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 (ap‐
24 plication) specific parts. This behavior also ensures that the channel
25 process honors the principal of an OTP-process so that it can be part
26 of a supervisor tree. This is a requirement of channel processes imple‐
27 menting a subsystem that will be added to the ssh applications supervi‐
28 sor 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 in‐
152 ternally, by the ssh daemon, or explicitly by the ssh client im‐
153 plementations. 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 The timeout values that can be returned by the callback functions have
160 the same semantics as in a gen_server. If the time-out occurs, han‐
161 dle_msg/2 is called as handle_msg(timeout, State).
162
164 Module:code_change(OldVsn, State, Extra) -> {ok, NewState}
165 Types:
167 OldVsn = term()
169 In the case of an upgrade, OldVsn is Vsn, and in the case
170 of a downgrade, OldVsn is {down,Vsn}. Vsn is defined by the
171 vsn attribute(s) of the old version of the callback module
172 Module. If no such attribute is defined, the version is the
173 checksum of the BEAM file.
174 State = term()
175 Internal state of the channel.
176 Extra = term()
177 Passed "as-is" from the {advanced,Extra} part of the update
178 instruction.
179 Converts process state when code is changed.
181 This function is called by a client-side channel when it is to
183 update its internal state during a release upgrade or downgrade,
184 that is, when the instruction {update,Module,Change,...}, where
185 Change={advanced,Extra}, is given in the appup file. For more
186 information, refer to Section 9.11.6 Release Handling Instruc‐
187 tions in the System Documentation.
188 Note:
190 Soft upgrade according to the OTP release concept is not
191 straight forward for the server side, as subsystem channel pro‐
192 cesses are spawned by the ssh application and hence added to its
193 supervisor tree. The subsystem channels can be upgraded when up‐
194 grading the user application, if the callback functions can han‐
195 dle two versions of the state, but this function cannot be used
196 in the normal way.
197 Module:init(Args) -> {ok, State} | {ok, State, timeout()} | {stop, Rea‐
200 son}
201 Types:
203 Args = term()
205 Last argument to start_link/4.
206 State = term()
207 Reason = term()
208 Makes necessary initializations and returns the initial channel
210 state if the initializations succeed.
211 For more detailed information on time-outs, see Section Callback
213 timeouts.
214 Module:handle_call(Msg, From, State) -> Result
216 Types:
218 Msg = term()
220 From = opaque()
221 Is to be used as argument to reply/2
222 State = term()
223 Result = {reply, Reply, NewState} | {reply, Reply, NewState,
224 timeout()} | {noreply, NewState} | {noreply , NewState, time‐
225 out()} | {stop, Reason, Reply, NewState} | {stop, Reason,
226 NewState}
227 Reply = term()
228 Will be the return value of call/[2,3]
229 NewState = term()
230 Reason = term()
231 Handles messages sent by calling call/[2,3]
233 For more detailed information on time-outs,, see Section Call‐
235 back timeouts.
236 Module:handle_cast(Msg, State) -> Result
238 Types:
240 Msg = term()
242 State = term()
243 Result = {noreply, NewState} | {noreply, NewState, timeout()}
244 | {stop, Reason, NewState}
245 NewState = term()
246 Reason = term()
247 Handles messages sent by calling cast/2.
249 For more detailed information on time-outs, see Section Callback
251 timeouts.
252 Module:handle_msg(Msg, State) -> {ok, State} | {stop, ChannelId, State}
254 Types:
256 Msg = timeout | term()
258 ChannelId = ssh:channel_id()
259 State = term()
260 Handles other messages than SSH Connection Protocol, call, or
262 cast messages sent to the channel.
263 Possible Erlang 'EXIT' messages is to be handled by this func‐
265 tion and all channels are to handle the following message.
266 {ssh_channel_up, ssh:channel_id(), ssh:connection_ref()}:
268 This is the first message that the channel receives. It is
269 sent just before the init/1 function returns successfully.
270 This is especially useful if the server wants to send a mes‐
271 sage to the client without first receiving a message from
272 it. If the message is not useful for your particular sce‐
273 nario, ignore it by immediately returning {ok, State}.
274 Module:handle_ssh_msg(Msg, State) -> {ok, State} | {stop, ChannelId,
276 State}
277 Types:
279 Msg = ssh_connection:event()
281 ChannelId = ssh:channel_id()
282 State = term()
283 Handles SSH Connection Protocol messages that may need service-
285 specific attention. For details, see ssh_connection:event().
286 The following message is taken care of by the ssh_client_channel
288 behavior.
289 {closed, ssh:channel_id()}:
291 The channel behavior sends a close message to the other
292 side, if such a message has not already been sent. Then it
293 terminates the channel with reason normal.
294 Module:terminate(Reason, State) -> _
296 Types:
298 Reason = term()
300 State = term()
301 This function is called by a channel process when it is about to
303 terminate. Before this function is called, ssh_connec‐
304 tion:close/2 is called, if it has not been called earlier. This
305 function does any necessary cleaning up. When it returns, the
306 channel process terminates with reason Reason. The return value
307 is ignored.
308Ericsson AB ssh 4.13.2.1 ssh_client_channel(3)