2016-01-14 13:35:25 +01:00
|
|
|
= cowboy_loop(3)
|
|
|
|
|
|
|
|
== Name
|
|
|
|
|
2016-12-23 17:20:54 +01:00
|
|
|
cowboy_loop - Loop handlers
|
2016-01-14 13:35:25 +01:00
|
|
|
|
|
|
|
== Description
|
|
|
|
|
2016-12-23 17:20:54 +01:00
|
|
|
The module `cowboy_loop` defines a callback interface for
|
|
|
|
long running HTTP connections.
|
2016-01-14 13:35:25 +01:00
|
|
|
|
2016-12-23 17:20:54 +01:00
|
|
|
You should switch to this behavior for long polling,
|
|
|
|
server-sent events and similar long-running requests.
|
2016-01-14 13:35:25 +01:00
|
|
|
|
2016-12-23 17:20:54 +01:00
|
|
|
There are generally two usage patterns:
|
2016-01-14 13:35:25 +01:00
|
|
|
|
2016-12-23 17:20:54 +01:00
|
|
|
* Loop until receiving a specific message, then send
|
|
|
|
a response and stop execution (for example long polling);
|
2016-01-14 13:35:25 +01:00
|
|
|
|
2016-12-23 17:20:54 +01:00
|
|
|
* Or initiate a response in `init/2` and stream the
|
|
|
|
body in `info/3` as necessary (for example server-sent events).
|
2016-01-14 13:35:25 +01:00
|
|
|
|
2016-12-23 17:20:54 +01:00
|
|
|
== Callbacks
|
2016-01-14 13:35:25 +01:00
|
|
|
|
2016-12-23 17:20:54 +01:00
|
|
|
Loop handlers implement the following interface:
|
2016-01-14 13:35:25 +01:00
|
|
|
|
2016-12-23 17:20:54 +01:00
|
|
|
[source,erlang]
|
|
|
|
----
|
|
|
|
init(Req, State)
|
|
|
|
-> {cowboy_loop, Req, State}
|
|
|
|
| {cowboy_loop, Req, State, hibernate}
|
2016-01-14 13:35:25 +01:00
|
|
|
|
2016-12-23 17:20:54 +01:00
|
|
|
info(Info, Req, State)
|
|
|
|
-> {ok, Req, State}
|
|
|
|
| {ok, Req, State, hibernate}
|
|
|
|
| {stop, Req, State}
|
2016-01-14 13:35:25 +01:00
|
|
|
|
2016-12-23 17:20:54 +01:00
|
|
|
terminate(Reason, Req, State) -> ok %% optional
|
2016-01-14 13:35:25 +01:00
|
|
|
|
2016-12-23 17:20:54 +01:00
|
|
|
Req :: cowboy_req:req()
|
|
|
|
State :: any()
|
|
|
|
Info :: any()
|
Allow passing options to sub protocols
Before this commit we had an issue where configuring a
Websocket connection was simply not possible without
doing magic, adding callbacks or extra return values.
The init/2 function only allowed setting hibernate
and timeout options.
After this commit, when switching to a different
type of handler you can either return
{module, Req, State}
or
{module, Req, State, Opts}
where Opts is any value (as far as the sub protocol
interface is concerned) and is ultimately checked
by the custom handlers.
A large protocol like Websocket would accept only
a map there, with many different options, while a
small interface like loop handlers would allow
passing hibernate and nothing else.
For Websocket, hibernate must be set from the
websocket_init/1 callback, because init/2 executes
in a separate process.
Sub protocols now have two callbacks: one with the
Opts value, one without.
The loop handler code was largely reworked and
simplified. It does not need to manage a timeout
or read from the socket anymore, it's the job of
the protocol code. A lot of unnecessary stuff was
therefore removed.
Websocket compression must now be enabled from
the handler options instead of per listener. This
means that a project can have two separate Websocket
handlers with different options. Compression is
still disabled by default, and the idle_timeout
value was changed from inifnity to 60000 (60 seconds),
as that's safer and is also a good value for mobile
devices.
2017-02-18 18:26:20 +01:00
|
|
|
Reason :: stop
|
2016-12-23 17:20:54 +01:00
|
|
|
| {crash, error | exit | throw, any()}
|
|
|
|
----
|
2016-01-14 13:35:25 +01:00
|
|
|
|
2016-12-23 17:20:54 +01:00
|
|
|
The `init/2` callback is common to all handlers. To switch
|
|
|
|
to the loop behavior, it must return `cowboy_loop` as the
|
|
|
|
first element of the tuple.
|
2016-01-14 13:35:25 +01:00
|
|
|
|
2016-12-23 17:20:54 +01:00
|
|
|
The `info/3` callback will be called for every Erlang message
|
|
|
|
received. It may choose to continue the receive loop or stop
|
|
|
|
it.
|
2016-01-14 13:35:25 +01:00
|
|
|
|
2016-12-23 17:20:54 +01:00
|
|
|
The optional `terminate/3` callback will ultimately be called
|
|
|
|
with the reason for the termination of the handler.
|
|
|
|
Cowboy will terminate the process right after this. There
|
|
|
|
is no need to perform any cleanup in this callback.
|
2016-01-14 13:35:25 +01:00
|
|
|
|
2016-12-23 17:20:54 +01:00
|
|
|
The following terminate reasons are defined for loop handlers:
|
2016-01-14 13:35:25 +01:00
|
|
|
|
2016-12-23 17:20:54 +01:00
|
|
|
stop::
|
|
|
|
The handler requested to close the connection by returning
|
|
|
|
a `stop` tuple.
|
|
|
|
|
|
|
|
{crash, Class, Reason}::
|
|
|
|
A crash occurred in the handler. `Class` and `Reason` can be
|
|
|
|
used to obtain more information about the crash. The function
|
|
|
|
`erlang:get_stacktrace/0` can also be called to obtain the
|
|
|
|
stacktrace of the process when the crash occurred.
|
|
|
|
|
|
|
|
== Changelog
|
|
|
|
|
Allow passing options to sub protocols
Before this commit we had an issue where configuring a
Websocket connection was simply not possible without
doing magic, adding callbacks or extra return values.
The init/2 function only allowed setting hibernate
and timeout options.
After this commit, when switching to a different
type of handler you can either return
{module, Req, State}
or
{module, Req, State, Opts}
where Opts is any value (as far as the sub protocol
interface is concerned) and is ultimately checked
by the custom handlers.
A large protocol like Websocket would accept only
a map there, with many different options, while a
small interface like loop handlers would allow
passing hibernate and nothing else.
For Websocket, hibernate must be set from the
websocket_init/1 callback, because init/2 executes
in a separate process.
Sub protocols now have two callbacks: one with the
Opts value, one without.
The loop handler code was largely reworked and
simplified. It does not need to manage a timeout
or read from the socket anymore, it's the job of
the protocol code. A lot of unnecessary stuff was
therefore removed.
Websocket compression must now be enabled from
the handler options instead of per listener. This
means that a project can have two separate Websocket
handlers with different options. Compression is
still disabled by default, and the idle_timeout
value was changed from inifnity to 60000 (60 seconds),
as that's safer and is also a good value for mobile
devices.
2017-02-18 18:26:20 +01:00
|
|
|
* *2.0*: Loop handlers no longer need to handle overflow/timeouts.
|
2016-12-23 17:20:54 +01:00
|
|
|
* *1.0*: Behavior introduced.
|
|
|
|
|
|
|
|
== See also
|
|
|
|
|
|
|
|
link:man:cowboy(7)[cowboy(7)],
|
|
|
|
link:man:cowboy_handler(3)[cowboy_handler(3)]
|