each request indefinitely (and cancels the context)
+	tlsServer := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		cancel()
+		<-finishedRequest
+	}))
+
+	tlsServerAddr := tlsServer.Listener.Addr().String()
+	log.Print("Test TLS WebSocket server listening on ", tlsServerAddr)
+	defer tlsServer.Close()
+	defer close(finishedRequest)
+
+	config, _ := NewConfig(fmt.Sprintf("wss://%s/echo", tlsServerAddr), "http://localhost")
+	config.TlsConfig = &tls.Config{
+		InsecureSkipVerify: true,
+	}
+
+	_, err := config.DialContext(ctx)
+	dialerr, ok := err.(*DialError)
+	if !ok {
+		t.Fatalf("DialError expected, got %#v", err)
+	}
+	if !errors.Is(dialerr.Err, context.Canceled) {
+		t.Fatalf("context.Canceled error expected, got %#v", dialerr.Err)
+	}
+}