CultLib/native/GameCult.Mesh.Quic.Native/README.md

GameCult.Mesh.Quic.Native

One MsQuic body for every CultMesh host that is not .NET: two roles (provider and consumer), two platforms (Windows x64 and Linux x64), and no callbacks across the host boundary.

The bridge owns MsQuic registration, configuration, listener, connection and stream handles, TLS credential loading, the cultmesh-state-v1 ALPN, the 1-byte-kind plus 4-byte-LE-length QUIC stream framing, and one event queue per runtime. It owns transport and nothing else: it never decodes a CultMesh frame, never decides delivery semantics, never coalesces, never reconnects, and in the v2 path never decides whether to trust a certificate. Frame meaning stays in GameCult.Mesh and in the TypeScript codec; trust stays with the host.

No host callbacks

Every crossing is the host calling in, including the one blocking wait. MsQuic's worker threads only ever push onto the queue and wake that wait, so no host runtime is called from a thread it does not own. That is what lets one binary serve a Node process through FFI and a Unity player through P/Invoke without either one's threading rules leaking into the other.

It is also why nothing here includes a Node header, a Unity header, or a JavaScript engine: the bridge does not know what is on the other side.

Two ABIs

v2 is the runtime-neutral queue API, and the one new hosts should use. It is stated once, in include/cultmesh_quic_native.h: the 64-byte event struct with its field order and asserted offsets, the thirteen exports with their signatures, the id and return-code conventions, the object lifetime rules and the threading rules. That file is the contract. This README does not restate it, and where the two ever disagree the header is right.

A host that can include it should. A host that cannot — koffi, Unity's P/Invoke — declares the same thing in its own FFI and is checked against the header by a test rather than by eye.

Two things worth reading before writing a host, because they are easy to get wrong from the outside:

• Return codes are negative on a bad call, on every platform. -1 is a bad call, -2 a rejected argument, <= -1000 a MsQuic refusal. QUIC_STATUS itself is not portable — a negative HRESULT on Windows, a positive errno on POSIX — so it never reaches a host; cultmesh_quic_last_status hands over the raw value for diagnostics and nothing else.
• cultmesh_quic_runtime_close quiesces. It marks the runtime closing, wakes every blocked cultmesh_quic_next_event, and waits for every in-flight call to return before it frees anything. No host call may begin after it starts.

A client connection defers certificate validation: the bridge indicates the certificate, emits event 3 carrying the DER, and answers MsQuic only when the host calls cultmesh_quic_connection_certificate_complete. If the host never answers, MsQuic's 10-second handshake timeout closes the connection and event 4 reports it. Providers load their certificate as PKCS12; the advertised cert-sha256 pin is computed by the host from that same PKCS12, not here.

v1 is the five exports the shipped Unity package imports by name (cultmesh_quic_open, _state, _poll, _error, _close). They are Windows only, matching CultMeshNativeQuicRealtimeTransport.CanConnect, and are implemented on top of a private v2 runtime holding one connection. They decide nothing the v2 path does not, with one exception: a v1 connection carries a SHA-256 pin that is compared here, in C, because that is the contract the managed connector was built against. A v2 connection never carries one.

Building

Windows x64, from the repo root:

powershell -File scripts/build-quic-native.ps1

MsQuic comes from Microsoft.Native.Quic.MsQuic.OpenSSL 2.5.9, pinned twice: the NuGet zip by digest and size, and the msquic.dll inside it by digest and size, because the archive is what the download is checked against and the DLL is what actually ships beside the bridge. The OpenSSL flavour rather than Schannel because Schannel's MsQuic refuses QUIC_CREDENTIAL_TYPE_CERTIFICATE_PKCS12, which is the only credential type a provider has on both platforms.

The build uses MSVC with /Brepro so that a build reproduces itself: the link timestamps are dropped, and building the same source twice gives the same bytes. It links the CRT statically (/MT), because a Node or Unity host without the Visual C++ redistributable cannot load a DLL that imports vcruntime140.dll, and the failure it reports names no missing runtime; the bridge carries its own.

The committed Unity plugin (unity/org.gamecult.cultlib/Runtime/Plugins/x86_64/gamecult_mesh_quic_native.dll) is this build: 302,080 bytes, /MT, OpenSSL MsQuic, no CRT import. It replaced an older 40,448-byte build — before /MT and before the move off Schannel, still importing VCRUNTIME140.dll and MSVCP140.dll — at the CultLib 1.0.60 / Studio 1.4.0 release.

Linux x64, on a Debian 13 host:

scripts/build-quic-native.sh

MsQuic comes from Microsoft's Debian 13 pool as a pinned .deb, and the POSIX headers from the msquic source tree at the matching tag; all four downloads are verified by SHA-256. The bridge is linked with -fvisibility=hidden so only the v2 exports leave the .so, and with RPATH $ORIGIN so the libmsquic.so.2 shipped beside it resolves without being installed system-wide.

A Linux host still needs MsQuic's own runtime dependencies present: libssl3t64, libnuma1, libxdp1, libnl-route-3-200.

The development loop for it is one committed image, scripts/quic-native-linux-dev.Dockerfile, pinned to the same debian:13 digest the release workflow builds in. It carries the toolchain, MsQuic's runtime dependencies, and setarch, because a sanitizer build of the runtime-lifetime scenarios needs personality(ADDR_NO_RANDOMIZE) and a container that cannot ask for that cannot run them:

docker build -t cultlib-quic-native-dev -f scripts/quic-native-linux-dev.Dockerfile scripts
docker run --rm --security-opt seccomp=unconfined -v "${PWD}:/src" -w /src cultlib-quic-native-dev bash -lc "
  scripts/build-quic-native.sh
  cmake -S native/GameCult.Mesh.Quic.Native -B artifacts/quic-native-tests/linux-x64 -G Ninja \
    -DCMAKE_BUILD_TYPE=Release -DCULTMESH_QUIC_BUILD_TESTS=ON -DCULTMESH_QUIC_DEBUG_ASSERTS=ON \
    -DMSQUIC_INCLUDE_DIR=\$(pwd)/artifacts/dependencies/msquic-linux-2.5.9/include \
    -DMSQUIC_LIB_DIR=\$(pwd)/artifacts/dependencies/msquic-linux-2.5.9/package/usr/lib/x86_64-linux-gnu
  cmake --build artifacts/quic-native-tests/linux-x64
  for scenario in closerace holdclose holdtimeout polltimeout pollbusy pollhammer zerotimeout payloadfit latecall waitseam; do
    setarch -R artifacts/quic-native-tests/linux-x64/bin/cultmesh_quic_native_tests \"\${scenario}\" || exit 1
  done
"

Both lines are run from the repository root, and the mount is that root wherever it is: ${PWD} in PowerShell, $(pwd) in a POSIX shell. MSQUIC_INCLUDE_DIR and MSQUIC_LIB_DIR need $(pwd) too, even though the cmake invocation itself already runs from /src: CMake resolves a relative path passed as a cache variable against the CMakeLists.txt that consumes it (native/GameCult.Mesh.Quic.Native), not against the directory cmake was invoked from, so a bare artifacts/... here looks for the dependency one level too deep and fails the compile before it reaches the loader. The test target's own build now copies libmsquic.so.2 from MSQUIC_LIB_DIR beside the built binaries, so nothing else here needs the packaged output directory scripts/build-quic-native.sh produces. CULTMESH_QUIC_BUILD_TESTS is off in the shipped configuration (see the CMakeLists.txt option comment); it turns on the scenario runner tests/cultmesh_quic_native_tests.cpp compiles into, and CULTMESH_QUIC_DEBUG_ASSERTS turns on both the bridge's internal invariant assertions and the four scenarios (holdclose, latecall, holdtimeout, waitseam) that need the development seam in section 7 of the header. Each scenario name is a positional argument to the built binary; run them individually to bisect a failure, or all ten as shown to cover the runtime-lifetime rules.

A Windows clone made before .gitattributes kept shell scripts at LF still has scripts/build-quic-native.sh with carriage returns, and pulling does not fix it: the script's content did not change, so git neither rewrites it nor reports it modified. The container then dies at once on the interpreter bash\r. From the repository root, in either shell, this checks the script out again under the current attributes:

git rm --cached -q scripts/build-quic-native.sh; git checkout HEAD -- scripts/build-quic-native.sh

--security-opt seccomp=unconfined is load-bearing, not caution. A ThreadSanitizer configuration needs the process's address space where it expects it, so a TSan run must be re-executed under setarch -R, which asks the kernel for personality(ADDR_NO_RANDOMIZE). Docker's default seccomp profile denies that call. Without it ThreadSanitizer dies before main with "unexpected memory mapping" — a configuration that never starts, not a scenario that passed.

A win32-x64 build of the scenario runner needs the checkout somewhere short — near a drive root rather than under a deep temporary directory. MSVC builds the bridge and its scenario runner through MSBuild, whose file tracker gives out on long paths, and the build then fails outright rather than naming the path as the cause.

Where an artifact was built is part of what it is. The Linux binary is linked against Debian 13's glibc, so a build from anywhere else is a different artifact whatever the file name says.