rmw_transport.h File Reference

Runtime-pluggable custom transport vtable (Phase 115.A). More...

#include <stddef.h>
#include <stdint.h>
#include "nros/rmw_ret.h"

Include dependency graph for rmw_transport.h:

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Data Structures
struct	nros_transport_ops_t

Macros
#define	NROS_TRANSPORT_OPS_ABI_VERSION_V1   ((uint32_t)1)

Functions
rmw_ret_t	nros_rmw_cffi_set_custom_transport (const nros_transport_ops_t *ops)

Detailed Description

Runtime-pluggable custom transport vtable (Phase 115.A).

Lets a consumer plug a custom byte-pipe (USB-CDC, BLE, RS-485, semihosting bridge, ring-buffer loopback, etc.) at runtime — no board-crate, Cargo-feature, or rebuild required. The active RMW backend (zenoh-pico, XRCE, dust-DDS, …) consumes this vtable as the read/write surface for every wire frame.

Mirrors micro-ROS's rmw_uros_set_custom_transport(framing, params, open, close, write, read) and is the C-side view of the Rust-side nros_rmw::NrosTransportOps (single #[repr(C)] layout; no parallel definitions to drift).

Threading contract (v1)

• read and write may NOT be invoked concurrently from different threads. The active backend serialises them through its drive-io / spin-once path.
• Callbacks may NOT be invoked from interrupt context. Wrap ISR-driven hardware in a queue + read poller.
• user_data is opaque to the runtime — its Send/Sync discipline is the caller's responsibility. The four fn pointers are always thread-safe by construction.

Versioning

• abi_version MUST be set to NROS_TRANSPORT_OPS_ABI_VERSION_V1 (1). Mismatched values are rejected at registration time with NROS_RMW_RET_INCOMPATIBLE_ABI and the previously-installed transport (if any) stays untouched.
• Major bump (V1 → V2): existing fields removed or reordered. Old consumers fail cleanly via the version check.
• Minor bump: struct gains an appended fn pointer. Version stays the same; new consumers detect the new fn via the size of the trailing _reserved region. Today there is none — V1 is the inaugural version.

See also

• Rust API: nros_rmw::custom_transport::{NrosTransportOps, set_custom_transport, peek_custom_transport, take_custom_transport} (the canonical Rust-side surface; this header mirrors its #[repr(C)] layout exactly).
• Porting guide: book/src/extending/custom-transport.md — when to use, full Rust/C/C++ examples, framing per backend.

Macro Definition Documentation

NROS_TRANSPORT_OPS_ABI_VERSION_V1

#define NROS_TRANSPORT_OPS_ABI_VERSION_V1   ((uint32_t)1)

Current ABI version of nros_transport_ops_t. Consumers MUST fill this in before passing the struct to rclc_set_custom_transport.

Function Documentation

nros_rmw_cffi_set_custom_transport()

rmw_ret_t nros_rmw_cffi_set_custom_transport

(

const nros_transport_ops_t *

ops

)

Install a custom transport for subsequent session opens.

The struct's contents are copied internally; the caller may stack-allocate. To clear the slot, pass NULL.

The fn pointer is exported from the nano-ros C staticlib (packages/api/nros-c/), where it forwards to the nros-rmw-cffi registry. C++ consumers should include <rclcpp/transport.hpp> (from nros-cpp) which calls this function under the hood.

Return values

NROS_RMW_RET_OK	on success (transport installed or cleared).
NROS_RMW_RET_INCOMPATIBLE_ABI	when ops is non-NULL but ops->abi_version does not match NROS_TRANSPORT_OPS_ABI_VERSION_V1. The previously installed transport (if any) is left untouched.