From cd66b62083072964ae68ff11acb5be391ee7c3f0 Mon Sep 17 00:00:00 2001
From: Dozer <mail@dozer.cc>
Date: Mon, 13 Jan 2020 05:00:18 +0800
Subject: [PATCH] gzip: Avoid duplicated Vary header (#2939)

---
 caddyhttp/gzip/gzip.go | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/caddyhttp/gzip/gzip.go b/caddyhttp/gzip/gzip.go
index 529365556..1df43b5b2 100644
--- a/caddyhttp/gzip/gzip.go
+++ b/caddyhttp/gzip/gzip.go
@@ -130,7 +130,19 @@ type gzipResponseWriter struct {
 func (w *gzipResponseWriter) WriteHeader(code int) {
 	w.Header().Del("Content-Length")
 	w.Header().Set("Content-Encoding", "gzip")
-	w.Header().Add("Vary", "Accept-Encoding")
+	varyList, exist := w.Header()["Vary"]
+	shouldAddVary := true
+	if exist {
+		for _, vary := range varyList {
+			if vary == "Accept-Encoding" {
+				shouldAddVary = false
+				break
+			}
+		}
+	}
+	if shouldAddVary {
+		w.Header().Add("Vary", "Accept-Encoding")
+	}
 	originalEtag := w.Header().Get("ETag")
 	if originalEtag != "" && !strings.HasPrefix(originalEtag, "W/") {
 		w.Header().Set("ETag", "W/"+originalEtag)