proxy: Unbuffered request optimization

caddyhttp/proxy/proxy.go

@@ -39,6 +39,9 @@ type Upstream interface {
 	// Gets how long to wait between selecting upstream
 	// hosts in the case of cascading failures.
 	GetTryInterval() time.Duration
+
+	// Gets the number of upstream hosts.
+	GetHostCount() int
 }
 
 // UpstreamHostDownFunc can be used to customize how Down behaves.
@@ -94,13 +97,26 @@ func (p Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
 	// outreq is the request that makes a roundtrip to the backend
 	outreq := createUpstreamRequest(r)
 
-	// record and replace outreq body
-	body, err := newBufferedBody(outreq.Body)
-	if err != nil {
-		return http.StatusBadRequest, errors.New("failed to read downstream request body")
-	}
-	if body != nil {
-		outreq.Body = body
+	// If we have more than one upstream host defined and if retrying is enabled
+	// by setting try_duration to a non-zero value, caddy will try to
+	// retry the request at a different host if the first one failed.
+	//
+	// This requires us to possibly rewind and replay the request body though,
+	// which in turn requires us to buffer the request body first.
+	//
+	// An unbuffered request is usually preferrable, because it reduces latency
+	// as well as memory usage. Furthermore it enables different kinds of
+	// HTTP streaming applications like gRPC for instance.
+	requiresBuffering := upstream.GetHostCount() > 1 && upstream.GetTryDuration() != 0
+
+	if requiresBuffering {
+		body, err := newBufferedBody(outreq.Body)
+		if err != nil {
+			return http.StatusBadRequest, errors.New("failed to read downstream request body")
+		}
+		if body != nil {
+			outreq.Body = body
+		}
 	}
 
 	// The keepRetrying function will return true if we should
@@ -173,15 +189,25 @@ func (p Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
 			downHeaderUpdateFn = createRespHeaderUpdateFn(host.DownstreamHeaders, replacer)
 		}
 
-		// rewind request body to its beginning
-		if err := body.rewind(); err != nil {
-			return http.StatusInternalServerError, errors.New("unable to rewind downstream request body")
+		// Before we retry the request we have to make sure
+		// that the body is rewound to it's beginning.
+		if bb, ok := outreq.Body.(*bufferedBody); ok {
+			if err := bb.rewind(); err != nil {
+				return http.StatusInternalServerError, errors.New("unable to rewind downstream request body")
+			}
 		}
 
 		// tell the proxy to serve the request
-		atomic.AddInt64(&host.Conns, 1)
-		backendErr = proxy.ServeHTTP(w, outreq, downHeaderUpdateFn)
-		atomic.AddInt64(&host.Conns, -1)
+		//
+		// NOTE:
+		//   The call to proxy.ServeHTTP can theoretically panic.
+		//   To prevent host.Conns from getting out-of-sync we thus have to
+		//   make sure that it's _always_ correctly decremented afterwards.
+		func() {
+			atomic.AddInt64(&host.Conns, 1)
+			defer atomic.AddInt64(&host.Conns, -1)
+			backendErr = proxy.ServeHTTP(w, outreq, downHeaderUpdateFn)
+		}()
 
 		// if no errors, we're done here
 		if backendErr == nil {

caddyhttp/proxy/proxy_test.go

@@ -954,6 +954,90 @@ func TestReverseProxyRetry(t *testing.T) {
 	}
 }
 
+func TestReverseProxyLargeBody(t *testing.T) {
+	log.SetOutput(ioutil.Discard)
+	defer log.SetOutput(os.Stderr)
+
+	// set up proxy
+	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		io.Copy(ioutil.Discard, r.Body)
+		r.Body.Close()
+	}))
+	defer backend.Close()
+
+	su, err := NewStaticUpstreams(caddyfile.NewDispenser("Testfile", strings.NewReader(`proxy / `+backend.URL)))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	p := &Proxy{
+		Next:      httpserver.EmptyNext, // prevents panic in some cases when test fails
+		Upstreams: su,
+	}
+
+	// middle is required to simulate closable downstream request body
+	middle := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, err = p.ServeHTTP(w, r)
+		if err != nil {
+			t.Error(err)
+		}
+	}))
+	defer middle.Close()
+
+	// Our request body will be 100MB
+	bodySize := uint64(100 * 1000 * 1000)
+
+	// We want to see how much memory the proxy module requires for this request.
+	// So lets record the mem stats before we start it.
+	begMemstats := &runtime.MemStats{}
+	runtime.ReadMemStats(begMemstats)
+
+	r, err := http.NewRequest("POST", middle.URL, &noopReader{len: bodySize})
+	if err != nil {
+		t.Fatal(err)
+	}
+	resp, err := http.DefaultTransport.RoundTrip(r)
+	if err != nil {
+		t.Fatal(err)
+	}
+	resp.Body.Close()
+
+	// Finally we need the mem stats after the request is done...
+	endMemstats := &runtime.MemStats{}
+	runtime.ReadMemStats(endMemstats)
+
+	// ...to calculate the total amount of allocated memory during the request.
+	totalAlloc := endMemstats.TotalAlloc - begMemstats.TotalAlloc
+
+	// If that's as much as the size of the body itself it's a serious sign that the
+	// request was not "streamed" to the upstream without buffering it first.
+	if totalAlloc >= bodySize {
+		t.Fatalf("proxy allocated too much memory: %d bytes", totalAlloc)
+	}
+}
+
+type noopReader struct {
+	len uint64
+	pos uint64
+}
+
+var _ io.Reader = &noopReader{}
+
+func (r *noopReader) Read(b []byte) (int, error) {
+	if r.pos >= r.len {
+		return 0, io.EOF
+	}
+	n := int(r.len - r.pos)
+	if n > len(b) {
+		n = len(b)
+	}
+	for i := range b[:n] {
+		b[i] = 0
+	}
+	r.pos += uint64(n)
+	return n, nil
+}
+
 func newFakeUpstream(name string, insecure bool) *fakeUpstream {
 	uri, _ := url.Parse(name)
 	u := &fakeUpstream{
@@ -998,6 +1082,7 @@ func (u *fakeUpstream) Select(r *http.Request) *UpstreamHost {
 func (u *fakeUpstream) AllowedPath(requestPath string) bool { return true }
 func (u *fakeUpstream) GetTryDuration() time.Duration       { return 1 * time.Second }
 func (u *fakeUpstream) GetTryInterval() time.Duration       { return 250 * time.Millisecond }
+func (u *fakeUpstream) GetHostCount() int                   { return 1 }
 
 // newWebSocketTestProxy returns a test proxy that will
 // redirect to the specified backendAddr. The function
@@ -1049,6 +1134,7 @@ func (u *fakeWsUpstream) Select(r *http.Request) *UpstreamHost {
 func (u *fakeWsUpstream) AllowedPath(requestPath string) bool { return true }
 func (u *fakeWsUpstream) GetTryDuration() time.Duration       { return 1 * time.Second }
 func (u *fakeWsUpstream) GetTryInterval() time.Duration       { return 250 * time.Millisecond }
+func (u *fakeWsUpstream) GetHostCount() int                   { return 1 }
 
 // recorderHijacker is a ResponseRecorder that can
 // be hijacked.

caddyhttp/proxy/upstream.go

@@ -423,6 +423,10 @@ func (u *staticUpstream) GetTryInterval() time.Duration {
 	return u.TryInterval
 }
 
+func (u *staticUpstream) GetHostCount() int {
+	return len(u.Hosts)
+}
+
 // RegisterPolicy adds a custom policy to the proxy.
 func RegisterPolicy(name string, policy func() Policy) {
 	supportedPolicies[name] = policy