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
+}