use http.ResposnseController

server.go

@@ -172,13 +172,11 @@ func (u *Upgrader) Upgrade(w http.ResponseWriter, r *http.Request, responseHeade
 		}
 	}
 
-	h, ok := w.(http.Hijacker)
-	if !ok {
+	netConn, brw, err := http.NewResponseController(w).Hijack()
+	switch {
+	case errors.Is(err, errors.ErrUnsupported):
 		return u.returnError(w, r, http.StatusInternalServerError, "websocket: response does not implement http.Hijacker")
-	}
-	var brw *bufio.ReadWriter
-	netConn, brw, err := h.Hijack()
-	if err != nil {
+	case err != nil:
 		return u.returnError(w, r, http.StatusInternalServerError, err.Error())
 	}
 

server_test.go

@@ -7,8 +7,10 @@ package websocket
 import (
 	"bufio"
 	"bytes"
+	"errors"
 	"net"
 	"net/http"
+	"net/http/httptest"
 	"reflect"
 	"strings"
 	"testing"
@@ -117,3 +119,23 @@ func TestBufioReuse(t *testing.T) {
 		}
 	}
 }
+
+func TestHijack_NotSupported(t *testing.T) {
+	t.Parallel()
+
+	req := httptest.NewRequest(http.MethodGet, "http://example.com", nil)
+	req.Header.Set("Upgrade", "websocket")
+	req.Header.Set("Connection", "upgrade")
+	req.Header.Set("Sec-Websocket-Key", "dGhlIHNhbXBsZSBub25jZQ==")
+	req.Header.Set("Sec-Websocket-Version", "13")
+
+	recorder := httptest.NewRecorder()
+
+	upgrader := Upgrader{}
+	_, err := upgrader.Upgrade(recorder, req, nil)
+
+	if want := (HandshakeError{}); !errors.As(err, &want) || recorder.Code != http.StatusInternalServerError {
+		t.Errorf("want %T and status_code=%d", want, http.StatusInternalServerError)
+		t.Fatalf("got err=%T and status_code=%d", err, recorder.Code)
+	}
+}