Lib/multifile.py

   1 # A class that makes each part of a multipart message "feel" like an
   2 # ordinary file, as long as you use fp.readline().  Allows recursive
   3 # use, for nested multipart messages.  Probably best used together
   4 # with module mimetools.
   5 #
   6 # Suggested use:
   7 #
   8 # real_fp = open(...)
   9 # fp = MultiFile(real_fp)
  10 #
  11 # "read some lines from fp"
  12 # fp.push(separator)
  13 # while 1:
  14 #       "read lines from fp until it returns an empty string" (A)
  15 #       if not fp.next(): break
  16 # fp.pop()
  17 # "read remaining lines from fp until it returns an empty string"
  18 #
  19 # The latter sequence may be used recursively at (A).
  20 # It is also allowed to use multiple push()...pop() sequences.
  21 # Note that if a nested multipart message is terminated by a separator
  22 # for an outer message, this is not reported, even though it is really
  23 # illegal input.
  24
  25 import sys
  26 import string
  27
  28 err = sys.stderr.write
  29
  30 Error = 'multifile.Error'
  31
  32 class MultiFile:
  33         #
  34         def __init__(self, fp):
  35                 self.fp = fp
  36                 self.stack = [] # Grows down
  37                 self.level = 0
  38                 self.last = 0
  39                 self.start = self.fp.tell()
  40                 self.posstack = [] # Grows down
  41         #
  42         def tell(self):
  43                 if self.level > 0:
  44                         return self.lastpos
  45                 return self.fp.tell() - self.start
  46         #
  47         def seek(self, pos):
  48                 if not 0 <= pos <= self.tell() or \
  49                                 self.level > 0 and pos > self.lastpos:
  50                         raise Error, 'bad MultiFile.seek() call'
  51                 self.fp.seek(pos + self.start)
  52                 self.level = 0
  53                 self.last = 0
  54         #
  55         def readline(self):
  56                 if self.level > 0: return ''
  57                 line = self.fp.readline()
  58                 if not line:
  59                         self.level = len(self.stack)
  60                         self.last = (self.level > 0)
  61                         if self.last:
  62                                 err('*** Sudden EOF in MultiFile.readline()\n')
  63                         return ''
  64                 if line[:2] <> '--': return line
  65                 n = len(line)
  66                 k = n
  67                 while k > 0 and line[k-1] in string.whitespace: k = k-1
  68                 mark = line[2:k]
  69                 if mark[-2:] == '--': mark1 = mark[:-2]
  70                 else: mark1 = None
  71                 for i in range(len(self.stack)):
  72                         sep = self.stack[i]
  73                         if sep == mark:
  74                                 self.last = 0
  75                                 break
  76                         elif mark1 <> None and sep == mark1:
  77                                 self.last = 1
  78                                 break
  79                 else:
  80                         return line
  81                 # Get here after break out of loop
  82                 self.lastpos = self.tell() - len(line)
  83                 self.level = i+1
  84                 if self.level > 1:
  85                         err('*** Missing endmarker in MultiFile.readline()\n')
  86                 return ''
  87         #
  88         def readlines(self):
  89                 list = []
  90                 while 1:
  91                         line = self.readline()
  92                         if not line: break
  93                         list.append(line)
  94                 return list
  95         #
  96         def read(self): # Note: no size argument -- read until EOF only!
  97                 return string.joinfields(self.readlines(), '')
  98         #
  99         def next(self):
 100                 while self.readline(): pass
 101                 if self.level > 1 or self.last:
 102                         return 0
 103                 self.level = 0
 104                 self.last = 0
 105                 self.start = self.fp.tell()
 106                 return 1
 107         #
 108         def push(self, sep):
 109                 if self.level > 0:
 110                         raise Error, 'bad MultiFile.push() call'
 111                 self.stack.insert(0, sep)
 112                 self.posstack.insert(0, self.start)
 113                 self.start = self.fp.tell()
 114         #
 115         def pop(self):
 116                 if self.stack == []:
 117                         raise Error, 'bad MultiFile.pop() call'
 118                 if self.level <= 1:
 119                         self.last = 0
 120                 else:
 121                         abslastpos = self.lastpos + self.start
 122                 self.level = max(0, self.level - 1)
 123                 del self.stack[0]
 124                 self.start = self.posstack[0]
 125                 del self.posstack[0]
 126                 if self.level > 0:
 127                         self.lastpos = abslastpos - self.start
 128         #