626 lines
25 KiB
Ruby
626 lines
25 KiB
Ruby
require 'net/ssh/loggable'
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require 'net/ssh/connection/constants'
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require 'net/ssh/connection/term'
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module Net; module SSH; module Connection
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# The channel abstraction. Multiple "channels" can be multiplexed onto a
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# single SSH channel, each operating independently and seemingly in parallel.
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# This class represents a single such channel. Most operations performed
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# with the Net::SSH library will involve using one or more channels.
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#
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# Channels are intended to be used asynchronously. You request that one be
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# opened (via Connection::Session#open_channel), and when it is opened, your
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# callback is invoked. Then, you set various other callbacks on the newly
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# opened channel, which are called in response to the corresponding events.
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# Programming with Net::SSH works best if you think of your programs as
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# state machines. Complex programs are best implemented as objects that
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# wrap a channel. See Net::SCP and Net::SFTP for examples of how complex
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# state machines can be built on top of the SSH protocol.
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#
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# ssh.open_channel do |channel|
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# channel.exec("/invoke/some/command") do |ch, success|
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# abort "could not execute command" unless success
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#
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# channel.on_data do |ch, data|
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# puts "got stdout: #{data}"
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# channel.send_data "something for stdin\n"
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# end
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#
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# channel.on_extended_data do |ch, type, data|
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# puts "got stderr: #{data}"
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# end
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#
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# channel.on_close do |ch|
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# puts "channel is closing!"
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# end
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# end
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# end
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#
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# ssh.loop
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#
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# Channels also have a basic hash-like interface, that allows programs to
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# store arbitrary state information on a channel object. This helps simplify
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# the writing of state machines, especially when you may be juggling
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# multiple open channels at the same time.
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#
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# Note that data sent across SSH channels are governed by maximum packet
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# sizes and maximum window sizes. These details are managed internally
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# by Net::SSH::Connection::Channel, so you may remain blissfully ignorant
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# if you so desire, but you can always inspect the current maximums, as
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# well as the remaining window size, using the reader attributes for those
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# values.
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class Channel
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include Constants, Loggable
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# The local id for this channel, assigned by the Net::SSH::Connection::Session instance.
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attr_reader :local_id
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# The remote id for this channel, assigned by the remote host.
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attr_reader :remote_id
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# The type of this channel, usually "session".
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attr_reader :type
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# The underlying Net::SSH::Connection::Session instance that supports this channel.
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attr_reader :connection
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# The maximum packet size that the local host can receive.
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attr_reader :local_maximum_packet_size
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# The maximum amount of data that the local end of this channel can
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# receive. This is a total, not per-packet.
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attr_reader :local_maximum_window_size
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# The maximum packet size that the remote host can receive.
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attr_reader :remote_maximum_packet_size
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# The maximum amount of data that the remote end of this channel can
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# receive. This is a total, not per-packet.
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attr_reader :remote_maximum_window_size
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# This is the remaining window size on the local end of this channel. When
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# this reaches zero, no more data can be received.
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attr_reader :local_window_size
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# This is the remaining window size on the remote end of this channel. When
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# this reaches zero, no more data can be sent.
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attr_reader :remote_window_size
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# A hash of properties for this channel. These can be used to store state
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# information about this channel. See also #[] and #[]=.
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attr_reader :properties
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# The output buffer for this channel. Data written to the channel is
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# enqueued here, to be written as CHANNEL_DATA packets during each pass of
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# the event loop. See Connection::Session#process and #enqueue_pending_output.
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attr_reader :output #:nodoc:
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# The list of pending requests. Each time a request is sent which requires
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# a reply, the corresponding callback is pushed onto this queue. As responses
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# arrive, they are shifted off the front and handled.
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attr_reader :pending_requests #:nodoc:
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# Instantiates a new channel on the given connection, of the given type,
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# and with the given id. If a block is given, it will be remembered until
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# the channel is confirmed open by the server, and will be invoked at
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# that time (see #do_open_confirmation).
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#
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# This also sets the default maximum packet size and maximum window size.
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def initialize(connection, type, local_id, &on_confirm_open)
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self.logger = connection.logger
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@connection = connection
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@type = type
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@local_id = local_id
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@local_maximum_packet_size = 0x10000
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@local_window_size = @local_maximum_window_size = 0x20000
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@on_confirm_open = on_confirm_open
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@output = Buffer.new
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@properties = {}
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@pending_requests = []
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@on_open_failed = @on_data = @on_extended_data = @on_process = @on_close = @on_eof = nil
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@on_request = {}
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@closing = @eof = false
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end
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# A shortcut for accessing properties of the channel (see #properties).
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def [](name)
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@properties[name]
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end
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# A shortcut for setting properties of the channel (see #properties).
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def []=(name, value)
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@properties[name] = value
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end
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# Syntactic sugar for executing a command. Sends a channel request asking
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# that the given command be invoked. If the block is given, it will be
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# called when the server responds. The first parameter will be the
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# channel, and the second will be true or false, indicating whether the
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# request succeeded or not. In this case, success means that the command
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# is being executed, not that it has completed, and failure means that the
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# command altogether failed to be executed.
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#
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# channel.exec "ls -l /home" do |ch, success|
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# if success
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# puts "command has begun executing..."
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# # this is a good place to hang callbacks like #on_data...
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# else
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# puts "alas! the command could not be invoked!"
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# end
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# end
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def exec(command, &block)
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send_channel_request("exec", :string, command, &block)
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end
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# Syntactic sugar for requesting that a subsystem be started. Subsystems
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# are a way for other protocols (like SFTP) to be run, using SSH as
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# the transport. Generally, you'll never need to call this directly unless
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# you are the implementor of something that consumes an SSH subsystem, like
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# SFTP.
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#
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# channel.subsystem("sftp") do |ch, success|
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# if success
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# puts "subsystem successfully started"
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# else
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# puts "subsystem could not be started"
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# end
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# end
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def subsystem(subsystem, &block)
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send_channel_request("subsystem", :string, subsystem, &block)
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end
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# Syntactic sugar for setting an environment variable in the remote
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# process' environment. Note that for security reasons, the server may
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# refuse to set certain environment variables, or all, at the server's
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# discretion. If you are connecting to an OpenSSH server, you will
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# need to update the AcceptEnv setting in the sshd_config to include the
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# environment variables you want to send.
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#
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# channel.env "PATH", "/usr/local/bin"
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def env(variable_name, variable_value, &block)
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send_channel_request("env", :string, variable_name, :string, variable_value, &block)
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end
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# A hash of the valid PTY options (see #request_pty).
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VALID_PTY_OPTIONS = { :term => "xterm",
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:chars_wide => 80,
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:chars_high => 24,
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:pixels_wide => 640,
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:pixels_high => 480,
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:modes => {} }
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# Requests that a pseudo-tty (or "pty") be made available for this channel.
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# This is useful when you want to invoke and interact with some kind of
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# screen-based program (e.g., vim, or some menuing system).
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#
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# Note, that without a pty some programs (e.g. sudo, or subversion) on
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# some systems, will not be able to run interactively, and will error
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# instead of prompt if they ever need some user interaction.
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#
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# Note, too, that when a pty is requested, user's shell configuration
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# scripts (.bashrc and such) are not run by default, whereas they are
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# run when a pty is not present.
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#
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# channel.request_pty do |ch, success|
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# if success
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# puts "pty successfully obtained"
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# else
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# puts "could not obtain pty"
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# end
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# end
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def request_pty(opts={}, &block)
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extra = opts.keys - VALID_PTY_OPTIONS.keys
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raise ArgumentError, "invalid option(s) to request_pty: #{extra.inspect}" if extra.any?
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opts = VALID_PTY_OPTIONS.merge(opts)
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modes = opts[:modes].inject(Buffer.new) do |memo, (mode, data)|
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memo.write_byte(mode).write_long(data)
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end
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# mark the end of the mode opcode list with a 0 byte
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modes.write_byte(0)
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send_channel_request("pty-req", :string, opts[:term],
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:long, opts[:chars_wide], :long, opts[:chars_high],
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:long, opts[:pixels_wide], :long, opts[:pixels_high],
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:string, modes.to_s, &block)
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end
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# Sends data to the channel's remote endpoint. This usually has the
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# effect of sending the given string to the remote process' stdin stream.
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# Note that it does not immediately send the data across the channel,
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# but instead merely appends the given data to the channel's output buffer,
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# preparatory to being packaged up and sent out the next time the connection
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# is accepting data. (A connection might not be accepting data if, for
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# instance, it has filled its data window and has not yet been resized by
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# the remote end-point.)
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#
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# This will raise an exception if the channel has previously declared
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# that no more data will be sent (see #eof!).
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#
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# channel.send_data("the password\n")
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def send_data(data)
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raise EOFError, "cannot send data if channel has declared eof" if eof?
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output.append(data.to_s)
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end
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# Returns true if the channel exists in the channel list of the session,
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# and false otherwise. This can be used to determine whether a channel has
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# been closed or not.
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#
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# ssh.loop { channel.active? }
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def active?
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connection.channels.key?(local_id)
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end
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# Runs the SSH event loop until the channel is no longer active. This is
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# handy for blocking while you wait for some channel to finish.
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#
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# channel.exec("grep ...") { ... }
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# channel.wait
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def wait
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connection.loop { active? }
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end
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# Returns true if the channel is currently closing, but not actually
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# closed. A channel is closing when, for instance, #close has been
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# invoked, but the server has not yet responded with a CHANNEL_CLOSE
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# packet of its own.
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def closing?
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@closing
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end
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# Requests that the channel be closed. If the channel is already closing,
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# this does nothing, nor does it do anything if the channel has not yet
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# been confirmed open (see #do_open_confirmation). Otherwise, it sends a
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# CHANNEL_CLOSE message and marks the channel as closing.
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def close
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return if @closing
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if remote_id
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@closing = true
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connection.send_message(Buffer.from(:byte, CHANNEL_CLOSE, :long, remote_id))
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end
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end
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# Returns true if the local end of the channel has declared that no more
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# data is forthcoming (see #eof!). Trying to send data via #send_data when
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# this is true will result in an exception being raised.
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def eof?
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@eof
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end
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# Tells the remote end of the channel that no more data is forthcoming
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# from this end of the channel. The remote end may still send data.
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def eof!
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return if eof?
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@eof = true
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connection.send_message(Buffer.from(:byte, CHANNEL_EOF, :long, remote_id))
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end
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# If an #on_process handler has been set up, this will cause it to be
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# invoked (passing the channel itself as an argument). It also causes all
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# pending output to be enqueued as CHANNEL_DATA packets (see #enqueue_pending_output).
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def process
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@on_process.call(self) if @on_process
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enqueue_pending_output
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end
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# Registers a callback to be invoked when data packets are received by the
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# channel. The callback is called with the channel as the first argument,
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# and the data as the second.
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#
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# channel.on_data do |ch, data|
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# puts "got data: #{data.inspect}"
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# end
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#
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# Data received this way is typically the data written by the remote
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# process to its +stdout+ stream.
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def on_data(&block)
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old, @on_data = @on_data, block
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old
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end
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# Registers a callback to be invoked when extended data packets are received
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# by the channel. The callback is called with the channel as the first
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# argument, the data type (as an integer) as the second, and the data as
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# the third. Extended data is almost exclusively used to send +stderr+ data
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# (+type+ == 1). Other extended data types are not defined by the SSH
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# protocol.
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#
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# channel.on_extended_data do |ch, type, data|
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# puts "got stderr: #{data.inspect}"
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# end
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def on_extended_data(&block)
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old, @on_extended_data = @on_extended_data, block
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old
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end
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# Registers a callback to be invoked for each pass of the event loop for
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# this channel. There are no guarantees on timeliness in the event loop,
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# but it will be called roughly once for each packet received by the
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# connection (not the channel). This callback is invoked with the channel
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# as the sole argument.
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#
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# Here's an example that accumulates the channel data into a variable on
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# the channel itself, and displays individual lines in the input one
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# at a time when the channel is processed:
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#
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# channel[:data] = ""
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#
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# channel.on_data do |ch, data|
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# channel[:data] << data
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# end
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#
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# channel.on_process do |ch|
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# if channel[:data] =~ /^.*?\n/
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# puts $&
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# channel[:data] = $'
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# end
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# end
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def on_process(&block)
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old, @on_process = @on_process, block
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old
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end
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# Registers a callback to be invoked when the server acknowledges that a
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# channel is closed. This is invoked with the channel as the sole argument.
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#
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# channel.on_close do |ch|
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# puts "remote end is closing!"
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# end
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def on_close(&block)
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old, @on_close = @on_close, block
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old
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end
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# Registers a callback to be invoked when the server indicates that no more
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# data will be sent to the channel (although the channel can still send
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# data to the server). The channel is the sole argument to the callback.
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#
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# channel.on_eof do |ch|
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# puts "remote end is done sending data"
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# end
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def on_eof(&block)
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old, @on_eof = @on_eof, block
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old
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end
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# Registers a callback to be invoked when the server was unable to open
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# the requested channel. The channel itself will be passed to the block,
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# along with the integer "reason code" for the failure, and a textual
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# description of the failure from the server.
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#
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# channel = session.open_channel do |ch|
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# # ..
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# end
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#
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# channel.on_open_failed { |ch, code, desc| ... }
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def on_open_failed(&block)
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old, @on_open_failed = @on_open_failed, block
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old
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end
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# Registers a callback to be invoked when a channel request of the given
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# type is received. The callback will receive the channel as the first
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# argument, and the associated (unparsed) data as the second. The data
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# will be a Net::SSH::Buffer that you will need to parse, yourself,
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# according to the kind of request you are watching.
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#
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# By default, if the request wants a reply, Net::SSH will send a
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# CHANNEL_SUCCESS response for any request that was handled by a registered
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# callback, and CHANNEL_FAILURE for any that wasn't, but if you want your
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# registered callback to result in a CHANNEL_FAILURE response, just raise
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# Net::SSH::ChannelRequestFailed.
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#
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# Some common channel requests that your programs might want to listen
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# for are:
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#
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# * "exit-status" : the exit status of the remote process will be reported
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# as a long integer in the data buffer, which you can grab via
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# data.read_long.
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# * "exit-signal" : if the remote process died as a result of a signal
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# being sent to it, the signal will be reported as a string in the
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# data, via data.read_string. (Not all SSH servers support this channel
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# request type.)
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#
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# channel.on_request "exit-status" do |ch, data|
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# puts "process terminated with exit status: #{data.read_long}"
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# end
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def on_request(type, &block)
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old, @on_request[type] = @on_request[type], block
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old
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end
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# Sends a new channel request with the given name. The extra +data+
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# parameter must either be empty, or consist of an even number of
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# arguments. See Net::SSH::Buffer.from for a description of their format.
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# If a block is given, it is registered as a callback for a pending
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# request, and the packet will be flagged so that the server knows a
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# reply is required. If no block is given, the server will send no
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# response to this request. Responses, where required, will cause the
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# callback to be invoked with the channel as the first argument, and
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# either true or false as the second, depending on whether the request
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# succeeded or not. The meaning of "success" and "failure" in this context
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# is dependent on the specific request that was sent.
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#
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# channel.send_channel_request "shell" do |ch, success|
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# if success
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# puts "user shell started successfully"
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# else
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# puts "could not start user shell"
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# end
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# end
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#
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# Most channel requests you'll want to send are already wrapped in more
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# convenient helper methods (see #exec and #subsystem).
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def send_channel_request(request_name, *data, &callback)
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info { "sending channel request #{request_name.inspect}" }
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msg = Buffer.from(:byte, CHANNEL_REQUEST,
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:long, remote_id, :string, request_name,
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:bool, !callback.nil?, *data)
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connection.send_message(msg)
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pending_requests << callback if callback
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end
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public # these methods are public, but for Net::SSH internal use only
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# Enqueues pending output at the connection as CHANNEL_DATA packets. This
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# does nothing if the channel has not yet been confirmed open (see
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# #do_open_confirmation). This is called automatically by #process, which
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# is called from the event loop (Connection::Session#process). You will
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# generally not need to invoke it directly.
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def enqueue_pending_output #:nodoc:
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return unless remote_id
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while output.length > 0
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length = output.length
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length = remote_window_size if length > remote_window_size
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length = remote_maximum_packet_size if length > remote_maximum_packet_size
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|
|
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"
|
|
@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
|
|
|
|
# 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
|
|
end
|
|
|
|
end; end; end
|