Class: Net::SSH::Service::Forward

Inherits:
Object
  • Object
show all
Includes:
Loggable
Defined in:
lib/net/ssh/service/forward.rb

Overview

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 Connection::Session#forward:

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

Defined Under Namespace

Classes: Remote

Instance Attribute Summary collapse

Attributes included from Loggable

#logger

Instance Method Summary collapse

Methods included from Loggable

#debug, #error, #fatal, #info, #lwarn

Constructor Details

#initialize(session) ⇒ Forward

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.



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# File 'lib/net/ssh/service/forward.rb', line 25

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('[email protected]', &method(:auth_agent_channel))
end

Instance Attribute Details

#session ⇒ Object (readonly)

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



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# File 'lib/net/ssh/service/forward.rb', line 17

def session
  @session
end

Instance Method Details

#active_locals ⇒ Object

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.



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# File 'lib/net/ssh/service/forward.rb', line 119

def active_locals
  @local_forwarded_ports.keys
end

#active_remote_destinations ⇒ Object

Returns all active remote forwarded ports and where they forward to. The returned value is a hash from [<forwarding port on the local host>, <local forwarding address>] to [<port on the remote host>, <remote bind address>].



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# File 'lib/net/ssh/service/forward.rb', line 220

def active_remote_destinations
  @remote_forwarded_ports.inject({}) do |result, (remote, local)|
    result[[local.port, local.host]] = remote
    result
  end
end

#active_remotes ⇒ Object

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.



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# File 'lib/net/ssh/service/forward.rb', line 213

def active_remotes
  @remote_forwarded_ports.keys
end

#agent(channel) ⇒ Object

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



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# File 'lib/net/ssh/service/forward.rb', line 240

def agent(channel)
  return if @agent_forwarded
  @agent_forwarded = true

  channel.send_channel_request("[email protected]") 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") ⇒ Object

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")



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# File 'lib/net/ssh/service/forward.rb', line 108

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") ⇒ Object

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"]) }



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# File 'lib/net/ssh/service/forward.rb', line 200

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) ⇒ Object

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.

To request an ephemeral port on the remote server, provide 0 (zero) for the port number. In all cases, this method will return the port that has been assigned.

ssh.forward.local(1234, "www.capify.org", 80)
assigned_port = ssh.forward.local("0.0.0.0", 0, "www.capify.org", 80)



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# File 'lib/net/ssh/service/forward.rb', line 56

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

  local_port = socket.addr[1] if local_port == 0 # ephemeral port was requested
  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})" }
      session.stop_listening_to(channel[:socket])
      channel[:socket].close
    end
  end

  local_port
end

#remote(port, host, remote_port, remote_host = "127.0.0.1") ⇒ Object Also known as: remote_to

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.

To request an ephemeral port on the remote server, provide 0 (zero) for the port number. The assigned port will show up in the # #active_remotes list.

remote_host is interpreted by the server per RFC 4254, which has these special values:

  • “” means that connections are to be accepted on all protocol families supported by the SSH implementation.

  • “0.0.0.0” means to listen on all IPv4 addresses.

  • “::” means to listen on all IPv6 addresses.

  • “localhost” means to listen on all protocol families supported by the SSH implementation on loopback addresses only ([RFC3330] and [RFC3513]).

  • “127.0.0.1” and “::1” indicate listening on the loopback interfaces for IPv4 and IPv6, respectively.

You may pass a block that will be called when the the port forward request receives a response. This block will be passed the remote_port that was actually bound to, or nil if the binding failed. If the block returns :no_exception, the “failed binding” exception will not be thrown.

If you want to block until the port is active, you could do something like this:

got_remote_port = nil
remote(port, host, remote_port, remote_host) do |actual_remote_port|
  got_remote_port = actual_remote_port || :error
  :no_exception # will yield the exception on my own thread
end
session.loop { !got_remote_port }
if got_remote_port == :error
  raise Net::SSH::Exception, "remote forwarding request failed"
end



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# File 'lib/net/ssh/service/forward.rb', line 166

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
      remote_port = response.read_long if remote_port == 0
      debug { "remote forward from remote #{remote_host}:#{remote_port} to #{host}:#{port} established" }
      @remote_forwarded_ports[[remote_port, remote_host]] = Remote.new(host, port)
      yield remote_port, remote_host if block_given?
    else
      instruction = if block_given?
        yield :error
      end
      unless instruction == :no_exception
        error { "remote forwarding request failed" }
        raise Net::SSH::Exception, "remote forwarding request failed"
      end
    end
  end
end