= cowboy_req:filter_cookies(3)

== Name

cowboy_req:filter_cookies - Filter cookie headers

== Description

[source,erlang]
----
filter_cookies(Names, Req) -> Req

Names :: [atom() | binary()]
----

Filter cookie headers.

This function is meant to be used before attempting to parse
or match cookies in order to remove cookies that are not
relevant and are potentially malformed. Because Cowboy by
default crashes on malformed cookies, this function allows
processing requests that would otherwise result in a 400
error.

Malformed cookies are unfortunately fairly common due to
the string-based interface provided by browsers and this
function provides a middle ground between Cowboy's strict
behavior and chaotic real world use cases.

Note that there may still be crashes even after filtering
cookies because this function does not correct malformed
values. Cookies that have malformed values should probably
be unset in an error response or in a redirect.

This function can be called even if there are no cookies
in the request.

== Arguments

Names::

The cookies that should be kept.

Req::

The Req object.

== Return value

The Req object is returned with its cookie header value
filtered.

== Changelog

* *2.7*: Function introduced.

== Examples

.Filter then parse cookies
[source,erlang]
----
Req = cowboy_req:filter_cookies([session_id, token], Req0),
Cookies = cowboy_req:parse_cookies(Req).
----

== See also

link:man:cowboy_req(3)[cowboy_req(3)],
link:man:cowboy_req:parse_cookies(3)[cowboy_req:parse_cookies(3)],
link:man:cowboy_req:match_cookies(3)[cowboy_req:match_cookies(3)]