2 files changed, 47 insertions, 0 deletions
diff --git a/src/net/http/httputil/reverseproxy.go b/src/net/http/httputil/reverseproxy.go
index 92d7f63af5..0e0731b08f 100644
--- a/src/net/http/httputil/reverseproxy.go
+++ b/src/net/http/httputil/reverseproxy.go
@@ -389,6 +389,11 @@ func (p *ReverseProxy) copyResponse(dst io.Writer, src io.Reader, flushInterval
 				latency: flushInterval,
 			}
 			defer mlw.stop()
+
+			// set up initial timer so headers get flushed even if body writes are delayed
+			mlw.flushPending = true
+			mlw.t = time.AfterFunc(flushInterval, mlw.delayedFlush)
+
 			dst = mlw
 		}
 	}
diff --git a/src/net/http/httputil/reverseproxy_test.go b/src/net/http/httputil/reverseproxy_test.go
index 5edefa08e5..367ba73ae2 100644
--- a/src/net/http/httputil/reverseproxy_test.go
+++ b/src/net/http/httputil/reverseproxy_test.go
@@ -9,6 +9,7 @@ package httputil
 import (
 	"bufio"
 	"bytes"
+	"context"
 	"errors"
 	"fmt"
 	"io"
@@ -317,6 +318,47 @@ func TestReverseProxyFlushInterval(t *testing.T) {
 	}
 }
 
+func TestReverseProxyFlushIntervalHeaders(t *testing.T) {
+	const expected = "hi"
+	stopCh := make(chan struct{})
+	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Add("MyHeader", expected)
+		w.WriteHeader(200)
+		w.(http.Flusher).Flush()
+		<-stopCh
+	}))
+	defer backend.Close()
+	defer close(stopCh)
+
+	backendURL, err := url.Parse(backend.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	proxyHandler := NewSingleHostReverseProxy(backendURL)
+	proxyHandler.FlushInterval = time.Microsecond
+
+	frontend := httptest.NewServer(proxyHandler)
+	defer frontend.Close()
+
+	req, _ := http.NewRequest("GET", frontend.URL, nil)
+	req.Close = true
+
+	ctx, cancel := context.WithTimeout(req.Context(), 10*time.Second)
+	defer cancel()
+	req = req.WithContext(ctx)
+
+	res, err := frontend.Client().Do(req)
+	if err != nil {
+		t.Fatalf("Get: %v", err)
+	}
+	defer res.Body.Close()
+
+	if res.Header.Get("MyHeader") != expected {
+		t.Errorf("got header %q; expected %q", res.Header.Get("MyHeader"), expected)
+	}
+}
+
 func TestReverseProxyCancelation(t *testing.T) {
 	const backendResponse = "I am the backend"