FFI wrapper for CreateProcess()

file.rb

require "rubygems"
require "ffi"

module WinProcess
  extend FFI::Library

  ffi_lib "kernel32"
  ffi_convention :stdcall

  class Error < StandardError
  end

  # typedef struct _STARTUPINFO {
  #   DWORD  cb;
  #   LPTSTR lpReserved;
  #   LPTSTR lpDesktop;
  #   LPTSTR lpTitle;
  #   DWORD  dwX;
  #   DWORD  dwY;
  #   DWORD  dwXSize;
  #   DWORD  dwYSize;
  #   DWORD  dwXCountChars;
  #   DWORD  dwYCountChars;
  #   DWORD  dwFillAttribute;
  #   DWORD  dwFlags;
  #   WORD   wShowWindow;
  #   WORD   cbReserved2;
  #   LPBYTE lpReserved2;
  #   HANDLE hStdInput;
  #   HANDLE hStdOutput;
  #   HANDLE hStdError;
  # } STARTUPINFO, *LPSTARTUPINFO;

  class StartupInfo < FFI::Struct
    layout :cb, :ulong,
           :lpReserved, :pointer,
           :lpDesktop, :pointer,
           :lpTitle, :pointer,
           :dwX, :ulong,
           :dwY, :ulong,
           :dwXSize, :ulong,
           :dwYSize, :ulong,
           :dwXCountChars, :ulong,
           :dwYCountChars, :ulong,
           :dwFillAttribute, :ulong,
           :wShowWindow, :ushort,
           :cbReserved2, :ushort,
           :lpReserved2, :pointer,
           :hStdInput, :pointer, # void ptr
           :hStdOutput, :pointer, # void ptr
           :hStdError, :pointer # void ptr
  end

  # typedef struct _PROCESS_INFORMATION {
  #   HANDLE hProcess;
  #   HANDLE hThread;
  #   DWORD  dwProcessId;
  #   DWORD  dwThreadId;
  # } PROCESS_INFORMATION, *LPPROCESS_INFORMATION;
  class ProcessInfo < FFI::Struct
    layout :hProcess, :pointer, # void ptr
           :hThread, :pointer, # void ptr
           :dwProcessId, :ulong,
           :dwThreadId, :ulong
  end


  # BOOL WINAPI CreateProcess(
  #   __in_opt     LPCTSTR lpApplicationName,
  #   __inout_opt  LPTSTR lpCommandLine,
  #   __in_opt     LPSECURITY_ATTRIBUTES lpProcessAttributes,
  #   __in_opt     LPSECURITY_ATTRIBUTES lpThreadAttributes,
  #   __in         BOOL bInheritHandles,
  #   __in         DWORD dwCreationFlags,
  #   __in_opt     LPVOID lpEnvironment,
  #   __in_opt     LPCTSTR lpCurrentDirectory,
  #   __in         LPSTARTUPINFO lpStartupInfo,
  #   __out        LPPROCESS_INFORMATION lpProcessInformation
  # );
  attach_function :create_process, :CreateProcessA,
                  [:pointer, :pointer, :pointer, :pointer, :bool,
                   :ulong, :pointer, :pointer, :pointer, :pointer], :bool

  attach_function :get_last_error, :GetLastError, [], :ulong

  #   DWORD WINAPI FormatMessage(
  #   __in      DWORD dwFlags,
  #   __in_opt  LPCVOID lpSource,
  #   __in      DWORD dwMessageId,
  #   __in      DWORD dwLanguageId,
  #   __out     LPTSTR lpBuffer,
  #   __in      DWORD nSize,
  #   __in_opt  va_list *Arguments
  # );
  attach_function :format_message, :FormatMessageA, [:ulong, :pointer, :ulong, :ulong,
                                                     :pointer, :ulong, :pointer], :ulong

  attach_function :close_handle, :CloseHandle, [:pointer], :bool

  FORMAT_MESSAGE_FROM_SYSTEM       = 0x00001000
  FORMAT_MESSAGE_ARGUMENT_ARRAY    = 0x00002000

  module_function

  def create(cmd, opts = {})
    cmd_ptr = FFI::MemoryPointer.from_string cmd

    si = StartupInfo.new
    pi = ProcessInfo.new

    if create_process(nil, cmd_ptr, nil, nil, !!opts[:inherit], 0, nil, nil, si, pi)
      close_handle pi[:hProcess]
      close_handle pi[:hThread]
      pi[:dwProcessId]  # returns the wrong pid?!
    else
      raise Error, last_error_message
    end
  end

  def last_error_message
    errnum = get_last_error()

    buf = FFI::MemoryPointer.new :char, 512
    flags = FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_ARGUMENT_ARRAY

    size = format_message(flags, nil, errnum, 0, buf, buf.size, nil)

    buf.read_string(size).strip
  end


end

p :pid => WinProcess.create("C:\\Windows\\System32\\regedt32.exe")

Thanks. This code has been folded into my ChildProcess gem:

http://github.com/jarib/childprocess

It uses java.lang.ProcessBuilder on JRuby though, so may not do exactly what you want.

a #pid method in the childprocess gem might be kind :)

What would you use it for? It's basically impossible on JRuby the way it's currently implemented, since we use ProcessBuilder et al there.

as a follow-up, 1.6.0RC2 now returns the correct pid's for (non shell-looking commands) in windows, though this might still be useful as something of a Process.spawn for jruby windows 1.8 (and 1.9 until it actually works there--doesn't yet I don't think)

Is the StartupInfo struct missing dwFlags?

http://msdn.microsoft.com/en-us/library/ms686331.aspx

@dsjbirch: It's there in the gem. I'm not maintaining the code in this gist ;)

@jarib, that is very cool!