test(quic): cover connection teardown

Every other QUIC test ends in std::_Exit(0), so nothing in the suite ever
ran a ~ClientQUIC. This adds 25 build-up/tear-down cycles with reader
threads parked inside RecieveSync -- the shape a reconnect loop has --
which aborts on ~10/20 runs against the current implementation.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -275,6 +275,7 @@ The library includes tests covering:
 - HTTP/3 external interop (`ShouldSend`) — live fetch from `cloudflare-quic.com:443`, exercises real TLS chain validation, mandatory control stream, peer-initiated unidi streams, and QPACK Huffman decoding
 - QUIC reliable streams (`ShouldSendRecieveQUICStream`)
 - QUIC unreliable datagrams (`ShouldSendRecieveQUICDatagram`)
+- QUIC connection teardown (`ShouldSurviveConnectionChurn`) — 25 build-up/tear-down cycles with reader threads parked inside `RecieveSync`, the shape a reconnect loop has; the rest of the QUIC tests end in `std::_Exit(0)` and so never run a `ClientQUIC` destructor
 - WebTransport echo (`ShouldEchoWebTransport`) — extended-CONNECT acceptance, draft-02 SETTINGS, bidi data stream framing (`WT_STREAM 0x41` + session-id varint), and byte-for-byte echo
 - HTTP/1.1 wire format (`ShouldParseHTTP1`) — serialisation, incremental parsing fed one byte at a time, chunked bodies with trailers, pipelining, interim 1xx, HTTP/1.0 and HEAD framing, and the malformed inputs the parser is required to reject
 - HTTP/1.1 round-trip (`ShouldSendRecieveHTTP1`) — routing, query strings, HEAD, 404 and a throwing handler

project.cpp

@@ -149,6 +149,7 @@ extern "C" Configuration CrafterBuildProject(std::span<const std::string_view> a
         cfg.AddTest("ShouldSendRecieveQUICDatagram").Dependencies({ &cfg });
         cfg.AddTest("ShouldSendRecieveQUICStream").Dependencies({ &cfg });
         cfg.AddTest("ShouldSurviveAbuseHTTP1").Dependencies({ &cfg });
+        cfg.AddTest("ShouldSurviveConnectionChurn").Dependencies({ &cfg });
     }
 
     return cfg;

tests/ShouldSurviveConnectionChurn/main.cpp

@@ -0,0 +1,136 @@
+//SPDX-License-Identifier: LGPL-3.0-only
+//SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®
+
+// Regression test for the connection-teardown race in ~ClientQUIC.
+//
+// QUICStream::Stop only *initiates* a graceful shutdown; the actual
+// MsQuicStreamClose happens later, from the terminal SHUTDOWN_COMPLETE
+// callback on an msquic worker thread. ~ClientQUIC used to call
+// MsQuicConnectionClose straight away, so a connection could be closed while
+// streams belonging to it were still open on the msquic side — which trips an
+// msquic bugcheck and aborts the process.
+//
+// Nothing else in the suite exercises this: every other QUIC test ends in
+// std::_Exit(0) and so never runs a ClientQUIC destructor. The shape that
+// breaks is a reconnect loop — build a connection, tear it down, build
+// another — which is exactly what this test does, `cycles` times.
+//
+// The blocked readers matter. Each inbound stream gets a thread parked inside
+// RecieveSync for the life of the connection (the shape a long-lived
+// streaming client has), so teardown happens with readers still inside the
+// receive path. An otherwise identical loop whose handler reads once and
+// returns does not reproduce.
+
+import Crafter.Network;
+import Crafter.Thread;
+import std;
+using namespace Crafter;
+
+namespace {
+    constexpr int cycles = 25;
+    constexpr int streamsPerConnection = 3;
+}
+
+int main() {
+    ThreadPool::Start();
+
+    // On a build where a teardown deadlocks rather than aborts, fail the test
+    // instead of hanging the whole suite.
+    std::thread watchdog([] {
+        std::this_thread::sleep_for(std::chrono::seconds(90));
+        std::println("timed out — a connection teardown never completed");
+        std::cout.flush();
+        std::_Exit(1);
+    });
+    watchdog.detach();
+
+    for (int i = 0; i < cycles; ++i) {
+        const std::uint16_t port = static_cast<std::uint16_t>(19200 + i);
+        const std::string alpn = "churn/1";
+
+        QUICServerCredentials serverCreds;
+        serverCreds.selfSigned = true;
+
+        std::mutex serverMutex;
+        std::vector<QUICStream> serverStreams;
+        ClientQUIC* accepted = nullptr;
+
+        auto listener = std::make_unique<ListenerQUIC>(
+            port, alpn, serverCreds, [&](ClientQUIC* peer) {
+                std::lock_guard lock(serverMutex);
+                accepted = peer;
+                for (int s = 0; s < streamsPerConnection; ++s) {
+                    QUICStream stream = peer->OpenStream(/*unidirectional=*/true);
+                    const char payload[] = "hello";
+                    stream.SendSync(payload, sizeof(payload) - 1, /*finish=*/false);
+                    serverStreams.push_back(std::move(stream));
+                }
+            });
+        listener->ListenAsyncAsync();
+
+        QUICClientCredentials clientCreds;
+        clientCreds.insecureNoServerValidation = true;
+
+        {
+            ClientQUIC client(std::string("localhost"), port, alpn, clientCreds);
+
+            std::mutex clientMutex;
+            std::condition_variable clientCv;
+            std::vector<std::thread> readers;
+            int started = 0;
+
+            client.OnStream([&](QUICStream stream) {
+                auto shared = std::make_shared<QUICStream>(std::move(stream));
+                std::thread reader([shared] {
+                    try {
+                        while (true) (void)shared->RecieveSync();
+                    } catch (...) {
+                        // Connection closed.
+                    }
+                });
+                std::lock_guard lock(clientMutex);
+                readers.push_back(std::move(reader));
+                ++started;
+                clientCv.notify_all();
+            });
+
+            {
+                std::unique_lock lock(clientMutex);
+                clientCv.wait_for(lock, std::chrono::seconds(5), [&] {
+                    return started == streamsPerConnection;
+                });
+                if (started != streamsPerConnection) {
+                    std::println("cycle {}: only {} of {} streams arrived",
+                                 i, started, streamsPerConnection);
+                    return 1;
+                }
+            }
+
+            client.Stop();
+            for (std::thread& reader : readers) {
+                if (reader.joinable()) reader.join();
+            }
+            // `client` is destroyed here, once the readers have unwound.
+        }
+
+        {
+            std::lock_guard lock(serverMutex);
+            // Deliberately the other order from the client side: destroy the
+            // connection while the app still holds its stream wrappers, so
+            // ~ClientQUIC has to cope with streams that are open as far as
+            // msquic is concerned.
+            delete accepted;
+            accepted = nullptr;
+            serverStreams.clear();
+        }
+        listener->Stop();
+        listener.reset();
+    }
+
+    std::println("survived {} connection teardowns", cycles);
+    std::cout.flush();
+    // Skip the static-dtor cleanup: msquic's RegistrationClose blocks until
+    // every connection it ever opened is fully drained, which the suite does
+    // not need to wait on. Everything this test asserts has already happened.
+    std::_Exit(0);
+}