zeroinstall/support.py

   1 """
   2 Useful support routines (for internal use).
   3
   4 These functions aren't really Zero Install specific; they're things we might
   5 wish were in the standard library.
   6
   7 @since: 0.27
   8 """
   9
  10 # Copyright (C) 2007, Thomas Leonard
  11 # See the README file for details, or visit http://0install.net.
  12
  13 import os, logging
  14
  15 def find_in_path(prog):
  16         """Search $PATH for prog.
  17         If prog is an absolute path, return it unmodified.
  18         @param prog: name of executable to find
  19         @return: the full path of prog, or None if not found
  20         @since: 0.27
  21         """
  22         if os.path.isabs(prog): return prog
  23         for d in os.environ['PATH'].split(':'):
  24                 path = os.path.join(d, prog)
  25                 if os.path.isfile(path):
  26                         return path
  27         return None
  28
  29 def read_bytes(fd, nbytes, null_ok = False):
  30         """Read exactly nbytes from fd.
  31         @param fd: file descriptor to read from
  32         @param nbytes: number of bytes to read
  33         @param null_ok: if True, it's OK to receive EOF immediately (we then return None)
  34         @return: the bytes read
  35         @raise Exception: if we received less than nbytes of data
  36         """
  37         data = ''
  38         while nbytes:
  39                 got = os.read(fd, nbytes)
  40                 if not got:
  41                         if null_ok and not data:
  42                                 return None
  43                         raise Exception("Unexpected end-of-stream. Data so far %s; expecting %d bytes more."
  44                                         % (repr(data), nbytes))
  45                 data += got
  46                 nbytes -= len(got)
  47         logging.debug("Message received: %s" % repr(data))
  48         return data
  49
  50 def pretty_size(size):
  51         """Format a size for printing.
  52         @param size: the size in bytes
  53         @type size: int (or None)
  54         @return: the formatted size
  55         @rtype: str
  56         @since: 0.27"""
  57         if size is None:
  58                 return '?'
  59         if size < 2048:
  60                 return '%d bytes' % size
  61         size = float(size)
  62         for unit in ('Kb', 'Mb', 'Gb', 'Tb'):
  63                 size /= 1024
  64                 if size < 2048:
  65                         break
  66         return '%.1f %s' % (size, unit)
  67
  68 def ro_rmtree(root):
  69         """Like shutil.rmtree, except that we also delete read-only items.
  70         @param root: the root of the subtree to remove
  71         @type root: str
  72         @since: 0.28"""
  73         import shutil
  74         for main, dirs, files in os.walk(root):
  75                 os.chmod(main, 0700)
  76         shutil.rmtree(root)