From 43b56d621b93f5450b037f2275179135d2d5587b Mon Sep 17 00:00:00 2001
From: Matthew Holt <mholt@users.noreply.github.com>
Date: Tue, 27 Jun 2017 12:10:03 -0600
Subject: [PATCH] Allow duplicate Server headers when proxying response

See discussion on commit c9b022b5e0384ab97812366aade0bb34304459af

If we overwrite the Server header, it becomes difficult/impossible to
know from the client whether the request was proxied through Caddy.
---
 caddyhttp/proxy/reverseproxy.go | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/caddyhttp/proxy/reverseproxy.go b/caddyhttp/proxy/reverseproxy.go
index 5fc4aed9..08bfdd56 100644
--- a/caddyhttp/proxy/reverseproxy.go
+++ b/caddyhttp/proxy/reverseproxy.go
@@ -413,8 +413,12 @@ func copyHeader(dst, src http.Header) {
 			if _, shouldSkip := skipHeaders[k]; shouldSkip {
 				continue
 			}
-			// otherwise, overwrite
-			dst.Del(k)
+			// otherwise, overwrite to avoid duplicated fields that can be
+			// problematic (see issue #1086) -- however, allow duplicate
+			// Server fields so we can see the reality of the proxying.
+			if k != "Server" {
+				dst.Del(k)
+			}
 		}
 		for _, v := range vv {
 			dst.Add(k, v)