Use http.ResponseController instead of http.Hijacker assertion

Fixes #455

accept.go

@@ -105,13 +105,6 @@ func accept(w http.ResponseWriter, r *http.Request, opts *AcceptOptions) (_ *Con
 		}
 	}
 
-	hj, ok := w.(http.Hijacker)
-	if !ok {
-		err = errors.New("http.ResponseWriter does not implement http.Hijacker")
-		http.Error(w, http.StatusText(http.StatusNotImplemented), http.StatusNotImplemented)
-		return nil, err
-	}
-
 	w.Header().Set("Upgrade", "websocket")
 	w.Header().Set("Connection", "Upgrade")
 
@@ -136,10 +129,14 @@ func accept(w http.ResponseWriter, r *http.Request, opts *AcceptOptions) (_ *Con
 		ginWriter.WriteHeaderNow()
 	}
 
-	netConn, brw, err := hj.Hijack()
+	netConn, brw, err := hijack(w)
 	if err != nil {
-		err = fmt.Errorf("failed to hijack connection: %w", err)
-		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+		if errors.Is(err, errHTTPHijackNotSupported) {
+			http.Error(w, http.StatusText(http.StatusNotImplemented), http.StatusNotImplemented)
+		} else {
+			err = fmt.Errorf("failed to hijack connection: %w", err)
+			http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+		}
 		return nil, err
 	}
 

hijack.go

@@ -0,0 +1,20 @@
+//go:build go1.20
+
+package websocket
+
+import (
+	"bufio"
+	"errors"
+	"net"
+	"net/http"
+)
+
+var errHTTPHijackNotSupported = errors.New("http.ResponseWriter does not implement http.Hijacker")
+
+func hijack(w http.ResponseWriter) (net.Conn, *bufio.ReadWriter, error) {
+	conn, rw, err := http.NewResponseController(w).Hijack()
+	if errors.Is(err, http.ErrNotSupported) {
+		return nil, nil, errHTTPHijackNotSupported
+	}
+	return conn, rw, err
+}

hijack_119.go

@@ -0,0 +1,20 @@
+//go:build !go1.20
+
+package websocket
+
+import (
+	"bufio"
+	"errors"
+	"net"
+	"net/http"
+)
+
+var errHTTPHijackNotSupported = errors.New("http.ResponseWriter does not implement http.Hijacker")
+
+func hijack(w http.ResponseWriter) (net.Conn, *bufio.ReadWriter, error) {
+	hj, ok := w.(http.Hijacker)
+	if !ok {
+		return nil, nil, errHTTPHijackNotSupported
+	}
+	return hj.Hijack()
+}