CNIP API suggestion

cnip.h

// The stack has two API: low level and high level
// Low level: used to hook it up to a hardware, to send/receive MAC frames
// High level: used to implement network apps, like HTTP/MQTT client/servers.

// Low level
// A device code does something like this:
// 
// void cnip_mac_out(char *buf, size_t len) {
//   bitbang_to_ethernet(buf, len);  // Push outgoing frame to the network
// }
//
// for (;;) {
//  char frame[1500];
//  size_t n = receive_frame(frame, sizeof(frame)); 
//  cnip_mac_in(frame, n);    // Process incoming frame
//  cnip_poll(current_time);  // Process timers, and call user high level handlers
// }
void cnip_mac_in(char *buf, size_t len);  // Implemented by CNIP
void cnip_mac_out(char *buf, size_t le);  // Must be implemented by user
void cnip_poll(time_t now);               // Must be called periodically or on event

// High level API - for creating network applications/services
// Example usage:
// void my_fn(struct cn_connection *c, int ev, void *ev_data) {
//   switch (ev) {
//     case EV_READ:
//       serve_http(c, c->recv_buffer);
//       break;
//   }
// }
//
// cn_tcp_listen(0, 80, my_fn, &minecraft_server_data);
struct cn_connection {
  ... stuff like local/remote addresses, incoming and outgoing IO buffers
};
// User-defined callback function, called on various events
enum { EV_ERROR, EV_CONNECT, EV_ACCEPT, EV_READ, EV_WRITE, EV_CLOSE };
typedef void (*cnip_fn_t)(struct cn_connection *, int ev, void *ev_data);

struct cn_connection *cnip_tcp_listen(uint32_t ip, uint16_t port, cnip_fn_t fn, void *fn_data);
struct cn_connection *cnip_tcp_connect(uint32_t ip, uint16_t port, cnip_fn_t fn, void *fn_data);