docs: Fix docs and examples related to r.Context() usage (#477)

Contributes to #474

README.md

@@ -63,7 +63,9 @@ http.HandlerFunc(func (w http.ResponseWriter, r *http.Request) {
 	}
 	defer c.CloseNow()
 
-	ctx, cancel := context.WithTimeout(r.Context(), time.Second*10)
+	// Set the context as needed. Use of r.Context() is not recommended
+	// to avoid surprising behavior (see http.Hijacker).
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second*10)
 	defer cancel()
 
 	var v interface{}

accept.go

@@ -79,6 +79,9 @@ func (opts *AcceptOptions) cloneWithDefaults() *AcceptOptions {
 // See the InsecureSkipVerify and OriginPatterns options to allow cross origin requests.
 //
 // Accept will write a response to w on all errors.
+//
+// Note that using the http.Request Context after Accept returns may lead to
+// unexpected behavior (see http.Hijacker).
 func Accept(w http.ResponseWriter, r *http.Request, opts *AcceptOptions) (*Conn, error) {
 	return accept(w, r, opts)
 }

internal/examples/chat/chat.go

@@ -70,7 +70,7 @@ func (cs *chatServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 // subscribeHandler accepts the WebSocket connection and then subscribes
 // it to all future messages.
 func (cs *chatServer) subscribeHandler(w http.ResponseWriter, r *http.Request) {
-	err := cs.subscribe(r.Context(), w, r)
+	err := cs.subscribe(w, r)
 	if errors.Is(err, context.Canceled) {
 		return
 	}
@@ -111,7 +111,7 @@ func (cs *chatServer) publishHandler(w http.ResponseWriter, r *http.Request) {
 //
 // It uses CloseRead to keep reading from the connection to process control
 // messages and cancel the context if the connection drops.
-func (cs *chatServer) subscribe(ctx context.Context, w http.ResponseWriter, r *http.Request) error {
+func (cs *chatServer) subscribe(w http.ResponseWriter, r *http.Request) error {
 	var mu sync.Mutex
 	var c *websocket.Conn
 	var closed bool
@@ -142,7 +142,7 @@ func (cs *chatServer) subscribe(ctx context.Context, w http.ResponseWriter, r *h
 	mu.Unlock()
 	defer c.CloseNow()
 
-	ctx = c.CloseRead(ctx)
+	ctx := c.CloseRead(context.Background())
 
 	for {
 		select {

internal/examples/echo/server.go

@@ -37,7 +37,7 @@ func (s echoServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 	l := rate.NewLimiter(rate.Every(time.Millisecond*100), 10)
 	for {
-		err = echo(r.Context(), c, l)
+		err = echo(c, l)
 		if websocket.CloseStatus(err) == websocket.StatusNormalClosure {
 			return
 		}
@@ -51,8 +51,8 @@ func (s echoServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 // echo reads from the WebSocket connection and then writes
 // the received message back to it.
 // The entire function has 10s to complete.
-func echo(ctx context.Context, c *websocket.Conn, l *rate.Limiter) error {
-	ctx, cancel := context.WithTimeout(ctx, time.Second*10)
+func echo(c *websocket.Conn, l *rate.Limiter) error {
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second*10)
 	defer cancel()
 
 	err := l.Wait(ctx)