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46 lines
1.3 KiB
Text
46 lines
1.3 KiB
Text
[[hooks]]
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== Hooks
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Hooks allow the user to customize Cowboy's behavior during specific
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operations.
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=== Onresponse
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The `onresponse` hook is called right before sending the response
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to the socket. It can be used for the purposes of logging responses,
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or for modifying the response headers or body. The best example is
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providing custom error pages.
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Note that this function MUST NOT crash. Cowboy may or may not send a
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reply if this function crashes. If a reply is sent, the hook MUST
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explicitly provide all headers that are needed.
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You can specify the `onresponse` hook when creating the listener.
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[source,erlang]
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----
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cowboy:start_http(my_http_listener, 100,
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[{port, 8080}],
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[
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{env, [{dispatch, Dispatch}]},
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{onresponse, fun ?MODULE:custom_404_hook/4}
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]
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).
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----
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The following hook function will provide a custom body for 404 errors
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when it has not been provided before, and will let Cowboy proceed with
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the default response otherwise.
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[source,erlang]
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----
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custom_404_hook(404, Headers, <<>>, Req) ->
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Body = <<"404 Not Found.">>,
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Headers2 = lists:keyreplace(<<"content-length">>, 1, Headers,
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{<<"content-length">>, integer_to_list(byte_size(Body))}),
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cowboy_req:reply(404, Headers2, Body, Req);
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custom_404_hook(_, _, _, Req) ->
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Req.
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----
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Again, make sure to always return the last request object obtained.
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