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require 'net/ssh/loggable'
require 'net/ssh/connection/constants'
require 'net/ssh/connection/term'
module Net; module SSH; module Connection
# The channel abstraction. Multiple "channels" can be multiplexed onto a
# single SSH channel, each operating independently and seemingly in parallel.
# This class represents a single such channel. Most operations performed
# with the Net::SSH library will involve using one or more channels.
#
# Channels are intended to be used asynchronously. You request that one be
# opened (via Connection::Session#open_channel), and when it is opened, your
# callback is invoked. Then, you set various other callbacks on the newly
# opened channel, which are called in response to the corresponding events.
# Programming with Net::SSH works best if you think of your programs as
# state machines. Complex programs are best implemented as objects that
# wrap a channel. See Net::SCP and Net::SFTP for examples of how complex
# state machines can be built on top of the SSH protocol.
#
# ssh.open_channel do |channel|
# channel.exec("/invoke/some/command") do |ch, success|
# abort "could not execute command" unless success
#
# channel.on_data do |ch, data|
# puts "got stdout: #{data}"
# channel.send_data "something for stdin\n"
# end
#
# channel.on_extended_data do |ch, type, data|
# puts "got stderr: #{data}"
# end
#
# channel.on_close do |ch|
# puts "channel is closing!"
# end
# end
# end
#
# ssh.loop
#
# Channels also have a basic hash-like interface, that allows programs to
# store arbitrary state information on a channel object. This helps simplify
# the writing of state machines, especially when you may be juggling
# multiple open channels at the same time.
#
# Note that data sent across SSH channels are governed by maximum packet
# sizes and maximum window sizes. These details are managed internally
# by Net::SSH::Connection::Channel, so you may remain blissfully ignorant
# if you so desire, but you can always inspect the current maximums, as
# well as the remaining window size, using the reader attributes for those
# values.
class Channel
include Constants, Loggable
# The local id for this channel, assigned by the Net::SSH::Connection::Session instance.
attr_reader :local_id
# The remote id for this channel, assigned by the remote host.
attr_reader :remote_id
# The type of this channel, usually "session".
attr_reader :type
# The underlying Net::SSH::Connection::Session instance that supports this channel.
attr_reader :connection
# The maximum packet size that the local host can receive.
attr_reader :local_maximum_packet_size
# The maximum amount of data that the local end of this channel can
# receive. This is a total, not per-packet.
attr_reader :local_maximum_window_size
# The maximum packet size that the remote host can receive.
attr_reader :remote_maximum_packet_size
# The maximum amount of data that the remote end of this channel can
# receive. This is a total, not per-packet.
attr_reader :remote_maximum_window_size
# This is the remaining window size on the local end of this channel. When
# this reaches zero, no more data can be received.
attr_reader :local_window_size
# This is the remaining window size on the remote end of this channel. When
# this reaches zero, no more data can be sent.
attr_reader :remote_window_size
# A hash of properties for this channel. These can be used to store state
# information about this channel. See also #[] and #[]=.
attr_reader :properties
# The output buffer for this channel. Data written to the channel is
# enqueued here, to be written as CHANNEL_DATA packets during each pass of
# the event loop. See Connection::Session#process and #enqueue_pending_output.
attr_reader :output #:nodoc:
# The list of pending requests. Each time a request is sent which requires
# a reply, the corresponding callback is pushed onto this queue. As responses
# arrive, they are shifted off the front and handled.
attr_reader :pending_requests #:nodoc:
# Instantiates a new channel on the given connection, of the given type,
# and with the given id. If a block is given, it will be remembered until
# the channel is confirmed open by the server, and will be invoked at
# that time (see #do_open_confirmation).
#
# This also sets the default maximum packet size and maximum window size.
def initialize(connection, type, local_id, max_pkt_size = 0x8000, max_win_size = 0x20000, &on_confirm_open)
self.logger = connection.logger
@connection = connection
@type = type
@local_id = local_id
@local_maximum_packet_size = max_pkt_size
@local_window_size = @local_maximum_window_size = max_win_size
@on_confirm_open = on_confirm_open
@output = Buffer.new
@properties = {}
@pending_requests = []
@on_open_failed = @on_data = @on_extended_data = @on_process = @on_close = @on_eof = nil
@on_request = {}
@closing = @eof = @sent_eof = @local_closed = @remote_closed = false
end
# A shortcut for accessing properties of the channel (see #properties).
def [](name)
@properties[name]
end
# A shortcut for setting properties of the channel (see #properties).
def []=(name, value)
@properties[name] = value
end
# Syntactic sugar for executing a command. Sends a channel request asking
# that the given command be invoked. If the block is given, it will be
# called when the server responds. The first parameter will be the
# channel, and the second will be true or false, indicating whether the
# request succeeded or not. In this case, success means that the command
# is being executed, not that it has completed, and failure means that the
# command altogether failed to be executed.
#
# channel.exec "ls -l /home" do |ch, success|
# if success
# puts "command has begun executing..."
# # this is a good place to hang callbacks like #on_data...
# else
# puts "alas! the command could not be invoked!"
# end
# end
def exec(command, &block)
send_channel_request("exec", :string, command, &block)
end
# Syntactic sugar for requesting that a subsystem be started. Subsystems
# are a way for other protocols (like SFTP) to be run, using SSH as
# the transport. Generally, you'll never need to call this directly unless
# you are the implementor of something that consumes an SSH subsystem, like
# SFTP.
#
# channel.subsystem("sftp") do |ch, success|
# if success
# puts "subsystem successfully started"
# else
# puts "subsystem could not be started"
# end
# end
def subsystem(subsystem, &block)
send_channel_request("subsystem", :string, subsystem, &block)
end
# Syntactic sugar for setting an environment variable in the remote
# process' environment. Note that for security reasons, the server may
# refuse to set certain environment variables, or all, at the server's
# discretion. If you are connecting to an OpenSSH server, you will
# need to update the AcceptEnv setting in the sshd_config to include the
# environment variables you want to send.
#
# channel.env "PATH", "/usr/local/bin"
def env(variable_name, variable_value, &block)
send_channel_request("env", :string, variable_name, :string, variable_value, &block)
end
# A hash of the valid PTY options (see #request_pty).
VALID_PTY_OPTIONS = { :term => "xterm",
:chars_wide => 80,
:chars_high => 24,
:pixels_wide => 640,
:pixels_high => 480,
:modes => {} }
# Requests that a pseudo-tty (or "pty") be made available for this channel.
# This is useful when you want to invoke and interact with some kind of
# screen-based program (e.g., vim, or some menuing system).
#
# Note, that without a pty some programs (e.g. sudo, or subversion) on
# some systems, will not be able to run interactively, and will error
# instead of prompt if they ever need some user interaction.
#
# Note, too, that when a pty is requested, user's shell configuration
# scripts (.bashrc and such) are not run by default, whereas they are
# run when a pty is not present.
#
# channel.request_pty do |ch, success|
# if success
# puts "pty successfully obtained"
# else
# puts "could not obtain pty"
# end
# end
def request_pty(opts={}, &block)
extra = opts.keys - VALID_PTY_OPTIONS.keys
raise ArgumentError, "invalid option(s) to request_pty: #{extra.inspect}" if extra.any?
opts = VALID_PTY_OPTIONS.merge(opts)
modes = opts[:modes].inject(Buffer.new) do |memo, (mode, data)|
memo.write_byte(mode).write_long(data)
end
# mark the end of the mode opcode list with a 0 byte
modes.write_byte(0)
send_channel_request("pty-req", :string, opts[:term],
:long, opts[:chars_wide], :long, opts[:chars_high],
:long, opts[:pixels_wide], :long, opts[:pixels_high],
:string, modes.to_s, &block)
end
# Sends data to the channel's remote endpoint. This usually has the
# effect of sending the given string to the remote process' stdin stream.
# Note that it does not immediately send the data across the channel,
# but instead merely appends the given data to the channel's output buffer,
# preparatory to being packaged up and sent out the next time the connection
# is accepting data. (A connection might not be accepting data if, for
# instance, it has filled its data window and has not yet been resized by
# the remote end-point.)
#
# This will raise an exception if the channel has previously declared
# that no more data will be sent (see #eof!).
#
# channel.send_data("the password\n")
def send_data(data)
raise EOFError, "cannot send data if channel has declared eof" if eof?
output.append(data.to_s)
end
# Returns true if the channel exists in the channel list of the session,
# and false otherwise. This can be used to determine whether a channel has
# been closed or not.
#
# ssh.loop { channel.active? }
def active?
connection.channels.key?(local_id)
end
# Runs the SSH event loop until the channel is no longer active. This is
# handy for blocking while you wait for some channel to finish.
#
# channel.exec("grep ...") { ... }
# channel.wait
def wait
connection.loop { active? }
end
# True if close() has been called; NOTE: if the channel has data waiting to
# be sent then the channel will close after all the data is sent. See
# closed?() to determine if we have actually sent CHANNEL_CLOSE to server.
# This may be true for awhile before closed? returns true if we are still
# sending buffered output to server.
def closing?
@closing
end
# True if we have sent CHANNEL_CLOSE to the remote server.
def local_closed?
@local_closed
end
def remote_closed?
@remote_closed
end
def remote_closed!
@remote_closed = true
end
# Requests that the channel be closed. It only marks the channel to be closed
# the CHANNEL_CLOSE message will be sent from event loop
def close
return if @closing
@closing = true
end
# Returns true if the local end of the channel has declared that no more
# data is forthcoming (see #eof!). Trying to send data via #send_data when
# this is true will result in an exception being raised.
def eof?
@eof
end
# Tells the remote end of the channel that no more data is forthcoming
# from this end of the channel. The remote end may still send data.
# The CHANNEL_EOF packet will be sent once the output buffer is empty.
def eof!
return if eof?
@eof = true
end
# If an #on_process handler has been set up, this will cause it to be
# invoked (passing the channel itself as an argument). It also causes all
# pending output to be enqueued as CHANNEL_DATA packets (see #enqueue_pending_output).
def process
@on_process.call(self) if @on_process
enqueue_pending_output
if @eof and not @sent_eof and output.empty? and remote_id and not @local_closed
connection.send_message(Buffer.from(:byte, CHANNEL_EOF, :long, remote_id))
@sent_eof = true
end
if @closing and not @local_closed and output.empty? and remote_id
connection.send_message(Buffer.from(:byte, CHANNEL_CLOSE, :long, remote_id))
@local_closed = true
connection.cleanup_channel(self)
end
end
# Registers a callback to be invoked when data packets are received by the
# channel. The callback is called with the channel as the first argument,
# and the data as the second.
#
# channel.on_data do |ch, data|
# puts "got data: #{data.inspect}"
# end
#
# Data received this way is typically the data written by the remote
# process to its +stdout+ stream.
def on_data(&block)
old, @on_data = @on_data, block
old
end
# Registers a callback to be invoked when extended data packets are received
# by the channel. The callback is called with the channel as the first
# argument, the data type (as an integer) as the second, and the data as
# the third. Extended data is almost exclusively used to send +stderr+ data
# (+type+ == 1). Other extended data types are not defined by the SSH
# protocol.
#
# channel.on_extended_data do |ch, type, data|
# puts "got stderr: #{data.inspect}"
# end
def on_extended_data(&block)
old, @on_extended_data = @on_extended_data, block
old
end
# Registers a callback to be invoked for each pass of the event loop for
# this channel. There are no guarantees on timeliness in the event loop,
# but it will be called roughly once for each packet received by the
# connection (not the channel). This callback is invoked with the channel
# as the sole argument.
#
# Here's an example that accumulates the channel data into a variable on
# the channel itself, and displays individual lines in the input one
# at a time when the channel is processed:
#
# channel[:data] = ""
#
# channel.on_data do |ch, data|
# channel[:data] << data
# end
#
# channel.on_process do |ch|
# if channel[:data] =~ /^.*?\n/
# puts $&
# channel[:data] = $'
# end
# end
def on_process(&block)
old, @on_process = @on_process, block
old
end
# Registers a callback to be invoked when the server acknowledges that a
# channel is closed. This is invoked with the channel as the sole argument.
#
# channel.on_close do |ch|
# puts "remote end is closing!"
# end
def on_close(&block)
old, @on_close = @on_close, block
old
end
# Registers a callback to be invoked when the server indicates that no more
# data will be sent to the channel (although the channel can still send
# data to the server). The channel is the sole argument to the callback.
#
# channel.on_eof do |ch|
# puts "remote end is done sending data"
# end
def on_eof(&block)
old, @on_eof = @on_eof, block
old
end
# Registers a callback to be invoked when the server was unable to open
# the requested channel. The channel itself will be passed to the block,
# along with the integer "reason code" for the failure, and a textual
# description of the failure from the server.
#
# channel = session.open_channel do |ch|
# # ..
# end
#
# channel.on_open_failed { |ch, code, desc| ... }
def on_open_failed(&block)
old, @on_open_failed = @on_open_failed, block
old
end
# Registers a callback to be invoked when a channel request of the given
# type is received. The callback will receive the channel as the first
# argument, and the associated (unparsed) data as the second. The data
# will be a Net::SSH::Buffer that you will need to parse, yourself,
# according to the kind of request you are watching.
#
# By default, if the request wants a reply, Net::SSH will send a
# CHANNEL_SUCCESS response for any request that was handled by a registered
# callback, and CHANNEL_FAILURE for any that wasn't, but if you want your
# registered callback to result in a CHANNEL_FAILURE response, just raise
# Net::SSH::ChannelRequestFailed.
#
# Some common channel requests that your programs might want to listen
# for are:
#
# * "exit-status" : the exit status of the remote process will be reported
# as a long integer in the data buffer, which you can grab via
# data.read_long.
# * "exit-signal" : if the remote process died as a result of a signal
# being sent to it, the signal will be reported as a string in the
# data, via data.read_string. (Not all SSH servers support this channel
# request type.)
#
# channel.on_request "exit-status" do |ch, data|
# puts "process terminated with exit status: #{data.read_long}"
# end
def on_request(type, &block)
old, @on_request[type] = @on_request[type], block
old
end
# Sends a new channel request with the given name. The extra +data+
# parameter must either be empty, or consist of an even number of
# arguments. See Net::SSH::Buffer.from for a description of their format.
# If a block is given, it is registered as a callback for a pending
# request, and the packet will be flagged so that the server knows a
# reply is required. If no block is given, the server will send no
# response to this request. Responses, where required, will cause the
# callback to be invoked with the channel as the first argument, and
# either true or false as the second, depending on whether the request
# succeeded or not. The meaning of "success" and "failure" in this context
# is dependent on the specific request that was sent.
#
# channel.send_channel_request "shell" do |ch, success|
# if success
# puts "user shell started successfully"
# else
# puts "could not start user shell"
# end
# end
#
# Most channel requests you'll want to send are already wrapped in more
# convenient helper methods (see #exec and #subsystem).
def send_channel_request(request_name, *data, &callback)
info { "sending channel request #{request_name.inspect}" }
fail "Channel open not yet confirmed, please call send_channel_request(or exec) from block of open_channel" unless remote_id
msg = Buffer.from(:byte, CHANNEL_REQUEST,
:long, remote_id, :string, request_name,
:bool, !callback.nil?, *data)
connection.send_message(msg)
pending_requests << callback if callback
end
public # these methods are public, but for Net::SSH internal use only
# Enqueues pending output at the connection as CHANNEL_DATA packets. This
# does nothing if the channel has not yet been confirmed open (see
# #do_open_confirmation). This is called automatically by #process, which
# is called from the event loop (Connection::Session#process). You will
# generally not need to invoke it directly.
def enqueue_pending_output #:nodoc:
return unless remote_id
while output.length > 0
length = output.length
length = remote_window_size if length > remote_window_size
length = remote_maximum_packet_size if length > remote_maximum_packet_size
if length > 0
connection.send_message(Buffer.from(:byte, CHANNEL_DATA, :long, remote_id, :string, output.read(length)))
output.consume!
@remote_window_size -= length
else
break
end
end
end
# Invoked when the server confirms that a channel has been opened.
# The remote_id is the id of the channel as assigned by the remote host,
# and max_window and max_packet are the maximum window and maximum
# packet sizes, respectively. If an open-confirmation callback was
# given when the channel was created, it is invoked at this time with
# the channel itself as the sole argument.
def do_open_confirmation(remote_id, max_window, max_packet) #:nodoc:
@remote_id = remote_id
@remote_window_size = @remote_maximum_window_size = max_window
@remote_maximum_packet_size = max_packet
connection.forward.agent(self) if connection.options[:forward_agent] && type == "session"
forward_local_env(connection.options[:send_env]) if connection.options[:send_env]
@on_confirm_open.call(self) if @on_confirm_open
end
# Invoked when the server failed to open the channel. If an #on_open_failed
# callback was specified, it will be invoked with the channel, reason code,
# and description as arguments. Otherwise, a ChannelOpenFailed exception
# will be raised.
def do_open_failed(reason_code, description)
if @on_open_failed
@on_open_failed.call(self, reason_code, description)
else
raise ChannelOpenFailed.new(reason_code, description)
end
end
# Invoked when the server sends a CHANNEL_WINDOW_ADJUST packet, and
# causes the remote window size to be adjusted upwards by the given
# number of bytes. This has the effect of allowing more data to be sent
# from the local end to the remote end of the channel.
def do_window_adjust(bytes) #:nodoc:
@remote_maximum_window_size += bytes
@remote_window_size += bytes
end
# Invoked when the server sends a channel request. If any #on_request
# callback has been registered for the specific type of this request,
# it is invoked. If +want_reply+ is true, a packet will be sent of
# either CHANNEL_SUCCESS or CHANNEL_FAILURE type. If there was no callback
# to handle the request, CHANNEL_FAILURE will be sent. Otherwise,
# CHANNEL_SUCCESS, unless the callback raised ChannelRequestFailed. The
# callback should accept the channel as the first argument, and the
# request-specific data as the second.
def do_request(request, want_reply, data) #:nodoc:
result = true
begin
callback = @on_request[request] or raise ChannelRequestFailed
callback.call(self, data)
rescue ChannelRequestFailed
result = false
end
if want_reply
msg = Buffer.from(:byte, result ? CHANNEL_SUCCESS : CHANNEL_FAILURE, :long, remote_id)
connection.send_message(msg)
end
end
# Invokes the #on_data callback when the server sends data to the
# channel. This will reduce the available window size on the local end,
# but does not actually throttle requests that come in illegally when
# the window size is too small. The callback is invoked with the channel
# as the first argument, and the data as the second.
def do_data(data) #:nodoc:
update_local_window_size(data.length)
@on_data.call(self, data) if @on_data
end
# Invokes the #on_extended_data callback when the server sends
# extended data to the channel. This will reduce the available window
# size on the local end. The callback is invoked with the channel,
# type, and data.
def do_extended_data(type, data)
update_local_window_size(data.length)
@on_extended_data.call(self, type, data) if @on_extended_data
end
# Invokes the #on_eof callback when the server indicates that no
# further data is forthcoming. The callback is invoked with the channel
# as the argument.
def do_eof
@on_eof.call(self) if @on_eof
end
# Invokes the #on_close callback when the server closes a channel.
# The channel is the only argument.
def do_close
@on_close.call(self) if @on_close
end
# Invokes the next pending request callback with +false+ as the second
# argument.
def do_failure
if callback = pending_requests.shift
callback.call(self, false)
else
error { "channel failure recieved with no pending request to handle it (bug?)" }
end
end
# Invokes the next pending request callback with +true+ as the second
# argument.
def do_success
if callback = pending_requests.shift
callback.call(self, true)
else
error { "channel success recieved with no pending request to handle it (bug?)" }
end
end
private
# Runs the SSH event loop until the remote confirmed channel open
# experimental api
def wait_until_open_confirmed
connection.loop { !remote_id }
end
# Updates the local window size by the given amount. If the window
# size drops to less than half of the local maximum (an arbitrary
# threshold), a CHANNEL_WINDOW_ADJUST message will be sent to the
# server telling it that the window size has grown.
def update_local_window_size(size)
@local_window_size -= size
if local_window_size < local_maximum_window_size/2
connection.send_message(Buffer.from(:byte, CHANNEL_WINDOW_ADJUST,
:long, remote_id, :long, 0x20000))
@local_window_size += 0x20000
@local_maximum_window_size += 0x20000
end
end
# Gets an +Array+ of local environment variables in the remote process'
# environment.
# A variable name can either be described by a +Regexp+ or +String+.
#
# channel.forward_local_env [/^GIT_.*$/, "LANG"]
def forward_local_env(env_variable_patterns)
Array(env_variable_patterns).each do |env_variable_pattern|
matched_variables = ENV.find_all do |env_name, _|
case env_variable_pattern
when Regexp then env_name =~ env_variable_pattern
when String then env_name == env_variable_pattern
end
end
matched_variables.each do |env_name, env_value|
self.env(env_name, env_value)
end
end
end
end
end; end; end