Minimal X-Macro Bridge

A minimal framework in C to provide publish/subscribe facilities and message bridging across embedded devices. Mainly relies on X-Macros to generate code for each defined message type. There are no external dependencies, the entire library is header only and well under 200 lines of code.

Use Case

• Eliminate all boilerplate code required for messaging between embedded devices, takes care of:
  • Generation of Message IDs when converting to and from byte frames.
  • Generation of serialization/deserialization methods for each message type.
  • Calling the correct serialization/deserialization that correspond to each message type.
  • Calling the correct MessageHandlers when a certain message type is received.
• Publish/subscribe framework allows for consolidation of various callbacks across the system.
• Centralized and portable bridge message definitions allow generation of cross-platform communication.

Usage

1. Create header files defining message types and bridge messages, see bridge_def.h
2. In any one compilation unit, call the GEN_BRIDGE_IMPLEMENTATION() macro, see bridge_impl.c
3. BRIDGE_SUBSCRIBE_ENDPOINT() subscribes FrameEndpoints (to send serialized outbound message frames)
4. message_subscribe() subscribes MessageHandlers (to receive deserialized inbound messages)
5. Call bridge_receive_frame() on message frame receive, to deserialize and publish message to subscribed handlers.
6. Call message_publish(MsgType_subscribers, &msg, src_ctx) to publish message to all subscribed handlers.
7. If a FrameEndpoint is subscribed, it will deserialize the message and trigger its defined frame_handler.
8. See loop back test example.

Demo

First install GCC, then to test:

git clone --recurse-submodules https://github.com/wzli/mxbridge.git
cd mxbridge
make
./build/test

Output:

send original message a: {"a":20, "b":40}
received message a: {"a":20, "b":40} src_ctx 0x1 dst_ctx (nil)
loopback frame: id 0 len 10 buf 0x7ffd7e1432ee ctx (nil)
received message a: {"a":20, "b":40} src_ctx (nil) dst_ctx (nil)

send original message b: {"x":-2.5, "y":{"a":34, "b":-22}}
received message b: {"x":-2.5, "y":{"a":34, "b":-22}} src_ctx 0x1 dst_ctx (nil)
loopback frame: id 1 len 14 buf 0x7ffd7e1432ea ctx (nil)
received message b: {"x":-2.5, "y":{"a":34, "b":-22}} src_ctx (nil) dst_ctx (nil)