Allow ResponseWriters to unwrap writers when flushing/hijacking (#2595)

* Allow ResponseWriters to unwrap writers when flushing/hijacking

Author: aldas

middleware/body_dump.go

@@ -3,6 +3,7 @@ package middleware
 import (
 	"bufio"
 	"bytes"
+	"errors"
 	"io"
 	"net"
 	"net/http"
@@ -98,9 +99,16 @@ func (w *bodyDumpResponseWriter) Write(b []byte) (int, error) {
 }
 
 func (w *bodyDumpResponseWriter) Flush() {
-	w.ResponseWriter.(http.Flusher).Flush()
+	err := responseControllerFlush(w.ResponseWriter)
+	if err != nil && errors.Is(err, http.ErrNotSupported) {
+		panic(errors.New("response writer flushing is not supported"))
+	}
 }
 
 func (w *bodyDumpResponseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
-	return w.ResponseWriter.(http.Hijacker).Hijack()
+	return responseControllerHijack(w.ResponseWriter)
+}
+
+func (w *bodyDumpResponseWriter) Unwrap() http.ResponseWriter {
+	return w.ResponseWriter
 }

middleware/body_dump_test.go

@@ -87,3 +87,53 @@ func TestBodyDumpFails(t *testing.T) {
 		}
 	})
 }
+
+func TestBodyDumpResponseWriter_CanNotFlush(t *testing.T) {
+	bdrw := bodyDumpResponseWriter{
+		ResponseWriter: new(testResponseWriterNoFlushHijack), // this RW does not support flush
+	}
+
+	assert.PanicsWithError(t, "response writer flushing is not supported", func() {
+		bdrw.Flush()
+	})
+}
+
+func TestBodyDumpResponseWriter_CanFlush(t *testing.T) {
+	trwu := testResponseWriterUnwrapperHijack{testResponseWriterUnwrapper: testResponseWriterUnwrapper{rw: httptest.NewRecorder()}}
+	bdrw := bodyDumpResponseWriter{
+		ResponseWriter: &trwu,
+	}
+
+	bdrw.Flush()
+	assert.Equal(t, 1, trwu.unwrapCalled)
+}
+
+func TestBodyDumpResponseWriter_CanUnwrap(t *testing.T) {
+	trwu := &testResponseWriterUnwrapper{rw: httptest.NewRecorder()}
+	bdrw := bodyDumpResponseWriter{
+		ResponseWriter: trwu,
+	}
+
+	result := bdrw.Unwrap()
+	assert.Equal(t, trwu, result)
+}
+
+func TestBodyDumpResponseWriter_CanHijack(t *testing.T) {
+	trwu := testResponseWriterUnwrapperHijack{testResponseWriterUnwrapper: testResponseWriterUnwrapper{rw: httptest.NewRecorder()}}
+	bdrw := bodyDumpResponseWriter{
+		ResponseWriter: &trwu, // this RW supports hijacking through unwrapping
+	}
+
+	_, _, err := bdrw.Hijack()
+	assert.EqualError(t, err, "can hijack")
+}
+
+func TestBodyDumpResponseWriter_CanNotHijack(t *testing.T) {
+	trwu := testResponseWriterUnwrapper{rw: httptest.NewRecorder()}
+	bdrw := bodyDumpResponseWriter{
+		ResponseWriter: &trwu, // this RW supports hijacking through unwrapping
+	}
+
+	_, _, err := bdrw.Hijack()
+	assert.EqualError(t, err, "feature not supported")
+}

middleware/compress.go

@@ -191,13 +191,15 @@ func (w *gzipResponseWriter) Flush() {
 	}
 
 	w.Writer.(*gzip.Writer).Flush()
-	if flusher, ok := w.ResponseWriter.(http.Flusher); ok {
-		flusher.Flush()
-	}
+	_ = responseControllerFlush(w.ResponseWriter)
+}
+
+func (w *gzipResponseWriter) Unwrap() http.ResponseWriter {
+	return w.ResponseWriter
 }
 
 func (w *gzipResponseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
-	return w.ResponseWriter.(http.Hijacker).Hijack()
+	return responseControllerHijack(w.ResponseWriter)
 }
 
 func (w *gzipResponseWriter) Push(target string, opts *http.PushOptions) error {

middleware/compress_test.go

@@ -311,6 +311,36 @@ func TestGzipWithStatic(t *testing.T) {
 	}
 }
 
+func TestGzipResponseWriter_CanUnwrap(t *testing.T) {
+	trwu := &testResponseWriterUnwrapper{rw: httptest.NewRecorder()}
+	bdrw := gzipResponseWriter{
+		ResponseWriter: trwu,
+	}
+
+	result := bdrw.Unwrap()
+	assert.Equal(t, trwu, result)
+}
+
+func TestGzipResponseWriter_CanHijack(t *testing.T) {
+	trwu := testResponseWriterUnwrapperHijack{testResponseWriterUnwrapper: testResponseWriterUnwrapper{rw: httptest.NewRecorder()}}
+	bdrw := gzipResponseWriter{
+		ResponseWriter: &trwu, // this RW supports hijacking through unwrapping
+	}
+
+	_, _, err := bdrw.Hijack()
+	assert.EqualError(t, err, "can hijack")
+}
+
+func TestGzipResponseWriter_CanNotHijack(t *testing.T) {
+	trwu := testResponseWriterUnwrapper{rw: httptest.NewRecorder()}
+	bdrw := gzipResponseWriter{
+		ResponseWriter: &trwu, // this RW supports hijacking through unwrapping
+	}
+
+	_, _, err := bdrw.Hijack()
+	assert.EqualError(t, err, "feature not supported")
+}
+
 func BenchmarkGzip(b *testing.B) {
 	e := echo.New()
 

middleware/middleware_test.go

@@ -1,7 +1,10 @@
 package middleware
 
 import (
+	"bufio"
+	"errors"
 	"github.com/stretchr/testify/assert"
+	"net"
 	"net/http"
 	"net/http/httptest"
 	"regexp"
@@ -90,3 +93,46 @@ func TestRewriteURL(t *testing.T) {
 		})
 	}
 }
+
+type testResponseWriterNoFlushHijack struct {
+}
+
+func (w *testResponseWriterNoFlushHijack) WriteHeader(statusCode int) {
+}
+
+func (w *testResponseWriterNoFlushHijack) Write([]byte) (int, error) {
+	return 0, nil
+}
+
+func (w *testResponseWriterNoFlushHijack) Header() http.Header {
+	return nil
+}
+
+type testResponseWriterUnwrapper struct {
+	unwrapCalled int
+	rw           http.ResponseWriter
+}
+
+func (w *testResponseWriterUnwrapper) WriteHeader(statusCode int) {
+}
+
+func (w *testResponseWriterUnwrapper) Write([]byte) (int, error) {
+	return 0, nil
+}
+
+func (w *testResponseWriterUnwrapper) Header() http.Header {
+	return nil
+}
+
+func (w *testResponseWriterUnwrapper) Unwrap() http.ResponseWriter {
+	w.unwrapCalled++
+	return w.rw
+}
+
+type testResponseWriterUnwrapperHijack struct {
+	testResponseWriterUnwrapper
+}
+
+func (w *testResponseWriterUnwrapperHijack) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	return nil, nil, errors.New("can hijack")
+}

middleware/responsecontroller_1.19.go

@@ -0,0 +1,41 @@
+//go:build !go1.20
+
+package middleware
+
+import (
+	"bufio"
+	"fmt"
+	"net"
+	"net/http"
+)
+
+// TODO: remove when Go 1.23 is released and we do not support 1.19 anymore
+func responseControllerFlush(rw http.ResponseWriter) error {
+	for {
+		switch t := rw.(type) {
+		case interface{ FlushError() error }:
+			return t.FlushError()
+		case http.Flusher:
+			t.Flush()
+			return nil
+		case interface{ Unwrap() http.ResponseWriter }:
+			rw = t.Unwrap()
+		default:
+			return fmt.Errorf("%w", http.ErrNotSupported)
+		}
+	}
+}
+
+// TODO: remove when Go 1.23 is released and we do not support 1.19 anymore
+func responseControllerHijack(rw http.ResponseWriter) (net.Conn, *bufio.ReadWriter, error) {
+	for {
+		switch t := rw.(type) {
+		case http.Hijacker:
+			return t.Hijack()
+		case interface{ Unwrap() http.ResponseWriter }:
+			rw = t.Unwrap()
+		default:
+			return nil, nil, fmt.Errorf("%w", http.ErrNotSupported)
+		}
+	}
+}

middleware/responsecontroller_1.20.go

@@ -0,0 +1,17 @@
+//go:build go1.20
+
+package middleware
+
+import (
+	"bufio"
+	"net"
+	"net/http"
+)
+
+func responseControllerFlush(rw http.ResponseWriter) error {
+	return http.NewResponseController(rw).Flush()
+}
+
+func responseControllerHijack(rw http.ResponseWriter) (net.Conn, *bufio.ReadWriter, error) {
+	return http.NewResponseController(rw).Hijack()
+}

response.go

@@ -2,6 +2,7 @@ package echo
 
 import (
 	"bufio"
+	"errors"
 	"net"
 	"net/http"
 )
@@ -84,14 +85,17 @@ func (r *Response) Write(b []byte) (n int, err error) {
 // buffered data to the client.
 // See [http.Flusher](https://golang.org/pkg/net/http/#Flusher)
 func (r *Response) Flush() {
-	r.Writer.(http.Flusher).Flush()
+	err := responseControllerFlush(r.Writer)
+	if err != nil && errors.Is(err, http.ErrNotSupported) {
+		panic(errors.New("response writer flushing is not supported"))
+	}
 }
 
 // Hijack implements the http.Hijacker interface to allow an HTTP handler to
 // take over the connection.
 // See [http.Hijacker](https://golang.org/pkg/net/http/#Hijacker)
 func (r *Response) Hijack() (net.Conn, *bufio.ReadWriter, error) {
-	return r.Writer.(http.Hijacker).Hijack()
+	return responseControllerHijack(r.Writer)
 }
 
 // Unwrap returns the original http.ResponseWriter.

response_test.go

@@ -57,6 +57,31 @@ func TestResponse_Flush(t *testing.T) {
 	assert.True(t, rec.Flushed)
 }
 
+type testResponseWriter struct {
+}
+
+func (w *testResponseWriter) WriteHeader(statusCode int) {
+}
+
+func (w *testResponseWriter) Write([]byte) (int, error) {
+	return 0, nil
+}
+
+func (w *testResponseWriter) Header() http.Header {
+	return nil
+}
+
+func TestResponse_FlushPanics(t *testing.T) {
+	e := New()
+	rw := new(testResponseWriter)
+	res := &Response{echo: e, Writer: rw}
+
+	// we test that we behave as before unwrapping flushers - flushing writer that does not support it causes panic
+	assert.PanicsWithError(t, "response writer flushing is not supported", func() {
+		res.Flush()
+	})
+}
+
 func TestResponse_ChangeStatusCodeBeforeWrite(t *testing.T) {
 	e := New()
 	rec := httptest.NewRecorder()

responsecontroller_1.19.go

@@ -0,0 +1,41 @@
+//go:build !go1.20
+
+package echo
+
+import (
+	"bufio"
+	"fmt"
+	"net"
+	"net/http"
+)
+
+// TODO: remove when Go 1.23 is released and we do not support 1.19 anymore
+func responseControllerFlush(rw http.ResponseWriter) error {
+	for {
+		switch t := rw.(type) {
+		case interface{ FlushError() error }:
+			return t.FlushError()
+		case http.Flusher:
+			t.Flush()
+			return nil
+		case interface{ Unwrap() http.ResponseWriter }:
+			rw = t.Unwrap()
+		default:
+			return fmt.Errorf("%w", http.ErrNotSupported)
+		}
+	}
+}
+
+// TODO: remove when Go 1.23 is released and we do not support 1.19 anymore
+func responseControllerHijack(rw http.ResponseWriter) (net.Conn, *bufio.ReadWriter, error) {
+	for {
+		switch t := rw.(type) {
+		case http.Hijacker:
+			return t.Hijack()
+		case interface{ Unwrap() http.ResponseWriter }:
+			rw = t.Unwrap()
+		default:
+			return nil, nil, fmt.Errorf("%w", http.ErrNotSupported)
+		}
+	}
+}