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Document how to recover from cookie parsing errors

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Loïc Hoguin 2019-10-06 10:18:16 +02:00
parent 3e23aff1d1
commit 62836cdddc
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2 changed files with 34 additions and 3 deletions
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5
doc/src/manual/cowboy_req.match_cookies.asciidoc
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@ -31,6 +31,10 @@ be converted through the use of constraints, making this
function able to extract, validate and convert values all function able to extract, validate and convert values all
in one step. in one step.
This function will crash on invalid cookie data. How to
handle this is explained in details in the manual page for
link:man:cowboy_req:parse_cookies(3)[cowboy_req:parse_cookies(3)].
== Arguments == Arguments
Fields:: Fields::
@ -85,4 +89,5 @@ An exception is triggered when the match fails.
== See also == See also
link:man:cowboy_req(3)[cowboy_req(3)], link:man:cowboy_req(3)[cowboy_req(3)],
link:man:cowboy_req:filter_cookies(3)[cowboy_req:filter_cookies(3)],
link:man:cowboy_req:parse_cookies(3)[cowboy_req:parse_cookies(3)] link:man:cowboy_req:parse_cookies(3)[cowboy_req:parse_cookies(3)]

32
doc/src/manual/cowboy_req.parse_cookies.asciidoc
View file

@ -18,10 +18,35 @@ Parse cookie headers.
Alias for link:man:cowboy_req:parse_header(3)[cowboy_req:parse_header(<<"cookie">>, Req)]. Alias for link:man:cowboy_req:parse_header(3)[cowboy_req:parse_header(<<"cookie">>, Req)].
When the cookie header is missing, `[]` is returned. When the cookie header is missing or empty, `[]` is returned.
While an empty cookie header is not valid, some clients do This function will crash on invalid cookie data. Because
send it. Cowboy will in this case also return `[]`. invalid cookies are fairly common when dealing with browsers
(because of the string interface that the Javascript API provides),
it is recommended to filter the cookie header value before
attempting to parse it. This can be accomplished by calling
the function link:man:cowboy_req:filter_cookies(3)[cowboy_req:filter_cookies(3)]
first. This does not guarantee that parsing succeeds. If it
still fails it is recommended to send an error response or
redirect with instructions to delete the relevant cookies:
.Recover from cookie parsing errors
[source,erlang]
----
Req1 = cowboy_req:filter_cookies([session_id, token], Req0),
try cowboy_req:parse_cookies(Req1) of
Cookies ->
do_something(Req1, Cookies)
catch _:_ ->
%% We can't parse the cookies we need, unset them
%% otherwise the browser will continue sending them.
Req2 = cowboy_req:set_resp_cookie(<<"session_id">>,
<<>>, Req1, #{max_age => 0}),
Req = cowboy_req:set_resp_cookie(<<"token">>,
<<>>, Req2, #{max_age => 0}),
cowboy_req:reply(500, Req)
end.
----
== Arguments == Arguments
@ -52,4 +77,5 @@ Cookies = cowboy_req:parse_cookies(Req),
link:man:cowboy_req(3)[cowboy_req(3)], link:man:cowboy_req(3)[cowboy_req(3)],
link:man:cowboy_req:parse_header(3)[cowboy_req:parse_header(3)], link:man:cowboy_req:parse_header(3)[cowboy_req:parse_header(3)],
link:man:cowboy_req:filter_cookies(3)[cowboy_req:filter_cookies(3)],
link:man:cowboy_req:match_cookies(3)[cowboy_req:match_cookies(3)] link:man:cowboy_req:match_cookies(3)[cowboy_req:match_cookies(3)]