/lib/linux/right_popen.rb

#--
# Copyright (c) 2009 RightScale Inc
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
#++

# RightScale.popen3 allows running external processes aynchronously
# while still capturing their standard and error outputs.
# It relies on EventMachine for most of its internal mechanisms.

require 'rubygems'
require 'eventmachine'
require 'tempfile'

module RightScale

  # ensure uniqueness of handler to avoid confusion.
  raise "#{PipeHandler.name} is already defined" if defined?(PipeHandler)

  module PipeHandler
    def initialize(target, handler)
      @target = target
      @handler = handler
    end

    def receive_data(data)
      @target.method(@handler).call(data) if @handler
    end
  end

  # ensure uniqueness of handler to avoid confusion.
  raise "#{InputHandler.name} is already defined" if defined?(InputHandler)

  module InputHandler
    def initialize(string)
      @string = string
    end

    def post_init
      send_data(@string) if @string
      close_connection_after_writing
    end
  end

  # Forks process to run given command asynchronously, hooking all three
  # standard streams of the child process.
  #
  # === Parameters
  # options[:pid_handler](Symbol):: Token for pid handler method name.
  # options[:temp_dir]:: Path to temporary directory where executable files are
  #                      created, default to /tmp if not specified
  #
  # See RightScale.popen3
  def self.popen3_imp(options)
    GC.start # To garbage collect open file descriptors from passed executions
    EM.next_tick do
      inr, inw = IO::pipe
      outr, outw = IO::pipe
      errr, errw = IO::pipe

      [inr, inw, outr, outw, errr, errw].each {|fdes| fdes.sync = true}

      pid = fork do
        options[:environment].each do |k, v|
          ENV[k.to_s] = v
        end unless options[:environment].nil?

        inw.close
        outr.close
        errr.close
        $stdin.reopen inr
        $stdout.reopen outw
        $stderr.reopen errw

        if options[:command].instance_of?(String)
          exec "sh", "-c", options[:command]
        else
          exec *options[:command]
        end
      end

      inr.close
      outw.close
      errw.close
      stderr = EM.attach(errr, PipeHandler, options[:target],
                         options[:stderr_handler])
      stdout = EM.attach(outr, PipeHandler, options[:target],
                         options[:stdout_handler])
      stdin = EM.attach(inw, InputHandler, options[:input])

      options[:target].method(options[:pid_handler]).call(pid) if
        options.key? :pid_handler

      wait_timer = EM::PeriodicTimer.new(1) do
        value = Process.waitpid2(pid, Process::WNOHANG)
        unless value.nil?
          begin
            ignored, status = value
            options[:target].method(options[:exit_handler]).call(status) if
              options[:exit_handler]
          ensure
            stdin.close_connection
            stdout.close_connection
            stderr.close_connection
            wait_timer.cancel
          end
        end
      end
    end
    true
  end
end