net/http: Don't write 'Connection: close' header multiple times.

When writing the 'Connection: close' header based on response Close
attribute we also check if it is already in the headers scheduled
to be written and skip if necessary.

Fixes #19499

Change-Id: I92357344a37ae385454ec8006114fa4cfa585810
Reviewed-on: https://go-review.googlesource.com/38076
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/response_test.go

@@ -949,3 +949,29 @@ func TestNeedsSniff(t *testing.T) {
 		t.Errorf("needsSniff empty Content-Type = %t; want %t", got, want)
 	}
 }
+
+// A response should only write out single Connection: close header. Tests #19499.
+func TestResponseWritesOnlySingleConnectionClose(t *testing.T) {
+	const connectionCloseHeader = "Connection: close"
+
+	res, err := ReadResponse(bufio.NewReader(strings.NewReader("HTTP/1.0 200 OK\r\n\r\nAAAA")), nil)
+	if err != nil {
+		t.Fatalf("ReadResponse failed %v", err)
+	}
+
+	var buf1 bytes.Buffer
+	if err = res.Write(&buf1); err != nil {
+		t.Fatalf("Write failed %v", err)
+	}
+	if res, err = ReadResponse(bufio.NewReader(&buf1), nil); err != nil {
+		t.Fatalf("ReadResponse failed %v", err)
+	}
+
+	var buf2 bytes.Buffer
+	if err = res.Write(&buf2); err != nil {
+		t.Fatalf("Write failed %v", err)
+	}
+	if count := strings.Count(buf2.String(), connectionCloseHeader); count != 1 {
+		t.Errorf("Found %d %q header", count, connectionCloseHeader)
+	}
+}

src/net/http/transfer.go

@@ -75,6 +75,7 @@ type transferWriter struct {
 	ContentLength    int64 // -1 means unknown, 0 means exactly none
 	Close            bool
 	TransferEncoding []string
+	Header           Header
 	Trailer          Header
 	IsResponse       bool
 	bodyReadError    error // any non-EOF error from reading Body
@@ -96,6 +97,7 @@ func newTransferWriter(r interface{}) (t *transferWriter, err error) {
 		t.Method = valueOrDefault(rr.Method, "GET")
 		t.Close = rr.Close
 		t.TransferEncoding = rr.TransferEncoding
+		t.Header = rr.Header
 		t.Trailer = rr.Trailer
 		atLeastHTTP11 = rr.protoAtLeastOutgoing(1, 1)
 		t.Body = rr.Body
@@ -114,6 +116,7 @@ func newTransferWriter(r interface{}) (t *transferWriter, err error) {
 		t.ContentLength = rr.ContentLength
 		t.Close = rr.Close
 		t.TransferEncoding = rr.TransferEncoding
+		t.Header = rr.Header
 		t.Trailer = rr.Trailer
 		atLeastHTTP11 = rr.ProtoAtLeast(1, 1)
 		t.ResponseToHEAD = noResponseBodyExpected(t.Method)
@@ -266,7 +269,7 @@ func (t *transferWriter) shouldSendContentLength() bool {
 }
 
 func (t *transferWriter) WriteHeader(w io.Writer) error {
-	if t.Close {
+	if t.Close && !hasToken(t.Header.get("Connection"), "close") {
 		if _, err := io.WriteString(w, "Connection: close\r\n"); err != nil {
 			return err
 		}