proxy: recognize client's cancellation

fix issue #1589
Signed-off-by: Tw <tw19881113@gmail.com>

caddyhttp/gzip/gzip.go

@@ -9,8 +9,6 @@ import (
 	"net/http"
 	"strings"
 
-	"errors"
-
 	"github.com/mholt/caddy"
 	"github.com/mholt/caddy/caddyhttp/httpserver"
 )
@@ -155,7 +153,7 @@ func (w *gzipResponseWriter) Push(target string, opts *http.PushOptions) error {
 		return pusher.Push(target, opts)
 	}
 
-	return errors.New("push is unavailable (probably chained http.ResponseWriter does not implement http.Pusher)")
+	return httpserver.NonFlusherError{Underlying: w.ResponseWriter}
 }
 
 // Interface guards

caddyhttp/header/header.go

@@ -9,7 +9,6 @@ import (
 	"net/http"
 	"strings"
 
-	"errors"
 	"github.com/mholt/caddy/caddyhttp/httpserver"
 )
 
@@ -141,7 +140,7 @@ func (rww *responseWriterWrapper) Push(target string, opts *http.PushOptions) er
 		return pusher.Push(target, opts)
 	}
 
-	return errors.New("push is unavailable (probably chained http.ResponseWriter does not implement http.Pusher)")
+	return httpserver.NonPusherError{Underlying: rww.ResponseWriter}
 }
 
 // Interface guards

caddyhttp/httpserver/error.go

@@ -8,6 +8,7 @@ var (
 	_ error = NonHijackerError{}
 	_ error = NonFlusherError{}
 	_ error = NonCloseNotifierError{}
+	_ error = NonPusherError{}
 )
 
 // NonHijackerError is more descriptive error caused by a non hijacker
@@ -42,3 +43,14 @@ type NonCloseNotifierError struct {
 func (c NonCloseNotifierError) Error() string {
 	return fmt.Sprintf("%T is not a closeNotifier", c.Underlying)
 }
+
+// NonPusherError is more descriptive error caused by a non pusher
+type NonPusherError struct {
+	// underlying type which doesn't implement pusher
+	Underlying interface{}
+}
+
+// Implement Error
+func (c NonPusherError) Error() string {
+	return fmt.Sprintf("%T is not a pusher", c.Underlying)
+}

caddyhttp/httpserver/recorder.go

@@ -2,7 +2,6 @@ package httpserver
 
 import (
 	"bufio"
-	"errors"
 	"net"
 	"net/http"
 	"time"
@@ -103,7 +102,7 @@ func (r *ResponseRecorder) Push(target string, opts *http.PushOptions) error {
 		return pusher.Push(target, opts)
 	}
 
-	return errors.New("push is unavailable (probably chained http.ResponseWriter does not implement http.Pusher)")
+	return NonPusherError{Underlying: r.ResponseWriter}
 }
 
 // Interface guards

caddyhttp/proxy/proxy.go

@@ -2,6 +2,7 @@
 package proxy
 
 import (
+	"context"
 	"errors"
 	"net"
 	"net/http"
@@ -103,7 +104,8 @@ func (p Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
 	replacer := httpserver.NewReplacer(r, nil, "")
 
 	// outreq is the request that makes a roundtrip to the backend
-	outreq := createUpstreamRequest(r)
+	outreq, cancel := createUpstreamRequest(w, r)
+	defer cancel()
 
 	// 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
@@ -131,7 +133,11 @@ func (p Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
 	// loop and try to select another host, or false if we
 	// should break and stop retrying.
 	start := time.Now()
-	keepRetrying := func() bool {
+	keepRetrying := func(backendErr error) bool {
+		// if downstream has canceled the request, break
+		if backendErr == context.Canceled {
+			return false
+		}
 		// if we've tried long enough, break
 		if time.Since(start) >= upstream.GetTryDuration() {
 			return false
@@ -150,7 +156,7 @@ func (p Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
 			if backendErr == nil {
 				backendErr = errors.New("no hosts available upstream")
 			}
-			if !keepRetrying() {
+			if !keepRetrying(backendErr) {
 				break
 			}
 			continue
@@ -238,7 +244,7 @@ func (p Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
 		}
 
 		// if we've tried long enough, break
-		if !keepRetrying() {
+		if !keepRetrying(backendErr) {
 			break
 		}
 	}
@@ -267,9 +273,23 @@ func (p Proxy) match(r *http.Request) Upstream {
 // that can be sent upstream.
 //
 // Derived from reverseproxy.go in the standard Go httputil package.
-func createUpstreamRequest(r *http.Request) *http.Request {
-	outreq := new(http.Request)
-	*outreq = *r // includes shallow copies of maps, but okay
+func createUpstreamRequest(rw http.ResponseWriter, r *http.Request) (*http.Request, context.CancelFunc) {
+	// Original incoming server request may be canceled by the
+	// user or by std lib(e.g. too many idle connections).
+	ctx, cancel := context.WithCancel(r.Context())
+	if cn, ok := rw.(http.CloseNotifier); ok {
+		notifyChan := cn.CloseNotify()
+		go func() {
+			select {
+			case <-notifyChan:
+				cancel()
+			case <-ctx.Done():
+			}
+		}()
+	}
+
+	outreq := r.WithContext(ctx) // includes shallow copies of maps, but okay
+
 	// We should set body to nil explicitly if request body is empty.
 	// For server requests the Request Body is always non-nil.
 	if r.ContentLength == 0 {
@@ -319,7 +339,7 @@ func createUpstreamRequest(r *http.Request) *http.Request {
 		outreq.Header.Set("X-Forwarded-For", clientIP)
 	}
 
-	return outreq
+	return outreq, cancel
 }
 
 func createRespHeaderUpdateFn(rules http.Header, replacer httpserver.Replacer) respUpdateFn {

caddyhttp/proxy/proxy_test.go

@@ -12,7 +12,6 @@ import (
 	"net"
 	"net/http"
 	"net/http/httptest"
-	"net/http/httptrace"
 	"net/url"
 	"os"
 	"path/filepath"
@@ -101,7 +100,7 @@ func TestReverseProxy(t *testing.T) {
 
 	// Make sure {upstream} placeholder is set
 	r.Body = ioutil.NopCloser(strings.NewReader("test"))
-	rr := httpserver.NewResponseRecorder(httptest.NewRecorder())
+	rr := httpserver.NewResponseRecorder(testResponseRecorder{httptest.NewRecorder()})
 	rr.Replacer = httpserver.NewReplacer(r, rr, "-")
 
 	p.ServeHTTP(rr, r)
@@ -1123,7 +1122,18 @@ func TestReverseProxyLargeBody(t *testing.T) {
 }
 
 func TestCancelRequest(t *testing.T) {
+	reqInFlight := make(chan struct{})
 	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		close(reqInFlight) // cause the client to cancel its request
+
+		select {
+		case <-time.After(10 * time.Second):
+			t.Error("Handler never saw CloseNotify")
+			return
+		case <-w.(http.CloseNotifier).CloseNotify():
+		}
+
+		w.WriteHeader(http.StatusOK)
 		w.Write([]byte("Hello, client"))
 	}))
 	defer backend.Close()
@@ -1140,26 +1150,21 @@ func TestCancelRequest(t *testing.T) {
 	defer cancel()
 	req = req.WithContext(ctx)
 
-	// add GotConn hook to cancel the request
-	gotC := make(chan struct{})
-	defer close(gotC)
-	trace := &httptrace.ClientTrace{
-		GotConn: func(connInfo httptrace.GotConnInfo) {
-			gotC <- struct{}{}
-		},
-	}
-	req = req.WithContext(httptrace.WithClientTrace(req.Context(), trace))
-
 	// wait for canceling the request
 	go func() {
-		<-gotC
+		<-reqInFlight
 		cancel()
 	}()
 
-	status, err := p.ServeHTTP(httptest.NewRecorder(), req)
-	if status != 0 || err != nil {
-		t.Errorf("expect proxy handle normally, but not, status:%d, err:%q",
-			status, err)
+	rec := httptest.NewRecorder()
+	status, err := p.ServeHTTP(rec, req)
+	expectedStatus, expectErr := http.StatusBadGateway, context.Canceled
+	if status != expectedStatus || err != expectErr {
+		t.Errorf("expect proxy handle return status[%d] with error[%v], but got status[%d] with error[%v]",
+			expectedStatus, expectErr, status, err)
+	}
+	if body := rec.Body.String(); body != "" {
+		t.Errorf("expect a blank response, but got %q", body)
 	}
 }
 
@@ -1310,6 +1315,28 @@ func (c *fakeConn) Close() error                       { return nil }
 func (c *fakeConn) Read(b []byte) (int, error)         { return c.readBuf.Read(b) }
 func (c *fakeConn) Write(b []byte) (int, error)        { return c.writeBuf.Write(b) }
 
+// testResponseRecorder wraps `httptest.ResponseRecorder`,
+// also implements `http.CloseNotifier`, `http.Hijacker` and `http.Pusher`.
+type testResponseRecorder struct {
+	*httptest.ResponseRecorder
+}
+
+func (testResponseRecorder) CloseNotify() <-chan bool { return nil }
+func (t testResponseRecorder) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	return nil, nil, httpserver.NonHijackerError{Underlying: t}
+}
+func (t testResponseRecorder) Push(target string, opts *http.PushOptions) error {
+	return httpserver.NonPusherError{Underlying: t}
+}
+
+// Interface guards
+var (
+	_ http.Pusher        = testResponseRecorder{}
+	_ http.Flusher       = testResponseRecorder{}
+	_ http.CloseNotifier = testResponseRecorder{}
+	_ http.Hijacker      = testResponseRecorder{}
+)
+
 func BenchmarkProxy(b *testing.B) {
 	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Write([]byte("Hello, client"))

caddyhttp/proxy/reverseproxy.go

@@ -12,7 +12,6 @@
 package proxy
 
 import (
-	"context"
 	"crypto/tls"
 	"io"
 	"net"
@@ -252,14 +251,6 @@ func (rp *ReverseProxy) ServeHTTP(rw http.ResponseWriter, outreq *http.Request,
 
 	rp.Director(outreq)
 
-	// Original incoming server request may be canceled by the
-	// user or by std lib(e.g. too many idle connections).
-	// Now we issue the new outgoing client request which
-	// doesn't depend on the original one. (issue 1345)
-	ctx, cancel := context.WithCancel(context.Background())
-	defer cancel()
-	outreq = outreq.WithContext(ctx)
-
 	res, err := transport.RoundTrip(outreq)
 	if err != nil {
 		return err