refine: return error instead of panic when response writer doesn't im…

…plement hijacker

response_writer.go

@@ -6,6 +6,7 @@ package gin
 
 import (
 	"bufio"
+	"errors"
 	"io"
 	"net"
 	"net/http"
@@ -109,7 +110,11 @@ func (w *responseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
 	if w.size < 0 {
 		w.size = 0
 	}
-	return w.ResponseWriter.(http.Hijacker).Hijack()
+	hijacker, ok := w.ResponseWriter.(http.Hijacker)
+	if !ok {
+		return nil, nil, errors.New("response writer does not support Hijack")
+	}
+	return hijacker.Hijack()
 }
 
 // CloseNotify implements the http.CloseNotifier interface.

response_writer_test.go

@@ -111,10 +111,8 @@ func TestResponseWriterHijack(t *testing.T) {
 	writer.reset(testWriter)
 	w := ResponseWriter(writer)
 
-	assert.Panics(t, func() {
-		_, _, err := w.Hijack()
-		require.NoError(t, err)
-	})
+	_, _, err := w.Hijack()
+	assert.Equal(t, "response writer does not support Hijack", err.Error())
 	assert.True(t, w.Written())
 
 	assert.Panics(t, func() {