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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
Download patch file Download diff file Expand all files Collapse all files

88
doc/src/manual/cowboy_handler.ezdoc
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@ -15,10 +15,96 @@ Environment output:
* result = ok
This module also defines the `cowboy_handler` behaviour that
defines the basic interface for handlers. All Cowboy handlers
implement at least the `init/2` callback, and may implement
the `terminate/3` callback optionally.
:: Types
None.
:: Terminate reasons
The following values may be received as the terminate reason
in the optional `terminate/3` callback. Different handler types
may define additional terminate reasons.
: normal
The connection was closed normally.
: {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.
:: Callbacks
: init(Req, Opts)
-> {ok, Req, State}
| {Module, Req, State}
| {Module, Req, State, hibernate}
| {Module, Req, State, Timeout}
| {Module, Req, State, Timeout, hibernate}
Types:
* Req = cowboy_req:req()
* Opts = any()
* State = any()
* Module = module()
* Timeout = timeout()
Process the request.
This function can be used to switch to an alternate handler
type by returning the name of the module to be used, along
with a few options.
For basic handlers this is the function where the response
should be sent. If no response is sent, Cowboy will ensure
that a `204 No Content` response is sent.
A crash in this callback will result in `terminate/3` being
called if it is defined, with the `State` argument set to
the value of `Opts` originally given to the `init/2` callback.
: terminate(Reason, Req, State) -> ok
Types:
* Reason = any()
* Req = cowboy_req:req()
* State = any()
Perform any necessary cleanup of the state.
This callback should release any resource currently in use,
clear any active timer and reset the process to its original
state, as it might be reused for future requests sent on the
same connection. Typical plain HTTP handlers rarely need to
use it.
A crash in this callback or an invalid return value will
result in the closing of the connection and the termination
of the process.
:: Exports
None.
: terminate(Reason, Req, State, Handler) -> ok
Types:
* Reason = any()
* Req = cowboy_req:req()
* State = any()
* Handler = module()
Call the optional `terminate/3` callback if it exists.
This function should always be called at the end of the execution
of a handler, to give it a chance to clean up or perform
miscellaneous operations.

57
doc/src/manual/cowboy_http_handler.ezdoc
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@ -1,57 +0,0 @@
::: cowboy_http_handler
The `cowboy_http_handler` behaviour defines the interface used
by plain HTTP handlers.
Unless noted otherwise, the callbacks will be executed sequentially.
:: Types
None.
:: Callbacks
: init({TransportName, ProtocolName}, Req, Opts)
-> {ok, Req, State} | {shutdown, Req, State}
Types:
* TransportName = tcp | ssl | atom()
* ProtocolName = http | atom()
* Req = cowboy_req:req()
* Opts = any()
* State = any()
Initialize the state for this request.
The `shutdown` return value can be used to skip the `handle/2`
call entirely.
: handle(Req, State) -> {ok, Req, State}
Types:
* Req = cowboy_req:req()
* State = any()
Handle the request.
This callback is where the request is handled and a response
should be sent. If a response is not sent, Cowboy will send
a `204 No Content` response automatically.
: terminate(Reason, Req, State) -> ok
Types:
* Reason = {normal, shutdown} | {error, atom()}
* Req = cowboy_req:req()
* State = any()
Perform any necessary cleanup of the state.
This callback should release any resource currently in use,
clear any active timer and reset the process to its original
state, as it might be reused for future requests sent on the
same connection. Typical plain HTTP handlers rarely need to
use it.

100
doc/src/manual/cowboy_loop.ezdoc Normal file
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@ -0,0 +1,100 @@
::: cowboy_loop
The `cowboy_loop` module implements a handler interface for
long running HTTP connections. It is the recommended interface
for long polling and server-sent events, amongst others.
This module is a sub protocol that defines three callbacks to
be implemented by handlers. The `init/2` and `terminate/3`
callbacks are common to all handler types and are documented
in the manual for the ^cowboy_handler module.
The `info/3` callback is specific to loop handlers and will be
called as many times as necessary until a reply is sent.
It is highly recommended to return a timeout value from the
`init/2` callback to ensure that the process is terminated
when no data has been received during that timespan. The
default timeout is `infinity`, which should only be used if
you have alternate means of ending inactive connections.
:: Types
None.
:: Terminate reasons
The following values may be received as the terminate reason
in the optional `terminate/3` callback.
: normal
The connection was closed normally before switching to the
loop sub protocol. This typically happens if an `ok` tuple is
returned from the `init/2` callback.
: shutdown
The handler requested to close the connection by returning
a `shutdown` tuple.
: timeout
The connection has been closed due to inactivity. The timeout
value can be configured from `init/2`. The response sent when
this happens is a `204 No Content`.
: {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.
: {error, overflow}
The connection is being closed and the process terminated
because the buffer Cowboy uses to keep data sent by the
client has reached its maximum. The buffer size can be
configured through the environment value `loop_max_buffer`
and defaults to 5000 bytes.
If the long running request comes with a body it is recommended
to process this body before switching to the loop sub protocol.
: {error, closed}
The socket has been closed brutally without a close frame being
received first.
: {error, Reason}
A socket error ocurred.
:: Callbacks
: info(Info, Req, State)
-> {ok, Req, State}
| {ok, Req, State, hibernate}
| {shutdown, Req, State}
Types:
* Info = any()
* Req = cowboy_req:req()
* State = any()
Handle the Erlang message received.
This function will be called every time an Erlang message
has been received. The message can be any Erlang term.
The `shutdown` return value can be used to stop the receive loop,
typically because a response has been sent.
The `hibernate` option will hibernate the process until
it receives another message.
:: Exports
None.

91
doc/src/manual/cowboy_loop_handler.ezdoc
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@ -1,91 +0,0 @@
::: cowboy_loop_handler
The `cowboy_loop_handler` behaviour defines the interface used
by HTTP handlers that do not send a response directly, instead
requiring a receive loop to process Erlang messages.
This interface is best fit for long-polling types of requests.
The `init/3` callback will always be called, followed by zero
or more calls to `info/3`. The `terminate/3` callback will
always be called last.
:: Types
None.
:: Callbacks
: init({TransportName, ProtocolName}, Req, Opts)
-> {loop, Req, State}
| {loop, Req, State, hibernate}
| {loop, Req, State, Timeout}
| {loop, Req, State, Timeout, hibernate}
| {shutdown, Req, State}
Types:
* TransportName = tcp | ssl | atom()
* ProtocolName = http | atom()
* Req = cowboy_req:req()
* Opts = any()
* State = any()
* Timeout = timeout()
Initialize the state for this request.
This callback will typically be used to register this process
to an event manager or a message queue in order to receive
the messages the handler wants to process.
The receive loop will run for a duration of up to `Timeout`
milliseconds after it last received data from the socket,
at which point it will stop and send a `204 No Content` reply.
By default this value is set to `infinity`. It is recommended
to either set this value or ensure by any other mechanism
that the handler will be closed after a certain period of
inactivity.
The `hibernate` option will hibernate the process until it
starts receiving messages.
The `shutdown` return value can be used to skip the receive
loop entirely.
: info(Info, Req, State) -> {ok, Req, State} | {loop, Req, State}
| {loop, Req, State, hibernate}
Types:
* Info = any()
* Req = cowboy_req:req()
* State = any()
Handle the Erlang message received.
This function will be called every time an Erlang message
has been received. The message can be any Erlang term.
The `ok` return value can be used to stop the receive loop,
typically because a response has been sent.
The `hibernate` option will hibernate the process until
it receives another message.
: terminate(Reason, Req, State) -> ok
Types:
* Reason = {normal, shutdown} | {normal, timeout} | {error, closed} | {error, overflow} | {error, atom()}
* Req = cowboy_req:req()
* State = any()
Perform any necessary cleanup of the state.
This callback will typically unregister from any event manager
or message queue it registered to in `init/3`.
This callback should release any resource currently in use,
clear any active timer and reset the process to its original
state, as it might be reused for future requests sent on the
same connection.

66
doc/src/manual/cowboy_rest.ezdoc
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@ -3,12 +3,13 @@
The `cowboy_rest` module implements REST semantics on top of
the HTTP protocol.
This module cannot be described as a behaviour due to most of
the callbacks it defines being optional. It has the same
semantics as a behaviour otherwise.
This module is a sub protocol that defines many callbacks
be implemented by handlers. The `init/2` and `terminate/3`
callbacks are common to all handler types and are documented
in the manual for the ^cowboy_handler module.
The only mandatory callback is `init/3`, needed to perform
the protocol upgrade.
All other callbacks are optional, though some may become
required depending on the return value of previous callbacks.
:: Types
@ -43,47 +44,24 @@ The media-type is the content-type, excluding the charset.
This value is always defined after the call to
`content_types_provided/2`.
:: Terminate reasons
The following values may be received as the terminate reason
in the optional `terminate/3` callback.
: normal
The connection was closed normally.
: {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.
:: Callbacks
: init({TransportName, ProtocolName}, Req, Opts)
-> {upgrade, protocol, cowboy_rest}
| {upgrade, protocol, cowboy_rest, Req, Opts}
Types:
* TransportName = tcp | ssl | atom()
* ProtocolName = http | atom()
* Req = cowboy_req:req()
* Opts = any()
Upgrade the protocol to `cowboy_rest`.
This is the only mandatory callback.
: rest_init(Req, Opts) -> {ok, Req, State}
Types:
* Req = cowboy_req:req()
* Opts = any()
* State = any()
Initialize the state for this request.
: rest_terminate(Req, State) -> ok
Types:
* Req = cowboy_req:req()
* State = any()
Perform any necessary cleanup of the state.
This callback should release any resource currently in use,
clear any active timer and reset the process to its original
state, as it might be reused for future requests sent on the
same connection.
: Callback(Req, State) -> {Value, Req, State} | {halt, Req, State}
Types:

133
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@ -2,8 +2,25 @@
The `cowboy_websocket` module implements the Websocket protocol.
The callbacks for websocket handlers are defined in the manual
for the `cowboy_websocket_handler` behaviour.
This module is a sub protocol that defines four callbacks to
be implemented by handlers. The `init/2` and `terminate/3`
callbacks are common to all handler types and are documented
in the manual for the ^cowboy_handler module.
The `websocket_handle/3` and `websocket_info/3` callbacks are
specific to Websocket handlers and will be called as many times
as necessary until the Websocket connection is closed.
The `init/2` callback can be used to negotiate Websocket protocol
extensions with the client. It is highly recommended to return a
timeout value from this callback to ensure that the process is
terminated when no data has been received during that timespan.
The default timeout is `infinity`, which should only be used if
you have alternate means of ending inactive connections.
Cowboy will terminate the process right after closing the
Websocket connection. This means that there is no real need to
perform any cleanup in the optional `terminate/3` callback.
:: Types
@ -31,6 +48,118 @@ Type: 7 | 8 | 13
The version of the Websocket protocol being used.
:: Terminate reasons
The following values may be received as the terminate reason
in the optional `terminate/3` callback.
: normal
The connection was closed normally before establishing a Websocket
connection. This typically happens if an `ok` tuple is returned
from the `init/2` callback.
: remote
The remote endpoint closed the connection without giving any
further details.
: {remote, Code, Payload}
The remote endpoint closed the connection with the given
`Code` and `Payload` as the reason.
: shutdown
The handler requested to close the connection, either by returning
a `shutdown` tuple or by sending a `close` frame.
: timeout
The connection has been closed due to inactivity. The timeout
value can be configured from `init/2`.
: {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.
: {error, badencoding}
A text frame was sent by the client with invalid encoding. All
text frames must be valid UTF-8.
: {error, badframe}
A protocol error has been detected.
: {error, closed}
The socket has been closed brutally without a close frame being
received first.
: {error, Reason}
A socket error ocurred.
:: Callbacks
: websocket_handle(InFrame, Req, State)
-> {ok, Req, State}
| {ok, Req, State, hibernate}
| {reply, OutFrame | [OutFrame], Req, State}
| {reply, OutFrame | [OutFrame], Req, State, hibernate}
| {shutdown, Req, State}
Types:
* InFrame = {text | binary | ping | pong, binary()}
* Req = cowboy_req:req()
* State = any()
* OutFrame = frame()
Handle the data received from the Websocket connection.
This function will be called every time data is received
from the Websocket connection.
The `shutdown` return value can be used to close the
connection. A close reply will also result in the connection
being closed.
The `hibernate` option will hibernate the process until
it receives new data from the Websocket connection or an
Erlang message.
: websocket_info(Info, Req, State)
-> {ok, Req, State}
| {ok, Req, State, hibernate}
| {reply, OutFrame | [OutFrame], Req, State}
| {reply, OutFrame | [OutFrame], Req, State, hibernate}
| {shutdown, Req, State}
Types:
* Info = any()
* Req = cowboy_req:req()
* State = any()
* OutFrame = frame()
Handle the Erlang message received.
This function will be called every time an Erlang message
has been received. The message can be any Erlang term.
The `shutdown` return value can be used to close the
connection. A close reply will also result in the connection
being closed.
The `hibernate` option will hibernate the process until
it receives another message or new data from the Websocket
connection.
:: Exports
None.

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doc/src/manual/cowboy_websocket_handler.ezdoc
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@ -1,133 +0,0 @@
::: cowboy_websocket_handler
The `cowboy_websocket_handler` behaviour defines the interface used
by Websocket handlers.
The `init/3` and `websocket_init/3` callbacks will always be called,
followed by zero or more calls to `websocket_handle/3` and
`websocket_info/3`. The `websocket_terminate/3` will always
be called last.
:: Types
None.
:: Callbacks
: init({TransportName, ProtocolName}, Req, Opts)
-> {upgrade, protocol, cowboy_websocket}
| {upgrade, protocol, cowboy_websocket, Req, Opts}
Types:
* TransportName = tcp | ssl | atom()
* ProtocolName = http | atom()
* Req = cowboy_req:req()
* Opts = any()
Upgrade the protocol to `cowboy_websocket`.
: websocket_init(TransportName, Req, Opts)
-> {ok, Req, State}
| {ok, Req, State, hibernate}
| {ok, Req, State, Timeout}
| {ok, Req, State, Timeout, hibernate}
| {shutdown, Req}
Types:
* TransportName = tcp | ssl | atom()
* Req = cowboy_req:req()
* Opts = any()
* State = any()
* Timeout = timeout()
Initialize the state for this session.
This function is called before the upgrade to Websocket occurs.
It can be used to negotiate Websocket protocol extensions
with the client. It will typically be used to register this process
to an event manager or a message queue in order to receive
the messages the handler wants to process.
The connection will stay up for a duration of up to `Timeout`
milliseconds after it last received data from the socket,
at which point it will stop and close the connection.
By default this value is set to `infinity`. It is recommended
to either set this value or ensure by any other mechanism
that the handler will be closed after a certain period of
inactivity.
The `hibernate` option will hibernate the process until it
starts receiving either data from the Websocket connection
or Erlang messages.
The `shutdown` return value can be used to close the connection
before upgrading to Websocket.
: websocket_handle(InFrame, Req, State)
-> {ok, Req, State}
| {ok, Req, State, hibernate}
| {reply, OutFrame | [OutFrame], Req, State}
| {reply, OutFrame | [OutFrame], Req, State, hibernate}
| {shutdown, Req, State}
Types:
* InFrame = {text | binary | ping | pong, binary()}
* Req = cowboy_req:req()
* State = any()
* OutFrame = cowboy_websocket:frame()
Handle the data received from the Websocket connection.
This function will be called every time data is received
from the Websocket connection.
The `shutdown` return value can be used to close the
connection. A close reply will also result in the connection
being closed.
The `hibernate` option will hibernate the process until
it receives new data from the Websocket connection or an
Erlang message.
: websocket_info(Info, Req, State)
-> {ok, Req, State}
| {ok, Req, State, hibernate}
| {reply, OutFrame | [OutFrame], Req, State}
| {reply, OutFrame | [OutFrame], Req, State, hibernate}
| {shutdown, Req, State}
Types:
* Info = any()
* Req = cowboy_req:req()
* State = any()
* OutFrame = cowboy_websocket:frame()
Handle the Erlang message received.
This function will be called every time an Erlang message
has been received. The message can be any Erlang term.
The `shutdown` return value can be used to close the
connection. A close reply will also result in the connection
being closed.
The `hibernate` option will hibernate the process until
it receives another message or new data from the Websocket
connection.
: websocket_terminate(Reason, Req, State) -> ok
Types:
* Reason = {normal, shutdown | timeout} | {remote, closed} | {remote, cowboy_websocket:close_code(), binary()} | {error, badencoding | badframe | closed | atom()}
* Req = cowboy_req:req()
* State = any()
Perform any necessary cleanup of the state.
The connection will be closed and the process stopped right
after this call.

4
doc/src/manual/index.ezdoc
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@ -5,8 +5,7 @@ The function reference documents the public interface of Cowboy.
* ^"The Cowboy Application^cowboy_app
* ^cowboy
* ^cowboy_handler
* ^cowboy_http_handler
* ^cowboy_loop_handler
* ^cowboy_loop
* ^cowboy_middleware
* ^cowboy_protocol
* ^cowboy_req
@ -16,5 +15,4 @@ The function reference documents the public interface of Cowboy.
* ^cowboy_static
* ^cowboy_sub_protocol
* ^cowboy_websocket
* ^cowboy_websocket_handler
* ^"HTTP status codes^http_status_codes