Disable br compression when no Accept-Encoding header is present

docs/content/middlewares/http/compress.md

@@ -55,7 +55,7 @@ http:
     Responses are compressed when the following criteria are all met:
 
     * The `Accept-Encoding` request header contains `gzip`, `*`, and/or `br` with or without [quality values](https://developer.mozilla.org/en-US/docs/Glossary/Quality_values).
-    If the `Accept-Encoding` request header is absent, it is meant as br compression is requested.
+    If the `Accept-Encoding` request header is absent, the response won't be encoded.
     If it is present, but its value is the empty string, then compression is disabled.
     * The response is not already compressed, i.e. the `Content-Encoding` response header is not already set.
     * The response`Content-Type` header is not one among the [excludedContentTypes options](#excludedcontenttypes).

pkg/middlewares/compress/compress.go

@@ -92,11 +92,11 @@ func (c *compress) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 		return
 	}
 
-	// Client allows us to do whatever we want, so we br compress.
-	// See https://www.rfc-editor.org/rfc/rfc9110.html#section-12.5.3
+	// Client doesn't specify a preferred encoding, for compatibility don't encode the request
+	// See https://github.com/traefik/traefik/issues/9734
 	acceptEncoding, ok := req.Header["Accept-Encoding"]
 	if !ok {
-		c.brotliHandler.ServeHTTP(rw, req)
+		c.next.ServeHTTP(rw, req)
 		return
 	}
 

pkg/middlewares/compress/compress_test.go

@@ -10,7 +10,6 @@ import (
 	"net/textproto"
 	"testing"
 
-	"github.com/andybalholm/brotli"
 	"github.com/klauspost/compress/gzhttp"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -35,7 +34,7 @@ func TestNegotiation(t *testing.T) {
 	}{
 		{
 			desc:        "no accept header",
-			expEncoding: "br",
+			expEncoding: "",
 		},
 		{
 			desc:            "unsupported accept header",
@@ -151,7 +150,7 @@ func TestShouldNotCompressWhenContentEncodingHeader(t *testing.T) {
 	assert.EqualValues(t, rw.Body.Bytes(), fakeCompressedBody)
 }
 
-func TestShouldCompressWhenNoAcceptEncodingHeader(t *testing.T) {
+func TestShouldNotCompressWhenNoAcceptEncodingHeader(t *testing.T) {
 	req := testhelpers.MustNewRequest(http.MethodGet, "http://localhost", nil)
 
 	fakeBody := generateBytes(gzhttp.DefaultMinSize)
@@ -167,12 +166,9 @@ func TestShouldCompressWhenNoAcceptEncodingHeader(t *testing.T) {
 	rw := httptest.NewRecorder()
 	handler.ServeHTTP(rw, req)
 
-	assert.Equal(t, brotliValue, rw.Header().Get(contentEncodingHeader))
-	assert.Equal(t, acceptEncodingHeader, rw.Header().Get(varyHeader))
-
-	got, err := io.ReadAll(brotli.NewReader(rw.Body))
-	require.NoError(t, err)
-	assert.Equal(t, got, fakeBody)
+	assert.Empty(t, rw.Header().Get(contentEncodingHeader))
+	assert.Empty(t, rw.Header().Get(varyHeader))
+	assert.EqualValues(t, rw.Body.Bytes(), fakeBody)
 }
 
 func TestShouldNotCompressWhenIdentityAcceptEncodingHeader(t *testing.T) {