From 2b2829f5855e4b2a6ba5e0ca5ccefd42fa2e9524 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Lo=C3=AFc=20Hoguin?= Date: Mon, 23 Sep 2013 15:44:10 +0200 Subject: Greatly expand on the Req object Cut in four different chapters: request, request body, response and cookies. --- guide/resp.md | 203 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 203 insertions(+) create mode 100644 guide/resp.md (limited to 'guide/resp.md') diff --git a/guide/resp.md b/guide/resp.md new file mode 100644 index 0000000..088b10d --- /dev/null +++ b/guide/resp.md @@ -0,0 +1,203 @@ +Sending a response +================== + +The Req object also allows you to send a response. + +You can only send one response. Any other attempt will +trigger a crash. The response may be sent in one go or +with its body streamed by chunks of arbitrary size. + +You can also set headers or the response body in advance +and Cowboy will use them when you finally do reply. + +Reply +----- + +You can send a reply with no particular headers or body. +Cowboy will make sure to send the mandatory headers with +the response. + +``` erlang +{ok, Req2} = cowboy_req:reply(200, Req). +``` + +You can define headers to be sent with the response. Note +that header names must be lowercase. Again, Cowboy will +make sure to send the mandatory headers with the response. + +``` erlang +{ok, Req2} = cowboy_req:reply(303, [ + {<<"location">>, <<"http://ninenines.eu">>} +], Req). +``` + +You can override headers that Cowboy would send otherwise. +Any header set by the user will be used over the ones set +by Cowboy. For example, you can advertise yourself as a +different server. + +``` erlang +{ok, Req2} = cowboy_req:reply(200, [ + {<<"server">>, <<"yaws">>} +], Req). +``` + +We also saw earlier how to force close the connection by +overriding the connection header. + +Finally, you can also send a body with the response. Cowboy +will automatically set the content-length header if you do. +We recommend that you set the content-type header so the +client may know how to read the body. + +``` erlang +{ok, Req2} = cowboy_req:reply(200, [ + {<<"content-type">>, <<"text/plain">> +], "Hello world!", Req). +``` + +Here is the same example but sending HTML this time. + +``` erlang +{ok, Req2} = cowboy_req:reply(200, [ + {<<"content-type">>, <<"text/html">>} +], "Hello world!

Hats off!

", Req). +``` + +Note that the reply is sent immediately. + +Chunked reply +------------- + +You can also stream the response body. First, you need to +initiate the reply by sending the response status code. +Then you can send the body in chunks of arbitrary size. + +``` erlang +{ok, Req2} = cowboy_req:chunked_reply(200, Req), +ok = cowboy_req:chunk("Hello...", Req2), +ok = cowboy_req:chunk("chunked...", Req2), +ok = cowboy_req:chunk("world!!", Req2). +``` + +You should make sure to match on `ok` as an error may be +returned. + +While it is possible to send a chunked response without +a content-type header, it is still recommended. You can +set this header or any other just like for normal replies. + +``` erlang +{ok, Req2} = cowboy_req:chunked_reply(200, [ + {<<"content-type">>, <<"text/html">>} +], Req), +ok = cowboy_req:chunk("Hello world!", Req2), +ok = cowboy_req:chunk("

Hats off!

", Req2). +``` + +Note that the reply and each chunk following it are sent +immediately. + +Preset response headers +----------------------- + +You can define response headers in advance. They will be +merged into the headers given in the reply call. Headers +in the reply call override preset response headers which +override the default Cowboy headers. + +``` erlang +Req2 = cowboy_req:set_resp_header(<<"allow">>, "GET", Req). +``` + +You can check if a response header has already been set. +This will only check the response headers that you set, +and not the ones Cowboy will add when actually sending +the reply. + +``` erlang +cowboy_req:has_resp_header(<<"allow">>, Req). +``` + +It will return `true` if the header is defined, and `false` +otherwise. + +Finally, you can also delete a preset response header if +needed. If you do, it will not be sent. + +``` erlang +Req2 = cowboy_req:delete_resp_header(<<"allow">>, Req). +``` + +Preset response body +-------------------- + +You can set the response body in advance. Note that this +body will be ignored if you then choose to send a chunked +reply, or if you send a reply with an explicit body. + +``` erlang +Req2 = cowboy_req:set_resp_body("Hello world!", Req). +``` + +You can also set a fun that will be called when it is time +to send the body. There are three different ways of doing +that. + +If you know the length of the body that needs to be sent, +you should specify it, as it will help clients determine +the remaining download time and allow them to inform the +user. + +``` erlang +F = fun (Socket, Transport) -> + Transport:send(Socket, "Hello world!") +end, +Req2 = cowboy_req:set_resp_body_fun(12, F, Req). +``` + +If you do not know the length of the body, you should use +a chunked response body fun instead. + +``` erlang +F = fun (SendChunk) -> + Body = lists:duplicate(random:uniform(1024, $a)), + SendChunk(Body) +end, +Req2 = cowboy_req:set_resp_body_fun(chunked, F, Req). +``` + +Finally, you can also send data on the socket directly, +without knowing the length in advance. Cowboy may be +forced to close the connection at the end of the response +though depending on the protocol capabilities. + +``` erlang +F = fun (Socket, Transport) -> + Body = lists:duplicate(random:uniform(1024, $a)), + Transport:send(Socket, Body) +end, +Req2 = cowboy_req:set_resp_body_fun(F, Req). +``` + +Sending files +------------- + +You can send files directly from disk without having to +read them. Cowboy will use the `sendfile` syscall when +possible, which means that the file is sent to the socket +directly from the kernel, which is a lot more performant +than doing it from userland. + +Again, it is recommended to set the size of the file if it +can be known in advance. + +``` erlang +F = fun (Socket, Transport) -> + Transport:sendfile(Socket, "priv/styles.css") +end, +Req2 = cowboy_req:set_resp_body_fun(FileSize, F, Req). +``` + +Please see the Ranch guide for more information about +sending files. -- cgit v1.2.3