1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
|
= cowboy_websocket(3)
== Name
cowboy_websocket - Websocket
== Description
The module `cowboy_websocket` implements Websocket
as a Ranch protocol. It also defines a callback interface
for handling Websocket connections.
== Callbacks
Websocket handlers must implement the following callback
interface:
[source,erlang]
----
init(Req, State)
-> {cowboy_websocket, Req, State}
| {cowboy_websocket, Req, State, Opts}
websocket_init(State) -> CallResult %% optional
websocket_handle(InFrame, State) -> CallResult
websocket_info(Info, State) -> CallResult
terminate(Reason, PartialReq, State) -> ok %% optional
Req :: cowboy_req:req()
PartialReq :: map()
State :: any()
Opts :: cowboy_websocket:opts()
InFrame :: ping | pong | {text | binary | ping | pong, binary()}
OutFrame :: cow_ws:frame() %% see types below
Info :: any()
CallResult :: {ok, State}
| {ok, State, hibernate}
| {reply, OutFrame | [OutFrame], State}
| {reply, OutFrame | [OutFrame], State, hibernate}
| {stop, State}
Reason :: normal | stop | timeout
| remote | {remote, cow_ws:close_code(), binary()}
| {error, badencoding | badframe | closed | atom()}
| {crash, error | exit | throw, any()}
----
The `init/2` callback is common to all handlers. To upgrade
the connection to Websocket, it must return `cowboy_websocket`
as the first element of the tuple.
Any operation requiring the HTTP request must be done in the
`init/2` function, as the Req object will not be available
after it returns. Websocket sub-protocol selection should
therefore be done in this function.
The optional `websocket_init/1` callback will be called once
the connection has been upgraded to Websocket. It can be used
to perform any required initialization of the handler.
Note that the `init/2` function does not run in the same
process as the Websocket callbacks. Any Websocket-specific
initialization must be done in `websocket_init/1`.
The `websocket_handle/2` callback will be called for every
frame received. The `websocket_info/2` callback will be
called for every Erlang message received.
All three Websocket callbacks may send one or more frames
back to the client (by returning a `reply` tuple) or terminate
the connection (by sending a `close` frame or returning a `stop`
tuple).
The optional `terminate/3` callback will ultimately be called
with the reason for the termination of the connection. This
callback is common to all handlers. Note that Websocket will
not provide the full Req object by default, to save memory.
Cowboy will terminate the process right after closing the
Websocket connection. This means that there is no need to
perform any cleanup in the `terminate/3` callback.
The following terminate reasons are defined for Websocket
connections:
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.
stop::
The handler requested to close the connection, either by returning
a `stop` 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.
== Types
=== cow_ws:frame()
[source,erlang]
----
frame() :: {text, iodata()}
| {binary, iodata()}
| ping | {ping, iodata()}
| pong | {pong, iodata()}
| close | {close, iodata()} | {close, close_code(), iodata()}
close_code() :: 1000..1003 | 1006..1011 | 3000..4999
----
Websocket frames that can be sent as a response.
Note that there is no need to send pong frames back as
Cowboy does it automatically for you.
=== opts()
[source,erlang]
----
opts() :: #{
compress => boolean(),
deflate_opts => cow_ws:deflate_opts()
idle_timeout => timeout(),
max_frame_size => non_neg_integer() | infinity,
req_filter => fun((cowboy_req:req()) -> map()),
validate_utf8 => boolean()
}
----
Websocket handler options.
This configuration is passed to Cowboy from the `init/2`
function:
[source,erlang]
----
init(Req, State) ->
Opts = #{compress => true},
{cowboy_websocket, Req, State, Opts}.
----
The default value is given next to the option name:
compress (false)::
Whether to enable the Websocket frame compression
extension. Frames will only be compressed for the
clients that support this extension.
deflate_opts (#{})::
Configuration for the permessage-deflate Websocket
extension. Allows configuring both the negotiated
options and the zlib compression options. The
defaults optimize the compression at the expense
of some memory and CPU.
idle_timeout (60000)::
Time in milliseconds that Cowboy will keep the
connection open without receiving anything from
the client.
max_frame_size (infinity)::
Maximum frame size in bytes allowed by this Websocket
handler. Cowboy will close the connection when
a client attempts to send a frame that goes over
this limit. For fragmented frames this applies
to the size of the reconstituted frame.
req_filter::
A function applied to the Req to compact it and
only keep required information. The Req is only
given back in the `terminate/3` callback. By default
it keeps the method, version, URI components and peer
information.
validate_utf8 (true)::
Whether Cowboy should verify that the payload of
`text` and `close` frames is valid UTF-8. This is
required by the protocol specification but in some
cases it may be more interesting to disable it in
order to save resources.
+
Note that `binary` frames do not have this UTF-8
requirement and are what should be used under
normal circumstances if necessary.
== Changelog
* *2.7*: The option `validate_utf8` has been added.
* *2.6*: Deflate options can now be configured via `deflate_opts`.
* *2.0*: The Req object is no longer passed to Websocket callbacks.
* *2.0*: The callback `websocket_terminate/3` was removed in favor of `terminate/3`.
* *1.0*: Protocol introduced.
== See also
link:man:cowboy(7)[cowboy(7)],
link:man:cowboy_handler(3)[cowboy_handler(3)],
link:man:cowboy_http(3)[cowboy_http(3)],
link:man:cowboy_http2(3)[cowboy_http2(3)]
|
