struct wslay_event_callbacks {
    wslay_event_recv_callback                recv_callback;
    wslay_event_send_callback                send_callback;
    wslay_event_genmask_callback             genmask_callback;
    wslay_event_on_frame_recv_start_callback on_frame_recv_start_callback;
    wslay_event_on_frame_recv_chunk_callback on_frame_recv_chunk_callback;
    wslay_event_on_frame_recv_end_callback   on_frame_recv_end_callback;
    wslay_event_on_msg_recv_callback         on_msg_recv_callback;
};

recv_callback is invoked by wslay_event_recv() when it wants to receive more data from peer. The implementation of this callback function must read data at most len bytes from peer and store them in buf and return the number of bytes read. flags is always 0 in this version.

If there is an error, return -1 and set error code WSLAY_ERR_CALLBACK_FAILURE using wslay_event_set_error(). Wslay event-based API on the whole assumes non-blocking I/O. If the cause of error is EAGAIN or EWOULDBLOCK, set WSLAY_ERR_WOULDBLOCK instead. This is important because it tells wslay_event_recv() to stop receiving further data and return.

send_callback is invoked by wslay_event_send() when it wants to send more data to peer. The implementation of this callback function must send data at most len bytes to peer and return the number of bytes sent. flags is the bitwise OR of zero or more of the following flag:

It provides some hints to tune performance and behaviour.

If there is an error, return -1 and set error code WSLAY_ERR_CALLBACK_FAILURE using wslay_event_set_error(). Wslay event-based API on the whole assumes non-blocking I/O. If the cause of error is EAGAIN or EWOULDBLOCK, set WSLAY_ERR_WOULDBLOCK instead. This is important because it tells wslay_event_send() to stop sending data and return.

genmask_callback is invoked by wslay_event_send() when it wants new mask key. As described in RFC6455, only the traffic from WebSocket client is masked, so this callback function is only needed if an event-based API is initialized for WebSocket client use. The implementation of this callback function must fill exactly len bytes of data in buf and return 0 on success. If there is an error, return -1 and set error code WSLAY_ERR_CALLBACK_FAILURE using wslay_event_set_error().

on_frame_recv_start_callback is invoked by wslay_event_recv() when a new frame starts to be received. This callback function is only invoked once for each frame. struct wslay_event_on_frame_recv_start_arg is defined as follows:

struct wslay_event_on_frame_recv_start_arg {
    uint8_t  fin;
    uint8_t  rsv;
    uint8_t  opcode;
    uint64_t payload_length;
};

fin, rsv and opcode is fin bit and reserved bits and opcode of a frame. payload_length is a payload length of a frame.

on_frame_recv_chunk_callback is invoked by wslay_event_recv() when a chunk of frame payload is received. struct wslay_event_on_frame_recv_chunk_arg is defined as follows:

struct wslay_event_on_frame_recv_chunk_arg {
    const uint8_t *data;
    size_t         data_length;
};

data points to a chunk of payload data. data_length is the length of a chunk.

on_frame_recv_end_callback is invoked by wslay_event_recv() when a frame is completely received.

on_msg_recv_callback is invoked by wslay_event_recv() when a message is completely received. struct wslay_event_on_msg_recv_arg is defined as follows:

struct wslay_event_on_msg_recv_arg {
    uint8_t        rsv;
    uint8_t        opcode;
    const uint8_t *msg;
    size_t         msg_length;
    uint16_t       status_code;
};

The rsv member and the opcode member are reserved bits and opcode of received message respectively. The rsv member is constructed as follows:

rsv = (RSV1 << 2) | (RSV2 << 1) | RSV3

The msg member points to the message of the received message. The msg_length member is the length of message. If a message is close control frame, in other words, opcode == WSLAY_CONNECTION_CLOSE, status_code is set to the status code in the close control frame. If no status code is included in the close control frame, status_code set to 0.