C语言MCP服务器

mcp-c

mcp-c is a small, transport-neutral C server for MCP protocol revision 2026-07-28. It targets POSIX and Zephyr/ESP32 and keeps the request hot path bounded and allocation-free inside the semantic core.

Implemented MCP methods:

• server/discover
• tools/list
• tools/call

The 2026 revision is stateless: there is no initialize handshake, protocol session, or Mcp-Session-Id. Every request carries its version and client capabilities in params._meta.

Build and run

Requirements: CMake, Ninja or Make, and a C99 compiler. libcoap is detected automatically; without it, HTTP and stdio still build.

make                  # one-command build
./scripts/run.sh      # one-command build + HTTP run

The default endpoint is http://127.0.0.1:8080/mcp. Run HTTP and CoAP together with:

./scripts/run.sh --transport all

Run all reproducible checks, including ASan/UBSan and local HTTP/CoAP integration:

make prove

The proof command writes a machine-readable artifact to build-proof/proof.json containing the test status, binary size, and SHA-256. Generate repeatable HTTP/CoAP latency and size measurements with make benchmark; the CSV is written to build-benchmark/results.csv.

Try it

curl http://127.0.0.1:8080/mcp \
  -H 'Content-Type: application/json' \
  -H 'Accept: application/json, text/event-stream' \
  -H 'MCP-Protocol-Version: 2026-07-28' \
  -H 'Mcp-Method: server/discover' \
  --data-binary '{"jsonrpc":"2.0","id":1,"method":"server/discover","params":{"_meta":{"io.modelcontextprotocol/protocolVersion":"2026-07-28","io.modelcontextprotocol/clientCapabilities":{}}}}'

The Linux and Zephyr examples register the same tools: echo, sensor.read_temperature, servo.set_angle, and servo.get_angle. On Linux and native_sim the servo is deterministic simulated state. The ESP32 build uses LEDC PWM on GPIO18 with a 20 ms period and a bounded 0–180 degree input.

ESP32

With the Zephyr SDK installed (validated with 0.17.4), the first invocation creates a local west workspace, checks out pinned Zephyr v4.3.0, and installs the Python dependencies. Build and flash in one command without storing Wi-Fi credentials in Git:

WIFI_SSID='your-network' WIFI_PASS='your-password' \
  ./scripts/build-zephyr.sh --flash

Add --monitor to keep the serial console open. The log prints the assigned IP and MCP URL. Connect the servo signal to GPIO18 and use a suitable external 5 V supply with a common ground; do not power a servo motor from the ESP32's 3.3 V pin.

After flashing, reproduce discovery plus a servo.set_angle/get_angle round-trip (the script restores 90 degrees) and write an ESP32 proof artifact:

MCP_DEVICE_IP=192.168.x.x make prove-esp32

Architecture

application tools
      ↓
MCP 2026-07-28 semantic core + bounded JSON
      ↓
HTTP transport | stdio transport | CoAP adapter | MQTT 5 binding
      ↓
BSD/Zephyr sockets | libcoap | Zephyr MQTT adapter
      ↓
optional TLS/DTLS provider

mcp_server_handle() accepts one complete JSON-RPC message and returns one complete response. mcp_request_ctx_t carries only opaque per-exchange data; the core contains no sockets, CoAP tokens, MQTT topics, or broker handles. Multiple bounded-poll transports may serve one registry in the same loop.

JSON is tokenized by a pinned MIT-licensed jsmn copy. IDs remain strings or integers exactly as received. The bounded writer escapes application text and fails closed on overflow. Limits such as MCP_MAX_JSON_TOKENS, MCP_MAX_TOOLS, request size, response size, and MQTT replay-cache size are configurable.

Transport status

HTTP SSE responses, subscriptions/listen, authorization, DTLS/TLS configuration, and multi-round-trip input_required results are not yet implemented. CoAP and MQTT are custom IoT bindings, not standard MCP transports. See the architecture notes and the transport documents for precise behavior.

The implementation tracks the official MCP 2026-07-28 specification and its Streamable HTTP binding.

License

MIT. The optional external libcoap dependency is BSD-2-Clause; jsmn retains its MIT license under third_party/jsmn/.