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@@ -128,7 +128,35 @@ in advance. This will ensure that the best response method
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is selected and help clients understand when the response
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is fully received.
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-// @todo Document trailers here.
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+Cowboy also provides a function to send response trailers.
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+Response trailers are semantically equivalent to the headers
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+you send in the response, only they are sent at the end.
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+This is especially useful to attach information to the
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+response that could not be generated until the response
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+body was fully generated.
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+
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+Trailer fields must be listed in the trailer header. Any
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+field not listed might be dropped by the client or an intermediary.
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+
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+[source,erlang]
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+----
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+Req = cowboy_req:stream_reply(200, #{
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+ <<"content-type">> => <<"text/html">>,
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+ <<"trailer">> => <<"expires, content-md5">>
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+}, Req0),
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+
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+cowboy_req:stream_body("<html><head>Hello world!</head>", nofin, Req),
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+cowboy_req:stream_body("<body><p>Hats off!</p></body></html>", nofin, Req),
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+
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+cowboy_req:stream_trailers(#{
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+ <<"expires">> => <<"Sun, 10 Dec 2017 19:13:47 GMT">>,
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+ <<"content-md5">> => <<"c6081d20ff41a42ce17048ed1c0345e2">>
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+}, Req).
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+----
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+
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+The stream ends with trailers. It is no longer possible to
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+send data after sending trailers. You cannot send trailers
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+after setting the `fin` flag when streaming the body.
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=== Preset response headers
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Loïc Hoguin