pjfanning opened a new pull request, #1259:
URL: https://github.com/apache/pekko-http/pull/1259
### Motivation
`totalBufferedData` feeds the connection-level flow controller, which emits
a WINDOW_UPDATE only while `outstanding + buffered` stays below half of
`incoming-connection-level-buffer-size`:
```scala
private def ifMoreThanHalfUsed(max: Int, outstanding: Int, buffered: Int):
Int = {
val totalReservedSpace = outstanding + buffered
if (totalReservedSpace < max / 2) max - totalReservedSpace else 0
}
```
It is incremented for every DATA frame received (`ReceivingData.handle`),
but was **not** decremented on the three paths that discard a non-empty buffer:
- `IncomingStreamBuffer.onRstStreamFrame` — cleared `buffer` after the peer
reset the stream;
- `IncomingStreamBuffer.onDownstreamFinish` — cleared it when the
application cancelled the entity stream;
- `CollectingIncomingData.onRstStreamFrame` — a no-op, even though the bytes
collected so far had already been counted.
A peer that sends data the handler never reads and then resets the stream
therefore ratchets `totalBufferedData` up permanently. Once the leaked total
reaches half the configured buffer size, the server stops replenishing the
connection window, it drains to zero, and **every stream on that connection
stalls**. Note the RST_STREAM throttle does not prevent this — even a
throttle-compliant reset rate leaks the counter.
### Modification
Add `IncomingStreamBuffer.discardBuffer()`, which subtracts what is still
buffered from `totalBufferedData` before clearing it, and use it on both
discard paths. Subtract the collected bytes in
`CollectingIncomingData.onRstStreamFrame` for the same reason.
### Result
Resetting or cancelling a stream releases the connection-level window its
buffered data reserved, so the connection keeps being replenished and no longer
stalls.
### Tests
- `sbt "http2-tests/testOnly
org.apache.pekko.http.impl.engine.http2.Http2ServerSpec
org.apache.pekko.http.impl.engine.http2.Http2ClientSpec
org.apache.pekko.http.impl.engine.http2.Http2ClientServerSpec"` — pass (174
tests). A new test buffers request data the handler never reads and resets the
stream six times over, with `incoming-connection-level-buffer-size` lowered to
the initial window so the effect is reached quickly, then asserts the
connection still accepts a request. Verified it fails with the fix stashed (the
peer runs out of connection window).
- `sbt http-core/mimaReportBinaryIssues` — pass (internal
`impl.engine.http2` change, no public API).
- Native `scalafmt` on the changed files — clean.
### References
None - releases buffered-data accounting when a stream is reset or cancelled
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