use a buffered writer for the http3 response writer

http3/response_writer.go

@@ -1,6 +1,7 @@
 package http3
 
 import (
+	"bufio"
 	"bytes"
 	"io"
 	"net/http"
@@ -12,7 +13,7 @@ import (
 )
 
 type responseWriter struct {
-	stream io.Writer
+	stream *bufio.Writer
 
 	header        http.Header
 	status        int // status code passed to WriteHeader
@@ -22,11 +23,12 @@ type responseWriter struct {
 }
 
 var _ http.ResponseWriter = &responseWriter{}
+var _ http.Flusher = &responseWriter{}
 
 func newResponseWriter(stream io.Writer, logger utils.Logger) *responseWriter {
 	return &responseWriter{
 		header: http.Header{},
-		stream: stream,
+		stream: bufio.NewWriter(stream),
 		logger: logger,
 	}
 }
@@ -79,10 +81,11 @@ func (w *responseWriter) Write(p []byte) (int, error) {
 	return w.stream.Write(p)
 }
 
-func (w *responseWriter) Flush() {}
-
-// test that we implement http.Flusher
-var _ http.Flusher = &responseWriter{}
+func (w *responseWriter) Flush() {
+	if err := w.stream.Flush(); err != nil {
+		w.logger.Errorf("could not flush to stream: %s", err.Error())
+	}
+}
 
 // copied from http2/http2.go
 // bodyAllowedForStatus reports whether a given response status code