diff options
author | Loïc Hoguin <[email protected]> | 2017-02-18 18:26:20 +0100 |
---|---|---|
committer | Loïc Hoguin <[email protected]> | 2017-02-18 18:26:20 +0100 |
commit | a45813c60f0f983a24ea29d491b37f0590fdd087 (patch) | |
tree | c7e741ac4a684b365e70f7ff73d0c4b6e34232a7 /doc/src/guide/sub_protocols.asciidoc | |
parent | 80f8cda7ff8fe6a575b4c2eaedd8451acf4fcef3 (diff) | |
download | cowboy-a45813c60f0f983a24ea29d491b37f0590fdd087.tar.gz cowboy-a45813c60f0f983a24ea29d491b37f0590fdd087.tar.bz2 cowboy-a45813c60f0f983a24ea29d491b37f0590fdd087.zip |
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.
Diffstat (limited to 'doc/src/guide/sub_protocols.asciidoc')
-rw-r--r-- | doc/src/guide/sub_protocols.asciidoc | 35 |
1 files changed, 19 insertions, 16 deletions
diff --git a/doc/src/guide/sub_protocols.asciidoc b/doc/src/guide/sub_protocols.asciidoc index 2ab96bc..83fa975 100644 --- a/doc/src/guide/sub_protocols.asciidoc +++ b/doc/src/guide/sub_protocols.asciidoc @@ -20,31 +20,31 @@ init(Req, State) -> {cowboy_websocket, Req, State}. ---- -The return value may also have a `Timeout` value and/or the -atom `hibernate`. These options are useful for long living -connections. When they are not provided, the timeout value -defaults to `infinity` and the hibernate value to `run`. +The returned tuple may also have a fourth element containing +options for the sub protocol. No option is universal. While +it will usually be a map of options, it doesn't have to be. +For example loop handlers accept the atom `hibernate`. The following snippet switches to the `my_protocol` sub protocol, sets the timeout value to 5 seconds and enables hibernation: -// @todo Yeah maybe what we really need is an Opts map. - [source,erlang] ---- init(Req, State) -> - {my_protocol, Req, State, 5000, hibernate}. + {my_protocol, Req, State, #{ + timeout => 5000, + compress => true}}. ---- -If a sub protocol does not make use of these options, it should -crash if it receives anything other than the default values. +Sub protocols should ignore unknown options so as to not waste +resources doing unnecessary validation. === Upgrade -After the `init/2` function returns, Cowboy will then call the -`upgrade/6` function. This is the only callback defined by the -`cowboy_sub_protocol` behavior. +After the `init/2` function returns, Cowboy will call either +the `upgrade/4` or the `upgrade/5` function. The former is called +when no options were given; the latter when they were given. The function is named `upgrade` because it mimics the mechanism of HTTP protocol upgrades. For some sub protocols, like Websocket, @@ -53,16 +53,19 @@ only an upgrade at Cowboy's level and the client has nothing to do about it. The upgrade callback receives the Req object, the middleware -environment, the handler and its options, and the aforementioned -timeout and hibernate values. +environment, the handler and its state, and for `upgrade/5` +also the aformentioned options. [source,erlang] ---- -upgrade(Req, Env, Handler, HandlerOpts, Timeout, Hibernate) -> +upgrade(Req, Env, Handler, State) -> + %% Sub protocol code here. + +upgrade(Req, Env, Handler, State, Opts) -> %% Sub protocol code here. ---- -This callback is expected to behave like a middleware and to +These callbacks are expected to behave like middlewares and to return an updated environment and Req object. Sub protocols are expected to call the `cowboy_handler:terminate/4` |