Auto add 'Vary' header after compression (#1585)

* Auto add 'Vary' header after compression

Add config `SetAddVaryHeaderForCompression` to enable
'Vary: Accept-Encoding' header when compression is used.

* feat: always set the Vary header

* create and use `ResponseHeader.AddVaryBytes`

* not export 'AddVaryBytes'

1 files changed, 12 insertions, 0 deletions

diff --git a/header.go b/header.go
index 5665e79..ca9062f 100644
--- a/header.go
+++ b/header.go
@@ -344,6 +344,18 @@ func (h *ResponseHeader) SetContentEncodingBytes(contentEncoding []byte) {
 	h.contentEncoding = append(h.contentEncoding[:0], contentEncoding...)
 }
 
+// addVaryBytes add value to the 'Vary' header if it's not included
+func (h *ResponseHeader) addVaryBytes(value []byte) {
+	v := h.peek(strVary)
+	if len(v) == 0 {
+		// 'Vary' is not set
+		h.SetBytesV(HeaderVary, value)
+	} else if !bytes.Contains(v, value) {
+		// 'Vary' is set and not contains target value
+		h.SetBytesV(HeaderVary, append(append(v, ','), value...))
+	} // else: 'Vary' is set and contains target value
+}
+
 // Server returns Server header value.
 func (h *ResponseHeader) Server() []byte {
 	return h.server