mcanbus workspace

This repository hosts two crates that share a common SocketCAN core:

Crate	What it is
mcanbus	Library: high-performance SocketCAN bindings for Linux (CAN 2.0 + CAN-FD, batched I/O, netlink).
socketcan-mcp	Binary: Model Context Protocol server that exposes SocketCAN to AI agents.

Both crates are MIT-licensed and meant to be lifted into other projects. They are extracted from the production code of mcandump and mcangen, and built by the makers of CANsole — a forthcoming desktop CAN debugger for working engineers.

What an agent does with this

socketcan-mcp turns SocketCAN into a typed RPC surface — agents talk to a CAN bus through structured tool calls, not by parsing candump output. A short transcript from a real session against a Scania S8 truck:

Me: I plugged a Scania S8 onto can0. Can you find its VIN?

Agent: Standard KWP2000 read — service 0x1A, local identifier 0x90, ISO-15765 extended addressing. Tester 0xF9 to target ECU 0x00.

Tool call:

isotp_request(iface="can0", tx_id="18DA00F9", rx_id="18DAF900",
              extended=true, payload="1A90")

Result:

{ duration_ms: 1,
  response: { len: 19,
    hex:   "5A905953325236583430303035343132373335",
    ascii: "Z.YS2R6X40005412735" } }

The leading 5A 90 is the KWP positive-response header (echo of service 1A + LID echo). The remaining 17 bytes are the VIN: YS2R6X40005412735. YS2 is Scania's manufacturer prefix; the rest decodes to an R-series cab with 6×4 drive configuration.

That same interaction took four MCP tool calls before isotp_request existed (one capture, one Single Frame, one Flow Control, one to read the Consecutive Frames). The library now handles segmentation and Flow Control; the agent handles the meaning.

For contrast, the shell-driven version is isotpsend and isotprecv running in two background processes, with the agent parsing line-by-line text output and racing stdout buffering for timing — every CAN frame becomes a string, every reply becomes a regex, every multi-frame transfer becomes process orchestration. Most of the agent's context window ends up on plumbing instead of on the diagnostic question. The MCP path is a single typed call returning a typed result.

See socketcan-mcp/ for the full tool list and a Claude Desktop / Claude Code config snippet.

Building

cargo build --release

cargo build will produce both the library and the MCP server binary.

Testing

A virtual CAN interface is required for most tests:

sudo ip link add dev vcan0 type vcan && sudo ip link set up vcan0
cargo test

License

MIT for everything in this workspace.