ssh_client_channel(3erl) Erlang Module Definition ssh_client_channel(3erl)
NAME
ssh_client_channel - -behaviour(ssh_client_channel). (Replaces
ssh_channel)
DESCRIPTION
Note:
This module replaces ssh_channel.
The old module is still available for compatibility, but should not be
used for new programs. The old module will not be maintained except for
some error corrections
SSH services (clients and servers) are implemented as channels that are
multiplexed over an SSH connection and communicates over the SSH Con-
nection Protocol. This module provides a callback API that takes care
of generic channel aspects for clients, such as flow control and close
messages. It lets the callback functions take care of the service (ap-
plication) specific parts. This behavior also ensures that the channel
process honors the principal of an OTP-process so that it can be part
of a supervisor tree. This is a requirement of channel processes imple-
menting a subsystem that will be added to the ssh applications supervi-
sor tree.
Note:
When implementing a ssh subsystem for daemons, use -behav-
iour(ssh_server_channel) (Replaces ssh_daemon_channel) instead.
Dont:
Functions in this module are not supposed to be called outside a module
implementing this behaviour!
EXPORTS
call(ChannelRef, Msg) ->
call(ChannelRef, Msg, Timeout) -> Reply | {error, Reason}
Types:
ChannelRef = pid()
As returned by start_link/4
Msg = term()
Timeout = timeout()
Reply = term()
Reason = closed | timeout
Makes a synchronous call to the channel process by sending a
message and waiting until a reply arrives, or a time-out occurs.
The channel calls Module:handle_call/3 to handle the message. If
the channel process does not exist, {error, closed} is returned.
cast(ChannelRef, Msg) -> ok
Types:
ChannelRef = pid()
As returned by start_link/4
Msg = term()
Sends an asynchronous message to the channel process and returns
ok immediately, ignoring if the destination node or channel
process does not exist. The channel calls Module:handle_cast/2
to handle the message.
enter_loop(State) -> _
Types:
State = term()
as returned by init/1
Makes an existing process an ssh_client_channel (replaces
ssh_channel) process. Does not return, instead the calling
process enters the ssh_client_channel (replaces ssh_channel)
process receive loop and become an ssh_client_channel process.
The process must have been started using one of the start func-
tions in proc_lib, see the proc_lib(3erl) manual page in STDLIB.
The user is responsible for any initialization of the process
and must call init/1.
init(Options) -> {ok, State} | {ok, State, Timeout} | {stop, Reason}
Types:
Options = [{Option, Value}]
State = term()
Timeout = timeout()
Reason = term()
The following options must be present:
{channel_cb, atom()}:
The module that implements the channel behaviour.
{init_args(), list()}:
The list of arguments to the init function of the callback
module.
{cm, ssh:connection_ref()}:
Reference to the ssh connection as returned by ssh:con-
nect/3.
{channel_id, ssh:channel_id()}:
Id of the ssh channel as returned by ssh_connection:ses-
sion_channel/2,4.
Note:
This function is normally not called by the user. The user only
needs to call if the channel process needs to be started with
help of proc_lib instead of calling start/4 or start_link/4.
reply(Client, Reply) -> _
Types:
Client = opaque()
Reply = term()
This function can be used by a channel to send a reply to a
client that called call/[2,3] when the reply cannot be defined
in the return value of Module:handle_call/3.
Client must be the From argument provided to the callback func-
tion handle_call/3. Reply is an arbitrary term, which is given
back to the client as the return value of call/[2,3].
start(SshConnection, ChannelId, ChannelCb, CbInitArgs) ->
start_link(SshConnection, ChannelId, ChannelCb, CbInitArgs) -> {ok,
ChannelRef} | {error, Reason}
Types:
SshConnection = ssh:connection_ref()
As returned by ssh:connect/3
ChannelId = ssh:channel_id()
As returned by ssh_connection:session_channel/[2,4].
ChannelCb = atom()
Name of the module implementing the service-specific parts
of the channel.
CbInitArgs = [term()]
Argument list for the init function in the callback module.
ChannelRef = pid()
Starts a process that handles an SSH channel. It is called in-
ternally, by the ssh daemon, or explicitly by the ssh client im-
plementations. The behavior sets the trap_exit flag to true.
CALLBACK FUNCTIONS
The following functions are to be exported from a ssh_client_channel
callback module.
The timeout values that can be returned by the callback functions have
the same semantics as in a gen_server. If the time-out occurs, han-
dle_msg/2 is called as handle_msg(timeout, State).
EXPORTS
Module:code_change(OldVsn, State, Extra) -> {ok, NewState}
Types:
OldVsn = term()
In the case of an upgrade, OldVsn is Vsn, and in the case
of a downgrade, OldVsn is {down,Vsn}. Vsn is defined by the
vsn attribute(s) of the old version of the callback module
Module. If no such attribute is defined, the version is the
checksum of the BEAM file.
State = term()
Internal state of the channel.
Extra = term()
Passed "as-is" from the {advanced,Extra} part of the update
instruction.
Converts process state when code is changed.
This function is called by a client-side channel when it is to
update its internal state during a release upgrade or downgrade,
that is, when the instruction {update,Module,Change,...}, where
Change={advanced,Extra}, is given in the appup file. For more
information, refer to Section 9.11.6 Release Handling Instruc-
tions in the System Documentation.
Note:
Soft upgrade according to the OTP release concept is not
straight forward for the server side, as subsystem channel pro-
cesses are spawned by the ssh application and hence added to its
supervisor tree. The subsystem channels can be upgraded when up-
grading the user application, if the callback functions can han-
dle two versions of the state, but this function cannot be used
in the normal way.
Module:init(Args) -> {ok, State} | {ok, State, timeout()} | {stop, Rea-
son}
Types:
Args = term()
Last argument to start_link/4.
State = term()
Reason = term()
Makes necessary initializations and returns the initial channel
state if the initializations succeed.
For more detailed information on time-outs, see Section Callback
timeouts.
Module:handle_call(Msg, From, State) -> Result
Types:
Msg = term()
From = opaque()
Is to be used as argument to reply/2
State = term()
Result = {reply, Reply, NewState} | {reply, Reply, NewState,
timeout()} | {noreply, NewState} | {noreply , NewState, time-
out()} | {stop, Reason, Reply, NewState} | {stop, Reason,
NewState}
Reply = term()
Will be the return value of call/[2,3]
NewState = term()
Reason = term()
Handles messages sent by calling call/[2,3]
For more detailed information on time-outs,, see Section Call-
back timeouts.
Module:handle_cast(Msg, State) -> Result
Types:
Msg = term()
State = term()
Result = {noreply, NewState} | {noreply, NewState, timeout()}
| {stop, Reason, NewState}
NewState = term()
Reason = term()
Handles messages sent by calling cast/2.
For more detailed information on time-outs, see Section Callback
timeouts.
Module:handle_msg(Msg, State) -> {ok, State} | {stop, ChannelId, State}
Types:
Msg = timeout | term()
ChannelId = ssh:channel_id()
State = term()
Handles other messages than SSH Connection Protocol, call, or
cast messages sent to the channel.
Possible Erlang 'EXIT' messages is to be handled by this func-
tion and all channels are to handle the following message.
{ssh_channel_up, ssh:channel_id(), ssh:connection_ref()}:
This is the first message that the channel receives. It is
sent just before the init/1 function returns successfully.
This is especially useful if the server wants to send a mes-
sage to the client without first receiving a message from
it. If the message is not useful for your particular sce-
nario, ignore it by immediately returning {ok, State}.
Module:handle_ssh_msg(Msg, State) -> {ok, State} | {stop, ChannelId,
State}
Types:
Msg = ssh_connection:event()
ChannelId = ssh:channel_id()
State = term()
Handles SSH Connection Protocol messages that may need service-
specific attention. For details, see ssh_connection:event().
The following message is taken care of by the ssh_client_channel
behavior.
{closed, ssh:channel_id()}:
The channel behavior sends a close message to the other
side, if such a message has not already been sent. Then it
terminates the channel with reason normal.
Module:terminate(Reason, State) -> _
Types:
Reason = term()
State = term()
This function is called by a channel process when it is about to
terminate. Before this function is called, ssh_connec-
tion:close/2 is called, if it has not been called earlier. This
function does any necessary cleaning up. When it returns, the
channel process terminates with reason Reason. The return value
is ignored.
Ericsson AB ssh 4.10 ssh_client_channel(3erl)