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Package paramiko :: Class Channel
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Type Channel

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.
Method Summary
  __init__(self, chanid)
Create a new channel.
  __del__(self)
str __repr__(self)
Return a string representation of this object, for debugging.
  close(self)
Close the channel.
bool exec_command(self, command)
Execute a command on the server.
int fileno(self)
Returns an OS-level file descriptor which can be used for polling, but but not for reading or writing).
int get_id(self)
Return the ID # for this channel.
str get_name(self)
Get the name of this channel that was previously set by set_name.
bool get_pty(self, term, width, height)
Request a pseudo-terminal from the server.
Transport get_transport(self)
Return the Transport associated with this channel.
float gettimeout(self)
Returns the timeout in seconds (as a float) associated with socket operations, or None if no timeout is set.
bool invoke_shell(self)
Request an interactive shell session on this channel.
bool invoke_subsystem(self, subsystem)
Request a subsystem on the server (for example, sftp).
ChannelFile makefile(self, *params)
Return a file-like object associated with this channel.
ChannelFile makefile_stderr(self, *params)
Return a file-like object associated with this channel's stderr stream.
str recv(self, nbytes)
Receive data from the channel.
int recv_exit_status(self)
Return the exit status from the process on the server.
boolean recv_ready(self)
Returns true if data is buffered and ready to be read from this channel.
str recv_stderr(self, nbytes)
Receive data from the channel's stderr stream.
boolean recv_stderr_ready(self)
Returns true if data is buffered and ready to be read from this channel's stderr stream.
bool resize_pty(self, width, height)
Resize the pseudo-terminal.
int send(self, s)
Send data to the channel.
  send_exit_status(self, status)
Send the exit status of an executed command to the client.
int send_stderr(self, s)
Send data to the channel on the "stderr" stream.
  sendall(self, s)
Send data to the channel, without allowing partial results.
  sendall_stderr(self, s)
Send data to the channel's "stderr" stream, without allowing partial results.
bool set_combine_stderr(self, combine)
Set whether stderr should be combined into stdout on this channel.
  set_name(self, name)
Set a name for this channel.
  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.
  settimeout(self, timeout)
Set a timeout on blocking read/write operations.
  shutdown(self, how)
Shut down one or both halves of the connection.
  shutdown_read(self)
Shutdown the receiving side of this socket, closing the stream in the incoming direction.
  shutdown_write(self)
Shutdown the sending side of this socket, closing the stream in the outgoing direction.
    Inherited from object
  __delattr__(...)
x.__delattr__('name') <==> del x.name
  __getattribute__(...)
x.__getattribute__('name') <==> x.name
  __hash__(x)
x.__hash__() <==> hash(x)
  __new__(T, S, ...)
T.__new__(S, ...) -> a new object with type S, a subtype of T
  __reduce__(...)
helper for pickle
  __reduce_ex__(...)
helper for pickle
  __setattr__(...)
x.__setattr__('name', value) <==> x.name = value
  __str__(x)
x.__str__() <==> str(x)

Class Variable Summary
int MIN_PACKET_SIZE = 1024                                                                  

Method Details

__init__(self, chanid)
(Constructor)

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.
Parameters:
chanid - the ID of this channel, as passed by an existing Transport.
           (type=int)
Overrides:
__builtin__.object.__init__

__repr__(self)
(Representation operator)

Return a string representation of this object, for debugging.
Returns:
str
Overrides:
__builtin__.object.__repr__

close(self)

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.

exec_command(self, command)

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.
Parameters:
command - a shell command to execute.
           (type=str)
Returns:
True if the operation succeeded; False if not.
           (type=bool)

fileno(self)

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 open hundreds or thousands of channels simultaneously, but it's still notable.
Returns:
an OS-level file descriptor
           (type=int)

Warning: This method causes channel reads to be slightly less efficient.

get_id(self)

Return the 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.
Returns:
the ID of this channel.
           (type=int)

Since: ivysaur

get_name(self)

Get the name of this channel that was previously set by set_name.
Returns:
the name of this channel.
           (type=str)

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

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.
Parameters:
term - the terminal type to emulate (for example, 'vt100').
           (type=str)
width - width (in characters) of the terminal screen
           (type=int)
height - height (in characters) of the terminal screen
           (type=int)
Returns:
True if the operation succeeded; False if not.
           (type=bool)

get_transport(self)

Return the Transport associated with this channel.
Returns:
the Transport that was used to create this channel.
           (type=Transport)

gettimeout(self)

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.
Returns:
timeout in seconds, or None.
           (type=float)

invoke_shell(self)

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.
Returns:
True if the operation succeeded; False if not.
           (type=bool)

invoke_subsystem(self, subsystem)

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.
Parameters:
subsystem - name of the subsystem being requested.
           (type=str)
Returns:
True if the operation succeeded; False if not.
           (type=bool)

makefile(self, *params)

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.
Returns:
object which can be used for python file I/O.
           (type=ChannelFile)

makefile_stderr(self, *params)

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.
Returns:
object which can be used for python file I/O.
           (type=ChannelFile)

Since: 1.1

recv(self, nbytes)

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.
Parameters:
nbytes - maximum number of bytes to read.
           (type=int)
Returns:
data.
           (type=str)
Raises:
socket.timeout - if no data is ready before the timeout set by settimeout.

recv_exit_status(self)

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.
Returns:
the exit code of the process on the server.
           (type=int)

Since: 1.2

recv_ready(self)

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.
Returns:
True if a recv call on this channel would immediately return at least one byte; False otherwise.
           (type=boolean)

recv_stderr(self, nbytes)

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.
Parameters:
nbytes - maximum number of bytes to read.
           (type=int)
Returns:
data.
           (type=str)
Raises:
socket.timeout - if no data is ready before the timeout set by settimeout.

Since: 1.1

recv_stderr_ready(self)

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.
Returns:
True if a recv_stderr call on this channel would immediately return at least one byte; False otherwise.
           (type=boolean)

Since: 1.1

resize_pty(self, width=80, height=24)

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.
Parameters:
width - new width (in characters) of the terminal screen
           (type=int)
height - new height (in characters) of the terminal screen
           (type=int)
Returns:
True if the operation succeeded; False if not.
           (type=bool)

send(self, s)

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.
Parameters:
s - data to send.
           (type=str)
Returns:
number of bytes actually sent.
           (type=int)
Raises:
socket.timeout - if no data could be sent before the timeout set by settimeout.

send_exit_status(self, status)

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.
Parameters:
status - the exit code of the process
           (type=int)

Since: 1.2

send_stderr(self, s)

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.
Parameters:
s - data to send.
           (type=str)
Returns:
number of bytes actually sent.
           (type=int)
Raises:
socket.timeout - if no data could be sent before the timeout set by settimeout.

Since: 1.1

sendall(self, s)

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.
Parameters:
s - data to send.
           (type=str)
Raises:
socket.timeout - if sending stalled for longer than the timeout set by settimeout.
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)

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.
Parameters:
s - data to send to the client as "stderr" output.
           (type=str)
Raises:
socket.timeout - if sending stalled for longer than the timeout set by settimeout.
socket.error - if an error occured before the entire string was sent.

Since: 1.1

set_combine_stderr(self, combine)

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.
Parameters:
combine - True if stderr output should be combined into stdout on this channel.
           (type=bool)
Returns:
previous setting.
           (type=bool)

Since: 1.1

set_name(self, name)

Set a name for this channel. Currently it's only used to set the name of the log level used for debugging. The name can be fetched with the get_name method.
Parameters:
name - new channel name.
           (type=str)

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. 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.

chan.setblocking(0) is equivalent to chan.settimeout(0); chan.setblocking(1) is equivalent to chan.settimeout(None).
Parameters:
blocking - 0 to set non-blocking mode; non-0 to set blocking mode.
           (type=int)

settimeout(self, timeout)

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).
Parameters:
timeout - seconds to wait for a pending read/write operation before raising socket.timeout, or None for no timeout.
           (type=float)

shutdown(self, how)

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.
Parameters:
how - 0 (stop receiving), 1 (stop sending), or 2 (stop receiving and sending).
           (type=int)

shutdown_read(self)

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.

Since: 1.2

shutdown_write(self)

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.

Since: 1.2


Class Variable Details

MIN_PACKET_SIZE

Type:
int
Value:
1024                                                                  

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