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Improve handler interface and documentation

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This change simplifies a little more the sub protocols mechanism.
Aliases have been removed. The renaming of loop handlers as long
polling handlers has been reverted.

Plain HTTP handlers now simply do their work in the init/2
callback. There is no specific code for them.

Loop handlers now follow the same return value as Websocket,
they use ok to continue and shutdown to stop.

Terminate reasons for all handler types have been documented.
The terminate callback is now appropriately called in all cases
(or should be).

Behaviors for all handler types have been moved in the module
that implement them. This means that cowboy_handler replaces
the cowboy_http_handler behavior, and similarly cowboy_loop
replaces cowboy_loop_handler, cowboy_websocket replaces
cowboy_websocket_handler. Finally cowboy_rest now has the
start of a behavior in it and will have the full list of
optional callbacks defined once Erlang 18.0 gets released.

The guide has been reorganized and should be easier to follow.
This commit is contained in:
Loïc Hoguin 2014-09-30 20:12:13 +03:00
parent 5ce4c2bfb4
commit 0dc063ab7d
82 changed files with 778 additions and 1037 deletions
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28
doc/src/guide/loop_handlers.ezdoc
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@ -8,7 +8,7 @@ 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.
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
@ -21,12 +21,12 @@ 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/3` and `terminate/3` callbacks which work the same as
the `init/2` and `terminate/3` callbacks which work the same as
for plain HTTP handlers.
:: Initialization
The `init/3` function must return a `loop` tuple to enable
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.
@ -35,7 +35,7 @@ This snippet enables the loop handler.
``` erlang
init(Req, Opts) ->
{long_polling, Req, Opts}.
{cowboy_loop, Req, Opts}.
```
However it is largely recommended that you set a timeout
@ -44,7 +44,7 @@ also makes the process hibernate.
``` erlang
init(Req, Opts) ->
{long_polling, Req, Opts, 30000, hibernate}.
{cowboy_loop, Req, Opts, 30000, hibernate}.
```
:: Receive loop
@ -61,9 +61,9 @@ message otherwise.
``` erlang
info({reply, Body}, Req, State) ->
Req2 = cowboy_req:reply(200, [], Body, Req),
{ok, Req2, State};
{shutdown, Req2, State};
info(_Msg, Req, State) ->
{loop, Req, State, hibernate}.
{ok, Req, State, hibernate}.
```
Do note that the `reply` tuple here may be any message
@ -76,17 +76,17 @@ 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 `ok` tuple should be returned.
If a reply is sent, then the `shutdown` tuple should be returned.
This will instruct Cowboy to end the request.
Otherwise a `loop` tuple should be returned.
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/3` callback and then using `cowboy_req:chunk/2`
`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
@ -96,15 +96,15 @@ and the loop is stopped by sending an `eof` message.
``` erlang
init(Req, Opts) ->
Req2 = cowboy_req:chunked_reply(200, [], Req),
{long_polling, Req2, Opts}.
{cowboy_loop, Req2, Opts}.
info(eof, Req, State) ->
{ok, Req, State};
{shutdown, Req, State};
info({chunk, Chunk}, Req, State) ->
cowboy_req:chunk(Chunk, Req),
{loop, Req, State};
{ok, Req, State};
info(_Msg, Req, State) ->
{loop, Req, State}.
{ok, Req, State}.
```
:: Cleaning up