mctp server

Platform-independent MCTP server core (openprot_mctp_server). Ported from the Hubris mctp-server, with OS-specific IPC (sys_reply, Leased, RecvMessage) stripped out so the router/handle/timeout logic can be host-tested without a kernel.

 target/<soc>/tests/.../main.rs          ← platform loop (Pigweed IPC, I2C, timers)
        │  wraps this crate via services/mctp/server-runtime
        ▼
 server/        Server<S: Sender, OUTSTANDING> — no_std, no OS deps
        │  dispatch.rs: decode wire::MctpRequestHeader → call Server → encode response
        ▼
 server.rs       mctp-lib::Router — handle allocation, routing, timeouts
        │  Sender (from mctp-lib)
        ▼
 transport-i2c/ (or any Sender impl)

server/dispatch never touch IPC, syscalls, or a clock source directly — the platform layer drives everything through now_millis and callback closures. See services/mctp/server-runtime for the Pigweed kernel loop that wraps this crate.

Modules

Module Role

server.rs (Server<S, OUTSTANDING>) Wraps mctp_lib::Router. req/listener/set_eid/get_eid/send mirror the wire ops directly. try_recv + register_recv implement non-blocking-then-deferred receive, one outstanding receive per handle; cancel_recv withdraws one. update(now_millis, recv_buf) advances the router and resolves any outstanding receives that are ready or timed out. next_recv_deadline() is the only timer the server asks its driver for.

dispatch.rs (dispatch_mctp_op, drive_pending) Decodes a raw IPC request (wire::MctpRequestHeader) and calls the matching Server method, encoding the reply in place. dispatch_mctp_op returns DispatchOutcome::Reply(n) when a response is ready immediately, or DispatchOutcome::Pending { handle } when a Recv was registered for later. A Recv that cannot be registered is answered with the error, never left pending. drive_pending is called after every event and no later than next_recv_deadline(); it calls on_ready(handle, response_bytes) once per handle that became ready.

Module	Role
`server.rs` (`Server<S, OUTSTANDING>`)	Wraps `mctp_lib::Router`. `req`/`listener`/`set_eid`/`get_eid`/`send` mirror the wire ops directly. `try_recv` + `register_recv` implement non-blocking-then-deferred receive, one outstanding receive per handle; `cancel_recv` withdraws one. `update(now_millis, recv_buf)` advances the router and resolves any outstanding receives that are ready or timed out. `next_recv_deadline()` is the only timer the server asks its driver for.
`dispatch.rs` (`dispatch_mctp_op`, `drive_pending`)	Decodes a raw IPC request (`wire::MctpRequestHeader`) and calls the matching `Server` method, encoding the reply in place. `dispatch_mctp_op` returns `DispatchOutcome::Reply(n)` when a response is ready immediately, or `DispatchOutcome::Pending { handle }` when a `Recv` was registered for later. A `Recv` that cannot be registered is answered with the error, never left pending. `drive_pending` is called after every event and no later than `next_recv_deadline()`; it calls `on_ready(handle, response_bytes)` once per handle that became ready.

Key invariants

No heap, no OS primitives. #![no_std]; MAX_LISTENERS/MAX_REQUESTS/ MAX_OUTSTANDING (ServerConfig) bound all allocation via heapless.
Payload limit is stack-configured. ServerConfig::MAX_PAYLOAD is sourced from mctp-estack via mctp_lib::config::MAX_PAYLOAD (tune with MCTP_ESTACK_MAX_MESSAGE at build time).
One response buffer, reused per call. drive_pending's on_ready callback must send response_bytes before returning — the buffer is overwritten for the next ready handle.
Protocol-agnostic. Any protocol that implements mctp::MsgType framing (SPDM, PLDM, echo) goes through the same Server/dispatch path; nothing here is aware of SPDM or PLDM specifically.

Test Coverage

bazelisk test //services/mctp/server:mctp_server_dispatch_test
bazelisk test //services/mctp/server:mctp_server_unit_test
bazelisk test //services/mctp/server:mctp_server_integration_test
bazelisk test //services/mctp/server:mctp_server_echo_test

All four are host-buildable (no kernel/QEMU); tests/common/mod.rs provides shared fixtures (BufferSender, DirectClient, etc.). See services/mctp/README.md for the full MCTP host test suite.

The kernel loop around this crate (services/mctp/server-runtime) is covered on QEMU, no board or I2C needed:

bazelisk test --config=virt_ast10x0 //target/ast10x0/tests/mctp/multi_protocol:multi_protocol_qemu_test

This is the multi-client case the runtime exists for: one server process serving two protocol tasks (SPDM- and PLDM-typed echo stand-ins) on separate IPC channels, with both parked in Recv at once, plus the drop-on-no-listener timeout path.