Merge pull request #11 from basecamp/disable-transparent-proxy-compre…

…ssion

Disable transparent proxy compression

internal/handler_test.go

@@ -33,6 +33,27 @@ func TestHandlerGzipCompression_when_proxying(t *testing.T) {
 	assert.Less(t, transferredSize, fixtureLength("loremipsum.txt"))
 }
 
+func TestHandlerGzipCompression_is_not_applied_when_not_requested(t *testing.T) {
+	fixtureLength := strconv.FormatInt(fixtureLength("loremipsum.txt"), 10)
+
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Length", fixtureLength)
+		w.Write(fixtureContent("loremipsum.txt"))
+	}))
+	defer upstream.Close()
+
+	h := NewHandler(handlerOptions(upstream.URL))
+
+	w := httptest.NewRecorder()
+	r := httptest.NewRequest("GET", "/", nil)
+	h.ServeHTTP(w, r)
+
+	assert.Equal(t, http.StatusOK, w.Code)
+	assert.Contains(t, w.Header().Get("Content-Type"), "text/plain")
+	assert.Empty(t, w.Header().Get("Content-Encoding"))
+	assert.Equal(t, fixtureLength, w.Header().Get("Content-Length"))
+}
+
 func TestHandlerGzipCompression_does_not_compress_images(t *testing.T) {
 	fixtureLength := strconv.FormatInt(fixtureLength("image.jpg"), 10)
 
@@ -79,6 +100,34 @@ func TestHandlerGzipCompression_when_sendfile(t *testing.T) {
 	assert.Less(t, transferredSize, fixtureLength("loremipsum.txt"))
 }
 
+func TestHandler_do_not_request_compressed_responses_from_upstream_unless_client_does(t *testing.T) {
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		acceptsGzip := r.Header.Get("Accept-Encoding") == "gzip"
+		shouldAcceptGzip := r.URL.Path == "/compressed"
+
+		assert.Equal(t, shouldAcceptGzip, acceptsGzip)
+		if acceptsGzip {
+			w.Header().Set("Content-Encoding", "gzip")
+		}
+	}))
+	defer upstream.Close()
+
+	h := NewHandler(handlerOptions(upstream.URL))
+
+	w := httptest.NewRecorder()
+	r := httptest.NewRequest("GET", "/plain", nil)
+	h.ServeHTTP(w, r)
+	assert.Equal(t, http.StatusOK, w.Code)
+	assert.Empty(t, w.Header().Get("Content-Encoding"))
+
+	w = httptest.NewRecorder()
+	r = httptest.NewRequest("GET", "/compressed", nil)
+	r.Header.Set("Accept-Encoding", "gzip")
+	h.ServeHTTP(w, r)
+	assert.Equal(t, http.StatusOK, w.Code)
+	assert.Equal(t, "gzip", w.Header().Get("Content-Encoding"))
+}
+
 func TestHandlerMaxRequestBody(t *testing.T) {
 	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {}))
 	defer upstream.Close()

internal/proxy_handler.go

@@ -12,6 +12,7 @@ import (
 func NewProxyHandler(targetUrl *url.URL, badGatewayPage string) http.Handler {
 	proxy := httputil.NewSingleHostReverseProxy(targetUrl)
 	proxy.ErrorHandler = ProxyErrorHandler(badGatewayPage)
+	proxy.Transport = createProxyTransport()
 
 	return proxy
 }
@@ -45,3 +46,28 @@ func isRequestEntityTooLarge(err error) bool {
 	var maxBytesError *http.MaxBytesError
 	return errors.As(err, &maxBytesError)
 }
+
+func createProxyTransport() *http.Transport {
+	// The default transport requests compressed responses even if the client
+	// didn't. If it receives a compressed response but the client wants
+	// uncompressed, the transport decompresses the response transparently.
+	//
+	// Although that seems helpful, it doesn't play well with X-Sendfile
+	// responses, as it may result in us being handed a reference to a file on
+	// disk that is already compressed, and we'd have to similarly decompress it
+	// before serving it to the client. This is wasteful, especially since there
+	// was probably an uncompressed version of it on disk already. It's also a bit
+	// fiddly to do on the fly without the ability to seek around in the
+	// uncompressed content.
+	//
+	// Compression between us and the upstream server is likely to be of limited
+	// use anyway, since we're only proxying from localhost. Given that fact --
+	// and the fact that most clients *will* request compressed responses anyway,
+	// which makes all of this moot -- our best option is to disable this
+	// on-the-fly compression.
+
+	transport := http.DefaultTransport.(*http.Transport).Clone()
+	transport.DisableCompression = true
+
+	return transport
+}