Sending RST_STREAM on closed Streams results in GOAWAY

[bengreenberg]

I'm seeing a race condition on pushes of small amounts of data that are canceled by the client. If the push data is small enough and transferred quickly enough, the server may receive a client's RST_STREAM frame after the pushed stream has already been closed. In this case, the http-2 server cannot find the stream id in the @streams hash, so it treats it as as unexpected stream identifier and sends GOAWAY with frame 0, killing the connection. Since the closed push stream is actually valid, I believe this is not correct and the RST_STEAM can be silently ignored in this case.

I have a fix for this that will not throw the error if the stream is in the @streams_recently_closed hash.

[bengreenberg]

Looking into this more, I believe this was introduced with #88 . I don't think the intent of that patch was the delete closed immediately. My fix only deletes the stream if its been closed for 15 seconds or longer.