sysinfo.rb

require 'ffi'

module SysInfo
  extend FFI::Library
  ffi_lib [FFI::Library::LIBC]

  class IfAddrs < FFI::Struct
    layout(
      :ifa_next, :pointer,
      :ifa_name, :pointer,
      :ifa_flags, :uint,
      :ifa_addr, :pointer
    )
  end

  class SockAddrIn < FFI::Struct
    layout(
      :sin_family, :short,
      :sin_port, :ushort,
      :sin_addr, :pointer,
      :sin_zero, :string
    )
  end

  attach_function :getloadavg,  [:pointer, :int], :int
  attach_function :gethostname, [:pointer, :int], :int
  attach_function :getifaddrs,  [:pointer],       :int
  attach_function :freeifaddrs, [:pointer],       :void
  attach_function :getnameinfo, [:pointer, :int, :pointer, :int, :string, :int, :int], :int

  module_function

  def loadavg
    ptr = FFI::MemoryPointer.new(:double, 3)
    return unless getloadavg(ptr, 3) == 3
    ptr.get_array_of_double(0, 3)
  end

  def hostname
    name = FFI::MemoryPointer.new(:pointer, 1)
    return unless gethostname(name, 1000) == 0
    name.read_string
  end

  NI_NUMERICHOST = 1
  NI_MAXHOST = 1025

  def ifaddrs
    ifap_ptr = FFI::MemoryPointer.new(:pointer)
    return unless getifaddrs(ifap_ptr) == 0
    return if ifap_ptr.null?

    hash = {}
    cur = IfAddrs.new(ifap_ptr.get_pointer(0))
    address_ptr = FFI::MemoryPointer.new(:pointer, NI_MAXHOST)

    begin
      key = cur[:ifa_name].read_string

      tmp = cur[:ifa_addr]
      getnameinfo(tmp, SockAddrIn.size, address_ptr, NI_MAXHOST, nil, 0, NI_NUMERICHOST)

      hash[key] = address_ptr.read_string
      cur = IfAddrs.new(cur[:ifa_next])
    end until cur.pointer.null?

    freeifaddrs(ifap_ptr)

    hash
  end
end


p SysInfo.loadavg
p SysInfo.hostname
p SysInfo.ifaddrs