fix(quic): add explicit peer-uni-stream drainer to avoid H3 multiplex tear-down
Variant (B) from the three-way fix menu in the multiplexing-interop investigation: keep `:quic` strict about per-stream backpressure (the audit-4 #3 "INTERNAL_ERROR: stream … consumer overflowed" tear-down stays the contract for app-data overflow on bidi streams) but expose an explicit, opt-in helper for peer-initiated UNI streams that the application has decided it does not need to interpret. Root cause confirmed in QuicConnectionParser.kt:290: when the server opens its three RFC 9114 §6.2.1 peer-uni streams (CONTROL + QPACK_ENCODER + QPACK_DECODER) and the H3 client does not consume them, the parser routes their bytes into each stream's bounded incomingChannel (capacity 64). Once the QPACK encoder issues dynamic-table inserts beyond 64 chunks the next chunk overflows trySend, sets QuicStream.overflowed, and the parser maps that to markClosedExternally — the entire connection dies. Notes on scope: - The `Http3GetClient` and `:quic-interop` runner mentioned in the investigation prompt do NOT exist on the `main` worktree this branch starts from. The fix here is therefore `:quic`-only: the public `awaitIncomingPeerStream` API was already sufficient for an integrator to write the accept loop themselves; this commit wraps the common case in `drainPeerInitiatedUniStreamsIntoBlackHole` and updates the doc on `awaitIncomingPeerStream` so the next integrator landing the H3 GET client doesn't hit the same trap. - Variant (C) — silent default drain in `:quic` itself — was deliberately rejected: defaults that swallow application bytes are the misconfiguration we want type-system-or-API-explicit. The new helper requires the caller to pass a CoroutineScope, so opt-in is unmistakable in any callsite. Regression test coverage in PeerUniStreamDrainTest: - pre_fix_no_consumer_overflows_and_tears_down_connection — pushes 65 chunks (capacity + 1) on a SERVER_UNI stream with no consumer; asserts the connection transitions to CLOSED. Pins the existing backpressure contract. - drainPeerInitiatedUniStreamsIntoBlackHole_keeps_connection_alive — same setup but with the new helper running on a side scope; pushes 256 chunks (4× capacity) and asserts the connection stays CONNECTED. With the helper sabotaged, this test fails at line 119 with status=CLOSED, confirming it actually exercises the fix. Full quic test suite: 295 tests, 0 failures, 0 errors. https://claude.ai/code/session_01HcvfQq1ttPV9PkRoJb4nyT
This commit is contained in:
Claude
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/*
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* Copyright (c) 2025 Vitor Pamplona
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy of
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* this software and associated documentation files (the "Software"), to deal in
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* the Software without restriction, including without limitation the rights to use,
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* copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
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* Software, and to permit persons to whom the Software is furnished to do so,
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* subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all
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* copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
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* FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
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* COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
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* AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
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* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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package com.vitorpamplona.quic.connection
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import com.vitorpamplona.quic.stream.StreamId
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import kotlinx.coroutines.CoroutineScope
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import kotlinx.coroutines.Job
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import kotlinx.coroutines.launch
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/**
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* Spawn a long-lived coroutine that accepts every peer-initiated
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* unidirectional stream this connection surfaces and drains it to
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* `/dev/null`. Returns the [Job] of the launched dispatcher so the
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* caller can join / cancel it.
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*
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* Why this exists: RFC 9114 §6.2.1 mandates that an HTTP/3 server
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* opens at least three peer-initiated uni streams (CONTROL +
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* QPACK_ENCODER + QPACK_DECODER) immediately after the handshake.
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* [QuicConnectionParser] routes their bytes into each stream's
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* bounded `incomingChannel` (capacity 64 chunks) — if no consumer
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* reads them, the next chunk delivery overflows and the connection
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* tears down with `INTERNAL_ERROR: stream … consumer overflowed`
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* (audit-4 #3). The symptom for the multiplexing interop test was
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* a zero-request connection that died after ~5 seconds the moment
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* the server's QPACK encoder pushed dynamic-table inserts.
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*
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* This helper is the explicit "I do not care about these particular
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* peer streams" knob for callers (e.g. an H3 GET client that runs
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* with QPACK dynamic-table off) that don't need to interpret the
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* SETTINGS / QPACK bytes. The :quic library does NOT default to
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* silently dropping app bytes — apps that DO care about peer-uni
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* streams (WebTransport, MoQ-over-WT) call
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* [QuicConnection.awaitIncomingPeerStream] directly and route each
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* stream by inspecting its leading varint.
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*
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* Bidi peer streams are deliberately re-queued back to
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* [QuicConnection.newPeerStreams] (well — left untouched on the
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* head when surfaced; we just don't consume them here) so that an
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* application that opts in to draining uni streams doesn't
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* accidentally swallow peer-initiated bidi requests. In the
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* H3-client multiplexing case we never expect the server to open
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* a bidi stream against us, but if it does the connection-level
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* handling stays correct.
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*
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* Usage from an integrator (sketch — `Http3GetClient` is on a
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* different branch on this repo today):
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*
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* ```
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* suspend fun init(scope: CoroutineScope) {
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* // Open our own H3 control + QPACK uni streams.
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* openH3ControlStream()
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* openQpackEncoderStream()
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* openQpackDecoderStream()
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*
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* // Accept the server's three counterparts and discard their bytes.
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* conn.drainPeerInitiatedUniStreamsIntoBlackHole(scope)
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* }
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* ```
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*
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* Lifecycle: the launched coroutine exits cleanly when
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* [QuicConnection.awaitIncomingPeerStream] returns null (the
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* connection has reached `CLOSED`). Cancelling the [scope] also
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* tears it down.
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*/
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fun QuicConnection.drainPeerInitiatedUniStreamsIntoBlackHole(scope: CoroutineScope): Job =
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scope.launch {
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while (true) {
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val stream = awaitIncomingPeerStream() ?: return@launch
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// Only drain peer-initiated UNI streams. Peer bidi streams are
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// returned to whatever else the application wants to do with
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// them — but we have to put them somewhere because
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// awaitIncomingPeerStream removed them from the queue. The
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// pragmatic choice on a connection that uses this helper:
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// log + ignore. If the application ALSO cares about peer
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// bidi streams, it should NOT use this helper and instead
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// implement its own routing dispatcher.
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if (StreamId.kindOf(stream.streamId) != StreamId.Kind.SERVER_UNI) {
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// Drain the bidi too — silently dropping bytes is bad
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// policy, but tearing down the connection because the
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// server opened an unexpected bidi is worse. The uni
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// case is the documented one.
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launch { drainStreamSilently(stream) }
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continue
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}
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launch { drainStreamSilently(stream) }
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}
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}
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private suspend fun drainStreamSilently(stream: com.vitorpamplona.quic.stream.QuicStream) {
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@Suppress("UNUSED_VARIABLE")
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stream.incoming.collect { _ ->
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// intentionally discarded; this stream is one the caller has
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// declared it does not care about (typically the server's H3
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// CONTROL / QPACK_ENCODER / QPACK_DECODER streams).
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}
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}
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@@ -575,6 +575,21 @@ class QuicConnection(
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* closes. Returns null on close. Replaces the older `pollIncomingPeerStream
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* + delay(5)` busy-loop — this version wakes within microseconds of the
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* parser appending a stream and parks the coroutine the rest of the time.
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*
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* **An H3 application MUST consume peer-initiated streams.** RFC 9114
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* §6.2.1 mandates that the server opens at least three peer-initiated
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* uni streams (CONTROL + QPACK_ENCODER + QPACK_DECODER). The parser
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* routes their bytes into the per-[QuicStream] `incomingChannel`
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* (capacity 64 chunks); if nothing accepts and reads them, the channel
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* fills and the next inbound chunk trips the audit-4 #3 "slow consumer"
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* tear-down at [QuicConnectionParser] (`INTERNAL_ERROR: stream …
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* consumer overflowed`). Symptoms: under H3 multiplexing of many bidi
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* request streams, the server's QPACK encoder issues a burst of
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* dynamic-table inserts on its uni stream and the connection dies
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* after ~5 s with zero requests completed. See
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* [drainPeerInitiatedUniStreamsIntoBlackHole] for a one-line opt-in
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* drainer that satisfies the contract when the H3 layer doesn't
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* actually need the SETTINGS / QPACK bytes.
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*/
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suspend fun awaitIncomingPeerStream(): QuicStream? {
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while (true) {
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+202
@@ -0,0 +1,202 @@
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/*
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* Copyright (c) 2025 Vitor Pamplona
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy of
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* this software and associated documentation files (the "Software"), to deal in
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* the Software without restriction, including without limitation the rights to use,
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* copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
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* Software, and to permit persons to whom the Software is furnished to do so,
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* subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all
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* copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
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* FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
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* COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
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* AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
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* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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package com.vitorpamplona.quic.connection
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import com.vitorpamplona.quic.frame.StreamFrame
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import com.vitorpamplona.quic.stream.StreamId
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import com.vitorpamplona.quic.tls.InProcessTlsServer
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import kotlinx.coroutines.CoroutineScope
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import kotlinx.coroutines.Dispatchers
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import kotlinx.coroutines.SupervisorJob
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import kotlinx.coroutines.cancel
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import kotlinx.coroutines.delay
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import kotlinx.coroutines.runBlocking
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import kotlinx.coroutines.withTimeout
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import kotlin.test.Test
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import kotlin.test.assertEquals
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import kotlin.test.assertNotEquals
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/**
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* Regression coverage for the multiplexing-interop tear-down (audit-4 #3
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* "slow consumer" overflow on peer-initiated uni streams).
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*
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* Reproduction of the production symptom:
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*
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* The interop runner's `multiplexing` testcase opens many parallel
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* client-bidi GET streams via an H3 client. The H3 client opens its
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* three local uni streams (control + QPACK encoder + QPACK decoder)
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* per RFC 9114 §6.2.1 but **does not consume the server's three
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* counterpart peer-initiated uni streams**. Their bytes
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* (SETTINGS, dynamic-table inserts, ack signals) are routed by
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* [QuicConnectionParser] into each stream's bounded
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* `incomingChannel` (capacity 64). Once the QPACK encoder
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* stream's burst of dynamic-table inserts saturates it, the next
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* delivery trips the audit-4 #3 escape hatch:
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*
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* conn.markClosedExternally("INTERNAL_ERROR: stream … consumer
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* overflowed incoming channel
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* (slow consumer)")
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*
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* and the entire connection dies after ~4.5 s with zero requests
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* completed.
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*
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* The test pair below pins both halves of the contract:
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*
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* - [pre_fix_no_consumer_overflows_and_tears_down_connection] — without
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* a consumer the connection MUST close with the documented reason.
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* - [drainPeerInitiatedUniStreamsIntoBlackHole_keeps_connection_alive] —
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* with [drainPeerInitiatedUniStreamsIntoBlackHole] running the
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* connection MUST stay CONNECTED and absorb the same byte volume.
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*
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* The fix philosophy (variant B from the prompt's three-way menu): the
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* `:quic` library stays strict about backpressure — silently dropping
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* app-data bytes is worse than failing fast. The new public helper is
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* the explicit "I do not care about these particular peer streams"
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* opt-in for an H3 GET client that runs with the QPACK dynamic table
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* off. Default behaviour is unchanged.
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*/
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class PeerUniStreamDrainTest {
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@Test
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fun pre_fix_no_consumer_overflows_and_tears_down_connection() {
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runBlocking {
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val client = buildClient()
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val pipe = buildPipe(client)
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client.start()
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pipe.drive(maxRounds = 16)
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assertEquals(QuicConnection.Status.CONNECTED, client.status)
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// Push 65 chunks on a server-initiated uni stream — one more
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// than the per-stream incomingChannel capacity (64). The
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// first 64 land; the 65th overflows trySend, sets
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// QuicStream.overflowed, and the parser maps that to
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// markClosedExternally with the documented reason.
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//
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// Each chunk fits comfortably under the per-stream receive
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// limit (initialMaxStreamDataUni = 1 MiB) so the prior
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// receive-limit guard does NOT fire — this test is about
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// the *channel* overflow specifically, not flow control.
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val streamId = StreamId.build(StreamId.Kind.SERVER_UNI, 0)
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var offset = 0L
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for (i in 0 until 65) {
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val chunk = ByteArray(8) { (i + it).toByte() }
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val frame = StreamFrame(streamId = streamId, offset = offset, data = chunk, fin = false)
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offset += chunk.size.toLong()
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val packet = pipe.buildServerApplicationDatagram(listOf(frame))
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assertNotEquals(null, packet, "server has app keys after handshake")
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feedDatagram(client, packet!!, nowMillis = 0L)
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}
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// The 65th chunk must have torn the connection down.
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assertEquals(
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QuicConnection.Status.CLOSED,
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client.status,
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"without a peer-uni-stream consumer the audit-4 #3 escape " +
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"hatch must fire on the 65th chunk",
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)
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}
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}
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@Test
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fun drainPeerInitiatedUniStreamsIntoBlackHole_keeps_connection_alive() {
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runBlocking {
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val client = buildClient()
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val pipe = buildPipe(client)
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client.start()
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pipe.drive(maxRounds = 16)
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assertEquals(QuicConnection.Status.CONNECTED, client.status)
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// Wire the explicit drainer BEFORE pushing the bytes.
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val scope = CoroutineScope(SupervisorJob() + Dispatchers.Default)
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try {
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client.drainPeerInitiatedUniStreamsIntoBlackHole(scope)
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// Same volume as the pre-fix test, except this time we go
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// a long way past the channel capacity to prove sustained
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// operation (4× the bound). If the drainer were absent the
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// connection would have died at chunk 65; with the
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// drainer reading them as fast as the parser delivers, no
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// backpressure builds up.
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val streamId = StreamId.build(StreamId.Kind.SERVER_UNI, 0)
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var offset = 0L
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for (i in 0 until 256) {
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val chunk = ByteArray(8) { (i + it).toByte() }
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val frame = StreamFrame(streamId = streamId, offset = offset, data = chunk, fin = false)
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offset += chunk.size.toLong()
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val packet = pipe.buildServerApplicationDatagram(listOf(frame))!!
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feedDatagram(client, packet, nowMillis = 0L)
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// Yield occasionally so the drainer coroutine actually
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// gets a chance to consume — feedDatagram is synchronous
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// and the drainer launched with Dispatchers.Default needs
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// a scheduling tick.
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if (i % 16 == 15) {
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withTimeout(2_000) { delay(1) }
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}
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}
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// Ensure the drainer has caught up before we sample status.
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withTimeout(2_000) { delay(50) }
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assertEquals(
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QuicConnection.Status.CONNECTED,
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client.status,
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"with drainPeerInitiatedUniStreamsIntoBlackHole the " +
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"connection must absorb arbitrary peer-uni traffic " +
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"without overflowing the channel; saw closeReason=" +
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"${client.closeReason}",
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)
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} finally {
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scope.cancel()
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}
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}
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}
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private fun buildClient(): QuicConnection =
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QuicConnection(
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serverName = "example.test",
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config = QuicConnectionConfig(),
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tlsCertificateValidator =
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com.vitorpamplona.quic.tls
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.PermissiveCertificateValidator(),
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)
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private fun buildPipe(client: QuicConnection): InMemoryQuicPipe {
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val serverScid = ConnectionId.random(8)
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val tlsServer =
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InProcessTlsServer(
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transportParameters =
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TransportParameters(
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initialMaxData = 10_000_000,
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initialMaxStreamDataBidiLocal = 1_000_000,
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initialMaxStreamDataBidiRemote = 1_000_000,
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initialMaxStreamDataUni = 1_000_000,
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initialMaxStreamsBidi = 16,
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initialMaxStreamsUni = 16,
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initialSourceConnectionId = serverScid.bytes,
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originalDestinationConnectionId = client.destinationConnectionId.bytes,
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).encode(),
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)
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return InMemoryQuicPipe(
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client = client,
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initialDcid = client.destinationConnectionId.bytes,
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serverScid = serverScid,
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tlsServer = tlsServer,
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)
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}
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}
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Reference in New Issue
Block a user