path: root/doc/src/guide
diff options
authorLoïc Hoguin <[email protected]>2017-02-18 18:26:20 +0100
committerLoïc Hoguin <[email protected]>2017-02-18 18:26:20 +0100
commita45813c60f0f983a24ea29d491b37f0590fdd087 (patch)
treec7e741ac4a684b365e70f7ff73d0c4b6e34232a7 /doc/src/guide
parent80f8cda7ff8fe6a575b4c2eaedd8451acf4fcef3 (diff)
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')
4 files changed, 29 insertions, 47 deletions
diff --git a/doc/src/guide/loop_handlers.asciidoc b/doc/src/guide/loop_handlers.asciidoc
index 2c82c53..dbee927 100644
--- a/doc/src/guide/loop_handlers.asciidoc
+++ b/doc/src/guide/loop_handlers.asciidoc
@@ -34,7 +34,7 @@ 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.
+This snippet enables the loop handler:
@@ -42,14 +42,12 @@ init(Req, State) ->
{cowboy_loop, Req, 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.
+This also makes the process hibernate:
init(Req, State) ->
- {cowboy_loop, Req, State, 30000, hibernate}.
+ {cowboy_loop, Req, State, hibernate}.
=== Receive loop
@@ -123,25 +121,6 @@ a subsequent request.
Please refer to the xref:handlers[Handlers chapter]
for general instructions about cleaning up.
-=== Timeout
-Note that this feature currently does not work. It will be
-brought back in a future 2.0 pre-release.
-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
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
-// @todo Yeah maybe what we really need is an Opts map.
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.
-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`
diff --git a/doc/src/guide/ws_handlers.asciidoc b/doc/src/guide/ws_handlers.asciidoc
index 011aa31..2c38b87 100644
--- a/doc/src/guide/ws_handlers.asciidoc
+++ b/doc/src/guide/ws_handlers.asciidoc
@@ -60,13 +60,13 @@ be:
init(Req, State) ->
case cowboy_req:parse_header(<<"sec-websocket-protocol">>, Req) of
undefined ->
- {ok, Req, State};
+ {cowboy_websocket, Req, State};
Subprotocols ->
case lists:keymember(<<"mqtt">>, 1, Subprotocols) of
true ->
Req2 = cowboy_req:set_resp_header(<<"sec-websocket-protocol">>,
<<"mqtt">>, Req),
- {ok, Req2, State};
+ {cowboy_websocket, Req2, State};
false ->
{stop, Req, State}
@@ -210,12 +210,13 @@ than needed.
The `init/2` callback can set the timeout to be used
for the connection. For example, this would make Cowboy
-close connections idle for more than 60 seconds:
+close connections idle for more than 30 seconds:
init(Req, State) ->
- {cowboy_websocket, Req, State, 60000}.
+ {cowboy_websocket, Req, State, #{
+ idle_timeout => 30000}}.
This value cannot be changed once it is set. It defaults to
diff --git a/doc/src/guide/ws_protocol.asciidoc b/doc/src/guide/ws_protocol.asciidoc
index 127c829..8fa0673 100644
--- a/doc/src/guide/ws_protocol.asciidoc
+++ b/doc/src/guide/ws_protocol.asciidoc
@@ -65,6 +65,5 @@ Cowboy's Websocket implementation also includes the
permessage-deflate and x-webkit-deflate-frame compression
-Cowboy will automatically use compression as long as the
-`websocket_compress` protocol option is set when starting
-the listener.
+Cowboy will automatically use compression when the
+`compress` option is returned from the `init/2` function.