Package paramiko :: Module channel :: Class Channel
[frames] | no frames]

Class Channel

source code

object --+
         |
        Channel

A secure tunnel across an SSH `.Transport`. A Channel is meant to behave like a socket, and has an API that should be indistinguishable from the Python socket API.

Because SSH2 has a windowing kind of flow control, if you stop reading data from a Channel and its buffer fills up, the server will be unable to send you any more data until you read some of it. (This won't affect other channels on the same transport -- all channels on a single transport are flow-controlled independently.) Similarly, if the server isn't reading data you send, calls to `send` may block, unless you set a timeout. This is exactly like a normal network socket, so it shouldn't be too surprising.

Instance Methods
 
__init__(self, chanid)
Create a new channel.
source code
 
__del__(self) source code
 
__repr__(self)
Return a string representation of this object, for debugging.
source code
 
get_pty(self, term='vt100', width=80, height=24, width_pixels=0, height_pixels=0)
Request a pseudo-terminal from the server.
source code
 
invoke_shell(self)
Request an interactive shell session on this channel.
source code
 
exec_command(self, command)
Execute a command on the server.
source code
 
invoke_subsystem(self, subsystem)
Request a subsystem on the server (for example, ``sftp``).
source code
 
resize_pty(self, width=80, height=24, width_pixels=0, height_pixels=0)
Resize the pseudo-terminal.
source code
 
exit_status_ready(self)
Return true if the remote process has exited and returned an exit status.
source code
 
recv_exit_status(self)
Return the exit status from the process on the server.
source code
 
send_exit_status(self, status)
Send the exit status of an executed command to the client.
source code
 
request_x11(self, screen_number=0, auth_protocol=None, auth_cookie=None, single_connection=False, handler=None)
Request an x11 session on this channel.
source code
 
request_forward_agent(self, handler)
Request for a forward SSH Agent on this channel.
source code
 
get_transport(self)
Return the `.Transport` associated with this channel.
source code
 
set_name(self, name)
Set a name for this channel.
source code
 
get_name(self)
Get the name of this channel that was previously set by `set_name`.
source code
 
get_id(self)
Return the `int` ID # for this channel.
source code
 
set_combine_stderr(self, combine)
Set whether stderr should be combined into stdout on this channel.
source code
 
settimeout(self, timeout)
Set a timeout on blocking read/write operations.
source code
 
gettimeout(self)
Returns the timeout in seconds (as a float) associated with socket operations, or ``None`` if no timeout is set.
source code
 
setblocking(self, blocking)
Set blocking or non-blocking mode of the channel: if ``blocking`` is 0, the channel is set to non-blocking mode; otherwise it's set to blocking mode.
source code
 
getpeername(self)
Return the address of the remote side of this Channel, if possible.
source code
 
close(self)
Close the channel.
source code
 
recv_ready(self)
Returns true if data is buffered and ready to be read from this channel.
source code
 
recv(self, nbytes)
Receive data from the channel.
source code
 
recv_stderr_ready(self)
Returns true if data is buffered and ready to be read from this channel's stderr stream.
source code
 
recv_stderr(self, nbytes)
Receive data from the channel's stderr stream.
source code
 
send_ready(self)
Returns true if data can be written to this channel without blocking.
source code
 
send(self, s)
Send data to the channel.
source code
 
send_stderr(self, s)
Send data to the channel on the "stderr" stream.
source code
 
sendall(self, s)
Send data to the channel, without allowing partial results.
source code
 
sendall_stderr(self, s)
Send data to the channel's "stderr" stream, without allowing partial results.
source code
 
makefile(self, *params)
Return a file-like object associated with this channel.
source code
 
makefile_stderr(self, *params)
Return a file-like object associated with this channel's stderr stream.
source code
 
fileno(self)
Returns an OS-level file descriptor which can be used for polling, but but not for reading or writing.
source code
 
shutdown(self, how)
Shut down one or both halves of the connection.
source code
 
shutdown_read(self)
Shutdown the receiving side of this socket, closing the stream in the incoming direction.
source code
 
shutdown_write(self)
Shutdown the sending side of this socket, closing the stream in the outgoing direction.
source code

Inherited from object: __delattr__, __format__, __getattribute__, __hash__, __new__, __reduce__, __reduce_ex__, __setattr__, __sizeof__, __str__, __subclasshook__

Properties

Inherited from object: __class__

Method Details

__init__(self, chanid)
(Constructor)

source code 

Create a new channel.  The channel is not associated with any
particular session or `.Transport` until the Transport attaches it.
Normally you would only call this method from the constructor of a
subclass of `.Channel`.

:param int chanid:
    the ID of this channel, as passed by an existing `.Transport`.

Overrides: object.__init__

__repr__(self)
(Representation operator)

source code 

Return a string representation of this object, for debugging.

Overrides: object.__repr__

get_pty(self, term='vt100', width=80, height=24, width_pixels=0, height_pixels=0)

source code 

Request a pseudo-terminal from the server.  This is usually used right
after creating a client channel, to ask the server to provide some
basic terminal semantics for a shell invoked with `invoke_shell`.
It isn't necessary (or desirable) to call this method if you're going
to exectue a single command with `exec_command`.

:param str term: the terminal type to emulate (for example, ``'vt100'``)
:param int width: width (in characters) of the terminal screen
:param int height: height (in characters) of the terminal screen
:param int width_pixels: width (in pixels) of the terminal screen
:param int height_pixels: height (in pixels) of the terminal screen

:raises SSHException:
    if the request was rejected or the channel was closed

invoke_shell(self)

source code 

Request an interactive shell session on this channel.  If the server
allows it, the channel will then be directly connected to the stdin,
stdout, and stderr of the shell.

Normally you would call `get_pty` before this, in which case the
shell will operate through the pty, and the channel will be connected
to the stdin and stdout of the pty.

When the shell exits, the channel will be closed and can't be reused.
You must open a new channel if you wish to open another shell.

:raises SSHException: if the request was rejected or the channel was
    closed

exec_command(self, command)

source code 

Execute a command on the server.  If the server allows it, the channel
will then be directly connected to the stdin, stdout, and stderr of
the command being executed.

When the command finishes executing, the channel will be closed and
can't be reused.  You must open a new channel if you wish to execute
another command.

:param str command: a shell command to execute.

:raises SSHException: if the request was rejected or the channel was
    closed

invoke_subsystem(self, subsystem)

source code 

Request a subsystem on the server (for example, ``sftp``).  If the
server allows it, the channel will then be directly connected to the
requested subsystem.

When the subsystem finishes, the channel will be closed and can't be
reused.

:param str subsystem: name of the subsystem being requested.

:raises SSHException:
    if the request was rejected or the channel was closed

resize_pty(self, width=80, height=24, width_pixels=0, height_pixels=0)

source code 

Resize the pseudo-terminal.  This can be used to change the width and
height of the terminal emulation created in a previous `get_pty` call.

:param int width: new width (in characters) of the terminal screen
:param int height: new height (in characters) of the terminal screen
:param int width_pixels: new width (in pixels) of the terminal screen
:param int height_pixels: new height (in pixels) of the terminal screen

:raises SSHException:
    if the request was rejected or the channel was closed

exit_status_ready(self)

source code 

Return true if the remote process has exited and returned an exit
status. You may use this to poll the process status if you don't
want to block in `recv_exit_status`. Note that the server may not
return an exit status in some cases (like bad servers).

:return:
    ``True`` if `recv_exit_status` will return immediately, else ``False``.

.. versionadded:: 1.7.3

recv_exit_status(self)

source code 

Return the exit status from the process on the server. This is mostly useful for retrieving the reults of an `exec_command`. If the command hasn't finished yet, this method will wait until it does, or until the channel is closed. If no exit status is provided by the server, -1 is returned.

:return: the exit code (as an `int`) of the process on the server.

.. versionadded:: 1.2

send_exit_status(self, status)

source code 

Send the exit status of an executed command to the client. (This really only makes sense in server mode.) Many clients expect to get some sort of status code back from an executed command after it completes.

:param int status: the exit code of the process

.. versionadded:: 1.2

request_x11(self, screen_number=0, auth_protocol=None, auth_cookie=None, single_connection=False, handler=None)

source code 

Request an x11 session on this channel.  If the server allows it,
further x11 requests can be made from the server to the client,
when an x11 application is run in a shell session.

From RFC4254::

    It is RECOMMENDED that the 'x11 authentication cookie' that is
    sent be a fake, random cookie, and that the cookie be checked and
    replaced by the real cookie when a connection request is received.

If you omit the auth_cookie, a new secure random 128-bit value will be
generated, used, and returned.  You will need to use this value to
verify incoming x11 requests and replace them with the actual local
x11 cookie (which requires some knoweldge of the x11 protocol).

If a handler is passed in, the handler is called from another thread
whenever a new x11 connection arrives.  The default handler queues up
incoming x11 connections, which may be retrieved using
`.Transport.accept`.  The handler's calling signature is::

    handler(channel: Channel, (address: str, port: int))

:param int screen_number: the x11 screen number (0, 10, etc)
:param str auth_protocol:
    the name of the X11 authentication method used; if none is given,
    ``"MIT-MAGIC-COOKIE-1"`` is used
:param str auth_cookie:
    hexadecimal string containing the x11 auth cookie; if none is
    given, a secure random 128-bit value is generated
:param bool single_connection:
    if True, only a single x11 connection will be forwarded (by
    default, any number of x11 connections can arrive over this
    session)
:param function handler:
    an optional handler to use for incoming X11 connections
:return: the auth_cookie used

request_forward_agent(self, handler)

source code 

Request for a forward SSH Agent on this channel.
This is only valid for an ssh-agent from OpenSSH !!!

:param function handler:
    a required handler to use for incoming SSH Agent connections

:return: True if we are ok, else False (at that time we always return ok)

:raises: SSHException in case of channel problem.

set_name(self, name)

source code 

Set a name for this channel. Currently it's only used to set the name of the channel in logfile entries. The name can be fetched with the `get_name` method.

:param str name: new channel name

get_id(self)

source code 

Return the `int` ID # for this channel.

The channel ID is unique across a `.Transport` and usually a small number. It's also the number passed to `.ServerInterface.check_channel_request` when determining whether to accept a channel request in server mode.

set_combine_stderr(self, combine)

source code 

Set whether stderr should be combined into stdout on this channel.
The default is ``False``, but in some cases it may be convenient to
have both streams combined.

If this is ``False``, and `exec_command` is called (or ``invoke_shell``
with no pty), output to stderr will not show up through the `recv`
and `recv_ready` calls.  You will have to use `recv_stderr` and
`recv_stderr_ready` to get stderr output.

If this is ``True``, data will never show up via `recv_stderr` or
`recv_stderr_ready`.

:param bool combine:
    ``True`` if stderr output should be combined into stdout on this
    channel.
:return: the previous setting (a `bool`).

.. versionadded:: 1.1

settimeout(self, timeout)

source code 

Set a timeout on blocking read/write operations.  The ``timeout``
argument can be a nonnegative float expressing seconds, or ``None``.  If
a float is given, subsequent channel read/write operations will raise
a timeout exception if the timeout period value has elapsed before the
operation has completed.  Setting a timeout of ``None`` disables
timeouts on socket operations.

``chan.settimeout(0.0)`` is equivalent to ``chan.setblocking(0)``;
``chan.settimeout(None)`` is equivalent to ``chan.setblocking(1)``.

:param float timeout:
    seconds to wait for a pending read/write operation before raising
    ``socket.timeout``, or ``None`` for no timeout.

gettimeout(self)

source code 

Returns the timeout in seconds (as a float) associated with socket operations, or ``None`` if no timeout is set. This reflects the last call to `setblocking` or `settimeout`.

setblocking(self, blocking)

source code 

Set blocking or non-blocking mode of the channel: if ``blocking`` is 0,
the channel is set to non-blocking mode; otherwise it's set to blocking
mode. Initially all channels are in blocking mode.

In non-blocking mode, if a `recv` call doesn't find any data, or if a
`send` call can't immediately dispose of the data, an error exception
is raised. In blocking mode, the calls block until they can proceed. An
EOF condition is considered "immediate data" for `recv`, so if the
channel is closed in the read direction, it will never block.

``chan.setblocking(0)`` is equivalent to ``chan.settimeout(0)``;
``chan.setblocking(1)`` is equivalent to ``chan.settimeout(None)``.

:param int blocking:
    0 to set non-blocking mode; non-0 to set blocking mode.

getpeername(self)

source code 

Return the address of the remote side of this Channel, if possible.

This simply wraps `.Transport.getpeername`, used to provide enough of a socket-like interface to allow asyncore to work. (asyncore likes to call ``'getpeername'``.)

close(self)

source code 

Close the channel. All future read/write operations on the channel will fail. The remote end will receive no more data (after queued data is flushed). Channels are automatically closed when their `.Transport` is closed or when they are garbage collected.

recv_ready(self)

source code 

Returns true if data is buffered and ready to be read from this
channel.  A ``False`` result does not mean that the channel has closed;
it means you may need to wait before more data arrives.

:return:
    ``True`` if a `recv` call on this channel would immediately return
    at least one byte; ``False`` otherwise.

recv(self, nbytes)

source code 

Receive data from the channel.  The return value is a string
representing the data received.  The maximum amount of data to be
received at once is specified by ``nbytes``.  If a string of length zero
is returned, the channel stream has closed.

:param int nbytes: maximum number of bytes to read.
:return: received data, as a `str`

:raises socket.timeout:
    if no data is ready before the timeout set by `settimeout`.

recv_stderr_ready(self)

source code 

Returns true if data is buffered and ready to be read from this
channel's stderr stream.  Only channels using `exec_command` or
`invoke_shell` without a pty will ever have data on the stderr
stream.

:return:
    ``True`` if a `recv_stderr` call on this channel would immediately
    return at least one byte; ``False`` otherwise.

.. versionadded:: 1.1

recv_stderr(self, nbytes)

source code 

Receive data from the channel's stderr stream.  Only channels using
`exec_command` or `invoke_shell` without a pty will ever have data
on the stderr stream.  The return value is a string representing the
data received.  The maximum amount of data to be received at once is
specified by ``nbytes``.  If a string of length zero is returned, the
channel stream has closed.

:param int nbytes: maximum number of bytes to read.
:return: received data as a `str`

:raises socket.timeout: if no data is ready before the timeout set by
    `settimeout`.

.. versionadded:: 1.1

send_ready(self)

source code 

Returns true if data can be written to this channel without blocking.
This means the channel is either closed (so any write attempt would
return immediately) or there is at least one byte of space in the 
outbound buffer. If there is at least one byte of space in the
outbound buffer, a `send` call will succeed immediately and return
the number of bytes actually written.

:return:
    ``True`` if a `send` call on this channel would immediately succeed
    or fail

send(self, s)

source code 

Send data to the channel.  Returns the number of bytes sent, or 0 if
the channel stream is closed.  Applications are responsible for
checking that all data has been sent: if only some of the data was
transmitted, the application needs to attempt delivery of the remaining
data.

:param str s: data to send
:return: number of bytes actually sent, as an `int`

:raises socket.timeout: if no data could be sent before the timeout set
    by `settimeout`.

send_stderr(self, s)

source code 

Send data to the channel on the "stderr" stream.  This is normally
only used by servers to send output from shell commands -- clients
won't use this.  Returns the number of bytes sent, or 0 if the channel
stream is closed.  Applications are responsible for checking that all
data has been sent: if only some of the data was transmitted, the
application needs to attempt delivery of the remaining data.

:param str s: data to send.
:return: number of bytes actually sent, as an `int`.

:raises socket.timeout:
    if no data could be sent before the timeout set by `settimeout`.

.. versionadded:: 1.1

sendall(self, s)

source code 

Send data to the channel, without allowing partial results.  Unlike
`send`, this method continues to send data from the given string until
either all data has been sent or an error occurs.  Nothing is returned.

:param str s: data to send.

:raises socket.timeout:
    if sending stalled for longer than the timeout set by `settimeout`.
:raises socket.error:
    if an error occured before the entire string was sent.

.. note::
    If the channel is closed while only part of the data hase been
    sent, there is no way to determine how much data (if any) was sent.
    This is irritating, but identically follows Python's API.

sendall_stderr(self, s)

source code 

Send data to the channel's "stderr" stream, without allowing partial
results.  Unlike `send_stderr`, this method continues to send data
from the given string until all data has been sent or an error occurs.
Nothing is returned.

:param str s: data to send to the client as "stderr" output.

:raises socket.timeout:
    if sending stalled for longer than the timeout set by `settimeout`.
:raises socket.error:
    if an error occured before the entire string was sent.
    
.. versionadded:: 1.1

makefile(self, *params)

source code 

Return a file-like object associated with this channel. The optional ``mode`` and ``bufsize`` arguments are interpreted the same way as by the built-in ``file()`` function in Python.

:return: `.ChannelFile` object which can be used for Python file I/O.

makefile_stderr(self, *params)

source code 

Return a file-like object associated with this channel's stderr stream. Only channels using `exec_command` or `invoke_shell` without a pty will ever have data on the stderr stream.

The optional ``mode`` and ``bufsize`` arguments are interpreted the same way as by the built-in ``file()`` function in Python. For a client, it only makes sense to open this file for reading. For a server, it only makes sense to open this file for writing.

:return: `.ChannelFile` object which can be used for Python file I/O.

.. versionadded:: 1.1

fileno(self)

source code 

Returns an OS-level file descriptor which can be used for polling, but but not for reading or writing. This is primaily to allow Python's ``select`` module to work.

The first time ``fileno`` is called on a channel, a pipe is created to simulate real OS-level file descriptor (FD) behavior. Because of this, two OS-level FDs are created, which will use up FDs faster than normal. (You won't notice this effect unless you have hundreds of channels open at the same time.)

:return: an OS-level file descriptor (`int`)

.. warning:

   This method causes channel reads to be slightly less efficient.

shutdown(self, how)

source code 

Shut down one or both halves of the connection.  If ``how`` is 0,
further receives are disallowed.  If ``how`` is 1, further sends
are disallowed.  If ``how`` is 2, further sends and receives are
disallowed.  This closes the stream in one or both directions.

:param int how:
    0 (stop receiving), 1 (stop sending), or 2 (stop receiving and
      sending).

shutdown_read(self)

source code 

Shutdown the receiving side of this socket, closing the stream in the incoming direction. After this call, future reads on this channel will fail instantly. This is a convenience method, equivalent to ``shutdown(0)``, for people who don't make it a habit to memorize unix constants from the 1970s.

.. versionadded:: 1.2

shutdown_write(self)

source code 

Shutdown the sending side of this socket, closing the stream in the outgoing direction. After this call, future writes on this channel will fail instantly. This is a convenience method, equivalent to ``shutdown(1)``, for people who don't make it a habit to memorize unix constants from the 1970s.

.. versionadded:: 1.2