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x/net/http2: misbehaved streams can cause connections to exhaust flow control #28204

jared2501 opened this Issue Oct 15, 2018 · 7 comments


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jared2501 commented Oct 15, 2018

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go1.11 darwin/amd64

Does this issue reproduce with the latest release?


What operating system and processor architecture are you using (go env)?

GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/_t/hg9f_j4x1q743pqh00kdv6m00000gn/T/go-build803039253=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do? / What did you expect to see? / What did you see instead?

Use httputil.ReverseProxy with an http2.Transport. I'm still trying to find a minimal reproducible example.

Basically, the http2.Transport is closing an HTTP/2 stream and then sending a number of DATA frames on the connection. The http2.Server is detecting that the stream has been half-closed by the remote and is following RFC7540 and responding with an ErrCodeStreamClosed (see http2/server.go).

However, since the http2.Server does not send a window update the remote http2.Transport does not add back the sent DATA frames to its flow control. This causes a re-used http2.Transport to eventually expend all connection flow control and halt sending.

A proposed fix that I've applied to my fork is to make the following patch

diff --git a/http2/server.go b/http2/server.go
index 56859d1..7a39456 100644
--- a/http2/server.go
+++ b/http2/server.go
@@ -1586,6 +1586,8 @@ func (sc *serverConn) processData(f *DataFrame) error {
        // "open" or "half-closed (local)" state, the recipient MUST respond with a
        // stream error (Section 5.4.2) of type STREAM_CLOSED.
        if state == stateClosed {
+               sc.inflow.take(int32(f.Length))
+               sc.sendWindowUpdate(nil, int(f.Length))
                return streamError(id, ErrCodeStreamClosed)
        if st == nil || state != stateOpen || st.gotTrailerHeader || st.resetQueued {

Although, one could argue that http2.Transport/httputil.Reverse proxy should be fixed to make sure that data frames aren't sent after a close.


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jared2501 commented Oct 15, 2018

I think this might be related to 8f38f28#diff-d863507a61be206d112f6e00e6d812a2 since it appears that the http.Server marks the stream as stateClosed if the handler panics, even though the remote side hasn't sent a RESET_STREAM frame. Therefore, the stream should be in "half-closed (local)" and so should send back WINDOW_UPDATE frames but it's not.


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FiloSottile commented Oct 15, 2018

/cc @bradfitz


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bradfitz commented Oct 17, 2018

Can you capture the logs (from setting GODEBUG=http2debug=2) while this happens?


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jared2501 commented Oct 17, 2018


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prashantv commented Dec 8, 2018

We ran into the same issue, and I've put together a small repro using the gRPC client, and a gRPC server hosted via the x/net HTTP/2 server:

This example doesn't contain use the reverse proxy, and the issue is exactly as @jared2501 pointed out -- when the server sends RST_STREAM with stream closed, it's not updating flow control, and so the client stops sending data.

When this test is run, the client reports a "deadline exceeded" (since it's waiting to send data, but never gets to it since the window is full):

--- FAIL: TestGRPCLargePayload (1.02s)
                        Error Trace:    repro_test.go:58
                        Error:          Received unexpected error:
                                        rpc error: code = DeadlineExceeded desc = context deadline exceeded
                        Test:           TestGRPCLargePayload
                        Messages:       Expect following requests to succeed

I have the GODEBUG=http2debug=2 logs:

The client doesn't stop sending frames, and so the server keeps responding with:
RST_STREAM stream=1 len=4 ErrCode=STREAM_CLOSED. However, there's no corresponding WINDOW_UPDATE (which it did before the stream was closed).

This seems like a regression introduced in golang/net@039a425 -- before that change, the code would send a window update.

I also have the "fix" (update flow-control) on a branch called "fix", where the test mostly passes. However, around 1-2% of the time, it still fails with the same error -- I think there might be other paths where the server sends RST_STREAM without taking flow control into account.


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jared2501 commented Dec 8, 2018

Hey @prashantv - glad to see you can repro my issue! I looked over your example and it's possible you're also being hit by #28634. Although, even with patches for this issue and #28634, I was still seeing some flow control issues when using grpc with a context with a timeout...


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fraenkel commented Dec 11, 2018

@prashantv You are correct. I did introduce a bug, but there is another one there too. Once we receive a data frame that does not cause a connection error, we must account for the data. The take() logic should be before all the additional state checks regardless of the path taken.

I believe there may also be a similar bug on the client side.

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