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author | Loïc Hoguin <[email protected]> | 2019-07-18 09:59:28 +0200 |
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committer | Loïc Hoguin <[email protected]> | 2019-07-18 10:08:46 +0200 |
commit | 136d443b5c38bee96f5d995dfea3629ef07564c3 (patch) | |
tree | 1d31540baebc43ca0b2dceeda212c44f5da7e7a8 /docs/en/cowboy/2.1/guide/loop_handlers.asciidoc | |
parent | e031713c0e8bd871248dbbbbdec1ea28609f4431 (diff) | |
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Announce Ranch 2.0.0-rc.1
Adds Ranch 2.0 documentation and removes documentation for
very old Cowboy and Ranch, along with Erlang.mk documentation
which is available on its own website.
Diffstat (limited to 'docs/en/cowboy/2.1/guide/loop_handlers.asciidoc')
-rw-r--r-- | docs/en/cowboy/2.1/guide/loop_handlers.asciidoc | 128 |
1 files changed, 0 insertions, 128 deletions
diff --git a/docs/en/cowboy/2.1/guide/loop_handlers.asciidoc b/docs/en/cowboy/2.1/guide/loop_handlers.asciidoc deleted file mode 100644 index 21bf8424..00000000 --- a/docs/en/cowboy/2.1/guide/loop_handlers.asciidoc +++ /dev/null @@ -1,128 +0,0 @@ -[[loop_handlers]] -== 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 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/2` and `terminate/3` callbacks which work the same as -for plain HTTP handlers. - -=== Initialization - -The `init/2` function must return a `cowboy_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: - -[source,erlang] ----- -init(Req, State) -> - {cowboy_loop, Req, State}. ----- - -This also makes the process hibernate: - -[source,erlang] ----- -init(Req, State) -> - {cowboy_loop, Req, State, 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. - -[source,erlang] ----- -info({reply, Body}, Req, State) -> - cowboy_req:reply(200, #{}, Body, Req), - {stop, Req, State}; -info(_Msg, Req, State) -> - {ok, 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 `stop` tuple should be returned. -This will instruct Cowboy to end the request. - -Otherwise an `ok` 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/2` 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 an `event` message is received, -and the loop is stopped by sending an `eof` message. - -[source,erlang] ----- -init(Req, State) -> - Req2 = cowboy_req:stream_reply(200, Req), - {cowboy_loop, Req2, State}. - -info(eof, Req, State) -> - {stop, Req, State}; -info({event, Data}, Req, State) -> - cowboy_req:stream_body(Data, nofin, Req), - {ok, Req, State}; -info(_Msg, Req, State) -> - {ok, 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 xref:handlers[Handlers chapter] -for general instructions about cleaning up. - -=== 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. |