Example to replace string search in facter in favor of system calls

interfaces.rb

#!/usr/bin/ruby

require 'socket'

# From bits/ioctls.h
SIOCGIFNETMASK = 0x891b # Netmask address
SIOCGIFHWADDR  = 0x8927 # hardware address
SIOCGIFADDR    = 0x8915 # PA address
SIOCGIFCONF    = 0x8912 # iface list

class Interface

  #def self.list
  #  sock = UDPSocket.new
  #
  #  # Query to get size of the interface buffer
  #  buf = [0,0].pack('lQ')
  #  sock.ioctl(SIOCGIFCONF, buf)
  #  buf_size = buf.unpack('l').first
  #
  #  # Generate a return buffer (must be a smarter way)
  #  data = ''
  #  for i in 1..buf_size
  #      data = data + "\0"
  #  end
  #
  #  # Get interface data
  #  buf = [buf_size,data].pack("la#{buf_size}")
  #  sock.ioctl(SIOCGIFCONF, buf);
  #  sock.close
  #
  #  # Unpack interface information (data part is an array of struct ifreq with the first
  #  # member is char ifrn_name[IFNAMSIZ] (16) and sizeof(struct ifreq) = 40)
  #  return buf
  #end
  
  def self.list
    sock = UDPSocket.new

    # Query to get size of the interface buffer
    buf = [0,0].pack('lQ')
    sock.ioctl(SIOCGIFCONF, buf)
    buf_size = buf.unpack('l').first

    # Generate a return buffer (must be a smarter way)
    data = ''
    for i in 1..buf_size
        data = data + " "
    end

    # Get interface data
    buf = [buf_size, data].pack("lP#{buf_size}")
    sock.ioctl(SIOCGIFCONF, buf)
    sock.close

    # Unpack interface information (data part is an array of struct ifreq with the first
    # member is char ifrn_name[IFNAMSIZ] (16) and sizeof(struct ifreq) = 40)
    names = []

    off = 0
    while off < buf_size
        name = data[off..off+16].unpack('a16').first
        print("Name #{name}\n")
        names << name
        off += 40
    end

    return names
  end

  def self.hw_address(iface)
    sock = UDPSocket.new
    buf = [iface,""].pack('a16h16')
    sock.ioctl(SIOCGIFHWADDR, buf);
    sock.close
    return buf[18..24].unpack("H2H2H2H2H2H2").join(":")
  end

  def self.netmask(iface)
    sock = UDPSocket.new
    buf = [iface,""].pack('a16h16')
    sock.ioctl(SIOCGIFNETMASK, buf);
    sock.close
    return buf[20..23].unpack("CCCC").join(".")
  end

  def self.ip_address(iface)
    sock = UDPSocket.new
    buf = [iface,""].pack('a16h16')
    sock.ioctl(SIOCGIFADDR, buf);
    sock.close
    buf[20..24].unpack("CCCC").join(".")
  end

  def self.list_all_ips
    # Slow for some reason. 5ms for each iteration.
    return Socket::getaddrinfo(Socket.gethostname, '', Socket::AF_INET).map { |x| x[3] }.uniq
  end
end

puts Interface.list

Perhaps data = ' ' * buf_size would do for the "must be a smarter way" section.