From 078d686a0ac0aed212db97d73bd1e4a9387a4956 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Lo=C3=AFc=20Hoguin?= Date: Sun, 6 Jul 2014 13:10:35 +0200 Subject: Provide installable man pages make docs: generate Markdown and man pages in doc/ make install-docs: install man pages to be usable directly Docs are generated from the ezdoc files in doc/src/. --- guide/loop_handlers.md | 148 ------------------------------------------------- 1 file changed, 148 deletions(-) delete mode 100644 guide/loop_handlers.md (limited to 'guide/loop_handlers.md') diff --git a/guide/loop_handlers.md b/guide/loop_handlers.md deleted file mode 100644 index 8689453..0000000 --- a/guide/loop_handlers.md +++ /dev/null @@ -1,148 +0,0 @@ -Loop handlers -============= - -Loop handlers are a special kind of HTTP handlers used when the -response can not be sent right away. The handler enters instead -a receive loop waiting for the right message before it can send -a response. - -Loop handlers are used for requests where a response might not -be immediately available, but where you would like to keep the -connection open for a while in case the response arrives. The -most known example of such practice is known as long-polling. - -Loop handlers can also be used for requests where a response is -partially available and you need to stream the response body -while the connection is open. The most known example of such -practice is known as server-sent events. - -While the same can be accomplished using plain HTTP handlers, -it is recommended to use loop handlers because they are well-tested -and allow using built-in features like hibernation and timeouts. - -Loop handlers essentially wait for one or more Erlang messages -and feed these messages to the `info/3` callback. It also features -the `init/3` and `terminate/3` callbacks which work the same as -for plain HTTP handlers. - -Initialization --------------- - -The `init/3` function must return a `loop` tuple to enable -loop handler behavior. This tuple may optionally contain -a timeout value and/or the atom `hibernate` to make the -process enter hibernation until a message is received. - -This snippet enables the loop handler. - -``` erlang -init(_Type, Req, _Opts) -> - {loop, Req, undefined_state}. -``` - -However it is largely recommended that you set a timeout -value. The next example sets a timeout value of 30s and -also makes the process hibernate. - -``` erlang -init(_Type, Req, _Opts) -> - {loop, Req, undefined_state, 30000, hibernate}. -``` - -Receive loop ------------- - -Once initialized, Cowboy will wait for messages to arrive -in the process' mailbox. When a message arrives, Cowboy -calls the `info/3` function with the message, the Req object -and the handler's state. - -The following snippet sends a reply when it receives a -`reply` message from another process, or waits for another -message otherwise. - -``` erlang -info({reply, Body}, Req, State) -> - {ok, Req2} = cowboy_req:reply(200, [], Body, Req), - {ok, Req2, State}; -info(_Msg, Req, State) -> - {loop, Req, State, hibernate}. -``` - -Do note that the `reply` tuple here may be any message -and is simply an example. - -This callback may perform any necessary operation including -sending all or parts of a reply, and will subsequently -return a tuple indicating if more messages are to be expected. - -The callback may also choose to do nothing at all and just -skip the message received. - -If a reply is sent, then the `ok` tuple should be returned. -This will instruct Cowboy to end the request. - -Otherwise a `loop` tuple should be returned. - -Streaming loop --------------- - -Another common case well suited for loop handlers is -streaming data received in the form of Erlang messages. -This can be done by initiating a chunked reply in the -`init/3` callback and then using `cowboy_req:chunk/2` -every time a message is received. - -The following snippet does exactly that. As you can see -a chunk is sent every time a `chunk` message is received, -and the loop is stopped by sending an `eof` message. - -``` erlang -init(_Type, Req, _Opts) -> - {ok, Req2} = cowboy_req:chunked_reply(200, [], Req), - {loop, Req2, undefined_state}. - -info(eof, Req, State) -> - {ok, Req, State}; -info({chunk, Chunk}, Req, State) -> - ok = cowboy_req:chunk(Chunk, Req), - {loop, Req, State}; -info(_Msg, Req, State) -> - {loop, Req, State}. -``` - -Cleaning up ------------ - -It is recommended that you set the connection header to -`close` when replying, as this process may be reused for -a subsequent request. - -Please refer to the [HTTP handlers chapter](http_handlers.md) -for general instructions about cleaning up. - -Timeout -------- - -By default Cowboy will not attempt to close the connection -if there is no activity from the client. This is not always -desirable, which is why you can set a timeout. Cowboy will -close the connection if no data was received from the client -after the configured time. The timeout only needs to be set -once and can't be modified afterwards. - -Because the request may have had a body, or may be followed -by another request, Cowboy is forced to buffer all data it -receives. This data may grow to become too large though, -so there is a configurable limit for it. The default buffer -size is of 5000 bytes, but it may be changed by setting the -`loop_max_buffer` middleware environment value. - -Hibernate ---------- - -To save memory, you may hibernate the process in between -messages received. This is done by returning the atom -`hibernate` as part of the `loop` tuple callbacks normally -return. Just add the atom at the end and Cowboy will hibernate -accordingly. -- cgit v1.2.3