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32 lines
1.3 KiB
Markdown
32 lines
1.3 KiB
Markdown
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---
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title: Event handler function
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---
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Each connection has an event handler function associated with it. That function
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must be implemented by user. Event handler is the key element of the Mongoose
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application, since it defines application's behavior. This is how an event
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handler function looks like:
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```c
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static void ev_handler(struct mg_connection *nc, int ev, void *ev_data) {
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switch (ev) {
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/* Event handler code that defines behavior of the connection */
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...
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}
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}
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```
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- `struct mg_connection *nc`: Connection that has received an event.
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- `int ev`: Event number, defined in `mongoose.h`. For example, when data
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arrives on inbound connection `ev` would be `MG_EV_RECV`.
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- `void *ev_data`: This pointer points to the event-specific data, and it has
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different meaning for different events. For example, for `MG_EV_RECV` event,
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`ev_data` is an `int *` pointer, pointing to the number of bytes received
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from the remote peer and saved into the receive IO buffer. Exact meaning of
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`ev_data` is described for each event. Protocol-specific events usually have
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`ev_data` pointing to structures that hold protocol-specific information.
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NOTE: `struct mg_connection` has `void *user_data` which is a placeholder for
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an application-specific data. Mongoose does not use that pointer. Event handler
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can store any kind of information there.
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