Add Accept-Encoding to Vary to prevent intermediate caches corruption (…

…#5)

go.mod

@@ -5,7 +5,5 @@ go 1.16
 require (
 	github.com/andybalholm/brotli v1.0.1
 	github.com/bool64/dev v0.1.18
-	github.com/davecgh/go-spew v1.1.1 // indirect
-	github.com/stretchr/testify v1.7.0
-	gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b // indirect
+	github.com/stretchr/testify v1.4.0
 )

go.sum

@@ -2,18 +2,14 @@ github.com/andybalholm/brotli v1.0.1 h1:KqhlKozYbRtJvsPrrEeXcO+N2l6NYT5A2QAFmSUL
 github.com/andybalholm/brotli v1.0.1/go.mod h1:loMXtMfwqflxFJPmdbJO0a3KNoPuLBgiu3qAvBg8x/Y=
 github.com/bool64/dev v0.1.18 h1:uMN5MsHrVWmtRoauefI8wD86b8vbXYnrCZlIhFGyuXI=
 github.com/bool64/dev v0.1.18/go.mod h1:cTHiTDNc8EewrQPy3p1obNilpMpdmlUesDkFTF2zRWU=
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
-github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
-github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
-github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
-github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
-gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
-gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b h1:h8qDotaEPuJATrMmW04NCwg7v22aHH28wwpauUhK9Oo=
-gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

server.go

@@ -296,6 +296,9 @@ func (s *Server) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 	fn := strings.TrimPrefix(req.URL.Path, "/")
 	ae := req.Header.Get("Accept-Encoding")
 
+	// Always add Accept-Encoding to Vary to prevent intermediate caches corruption.
+	rw.Header().Add("Vary", "Accept-Encoding")
+
 	if ae != "" {
 		minInfo, minEnc := s.minEnc(strings.ToLower(ae), fn)
 

server_test.go

@@ -181,6 +181,7 @@ func TestServer_ServeHTTP_get_gz(t *testing.T) {
 	assert.Equal(t, http.StatusOK, rw.Code)
 	assert.Equal(t, "gzip", rw.Header().Get("Content-Encoding"))
 	assert.Equal(t, "1bp69hxb9nd93.gz", rw.Header().Get("Etag"))
+	assert.Equal(t, "Accept-Encoding", rw.Header().Get("Vary"))
 	assert.NotEmpty(t, rw.Body.String())
 
 	r, err := gzip.NewReader(rw.Body)