View Source ssh_client_channel behaviour (ssh v5.2.3)
-behaviour(ssh_client_channel). (Replaces ssh_channel)
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 Connection 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 (application) 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
implementing a subsystem that will be added to the ssh
applications supervisor
tree.
Note
When implementing a
ssh
subsystem for daemons, use -behaviour(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!
Callback timeouts
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, handle_msg/2
is called as
handle_msg(timeout, State).
Summary
Callbacks: Callback Functions
Converts process state when code is changed.
Handles messages sent by calling call/2,3
Handles messages sent by calling cast/2
.
Handles other messages than SSH Connection Protocol, call, or cast messages sent to the channel.
Handles SSH Connection Protocol messages that may need service-specific
attention. For details, see ssh_connection:event/0
.
Makes necessary initializations and returns the initial channel state if the initializations succeed.
This function is called by a channel process when it is about to terminate.
Before this function is called,
ssh_connection: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.
Functions
Equivalent to call/3
.
call(ChannelRef, Msg, Timeout) -> Reply | {error, Reason}
cast(ChannelRef, Msg) -> ok
enterloop(State) ->
init(Options) -> {ok, State} | {ok, State, Timeout} | {stop, Reason}
reply(Client, Reply) -> _
start_link(SshConnection, ChannelId, ChannelCb, CbInitArgs) -> {ok, ChannelRef} | {error, Reason}
Types
-opaque client()
Callbacks: Callback Functions
-callback code_change(OldVsn :: term() | {down, term()}, State :: term(), Extra :: term()) -> {ok, NewState :: term()} | {error, Reason :: term()}.
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 Instructions in the
System Documentation.
Note
Soft upgrade according to the OTP release concept is not straight forward for the server side, as subsystem channel processes are spawned by the
ssh
application and hence added to its supervisor tree. The subsystem channels can be upgraded when upgrading the user application, if the callback functions can handle two versions of the state, but this function cannot be used in the normal way.
-callback handle_call(Request :: term(), From :: {pid(), Tag :: term()}, State :: term()) -> {reply, Reply :: term(), NewState :: term()} | {reply, Reply :: term(), NewState :: term(), timeout() | hibernate} | {noreply, NewState :: term()} | {noreply, NewState :: term(), timeout() | hibernate} | {stop, Reason :: term(), Reply :: term(), NewState :: term()} | {stop, Reason :: term(), NewState :: term()}.
Handles messages sent by calling call/2,3
For more detailed information on time-outs,, see Section Callback timeouts.
-callback handle_cast(Request :: term(), State :: term()) -> {noreply, NewState :: term()} | {noreply, NewState :: term(), timeout() | hibernate} | {stop, Reason :: term(), NewState :: term()}.
Handles messages sent by calling cast/2
.
For more detailed information on time-outs, see Section Callback timeouts.
-callback handle_msg(Msg :: term(), State :: term()) -> {ok, State :: term()} | {stop, 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 function and all channels are to handle the following message.
{ssh_channel_up, ``t:ssh:channel_id/0``, ``t:ssh:connection_ref/0``}
- This is the first message that the channel receives. It is sent just before theinit/1
function returns successfully. This is especially useful if the server wants to send a message to the client without first receiving a message from it. If the message is not useful for your particular scenario, ignore it by immediately returning{ok, State}
.
-callback handle_ssh_msg(ssh_connection:event(), State :: term()) -> {ok, State :: term()} | {stop, ChannelId :: ssh:channel_id(), State :: term()}.
Handles SSH Connection Protocol messages that may need service-specific
attention. For details, see ssh_connection:event/0
.
The following message is taken care of by the ssh_client_channel
behavior.
{closed, ``t:ssh:channel_id/0``}
- 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 reasonnormal
.
-callback init(Args :: term()) -> {ok, State :: term()} | {ok, State :: term(), timeout() | hibernate} | {stop, Reason :: term()} | ignore.
Makes necessary initializations and returns the initial channel state if the initializations succeed.
For more detailed information on time-outs, see Section Callback timeouts.
-callback terminate(Reason :: normal | shutdown | {shutdown, term()} | term(), State :: term()) -> term().
This function is called by a channel process when it is about to terminate.
Before this function is called,
ssh_connection: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.
Functions
-spec call(ChannelRef, Msg) -> Reply | {error, Reason} when ChannelRef :: pid(), Msg :: term(), Reply :: term(), Reason :: closed | timeout.
Equivalent to call/3
.
-spec call(ChannelRef, Msg, Timeout) -> Reply | {error, Reason} when ChannelRef :: pid(), Msg :: term(), Timeout :: timeout(), Reply :: term(), Reason :: closed | timeout.
call(ChannelRef, Msg, Timeout) -> Reply | {error, Reason}
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
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.
-spec enter_loop(State) -> _ when State :: term().
enterloop(State) ->
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 functions in proc_lib
, see the proc_lib
manual page in STDLIB.
The user is responsible for any initialization of the process and must call
init/1
.
-spec init(Options) -> {ok, State} | {ok, State, Timeout} | {stop, Reason} when Options :: [[{Option :: term(), Value :: term()}]], State :: term(), Timeout :: timeout(), Reason :: term().
init(Options) -> {ok, State} | {ok, State, Timeout} | {stop, Reason}
The following options must be present:
{channel_cb, atom()}
- The module that implements the channel behaviour.{init_args(), list()}
- The list of arguments to theinit
function of the callback module.{cm, ``t:ssh:connection_ref/0``}
- Reference to thessh
connection as returned byssh:connect/3
.{channel_id, ``t:ssh:channel_id/0``}
- Id of thessh
channel as returned by ssh_connection:session_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 callingstart/4
orstart_link/4
.
reply(Client, Reply) -> _
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 function
handle_call/3
. Reply
is an arbitrary term, which is
given back to the client as the return value of [call/[2,3].](call/2
)
start(SshConnection, ChannelId, ChannelCb, CbInitArgs)
View Source (since OTP 21.0)-spec start(SshConnection, ChannelId, ChannelCb, CbInitArgs) -> {ok, ChannelRef} | {error, Reason :: term()} when SshConnection :: ssh:connection_ref(), ChannelId :: ssh:channel_id(), ChannelCb :: atom(), CbInitArgs :: [term()], ChannelRef :: pid().
Equivalent to start_link/4
.
start_link(SshConnection, ChannelId, ChannelCb, CbInitArgs)
View Source (since OTP 21.0)-spec start_link(SshConnection, ChannelId, ChannelCb, CbInitArgs) -> {ok, ChannelRef} | {error, Reason :: term()} when SshConnection :: ssh:connection_ref(), ChannelId :: ssh:channel_id(), ChannelCb :: atom(), CbInitArgs :: [term()], ChannelRef :: pid().
start_link(SshConnection, ChannelId, ChannelCb, CbInitArgs) -> {ok, ChannelRef} | {error, Reason}
Starts a process that handles an SSH channel. It is called internally, by the
ssh
daemon, or explicitly by the ssh
client implementations. The behavior
sets the trap_exit
flag to true
.