cowboy_req:stream_events(3)

Name

cowboy_req:stream_events - Stream events

Description

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 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 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

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

cowboy_req(3), cowboy_req:stream_reply(3), cowboy_req:stream_body(3), cowboy_req:stream_trailers(3)