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Diffstat (limited to 'guide/loop_handlers.md')
-rw-r--r-- | guide/loop_handlers.md | 30 |
1 files changed, 19 insertions, 11 deletions
diff --git a/guide/loop_handlers.md b/guide/loop_handlers.md index 6d67c62..64cf80a 100644 --- a/guide/loop_handlers.md +++ b/guide/loop_handlers.md @@ -16,15 +16,23 @@ 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. -Callbacks ---------- - -@todo Describe the callbacks. - Usage ----- -@todo Explain how to use them. +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. + +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/2` callbacks which work the same as +for plain HTTP handlers. The following handler waits for a message `{reply, Body}` before sending a response. If this message doesn't arrive within 60 @@ -41,14 +49,14 @@ this message. -export([terminate/2]). init({tcp, http}, Req, Opts) -> - {loop, Req, undefined_state, 60000, hibernate}. + {loop, Req, undefined_state, 60000, hibernate}. info({reply, Body}, Req, State) -> - {ok, Req2} = cowboy_req:reply(200, [], Body, Req), - {ok, Req2, State}; + {ok, Req2} = cowboy_req:reply(200, [], Body, Req), + {ok, Req2, State}; info(Message, Req, State) -> - {loop, Req, State, hibernate}. + {loop, Req, State, hibernate}. terminate(Req, State) -> - ok. + ok. ``` |