New module to support decoding multipart messages (also see mimetools).

Lib/multifile.py

@@ -0,0 +1,118 @@
+# A class that makes each part of a multipart message "feel" like an
+# ordinary file, as long as you use fp.readline().  Allows recursive
+# use, for nested multipart messages.  Probably best used together
+# with module mimetools.
+#
+# Suggested use:
+#
+# real_fp = open(...)
+# fp = MultiFile().init(real_fp)
+#
+# "read some lines from fp"
+# fp.push(separator)
+# while 1:
+#	"read lines from fp until it returns an empty string" (A)
+#	if not fp.next(): break
+# fp.pop()
+# "read remaining lines from fp until it returns an empty string"
+#
+# The latter sequence may be used recursively at (A).
+# It is also allowed to use multiple push()...pop() sequences.
+# Note that if a nested multipart message is terminated by a separator
+# for an outer message, this is not reported, even though it is really
+# illegal input.
+
+import sys
+import string
+
+err = sys.stderr.write
+
+Error = 'multifile.Error'
+
+class MultiFile:
+	#
+	def init(self, fp):
+		self.fp = fp
+		self.stack = [] # Grows down
+		self.level = 0
+		self.last = 0
+		self.start = self.fp.tell()
+		self.posstack = [] # Grows down
+		return self
+	#
+	def tell(self):
+		if self.level > 0:
+			return self.lastpos
+		return self.fp.tell() - self.start
+	#
+	def seek(self, pos):
+		if not 0 <= pos <= self.tell() or \
+				self.level > 0 and pos > self.lastpos:
+			raise Error, 'bad MultiFile.seek() call'
+		self.fp.seek(pos + self.start)
+		self.level = 0
+		self.last = 0
+	#
+	def readline(self):
+		if self.level > 0: return ''
+		line = self.fp.readline()
+		if not line:
+			self.level = len(self.stack)
+			self.last = (self.level > 0)
+			if self.last:
+				err('*** Sudden EOF in MultiFile.readline()\n')
+			return ''
+		if line[:2] <> '--': return line
+		n = len(line)
+		k = n
+		while k > 0 and line[k-1] in string.whitespace: k = k-1
+		mark = line[2:k]
+		if mark[-2:] == '--': mark1 = mark[:-2]
+		else: mark1 = None
+		for i in range(len(self.stack)):
+			sep = self.stack[i]
+			if sep == mark:
+				self.last = 0
+				break
+			elif mark1 <> None and sep == mark1:
+				self.last = 1
+				break
+		else:
+			return line
+		# Get here after break out of loop
+		self.lastpos = self.tell() - len(line)
+		self.level = i+1
+		if self.level > 1:
+			err('*** Missing endmarker in MultiFile.readline()\n')
+		return ''
+	#
+	def next(self):
+		while self.readline(): pass
+		if self.level > 1 or self.last:
+			return 0
+		self.level = 0
+		self.last = 0
+		self.start = self.fp.tell()
+		return 1
+	#
+	def push(self, sep):
+		if self.level > 0:
+			raise Error, 'bad MultiFile.push() call'
+		self.stack.insert(0, sep)
+		self.posstack.insert(0, self.start)
+		self.start = self.fp.tell()
+	#
+	def pop(self):
+		if self.stack == []:
+			raise Error, 'bad MultiFile.pop() call'
+		if self.level <= 1:
+			self.last = 0
+		else:
+			abslastpos = self.lastpos + self.start
+		self.level = max(0, self.level - 1)
+		del self.stack[0]
+		self.start = self.posstack[0]
+		del self.posstack[0]
+		if self.level > 0:
+			self.lastpos = abslastpos - self.start
+	#