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|
require 'thread'
require 'net/ssh'
require 'net/ssh/version'
# A Gateway is an object that allows you to tunnel network connections through
# a publicly visible host to a host hidden behind it. This is particularly
# useful when dealing with hosts behind a firewall. One host will generally
# be visible (and accessible) outside the firewall, while the others will all
# be behind the firewall, and the only way to access those restricted hosts
# is by first logging into the publicly visible host, and from thence logging
# into the restricted ones.
#
# This class makes it easy to programmatically connect to these restricted
# hosts via SSH. You can either simply forward a port from the local host to
# the remote host, or you can open a new Net::SSH connection to the remote
# host via a forwarded port.
#
# require 'net/ssh/gateway'
#
# gateway = Net::SSH::Gateway.new('host.name', 'user')
#
# gateway.open('hidden.host', 80) do |port|
# Net::HTTP.get_print '127.0.0.1', '/path', port
# end
#
# gateway.ssh('hidden.host', 'user') do |ssh|
# puts ssh.exec!("hostname")
# end
#
# gateway.shutdown!
#
# Port numbers are allocated automatically, beginning at MAX_PORT and
# decrementing on each request for a new port until MIN_PORT is reached. If
# a port is already in use, this is detected and a different port will be
# assigned.
class Net::SSH::Gateway
# A trivial class for representing the version of this library.
class Version < Net::SSH::Version
# The major component of the library's version
MAJOR = 1
# The minor component of the library's version
MINOR = 1
# The tiny component of the library's version
TINY = 1
# The library's version as a Version instance
CURRENT = new(MAJOR, MINOR, TINY)
# The library's version as a String instance
STRING = CURRENT.to_s
end
# The maximum port number that the gateway will attempt to use to forward
# connections from.
MAX_PORT = 65535
# The minimum port number that the gateway will attempt to use to forward
# connections from.
MIN_PORT = 1024
# Instantiate a new Gateway object, using the given remote host as the
# tunnel. The arguments here are identical to those for Net::SSH.start, and
# are passed as given to that method to start up the gateway connection.
#
# gateway = Net::SSH::Gateway.new('host', 'user', :password => "password")
#
# As of 1.1 there is an additional option to specify the wait time for
# the gateway thread. The default is 0.001 seconds and can be changed
# with the :loop_wait option.
#
def initialize(host, user, options={})
@session = Net::SSH.start(host, user, options)
@session_mutex = Mutex.new
@port_mutex = Mutex.new
@next_port = MAX_PORT
@loop_wait = options.delete(:loop_wait) || 0.001
initiate_event_loop!
end
# Returns +true+ if the gateway is currently open and accepting connections.
# This will be the case unless #shutdown! has been invoked.
def active?
@active
end
# Shuts down the gateway by closing all forwarded ports and then closing
# the gateway's SSH session.
def shutdown!
return unless active?
@session_mutex.synchronize do
# cancel all active forward channels
@session.forward.active_locals.each do |lport, host, port|
@session.forward.cancel_local(lport)
end
end
@active = false
@thread.join
@session.close
end
# Opens a new port on the local host and forwards it to the given host/port
# via the gateway host. If a block is given, the newly allocated port
# number will be yielded to the block, and the port automatically closed
# (see #close) when the block finishes. Otherwise, the port number will be
# returned, and the caller is responsible for closing the port (#close).
#
# gateway.open('host', 80) do |port|
# # ...
# end
#
# port = gateway.open('host', 80)
# # ...
# gateway.close(port)
#
# If +local_port+ is not specified, the next available port will be used.
def open(host, port, local_port=nil)
ensure_open!
actual_local_port = local_port || next_port
@session_mutex.synchronize do
@session.forward.local(actual_local_port, host, port)
end
if block_given?
begin
yield actual_local_port
ensure
close(actual_local_port)
end
else
return actual_local_port
end
rescue Errno::EADDRINUSE
raise if local_port # if a local port was explicitly requested, bubble the error up
retry
end
# Cancels port-forwarding over an open port that was previously opened via
# #open.
def close(port)
ensure_open!
@session_mutex.synchronize do
@session.forward.cancel_local(port)
end
end
# Forwards a new connection to the given +host+ and opens a new Net::SSH
# connection to that host over the forwarded port. If a block is given,
# the new SSH connection will be yielded to the block, and autoclosed
# when the block terminates. The forwarded port will be autoclosed as well.
# If no block was given, the new SSH connection will be returned, and it
# is up to the caller to terminate both the connection and the forwarded
# port when done.
#
# gateway.ssh('host', 'user') do |ssh|
# # ...
# end
#
# ssh = gateway.ssh('host', 'user')
# # ...
# ssh.close
# gateway.close(ssh.transport.port)
def ssh(host, user, options={}, &block)
local_port = open(host, options[:port] || 22)
begin
Net::SSH.start("127.0.0.1", user, options.merge(:port => local_port), &block)
ensure
close(local_port) if block || $!
end
end
private
# Raises a RuntimeError if the gateway is not active. This is used as a
# sanity check to make sure a client doesn't try to call any methods on
# a closed gateway.
def ensure_open!
raise "attempt to use a closed gateway" unless active?
end
# Fires up the gateway session's event loop within a thread, so that it
# can run in the background. The loop will run for as long as the gateway
# remains active.
def initiate_event_loop!
@active = true
@thread = Thread.new do
while @active
@session_mutex.synchronize do
@session.process(@loop_wait)
end
Thread.pass
end
end
end
# Grabs the next available port number and returns it.
def next_port
@port_mutex.synchronize do
port = @next_port
@next_port -= 1
@next_port = MAX_PORT if @next_port < MIN_PORT
port
end
end
end
|
