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WebSocketManager Controller (Native C Worker)

A pure-C port of the WebSocketManager controller for the NativeDllEngine. Demonstrates how to implement the worker ABI in C without the C# runtime or any FlatBuffers C++ runtime dependency.

Topic: command.websocketmanagercontroller Group: websocketmanagercontroller MIME type: application/x-nativedll

Architecture

Command Event (CloudEvent on command.websocketmanagercontroller)
  ↓
Dapr Pubsub → WorkManager → NativeDllEngine → Process (C export)
  ↓
main.c entry → command dispatch
  ↓
cloudevent_fb.c (hand-rolled FlatBuffer reader)
  ↓
commands.c handlers (9 command types)
  ↓
host->gateway_call (C ABI host callback, raw function pointer)
  ↓
Returns response FlatBuffer (WorkerResponse)

Building

cd dotnet
bash scripts/build_websocket_manager_controller.native.sh

The build script: 1. Compiles all .c files in src/ with cc -shared -fPIC -O2. 2. Outputs bin/native/worker.zip containing the shared library: 

worker.zip/
├── manifest.json
└── runtimes/<rid>/native/libcontroller.<so|dylib|dll>

The manifest.json declares abi_version: 1 and library: "controller".

Running

WORKER_B64=$(base64 -i bin/native/worker.zip | tr -d '\n')
curl -X POST http://localhost:25001/v1/workers \
  -H "Content-Type: application/json" \
  -d "{
    \"code_source\": {\"content\": \"$WORKER_B64\"},
    \"mime_type\": \"application/x-nativedll\",
    \"topic\": \"command.websocketmanagercontroller\",
    \"group\": \"websocketmanagercontroller\"
  }" | python3 -c "import sys,json; print(json.load(sys.stdin)['id'])" | xargs -I{} curl -X POST http://localhost:25001/v1/workers/{}/start

Files

File Purpose
src/main.c Process and FreeResult exports + command dispatch
src/commands.c 9 command handlers (create, subscribe, unsubscribe, publish, stop_publish, send_raw, list, disconnect, stop)
src/cloudevent_fb.c/.h Hand-rolled FlatBuffer reader for CloudEvent input
src/worker_resp_fb.c/.h Hand-rolled FlatBuffer writer for WorkerResponse output
src/json.c/.h Minimal JSON parser/builder for command envelope and base64
manifest.json Worker manifest (abi_version: 1, library: "controller")

Key Differences from the C# AOT Version

Aspect C# NativeAOT C
CloudEvent decode Vendored C# bindings (CloudEventCodec) Hand-rolled FlatBuffer reader
JSON parsing System.Text.Json Hand-rolled JSON parser
Gateway calls NativeApiGateway.InvokeAsync Direct host->gateway_call
Binary size ~1-2 MB (AOT runtime) ~30 KB
Dependencies Virtufin.Worker.DevKit NuGet libc only
Compile time ~30 s (NativeAOT) <1 s (cc -shared)

Limitations

This minimal C implementation focuses on demonstrating the ABI. A production C worker would need:

  • A proper FlatBuffer writer for result_event (currently only builds empty WorkerResponse or error_message).
  • Proper connection state tracking (currently handle_stop is a no-op).
  • More robust JSON parsing with full escape handling.
  • Thread-safe connection state if the engine calls Process concurrently from multiple threads.

See Also