Fix flushing in Gzip middleware (#1317)

* Make Gzip response Writer also call Flush of underlying Writer
* Add unit test for chunked responses with Gzip

middleware/compress.go

@@ -111,6 +111,9 @@ func (w *gzipResponseWriter) Write(b []byte) (int, error) {
 
 func (w *gzipResponseWriter) Flush() {
 	w.Writer.(*gzip.Writer).Flush()
+	if flusher, ok := w.ResponseWriter.(http.Flusher); ok {
+		flusher.Flush()
+	}
 }
 
 func (w *gzipResponseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {

middleware/compress_test.go

@@ -3,6 +3,7 @@ package middleware
 import (
 	"bytes"
 	"compress/gzip"
+	"io"
 	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
@@ -44,6 +45,49 @@ func TestGzip(t *testing.T) {
 		buf.ReadFrom(r)
 		assert.Equal("test", buf.String())
 	}
+
+	chunkBuf := make([]byte, 5)
+
+	// Gzip chunked
+	req = httptest.NewRequest(http.MethodGet, "/", nil)
+	req.Header.Set(echo.HeaderAcceptEncoding, gzipScheme)
+	rec = httptest.NewRecorder()
+
+	c = e.NewContext(req, rec)
+	Gzip()(func(c echo.Context) error {
+		c.Response().Header().Set("Content-Type", "text/event-stream")
+		c.Response().Header().Set("Transfer-Encoding", "chunked")
+
+		// Write and flush the first part of the data
+		c.Response().Write([]byte("test\n"))
+		c.Response().Flush()
+
+		// Read the first part of the data
+		assert.True(rec.Flushed)
+		assert.Equal(gzipScheme, rec.Header().Get(echo.HeaderContentEncoding))
+		r.Reset(rec.Body)
+
+		_, err = io.ReadFull(r, chunkBuf)
+		assert.NoError(err)
+		assert.Equal("test\n", string(chunkBuf))
+
+		// Write and flush the second part of the data
+		c.Response().Write([]byte("test\n"))
+		c.Response().Flush()
+
+		_, err = io.ReadFull(r, chunkBuf)
+		assert.NoError(err)
+		assert.Equal("test\n", string(chunkBuf))
+
+		// Write the final part of the data and return
+		c.Response().Write([]byte("test"))
+		return nil
+	})(c)
+
+	buf := new(bytes.Buffer)
+	defer r.Close()
+	buf.ReadFrom(r)
+	assert.Equal("test", buf.String())
 }
 
 func TestGzipNoContent(t *testing.T) {