class Net::SSH::Service::Forward

This class implements various port forwarding services for use by Net::SSH clients. The Forward class should never need to be instantiated directly; instead, it should be accessed via the singleton instance returned by Net::SSH::Connection::Session#forward:

ssh.forward.local(1234, "www.capify.org", 80)

Attributes

session[R]

The underlying connection service instance that the port-forwarding services employ.

Public Class Methods

new(session) click to toggle source

Instantiates a new Forward service instance atop the given connection service session. This will register new channel open handlers to handle the specialized channels that the SSH port forwarding protocols employ.

# File lib/net/ssh/service/forward.rb, line 24
def initialize(session)
  @session = session
  self.logger = session.logger
  @remote_forwarded_ports = {}
  @local_forwarded_ports = {}
  @agent_forwarded = false

  session.on_open_channel('forwarded-tcpip', &method(:forwarded_tcpip))
  session.on_open_channel('auth-agent', &method(:auth_agent_channel))
  session.on_open_channel('auth-agent@openssh.com', &method(:auth_agent_channel))
end

Public Instance Methods

active_locals() click to toggle source

Returns a list of all active locally forwarded ports. The returned value is an array of arrays, where each element is a two-element tuple consisting of the local port and bind address corresponding to the forwarding port.

# File lib/net/ssh/service/forward.rb, line 110
def active_locals
  @local_forwarded_ports.keys
end
active_remotes() click to toggle source

Returns all active forwarded remote ports. The returned value is an array of two-element tuples, where the first element is the port on the remote host and the second is the bind address.

# File lib/net/ssh/service/forward.rb, line 168
def active_remotes
  @remote_forwarded_ports.keys
end
agent(channel) click to toggle source

Enables SSH agent forwarding on the given channel. The forwarded agent will remain active even after the channel closes–the channel is only used as the transport for enabling the forwarded connection. You should never need to call this directly–it is called automatically the first time a session channel is opened, when the connection was created with :forward_agent set to true:

Net::SSH.start("remote.host", "me", :forward_agent => true) do |ssh|
  ssh.open_channel do |ch|
    # agent will be automatically forwarded by this point
  end
  ssh.loop
end
# File lib/net/ssh/service/forward.rb, line 185
def agent(channel)
  return if @agent_forwarded
  @agent_forwarded = true

  channel.send_channel_request("auth-agent-req@openssh.com") do |achannel, success|
    if success
      debug { "authentication agent forwarding is active" }
    else
      achannel.send_channel_request("auth-agent-req") do |a2channel, success2|
        if success2
          debug { "authentication agent forwarding is active" }
        else
          error { "could not establish forwarding of authentication agent" }
        end
      end
    end
  end
end
cancel_local(port, bind_address="127.0.0.1") click to toggle source

Terminates an active local forwarded port. If no such forwarded port exists, this will raise an exception. Otherwise, the forwarded connection is terminated.

ssh.forward.cancel_local(1234)
ssh.forward.cancel_local(1234, "0.0.0.0")
# File lib/net/ssh/service/forward.rb, line 99
def cancel_local(port, bind_address="127.0.0.1")
  socket = @local_forwarded_ports.delete([port, bind_address])
  socket.shutdown rescue nil
  socket.close rescue nil
  session.stop_listening_to(socket)
end
cancel_remote(port, host="127.0.0.1") click to toggle source

Requests that a remote forwarded port be cancelled. The remote forwarded port on the remote host, bound to the given address on the remote host, will be terminated, but not immediately. This method returns immediately after queueing the request to be sent to the server. If for some reason the port cannot be cancelled, an exception will be raised (asynchronously).

If you want to know when the connection has been cancelled, it will no longer be present in the active_remotes list. If you want to block until the port is no longer active, you could do something like this:

ssh.forward.cancel_remote(1234, "0.0.0.0")
ssh.loop { ssh.forward.active_remotes.include?([1234, "0.0.0.0"]) }
# File lib/net/ssh/service/forward.rb, line 155
def cancel_remote(port, host="127.0.0.1")
  session.send_global_request("cancel-tcpip-forward", :string, host, :long, port) do |success, response|
    if success
      @remote_forwarded_ports.delete([port, host])
    else
      raise Net::SSH::Exception, "could not cancel remote forward request on #{host}:#{port}"
    end
  end
end
local(*args) click to toggle source

Starts listening for connections on the local host, and forwards them to the specified remote host/port via the SSH connection. This method accepts either three or four arguments. When four arguments are given, they are:

  • the local address to bind to

  • the local port to listen on

  • the remote host to forward connections to

  • the port on the remote host to connect to

If three arguments are given, it is as if the local bind address is “127.0.0.1”, and the rest are applied as above.

ssh.forward.local(1234, "www.capify.org", 80)
ssh.forward.local("0.0.0.0", 1234, "www.capify.org", 80)
# File lib/net/ssh/service/forward.rb, line 51
def local(*args)
  if args.length < 3 || args.length > 4
    raise ArgumentError, "expected 3 or 4 parameters, got #{args.length}"
  end

  local_port_type = :long

  socket = begin
    if defined?(UNIXServer) and args.first.class == UNIXServer
      local_port_type = :string
      args.shift
    else
      bind_address = "127.0.0.1"
      bind_address = args.shift if args.first.is_a?(String) && args.first =~ /\D/
      local_port = args.shift.to_i
      local_port_type = :long
      TCPServer.new(bind_address, local_port)
    end
  end

  remote_host = args.shift
  remote_port = args.shift.to_i

  @local_forwarded_ports[[local_port, bind_address]] = socket

  session.listen_to(socket) do |server|
    client = server.accept
    debug { "received connection on #{socket}" }

    channel = session.open_channel("direct-tcpip", :string, remote_host, :long, remote_port, :string, bind_address, local_port_type, local_port) do |achannel|
      achannel.info { "direct channel established" }
    end

    prepare_client(client, channel, :local)
  
    channel.on_open_failed do |ch, code, description|
      channel.error { "could not establish direct channel: #{description} (#{code})" }
      channel[:socket].close
    end
  end
end
remote(port, host, remote_port, remote_host="127.0.0.1") click to toggle source

Requests that all connections on the given remote-port be forwarded via the local host to the given port/host. The last argument describes the bind address on the remote host, and defaults to 127.0.0.1.

This method will return immediately, but the port will not actually be forwarded immediately. If the remote server is not able to begin the listener for this request, an exception will be raised asynchronously.

If you want to know when the connection is active, it will show up in the active_remotes list. If you want to block until the port is active, you could do something like this:

ssh.forward.remote(80, "www.google.com", 1234, "0.0.0.0")
ssh.loop { !ssh.forward.active_remotes.include?([1234, "0.0.0.0"]) }
# File lib/net/ssh/service/forward.rb, line 128
def remote(port, host, remote_port, remote_host="127.0.0.1")
  session.send_global_request("tcpip-forward", :string, remote_host, :long, remote_port) do |success, response|
    if success
      debug { "remote forward from remote #{remote_host}:#{remote_port} to #{host}:#{port} established" }
      @remote_forwarded_ports[[remote_port, remote_host]] = Remote.new(host, port)
    else
      error { "remote forwarding request failed" }
      raise Net::SSH::Exception, "remote forwarding request failed"
    end
  end
end
Also aliased as: remote_to
remote_to(port, host, remote_port, remote_host="127.0.0.1")

an alias, for token backwards compatibility with the 1.x API

Alias for: remote

Private Instance Methods

auth_agent_channel(session, channel, packet) click to toggle source

The callback used when an auth-agent channel is requested by the server.

# File lib/net/ssh/service/forward.rb, line 283
def auth_agent_channel(session, channel, packet)
  info { "opening auth-agent channel" }
  channel[:invisible] = true

  begin
    agent = Authentication::Agent.connect(logger)
    prepare_client(agent.socket, channel, :agent)
  rescue Exception => e
    error { "attempted to connect to agent but failed: #{e.class.name} (#{e.message})" }
    raise Net::SSH::ChannelOpenFailed.new(2, "could not connect to authentication agent")
  end
end
forwarded_tcpip(session, channel, packet) click to toggle source

The callback used when a new “forwarded-tcpip” channel is requested by the server. This will open a new socket to the host/port specified when the forwarded connection was first requested.

# File lib/net/ssh/service/forward.rb, line 262
def forwarded_tcpip(session, channel, packet)
  connected_address  = packet.read_string
  connected_port     = packet.read_long
  originator_address = packet.read_string
  originator_port    = packet.read_long

  remote = @remote_forwarded_ports[[connected_port, connected_address]]

  if remote.nil?
    raise Net::SSH::ChannelOpenFailed.new(1, "unknown request from remote forwarded connection on #{connected_address}:#{connected_port}")
  end

  client = TCPSocket.new(remote.host, remote.port)
  info { "connected #{connected_address}:#{connected_port} originator #{originator_address}:#{originator_port}" }

  prepare_client(client, channel, :remote)
rescue SocketError => err
  raise Net::SSH::ChannelOpenFailed.new(2, "could not connect to remote host (#{remote.host}:#{remote.port}): #{err.message}")
end
prepare_client(client, channel, type) click to toggle source

Perform setup operations that are common to all forwarded channels. client is a socket, channel is the channel that was just created, and type is an arbitrary string describing the type of the channel.

# File lib/net/ssh/service/forward.rb, line 209
def prepare_client(client, channel, type)
  client.extend(Net::SSH::BufferedIo)
  client.extend(Net::SSH::ForwardedBufferedIo)
  client.logger = logger

  session.listen_to(client)
  channel[:socket] = client

  channel.on_data do |ch, data|  
    debug { "data:#{data.length} on #{type} forwarded channel" }
    ch[:socket].enqueue(data)
  end
  
  # Handles server close on the sending side by Miklós Fazekas
  channel.on_eof do |ch|
    debug { "eof #{type} on #{type} forwarded channel" }
    begin
      ch[:socket].send_pending
      ch[:socket].shutdown Socket::SHUT_WR
    rescue IOError => e
      if e.message =~ /closed/ then
        debug { "epipe in on_eof => shallowing exception:#{e}" }
      else
        raise
      end
    rescue Errno::EPIPE => e
      debug { "epipe in on_eof => shallowing exception:#{e}" }
    rescue Errno::ENOTCONN => e
      debug { "enotconn in on_eof => shallowing exception:#{e}" }
    end
  end
  
  channel.on_close do |ch|
    debug { "closing #{type} forwarded channel" }
    ch[:socket].close if !client.closed?
    session.stop_listening_to(ch[:socket])
  end

  channel.on_process do |ch|
    if ch[:socket].closed?
      ch.info { "#{type} forwarded connection closed" }
      ch.close
    elsif ch[:socket].available > 0
      data = ch[:socket].read_available(8192)
      ch.debug { "read #{data.length} bytes from client, sending over #{type} forwarded connection" }
      ch.send_data(data)
    end
  end
end