cnip_app.c

// This file contains two sketches for the end-user networking API that implements
// a simple WS service: WS message with JSON input {"pin": 12, "val": 0}, and JSON response {"status": true}

// WS handler, streaming API (think AVR)
// We don't buffer an incoming WS message. Instead, we feed
// TCP stack, and user handler, byte-by-byte.
// Some important values from the parsed HTTP header gets stored
// and passed to the user handler.
void ws_handler(struct conn *c, int event, size_t content_len, size_t receided_so_far, uint8_t byte) {
  if (event == EVENT_INCOMING_BYTE) {
    // Assume we have some sort of a streaming JSON parser. We feed it
    if (received_so_far == 0) {
      struct context *context = calloc(1, sizeof(*context));
      set_user_data(c, context);
    }
    struct context *context = get_user_data(c);
    // E.g. for parsing JSON, this state machine is quite complex, see any JSON library.
    switch (context->state) {
      case STATE_FOO:
        ....
        break;
      case BAR:
        ...
        break;
      case BAZ:
        ...
        break;
      case BLAH:
        ...
        break;
      default:
        ...
        break;
    }
    
    if (received_so_far >= content_len) {
      if (context->pin < 0 || context->val < 0) ....
      gpio_write(context->pin, context->value);
      conn_send("{\"status\":true}");
      free(context);
      set_user_data(NULL);
    }
  } else if (event == EVENT_ABNORMAL_TERMINATION) {
    ...
  }
}

// API handler, buffered API.
// We don't need an event here, cause we call this only when full WS message gets buffered.
void ws_handler(struct conn *c, char *buf, size_t len) {
  int pin = json_fetch_int(buf, len, "$.pin");
  int val = json_fetch_int(buf, len, "$.val");
  gpio_write(pin, val);
  conn_send("{\"status\":true}");
}