net/http/httputil: remove all fields in Connection header

In the reverseproxy, replace use (Header).Get, which returns only one value
of a multiple value header, with using the Header map directly. Also fixes
corresponding tests which hid the bug, and adds more tests.

Fixes #30303

Change-Id: Ic9094b5983043460697748759f6dfd95fc111db7
GitHub-Last-Rev: b41038143f602d4286cb46c542d40de02e6e639d
GitHub-Pull-Request: golang/go#30687
Reviewed-on: https://go-review.googlesource.com/c/go/+/166298
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/src/net/http/httputil/reverseproxy.go b/src/net/http/httputil/reverseproxy.go
index a9bfcae487..7bb469e5c3 100644
--- a/src/net/http/httputil/reverseproxy.go
+++ b/src/net/http/httputil/reverseproxy.go
@@ -345,10 +345,10 @@ func shouldPanicOnCopyError(req *http.Request) bool {
 // removeConnectionHeaders removes hop-by-hop headers listed in the "Connection" header of h.
 // See RFC 7230, section 6.1
 func removeConnectionHeaders(h http.Header) {
-	if c := h.Get("Connection"); c != "" {
-		for _, f := range strings.Split(c, ",") {
-			if f = strings.TrimSpace(f); f != "" {
-				h.Del(f)
+	for _, f := range h["Connection"] {
+		for _, sf := range strings.Split(f, ",") {
+			if sf = strings.TrimSpace(sf); sf != "" {
+				h.Del(sf)
 			}
 		}
 	}