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= cowboy_req:stream_events(3)

== Name

cowboy_req:stream_events - Stream events

== Description

[source,erlang]
----
stream_events(Events, IsFin, Req :: cowboy_req:req()) -> ok

Events :: Event | [Event]
IsFin  :: fin | nofin

Event  :: #{
    comment => iodata(),
    data    => iodata(),
    event   => iodata() | atom(),
    id      => iodata(),
    retry   => non_neg_integer()
}
----

Stream events.

This function should only be used for `text/event-stream`
responses when using server-sent events. Cowboy will
automatically encode the given events to their text
representation.

This function may be called as many times as needed after
initiating a response using the
link:man:cowboy_req:stream_reply(3)[cowboy_req:stream_reply(3)]
function.

The second argument indicates if this call is the final
call. Use the `nofin` value until you know no more data
will be sent. The final call should use `fin` (possibly
with an empty data value) or be a call to the
link:man:cowboy_req:stream_trailers(3)[cowboy_req:stream_trailers(3)]
function.

Note that not using `fin` for the final call is not an
error; Cowboy will take care of it when the request
handler terminates if needed. Depending on the resource
it may however be more efficient to do it as early as
possible.

You do not need to handle HEAD requests specifically as
Cowboy will ensure no data is sent when you call this function.

== Arguments

Events::

Events to be sent. All fields are optional.

IsFin::

A flag indicating whether this is the final piece of data
to be sent.

Req::

The Req object.

== Return value

The atom `ok` is always returned. It can be safely ignored.

== Changelog

* *2.5*: Function introduced.

== Examples

.Stream events
[source,erlang]
----
Req = cowboy_req:stream_reply(200, #{
    <<"content-type">> => <<"text/event-stream">>
}, Req0),
cowboy_req:stream_events(#{
    id => <<"comment-123">>,
    event => <<"add_comment">>,
    data => <<"Hello,\n\nI noticed something wrong in ...">>
}, nofin, Req),
timer:sleep(1000),
cowboy_req:stream_events(#{
    event => <<"debug">>,
    data => io_lib:format("An error occurred: ~p~n", [Error])
}, fin, Req).
----

== See also

link:man:cowboy_req(3)[cowboy_req(3)],
link:man:cowboy_req:stream_reply(3)[cowboy_req:stream_reply(3)],
link:man:cowboy_req:stream_body(3)[cowboy_req:stream_body(3)],
link:man:cowboy_req:stream_trailers(3)[cowboy_req:stream_trailers(3)]