mongoose/docs/http/events.md

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---
title: HTTP events
---
As discussed in the overview, `mg_set_protocol_http_websocket()` function
parses incoming data, treats it as HTTP or WebSocket, and triggers high-level
HTTP or WebSocket events. Here is a list of events specific to HTTP.
- MG_EV_HTTP_REQUEST: An HTTP request has arrived. Parsed request
is passed as
`struct http_message` through the handler's `void *ev_data` pointer.
- MG_EV_HTTP_REPLY: An HTTP reply has arrived. Parsed reply is
passed as `struct http_message` through the handler's `void *ev_data`
pointer.
- MG_EV_HTTP_MULTIPART_REQUEST: A multipart POST request has arrived.
This event is sent before body is parsed. After this, the user
should expect a sequence of MG_EV_HTTP_PART_BEGIN/DATA/END requests.
This is also the last time when headers and other request fields are
accessible.
- MG_EV_HTTP_CHUNK: An HTTP chunked-encoding chunk has arrived.
The parsed HTTP reply is passed as `struct http_message` through the
handler's `void *ev_data` pointer. `http_message::body` would contain
incomplete, reassembled HTTP body.
It will grow with every new chunk that arrives, and it can
potentially consume a lot of memory. The event handler may process
the body as chunks are coming, and signal Mongoose to delete processed
body by setting `MG_F_DELETE_CHUNK` in `mg_connection::flags`. When
the last zero chunk is received,
Mongoose sends `MG_EV_HTTP_REPLY` event with
full reassembled body (if handler did not signal to delete chunks) or
with empty body (if handler did signal to delete chunks).
- MG_EV_HTTP_PART_BEGIN: a new part of multipart message is started,
extra parameters are passed in mg_http_multipart_part
- MG_EV_HTTP_PART_DATA: a new portion of data from the multiparted message
no additional headers are available, only data and data size
- MG_EV_HTTP_PART_END: a final boundary received, analogue to maybe used to
find the end of packet
Note: Mongoose should be compiled with MG_ENABLE_HTTP_STREAMING_MULTIPART
to enable multipart events.