ssh_channel
(ssh)-behaviour(ssh_channel).
SSH services (clients and servers) are implemented as channels
that are multiplexed over an SSH connection and communicates via
the
Note!
When implementing a SSH subsystem use the
-behaviour(ssh_daemon_channel).
instead of -behaviour(ssh_channel).
as the only relevant callback functions for subsystems are
init/1, handle_ssh_msg/2, handle_msg/2 and terminate/2, so the ssh_daemon_channel
behaviour is limited version of the ssh_channel behaviour.
DATA TYPES
Type definitions that are used more than once in this module and/or abstractions to indicate the intended use of the data type:
boolean() = true | false
string() = list of ASCII characters
timeout() = infinity | integer() - in milliseconds.
ssh_connection_ref() - opaque to the user returned by
ssh:connect/3 or sent to an SSH channel process
ssh_channel_id() = integer()
ssh_data_type_code() = 1 ("stderr") | 0 ("normal") are
currently valid values see
Functions
call(ChannelRef, Msg) ->
call(ChannelRef, Msg, Timeout) -> Reply | {error, Reason}
ChannelRef = pid()
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 timeout
occurs. The channel will call Module:handle_call/3
to handle the message. If the channel process does not exist
{error, closed}
is returned.
cast(ChannelRef, Msg) -> ok
ChannelRef = pid()
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 will call Module:handle_cast/2 to handle the message.
enter_loop(State) -> _
State = term() - as returned by ssh_channel:init/1
Makes an existing process an ssh_channel
process. Does not return, instead the calling process will
enter the ssh_channel
process receive loop and become an
ssh_channel process.
The process must have been started using
one of the start functions in proc_lib, see proc_lib(3). The
user is responsible for any initialization of the process
and needs to call ssh_channel:init/1
init(Options) -> {ok, State} | {ok, State, Timeout} | {stop, Reason}
Options = [{Option, Value}]
State = term()
Timeout = timeout()
Reason = term()
The following options must be present:
{channel_cb, atom()}
{init_args(), list()}
{cm, connection_ref()}
{channel_id, channel_id()}
Note!
This function is normally not called by the
user. The user only needs to call if for some reason the
channel process needs to be started with help of
proc_lib
instead of calling
ssh_channel:start/4
or
ssh_channel:start_link/4
reply(Client, Reply) -> _
Client - opaque to the user, see explanation below
Reply = term()
This function can be used by a channel to explicitly 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 will be given back to the client as the return value of
ssh_channel:call/[2,3].>
start(SshConnection, ChannelId, ChannelCb, CbInitArgs) ->
start_link(SshConnection, ChannelId, ChannelCb, CbInitArgs) -> {ok, ChannelRef} | {error, Reason}
SshConnection = ssh_connection_ref()
ChannelId = ssh_channel_id()
ChannelCb = atom()
CbInitArgs = [term()]
ChannelRef = pid()
Starts a processes that handles an SSH channel. It will be
called internally by the SSH daemon or explicitly by the SSH
client implementations. The behavior will set the
trap_exit
flag to true.
CALLBACK TIMEOUTS
The timeout values that may be returned by the callback functions
has the same semantics as in a gen_server
If the timeout occurs handle_msg/2
will be called as handle_msg(timeout, State).
Functions
Module:code_change(OldVsn, State, Extra) -> {ok, NewState}
OldVsn = term()
State = term()
Extra = term()
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.{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
should update its internal state during a release
upgrade/downgrade, i.e. when the instruction
{update,Module,Change,...}
where
Change={advanced,Extra}
is given in the appup
file. See OTP
Design Principles for more information.
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. It could be possible to upgrade the subsystem channels, when upgrading the user application, if the callback functions can handle two versions of the state, but this function can not be used in the normal way.
Module:init(Args) -> {ok, State} | {ok, State, timeout()} | {stop, Reason}
Args = term()
State = term()
Reason = term()
Makes necessary initializations and returns the initial channel state if the initializations succeed.
For more detailed information on timeouts see the section CALLBACK TIMEOUTS.
Module:handle_call(Msg, From, State) -> Result
Msg = term()
From = opaque to the user should be used as argument to ssh_channel:reply/2
State = term()
Result = {reply, Reply, NewState} | {reply, Reply, NewState, timeout()} | {noreply, NewState} | {noreply , NewState, timeout()} | {stop, Reason, Reply, NewState} | {stop, Reason, NewState}
Reply = term() - will be the return value of ssh_channel:call/[2,3]
NewState = term()
Reason = term()
Handles messages sent by calling ssh_channel:call/[2,3]
For more detailed information on timeouts see the section CALLBACK TIMEOUTS.
Module:handle_cast(Msg, State) -> Result
Msg = term()
State = term()
Result = {noreply, NewState} | {noreply, NewState, timeout()} | {stop, Reason, NewState}
NewState = term()
Reason = term()
Handles messages sent by calling
ssh_channel:cast/2
For more detailed information on timeouts see the section CALLBACK TIMEOUTS.
Module:handle_msg(Msg, State) -> {ok, State} | {stop, ChannelId, State}
Msg = timeout | term()
ChannelId = ssh_channel_id()
State = term()
Handle other messages than ssh connection protocol, call or cast messages sent to the channel.
Possible erlang 'EXIT'-messages should be handled by this function and all channels should handle the following message.
{ssh_channel_up, ssh_channel_id(),
ssh_connection_ref()}
Module:handle_ssh_msg(Msg, State) -> {ok, State} | {stop, ChannelId, State}
Msg = ssh_connection:event()
ChannelId = ssh_channel_id()
State = term()
Handles SSH connection protocol messages that may need service specific attention.
The following message is completely taken care of by the SSH channel behavior
{closed, ssh_channel_id()}
Module:terminate(Reason, State) -> _
Reason = term()
State = term()
This function is called by a channel process when it is
about to terminate. Before this function is called ssh_connection:close/2
will be called if it has not been called earlier.
This function should do any necessary cleaning
up. When it returns, the channel process terminates with
reason Reason
. The return value is ignored.