1ssh_client_channel(3) Erlang Module Definition ssh_client_channel(3)
2
6 ssh_client_channel - -behaviour(ssh_client_channel). (Replaces
7 ssh_channel)
8
11 Note:
12 This module replaces ssh_channel.
13 The old module is still available for compatibility, but should not be
15 used for new programs. The old module will not be maintained except for
16 some error corrections
17 SSH services (clients and servers) are implemented as channels that are
20 multiplexed over an SSH connection and communicates over the SSH Con‐
21 nection Protocol. This module provides a callback API that takes care
22 of generic channel aspects for clients, such as flow control and close
23 messages. It lets the callback functions take care of the service
24 (application) specific parts. This behavior also ensures that the chan‐
25 nel process honors the principal of an OTP-process so that it can be
26 part of a supervisor tree. This is a requirement of channel processes
27 implementing a subsystem that will be added to the ssh applications
28 supervisor tree.
29 Note:
31 When implementing a ssh subsystem for daemons, use -behav‐
32 iour(ssh_server_channel) (Replaces ssh_daemon_channel) instead.
33 Dont:
36 Functions in this module are not supposed to be called outside a module
37 implementing this behaviour!
38
41 call(ChannelRef, Msg) ->
42 call(ChannelRef, Msg, Timeout) -> Reply | {error, Reason}
43 Types:
45 ChannelRef = pid()
47 As returned by start_link/4
48 Msg = term()
49 Timeout = timeout()
50 Reply = term()
51 Reason = closed | timeout
52 Makes a synchronous call to the channel process by sending a
54 message and waiting until a reply arrives, or a time-out occurs.
55 The channel calls Module:handle_call/3 to handle the message. If
56 the channel process does not exist, {error, closed} is returned.
57 cast(ChannelRef, Msg) -> ok
59 Types:
61 ChannelRef = pid()
63 As returned by start_link/4
64 Msg = term()
65 Sends an asynchronous message to the channel process and returns
67 ok immediately, ignoring if the destination node or channel
68 process does not exist. The channel calls Module:handle_cast/2
69 to handle the message.
70 enter_loop(State) -> _
72 Types:
74 State = term()
76 as returned by init/1
77 Makes an existing process an ssh_client_channel (replaces
79 ssh_channel) process. Does not return, instead the calling
80 process enters the ssh_client_channel (replaces ssh_channel)
81 process receive loop and become an ssh_client_channel process.
82 The process must have been started using one of the start func‐
83 tions in proc_lib, see the proc_lib(3) manual page in STDLIB.
84 The user is responsible for any initialization of the process
85 and must call init/1.
86 init(Options) -> {ok, State} | {ok, State, Timeout} | {stop, Reason}
88 Types:
90 Options = [{Option, Value}]
92 State = term()
93 Timeout = timeout()
94 Reason = term()
95 The following options must be present:
97 {channel_cb, atom()}:
99 The module that implements the channel behaviour.
100 {init_args(), list()}:
102 The list of arguments to the init function of the callback
103 module.
104 {cm, ssh:connection_ref()}:
106 Reference to the ssh connection as returned by ssh:con‐
107 nect/3.
108 {channel_id, ssh:channel_id()}:
110 Id of the ssh channel as returned by ssh_connection:ses‐
111 sion_channel/2,4.
112 Note:
114 This function is normally not called by the user. The user only
115 needs to call if the channel process needs to be started with
116 help of proc_lib instead of calling start/4 or start_link/4.
117 reply(Client, Reply) -> _
120 Types:
122 Client = opaque()
124 Reply = term()
125 This function can be used by a channel to send a reply to a
127 client that called call/[2,3] when the reply cannot be defined
128 in the return value of Module:handle_call/3.
129 Client must be the From argument provided to the callback func‐
131 tion handle_call/3. Reply is an arbitrary term, which is given
132 back to the client as the return value of call/[2,3].
133 start(SshConnection, ChannelId, ChannelCb, CbInitArgs) ->
135 start_link(SshConnection, ChannelId, ChannelCb, CbInitArgs) -> {ok,
136 ChannelRef} | {error, Reason}
137 Types:
139 SshConnection = ssh:connection_ref()
141 As returned by ssh:connect/3
142 ChannelId = ssh:channel_id()
143 As returned by ssh_connection:session_channel/[2,4].
144 ChannelCb = atom()
145 Name of the module implementing the service-specific parts
146 of the channel.
147 CbInitArgs = [term()]
148 Argument list for the init function in the callback module.
149 ChannelRef = pid()
150 Starts a process that handles an SSH channel. It is called
152 internally, by the ssh daemon, or explicitly by the ssh client
153 implementations. The behavior sets the trap_exit flag to true.
154
156 The following functions are to be exported from a ssh_client_channel
157 callback module.
158 Callback timeouts
160 The timeout values that can be returned by the callback functions have
161 the same semantics as in a gen_server. If the time-out occurs, han‐
162 dle_msg/2 is called as handle_msg(timeout, State).
163
165 Module:code_change(OldVsn, State, Extra) -> {ok, NewState}
166 Types:
168 OldVsn = term()
170 In the case of an upgrade, OldVsn is Vsn, and in the case
171 of a downgrade, OldVsn is {down,Vsn}. Vsn is defined by the
172 vsn attribute(s) of the old version of the callback module
173 Module. If no such attribute is defined, the version is the
174 checksum of the BEAM file.
175 State = term()
176 Internal state of the channel.
177 Extra = term()
178 Passed "as-is" from the {advanced,Extra} part of the update
179 instruction.
180 Converts process state when code is changed.
182 This function is called by a client-side channel when it is to
184 update its internal state during a release upgrade or downgrade,
185 that is, when the instruction {update,Module,Change,...}, where
186 Change={advanced,Extra}, is given in the appup file. For more
187 information, refer to Section 9.11.6 Release Handling Instruc‐
188 tions in the System Documentation.
189 Note:
191 Soft upgrade according to the OTP release concept is not
192 straight forward for the server side, as subsystem channel pro‐
193 cesses are spawned by the ssh application and hence added to its
194 supervisor tree. The subsystem channels can be upgraded when
195 upgrading the user application, if the callback functions can
196 handle two versions of the state, but this function cannot be
197 used in the normal way.
198 Module:init(Args) -> {ok, State} | {ok, State, timeout()} | {stop, Rea‐
201 son}
202 Types:
204 Args = term()
206 Last argument to start_link/4.
207 State = term()
208 Reason = term()
209 Makes necessary initializations and returns the initial channel
211 state if the initializations succeed.
212 For more detailed information on time-outs, see Section Callback
214 timeouts.
215 Module:handle_call(Msg, From, State) -> Result
217 Types:
219 Msg = term()
221 From = opaque()
222 Is to be used as argument to reply/2
223 State = term()
224 Result = {reply, Reply, NewState} | {reply, Reply, NewState,
225 timeout()} | {noreply, NewState} | {noreply , NewState, time‐
226 out()} | {stop, Reason, Reply, NewState} | {stop, Reason,
227 NewState}
228 Reply = term()
229 Will be the return value of call/[2,3]
230 NewState = term()
231 Reason = term()
232 Handles messages sent by calling call/[2,3]
234 For more detailed information on time-outs,, see Section Call‐
236 back timeouts.
237 Module:handle_cast(Msg, State) -> Result
239 Types:
241 Msg = term()
243 State = term()
244 Result = {noreply, NewState} | {noreply, NewState, timeout()}
245 | {stop, Reason, NewState}
246 NewState = term()
247 Reason = term()
248 Handles messages sent by calling cast/2.
250 For more detailed information on time-outs, see Section Callback
252 timeouts.
253 Module:handle_msg(Msg, State) -> {ok, State} | {stop, ChannelId, State}
255 Types:
257 Msg = timeout | term()
259 ChannelId = ssh:channel_id()
260 State = term()
261 Handles other messages than SSH Connection Protocol, call, or
263 cast messages sent to the channel.
264 Possible Erlang 'EXIT' messages is to be handled by this func‐
266 tion and all channels are to handle the following message.
267 {ssh_channel_up, ssh:channel_id(), ssh:connection_ref()}:
269 This is the first message that the channel receives. It is
270 sent just before the init/1 function returns successfully.
271 This is especially useful if the server wants to send a mes‐
272 sage to the client without first receiving a message from
273 it. If the message is not useful for your particular sce‐
274 nario, ignore it by immediately returning {ok, State}.
275 Module:handle_ssh_msg(Msg, State) -> {ok, State} | {stop, ChannelId,
277 State}
278 Types:
280 Msg = ssh_connection:event()
282 ChannelId = ssh:channel_id()
283 State = term()
284 Handles SSH Connection Protocol messages that may need service-
286 specific attention. For details, see ssh_connection:event().
287 The following message is taken care of by the ssh_client_channel
289 behavior.
290 {closed, ssh:channel_id()}:
292 The channel behavior sends a close message to the other
293 side, if such a message has not already been sent. Then it
294 terminates the channel with reason normal.
295 Module:terminate(Reason, State) -> _
297 Types:
299 Reason = term()
301 State = term()
302 This function is called by a channel process when it is about to
304 terminate. Before this function is called, ssh_connec‐
305 tion:close/2 is called, if it has not been called earlier. This
306 function does any necessary cleaning up. When it returns, the
307 channel process terminates with reason Reason. The return value
308 is ignored.
309Ericsson AB ssh 4.9 ssh_client_channel(3)