mongoose/docs/design-concept/events.md

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Events

Mongoose accepts incoming connections, reads and writes data, and calls specified event handler for each connection when appropriate. Typical event sequence is this:

• For outbound connection: MG_EV_CONNECT -> (MG_EV_RECV, MG_EV_SEND, MG_EV_POLL ...) -> MG_EV_CLOSE
• For inbound connection: MG_EV_ACCEPT -> (MG_EV_RECV, MG_EV_SEND, MG_EV_POLL ...) -> MG_EV_CLOSE

Below is a list of core events triggered by Mongoose (note that each protocol triggers protocol-specific events in addition to the core ones):

• MG_EV_ACCEPT: sent when new server connection is accepted by a listening connection. void *ev_data is union socket_address of the remote peer.

• MG_EV_CONNECT: sent when a new outbound connection created by mg_connect() either failed or succeeded. void *ev_data is int *success. If success is 0, then connection has been established, otherwise it contains error code. See mg_connect_opt() function for code example.

• MG_EV_RECV: New data is received and appended to the end of recv_mbuf. void *ev_data is int *num_received_bytes. Typically, event handler should check received data in nc->recv_mbuf, discard processed data by calling mbuf_remove(), set connection flags nc->flags if necessary (see struct mg_connection), and write data the remote peer by output functions like mg_send().

  WARNING: Mongoose uses realloc() to expand receive buffer. It is user's responsibility to discard processed data from the beginning of receive buffer, note the mbuf_remove() call in the example above.

• MG_EV_SEND: Mongoose has written data to the remote peer and discarded written data from the mg_connection::send_mbuf. void *ev_data is int *num_sent_bytes.

  NOTE: Mongoose output functions only append data to the mg_connection::send_mbuf, they do not do any socket writes. An actual IO is done by mg_mgr_poll(). MG_EV_SEND event is just a notification about an IO has been done.

• MG_EV_POLL: Sent to all connections on each invocation of mg_mgr_poll(). This event could be used to do any housekeeping, for example check whether certain timeout has expired and close the connection, or send heartbeet message, et cetera.

• MG_EV_TIMER: Sent to the connection if mg_set_timer() was called.