[release-branch.go1.15-bundle] http2: wait until the request body has been written

When the clientConn is done with a request, if there is a request body,
we must wait until the body is written otherwise there can be a race
when attempting to rewind the body.

Updates golang/go#42539

Change-Id: I77606cc19372eea8bbd8995102354f092b8042be
Reviewed-on: https://go-review.googlesource.com/c/net/+/253259
Reviewed-by: Damien Neil <[email protected]>
Trust: Emmanuel Odeke <[email protected]>
Run-TryBot: Emmanuel Odeke <[email protected]>
TryBot-Result: Go Bot <[email protected]>
(cherry picked from commit ff519b6)
Reviewed-on: https://go-review.googlesource.com/c/net/+/288012
Trust: Damien Neil <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: fraenkel

http2/transport.go

@@ -1092,6 +1092,9 @@ func (cc *ClientConn) roundTrip(req *http.Request) (res *http.Response, gotErrAf
 			// we can keep it.
 			bodyWriter.cancel()
 			cs.abortRequestBodyWrite(errStopReqBodyWrite)
+			if hasBody && !bodyWritten {
+				<-bodyWriter.resc
+			}
 		}
 		if re.err != nil {
 			cc.forgetStreamID(cs.ID)
@@ -1112,6 +1115,7 @@ func (cc *ClientConn) roundTrip(req *http.Request) (res *http.Response, gotErrAf
 			} else {
 				bodyWriter.cancel()
 				cs.abortRequestBodyWrite(errStopReqBodyWriteAndCancel)
+				<-bodyWriter.resc
 			}
 			cc.forgetStreamID(cs.ID)
 			return nil, cs.getStartedWrite(), errTimeout
@@ -1121,6 +1125,7 @@ func (cc *ClientConn) roundTrip(req *http.Request) (res *http.Response, gotErrAf
 			} else {
 				bodyWriter.cancel()
 				cs.abortRequestBodyWrite(errStopReqBodyWriteAndCancel)
+				<-bodyWriter.resc
 			}
 			cc.forgetStreamID(cs.ID)
 			return nil, cs.getStartedWrite(), ctx.Err()
@@ -1130,6 +1135,7 @@ func (cc *ClientConn) roundTrip(req *http.Request) (res *http.Response, gotErrAf
 			} else {
 				bodyWriter.cancel()
 				cs.abortRequestBodyWrite(errStopReqBodyWriteAndCancel)
+				<-bodyWriter.resc
 			}
 			cc.forgetStreamID(cs.ID)
 			return nil, cs.getStartedWrite(), errRequestCanceled
@@ -1139,6 +1145,7 @@ func (cc *ClientConn) roundTrip(req *http.Request) (res *http.Response, gotErrAf
 			// forgetStreamID.
 			return nil, cs.getStartedWrite(), cs.resetErr
 		case err := <-bodyWriter.resc:
+			bodyWritten = true
 			// Prefer the read loop's response, if available. Issue 16102.
 			select {
 			case re := <-readLoopResCh:
@@ -1149,7 +1156,6 @@ func (cc *ClientConn) roundTrip(req *http.Request) (res *http.Response, gotErrAf
 				cc.forgetStreamID(cs.ID)
 				return nil, cs.getStartedWrite(), err
 			}
-			bodyWritten = true
 			if d := cc.responseHeaderTimeout(); d != 0 {
 				timer := time.NewTimer(d)
 				defer timer.Stop()

http2/transport_test.go

@@ -4630,3 +4630,48 @@ func TestTransportRoundtripCloseOnWriteError(t *testing.T) {
 		t.Fatal("expected closed")
 	}
 }
+
+// Issue 31192: A failed request may be retried if the body has not been read
+// already. If the request body has started to be sent, one must wait until it
+// is completed.
+func TestTransportBodyRewindRace(t *testing.T) {
+	st := newServerTester(t, func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Connection", "close")
+		w.WriteHeader(http.StatusOK)
+		return
+	}, optOnlyServer)
+	defer st.Close()
+
+	tr := &http.Transport{
+		TLSClientConfig: tlsConfigInsecure,
+		MaxConnsPerHost: 1,
+	}
+	err := ConfigureTransport(tr)
+	if err != nil {
+		t.Fatal(err)
+	}
+	client := &http.Client{
+		Transport: tr,
+	}
+
+	const clients = 50
+
+	var wg sync.WaitGroup
+	wg.Add(clients)
+	for i := 0; i < clients; i++ {
+		req, err := http.NewRequest("POST", st.ts.URL, bytes.NewBufferString("abcdef"))
+		if err != nil {
+			t.Fatalf("unexpect new request error: %v", err)
+		}
+
+		go func() {
+			defer wg.Done()
+			res, err := client.Do(req)
+			if err == nil {
+				res.Body.Close()
+			}
+		}()
+	}
+
+	wg.Wait()
+}