fips/testing/native-api/README.md

Native Datagram API Harness

Checks for the experimental native datagram API: a client process opens a flow to a remote pubkey over a Unix socket, receives a file descriptor, and sends and receives datagrams on it with no IPv6 emulation and no TUN device.

Design of record: design/native-api/v1-datagram-experiment.md in the project workspace, which is a separate tree from this repository. The feature is off by default and Unix only.

Shape

The client runs in its own container, reaching the daemon through a bind-mounted /run/fips. That is the real deployment shape — a separate process with its own filesystem opening the socket — rather than a test speaking to the daemon from inside the daemon's container. It also makes the access policy observable: the host sees the socket file and reads its mode directly.

The step scripts are Python rather than Rust so a check changes without rebuilding the daemon, which is what keeps the outside-in loop fast. That buys speed at the cost of covering nothing of the Rust surface a caller links against, so two compiled programs run here as well, both built on fips::native::client: examples/native-echo.rs, which arrived with A5 and serves the echo check, and examples/native-surface.rs, which walks the whole public surface against a live daemon.

The table covers this directory and the two example programs the driver runs.

File	What it is
test.sh	The driver. Holds the scenarios and the pass/fail accounting.
client.py	A thin RPC client. Runs a script of steps over one connection and checks the replies.
control.py	A thin control-socket client, used to read show_native_flows back while a flow is open.
node.yaml	One node with the API enabled, no TUN, no DNS, no peers. Turns the debug commands on.
node-api-off.yaml	The same node with the API disabled, for the default-off check.
node-debug-off.yaml	The API enabled and the debug commands left at their default, for the gate check.
../../examples/native-echo.rs	The echo server for check_echo_round_trip. A program shape to copy.
../../examples/native-surface.rs	The surface walk for check_surface_walk. An assertion harness, not a shape to copy.

Running

cargo build --release --bins --examples   # the driver refuses a stale binary
./testing/native-api/test.sh

FIPS_TEST_IMAGE is used when set, which is how ci-local.sh passes its per-run image. There is deliberately no fips-test:latest to fall back on, so a consumer that stops reading the variable fails loudly. Without it the driver builds a minimal image from the locally compiled binary.

The driver refuses to run against a stale binary. Three binaries are built or read from this tree, the daemon and the two examples, and each is probed against what it is actually built from: src/ plus Cargo.toml for all three, this directory's *.py because the harness client is bind-mounted live rather than built in, and, for an example, its own .rs and no other. A guard rooted only at src/ would let a stale example pass a check written about new code. A stale binary is the worst outcome available here: the checks would run and report a verdict about code that is not the working tree's.

An example is probed against its own source rather than all of examples/ because cargo does not relink target/release/fips when only an example changes. Probing the daemon against every example would leave it permanently older than a just-edited one, and the rebuild the refusal prescribes would not clear the condition.

All three binaries must come from one profile directory. resolve_image refuses a profile that holds only the daemon, which is what a bare cargo build --release leaves behind.

Increments

The API is built outside-in, and this harness grows with it. Each increment's checks must pass before the next one starts.

#	What it covers	State
A1	The socket, its access mode, the line framing, the command validation, the reserved-port refusals, and that the API is off by default	present
A2	Descriptor passing over SCM_RIGHTS, message boundaries, poll readability, close reaching the daemon, flow isolation	present
A3	Port ownership across clients, listening and accepting, the dispatch order, and reclaim when a descriptor closes	present
A4	The end-to-end path between two nodes, and that a queued datagram is not IPv6-compressed	present
A5	Counters, show_native_flows read back over the control socket, the Rust client module and echo example, and the debug-command gate	present
A6	Every public item of fips::native::client walked against a live daemon: the five setup entry points, all eight ToFipsAddr spellings, the deadlines, non-blocking mode, the descriptor traits, and the payload limit	present

The "stub": true marker is gone. It meant "this flow reaches no peer", and after A4 every flow does. max_payload is now the real limit — the transport MTU less the FIPS encapsulation and the port header, 1362 bytes on a 1472-byte transport — and the end-to-end check asserts that number rather than accepting whatever is reported.

The tightening it existed for happened three times. A1's connect checks failed the moment A2 began returning a descriptor, because client.py treats an unannounced descriptor as a defect rather than ignoring it. A1's accept and reject checks failed when A3 gave those commands a real registry, since a flow no listener announced became a refusal. And the remaining stub assertions failed at A4 when the field disappeared. Checks that had quietly kept passing would have been worth nothing.

The accept and reject commands are gone, and so is the incoming event. A listener now returns its own descriptor, so it is pollable, accepting is one recvmsg on it that carries the arriving flow's descriptor, and refusing a flow is closing that descriptor. The command socket carries replies only, in command order. A step names a listener descriptor with keep_listener and takes flows off it with an accept step; every descriptor a reply carries must be named, or the run fails rather than dropping a flow silently.

The backlog is no longer the bound a client sees. It bounds arrivals the daemon has announced and not yet wired, and the daemon drains that queue itself, so a listener that never accepts is bounded by its send buffer and by node.native_api.max_flows instead. check_backlog_is_not_the_clients_bound asserts the change; the drop paths behind the new bound are covered by the daemon's own tests, because neither is a number a shell check can produce.

One peer is held to a quarter of max_flows as inbound flows, 64 at the default. check_one_peer_is_held_to_its_share accepts each arrival as it is announced and closes it unwritten, which the daemon pins until the listener closes, so the share rather than the send buffer decides the 65th arrival.

Flow identifiers are assigned by the node and keep counting up for its lifetime. A check must capture one with keep_flow rather than assume a literal, or it holds only for the first flow the daemon ever made.

The surface walk

check_surface_walk runs examples/native-surface.rs against the shared single node, last among the single-node checks. Its subject is the Rust surface rather than the wire: until it existed, FipsStream::connect, connect_from, connect_at, FipsListener::bind and bind_at had no coverage of any kind, and every other public item was exercised only against the hand-written stand-in daemon in the crate's unit tests. That stand-in has already hidden a real defect once, by being kinder than the daemon, which is why the walk talks to the real one.

The node starts each ephemeral port search at a random port, so the walk asserts only that its own ephemeral ports are >= 49152, and takes its named ports from the otherwise unused 4800-4809 band.

The check asserts three things, not one: that the container exited 0, that its completion line is there, and that the count in that line equals SURFACE_ASSERTIONS in test.sh. The third is the anti-silence measure. The binary prints the recorder's own counter rather than a literal, so an assertion block that stopped running — a #[cfg] gate that no longer matches, an early return — still exits 0 and still prints the line, and only the count betrays it. The number is deliberately brittle: adding an assertion must force an edit in test.sh, so the two cannot drift apart quietly.

A hang has to become a red, and has to name itself. The walk's own subjects fail by blocking forever: a read deadline never applied to the descriptor, a set_nonblocking that did nothing. The binary arms a 30-second watchdog that prints the assertion it was in and exits 1, and run_surface_at bounds the container at 60 seconds as a backstop for a wedge before that thread is armed.

timeout 60 docker run is not that backstop, which a break-check measured rather than a reading of the manual. timeout signals the docker client, the client proxies SIGTERM to the container, and the walk is PID 1 there with no handler for it, so the kernel discards the signal: the container was still up five minutes after the bound passed and docker run never returned. The helper runs the container detached, polls its state, and removes it by force, since docker rm -f is a SIGKILL and PID 1 cannot discard that.

The two-node check

check_end_to_end is the only check that runs more than one node. It derives two identities with testing/lib/derive_keys.py, brings both up on their own docker network peered by npub, and sends a datagram from a client on one to a client on the other.

Three orderings are waited on explicitly rather than assumed, each because assuming it produced an intermittent failure:

• The link forms before either client runs, watched for by the spanning tree adopting a parent. Not by a peer-promotion log line: on this path — a configured peer, dialled outbound — that line is never emitted.
• The listener has bound its port before the sender starts, watched for in the listener's own output. Launching it first is not the same as it having registered.
• The client runs unbuffered (python3 -u). Without it the marker above never reaches the log file, so the wait cannot see it and every run fails at the gate meant to make the check reliable.

The payload is deliberately not a valid IPv6 packet, and it is sent before any session exists so it goes through the native pending queue. If a native datagram were ever routed through the TUN pending queue it would be handed to the IPv6 compressor, which would refuse it, and this check would fail. The trap is asserted rather than trusted.