[Python-bugs-list] [Bug #116636] Bug in StringIO.write()

[noreply@sourceforge.net]

Bug #116636, was updated on 2000-Oct-11 10:53
Here is a current snapshot of the bug.

Project: Python
Category: Library
Status: Open
Resolution: None
Bug Group: None
Priority: 5
Summary: Bug in StringIO.write()

Details: If the file position is less than the end of the "file", and a write is performed extending past then end of the file, the data string is corrupted. 100% reliable failure on all platforms!

This is apparently an old bug (since 1.5.2 at least), but still exists in 2.0c1.

To reproduce:

	s = StringIO("abcdef")
	s.seek(3)
	s.write("uvwxyz")	# write data that starts before the end
				# of the buffer and extends beyond the end
				# (self.len is not properly updated in this case)
	s.write("m")		# this incorrectly pads the buffer with '\0'
	print `s.getvalue()`

The result is:

	'abcuvwxyz\000\000\000m'

I fixed my copy by adding the following lines to the StingIO.write method:

	def write(self, s):
		if self.closed:
			raise ValueError, "I/O operation on closed file"
		if not s: return
		if self.pos > self.len:
			self.buflist.append('\0'*(self.pos - self.len))
			self.len = self.pos
		newpos = self.pos + len(s)
		if self.pos < self.len:
			if self.buflist:
				self.buf = self.buf + string.joinfields(self.buflist, '')
				self.buflist = []
			self.buflist = [self.buf[:self.pos], s, self.buf[newpos:]]
			self.buf = ''
			if self.len < newpos:		# ADDED LINE
				self.len = newpos	# ADDED LINE
		else:
			self.buflist.append(s)
			self.len = newpos
		self.pos = newpos

Bob
bobalex@rsv.ricoh.com


For detailed info, follow this link:
http://sourceforge.net/bugs/?func=detailbug&bug_id=116636&group_id=5470