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= cowboy_req:push(3)

== Name

cowboy_req:push - Push a resource to the client

== Description

[source,erlang]
----
push(Path, Headers, Req :: cowboy_req:req())
    -> push(Path, Headers, Req, #{})

push(Path, Headers, Req :: cowboy_req:req(), Opts)
    -> ok

Path    :: iodata()                %% case sensitive
Headers :: cowboy:http_headers()
Opts    :: cowboy_req:push_opts()
----

Push a resource to the client.

Cowboy handles push requests the same way as if they came
from the client, including the creation of a request handling
process, routing and middlewares and so on.

This function does nothing when the HTTP/1.1 protocol is
used. You may call it safely without first checking whether
the connection uses HTTP/2.

The header names must be given as lowercase binary strings.
While header names are case insensitive, Cowboy requires them
to be given as lowercase to function properly.

Note that the headers must be the headers the client is expected
to send if it were to perform the request. They are therefore
request headers, and not response headers.

By default, Cowboy will use the GET method, an empty query string,
and take the scheme, host and port directly from the current
request's URI. You can override them by passing options.

Note that clients may cancel the push or ignore it entirely.
For example browsers may ignore the resource when the connection
is not considered secure.

It is not possible to push resources after sending a response.
Any attempt will result in an error.

== Arguments

Path::

The status code for the response.

Headers::

The response headers.
+
Header names must be given as lowercase binary strings.

Req::

The Req object.

Opts::

Customize the HTTP method or the URI scheme, host, port
or query string.

== Return value

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

== Changelog

* *2.0*: Function introduced.

== Examples

.Push a resource
[source,erlang]
----
cowboy_req:push("/static/style.css", #{
    <<"accept">> => <<"text/css">>
}, Req),
----

.Push a resource with a custom host
[source,erlang]
----
cowboy_req:push("/static/style.css", #{
    <<"accept">> => <<"text/css">>
}, #{host => <<"cdn.example.org">>}, Req),
----

== See also

link:man:cowboy_req(3)[cowboy_req(3)],
link:man:cowboy_req:inform(3)[cowboy_req:inform(3)],
link:man:cowboy_req:reply(3)[cowboy_req:reply(3)],
link:man:cowboy_req:stream_reply(3)[cowboy_req:stream_reply(3)]