net/http/httputil: flush ReverseProxy immediately if Content-Length is -1

Finish up a prior TODO by making ReverseProxy flush immediately
if Content-Length is -1, which is a case that can occur if for
example we have a streamed response, or chunked encoding, or when
the body's length wasn't known.

Fixes #41642

Change-Id: I30babaaf3e14837b99e3ecdc562a0a0e50c579bf
GitHub-Last-Rev: efc019a9fe361082d40bee77317018c3b80451a3
GitHub-Pull-Request: golang/go#41858
Reviewed-on: https://go-review.googlesource.com/c/go/+/260637
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Ian Lance Taylor <iant@golang.org>
Trust: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

1 files changed, 17 insertions, 2 deletions

diff --git a/src/net/http/httputil/reverseproxy_test.go b/src/net/http/httputil/reverseproxy_test.go
index 764939fb0f..ea786864d8 100644
--- a/src/net/http/httputil/reverseproxy_test.go
+++ b/src/net/http/httputil/reverseproxy_test.go
@@ -1067,7 +1067,6 @@ func TestSelectFlushInterval(t *testing.T) {
 	tests := []struct {
 		name string
 		p    *ReverseProxy
-		req  *http.Request
 		res  *http.Response
 		want time.Duration
 	}{
@@ -1097,10 +1096,26 @@ func TestSelectFlushInterval(t *testing.T) {
 			p:    &ReverseProxy{FlushInterval: 0},
 			want: -1,
 		},
+		{
+			name: "Content-Length: -1, overrides non-zero",
+			res: &http.Response{
+				ContentLength: -1,
+			},
+			p:    &ReverseProxy{FlushInterval: 123},
+			want: -1,
+		},
+		{
+			name: "Content-Length: -1, overrides zero",
+			res: &http.Response{
+				ContentLength: -1,
+			},
+			p:    &ReverseProxy{FlushInterval: 0},
+			want: -1,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			got := tt.p.flushInterval(tt.req, tt.res)
+			got := tt.p.flushInterval(tt.res)
 			if got != tt.want {
 				t.Errorf("flushLatency = %v; want %v", got, tt.want)
 			}