## Copyright (C) 2000-2001 The ViewCVS Group. All Rights Reserved.## By using this file, you agree to the terms and conditions set forth in# the LICENSE.html file which can be found at the top level of the ViewCVS# distribution or at http://viewcvs.sourceforge.net/license-1.html.## Contact information:#   Greg Stein, PO Box 760, Palo Alto, CA, 94302#   gstein@lyra.org, http://viewcvs.sourceforge.net/## -----------------------------------------------------------------------## popen.py: a replacement for os.popen()## This implementation of popen() provides a cmd + args calling sequence,# rather than a system() type of convention. The shell facilities are not# available, but that implies we can avoid worrying about shell hacks in# the arguments.## -----------------------------------------------------------------------#import osimport sysdef popen(cmd, args, mode, capture_err=1):  # flush the stdio buffers since we are about to change the FD under them  sys.stdout.flush()  sys.stderr.flush()  r, w = os.pipe()  pid = os.fork()  if pid:    # in the parent    # close the descriptor that we don't need and return the other one.    if mode == 'r':      os.close(w)      return _pipe(os.fdopen(r, 'r'), pid)    os.close(r)    return _pipe(os.fdopen(w, 'w'), pid)  # in the child  # we'll need /dev/null for the discarded I/O  null = os.open('/dev/null', os.O_RDWR)  if mode == 'r':    # hook stdout/stderr to the "write" channel    os.dup2(w, 1)    # "close" stdin; the child shouldn't use it    ### this isn't quite right... we may want the child to read from stdin    os.dup2(null, 0)    # what to do with errors?    if capture_err:      os.dup2(w, 2)    else:      os.dup2(null, 2)  else:    # hook stdin to the "read" channel    os.dup2(r, 0)    # "close" stdout/stderr; the child shouldn't use them    ### this isn't quite right... we may want the child to write to these    os.dup2(null, 1)    os.dup2(null, 2)  # don't need these FDs any more  os.close(null)  os.close(r)  os.close(w)  # the stdin/stdout/stderr are all set up. exec the target  try:    os.execvp(cmd, (cmd,) + tuple(args))  except:    # aid debugging, if the os.execvp above fails for some reason:    import string    print "<h2>exec failed:</h2><pre>", cmd, string.join(args), "</pre>"    raise  # crap. shouldn't be here.  sys.exit(127)def pipe_cmds(cmds):  # flush the stdio buffers since we are about to change the FD under them  sys.stdout.flush()  sys.stderr.flush()  prev_r, parent_w = os.pipe()  null = os.open('/dev/null', os.O_RDWR)  for cmd in cmds[:-1]:    r, w = os.pipe()    pid = os.fork()    if not pid:      # in the child      # hook up stdin to the "read" channel      os.dup2(prev_r, 0)      # hook up stdout to the output channel      os.dup2(w, 1)      # toss errors      os.dup2(null, 2)      # close these extra descriptors      os.close(prev_r)      os.close(parent_w)      os.close(null)      os.close(r)      os.close(w)      # time to run the command      try:        os.execvp(cmd[0], cmd)      except:        pass      sys.exit(127)    # in the parent    # we don't need these any more    os.close(prev_r)    os.close(w)    # the read channel of this pipe will feed into to the next command    prev_r = r  # no longer needed  os.close(null)  # done with most of the commands. set up the last command to write to stdout  pid = os.fork()  if not pid:    # in the child (the last command)    # hook up stdin to the "read" channel    os.dup2(prev_r, 0)    # close these extra descriptors    os.close(prev_r)    os.close(parent_w)    # run the last command    try:      os.execvp(cmds[-1][0], cmds[-1])    except:      pass    sys.exit(127)  # not needed any more  os.close(prev_r)  # write into the first pipe, wait on the final process  return _pipe(os.fdopen(parent_w, 'w'), pid)class _pipe:  "Wrapper for a file which can wait() on a child process at close time."  def __init__(self, file, child_pid):    self.file = file    self.child_pid = child_pid  def eof(self):    pid, status = os.waitpid(self.child_pid, os.WNOHANG)    if pid:      self.file.close()      self.file = None      return status    return None  def close(self):    if self.file:      self.file.close()      self.file = None      return os.waitpid(self.child_pid, 0)[1]    return None  def __getattr__(self, name):    return getattr(self.file, name)  def __del__(self):    if self.file:      self.close()