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buffers.py
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buffers.py
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##############################################################################
#
# Copyright (c) 2001-2004 Zope Foundation and Contributors.
# All Rights Reserved.
#
# This software is subject to the provisions of the Zope Public License,
# Version 2.1 (ZPL). A copy of the ZPL should accompany this distribution.
# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
# FOR A PARTICULAR PURPOSE.
#
##############################################################################
"""Buffers
"""
try:
from cStringIO import StringIO
except ImportError: # pragma: no cover
from StringIO import StringIO
# copy_bytes controls the size of temp. strings for shuffling data around.
COPY_BYTES = 1 << 18 # 256K
# The maximum number of bytes to buffer in a simple string.
STRBUF_LIMIT = 8192
class FileBasedBuffer(object):
remain = 0
def __init__(self, file, from_buffer=None):
self.file = file
if from_buffer is not None:
from_file = from_buffer.getfile()
read_pos = from_file.tell()
from_file.seek(0)
while 1:
data = from_file.read(COPY_BYTES)
if not data:
break
file.write(data)
self.remain = int(file.tell() - read_pos)
from_file.seek(read_pos)
file.seek(read_pos)
def __len__(self):
return self.remain
def append(self, s):
file = self.file
read_pos = file.tell()
file.seek(0, 2)
file.write(s)
file.seek(read_pos)
self.remain = self.remain + len(s)
def get(self, bytes=-1, skip=False):
file = self.file
if not skip:
read_pos = file.tell()
if bytes < 0:
# Read all
res = file.read()
else:
res = file.read(bytes)
if skip:
self.remain -= len(res)
else:
file.seek(read_pos)
return res
def skip(self, bytes, allow_prune=0):
if self.remain < bytes:
raise ValueError("Can't skip %d bytes in buffer of %d bytes" % (
bytes, self.remain))
self.file.seek(bytes, 1)
self.remain = self.remain - bytes
def newfile(self):
raise NotImplementedError()
def prune(self):
file = self.file
if self.remain == 0:
read_pos = file.tell()
file.seek(0, 2)
sz = file.tell()
file.seek(read_pos)
if sz == 0:
# Nothing to prune.
return
nf = self.newfile()
while 1:
data = file.read(COPY_BYTES)
if not data:
break
nf.write(data)
self.file = nf
def getfile(self):
return self.file
class TempfileBasedBuffer(FileBasedBuffer):
def __init__(self, from_buffer=None):
FileBasedBuffer.__init__(self, self.newfile(), from_buffer)
def newfile(self):
from tempfile import TemporaryFile
return TemporaryFile('w+b')
class StringIOBasedBuffer(FileBasedBuffer):
def __init__(self, from_buffer=None):
if from_buffer is not None:
FileBasedBuffer.__init__(self, StringIO(), from_buffer)
else:
# Shortcut. :-)
self.file = StringIO()
def newfile(self):
return StringIO()
class OverflowableBuffer(object):
"""
This buffer implementation has four stages:
- No data
- String-based buffer
- StringIO-based buffer
- Temporary file storage
The first two stages are fastest for simple transfers.
"""
overflowed = 0
buf = None
strbuf = '' # String-based buffer.
def __init__(self, overflow):
# overflow is the maximum to be stored in a StringIO buffer.
self.overflow = overflow
def __len__(self):
buf = self.buf
if buf is not None:
return len(buf)
else:
return len(self.strbuf)
def _create_buffer(self):
# print 'creating buffer'
strbuf = self.strbuf
if len(strbuf) >= self.overflow:
self._set_large_buffer()
else:
self._set_small_buffer()
buf = self.buf
if strbuf:
buf.append(self.strbuf)
self.strbuf = ''
return buf
def _set_small_buffer(self):
self.buf = StringIOBasedBuffer(self.buf)
self.overflowed = 0
def _set_large_buffer(self):
self.buf = TempfileBasedBuffer(self.buf)
self.overflowed = 1
def append(self, s):
buf = self.buf
if buf is None:
strbuf = self.strbuf
if len(strbuf) + len(s) < STRBUF_LIMIT:
self.strbuf = strbuf + s
return
buf = self._create_buffer()
buf.append(s)
sz = len(buf)
if not self.overflowed:
if sz >= self.overflow:
self._set_large_buffer()
def get(self, bytes=-1, skip=0):
buf = self.buf
if buf is None:
strbuf = self.strbuf
if not skip:
return strbuf
buf = self._create_buffer()
return buf.get(bytes, skip)
def skip(self, bytes, allow_prune=0):
buf = self.buf
if buf is None:
strbuf = self.strbuf
if allow_prune and bytes == len(strbuf):
# We could slice instead of converting to
# a buffer, but that would eat up memory in
# large transfers.
self.strbuf = ''
return
buf = self._create_buffer()
buf.skip(bytes, allow_prune)
def prune(self):
"""
A potentially expensive operation that removes all data
already retrieved from the buffer.
"""
buf = self.buf
if buf is None:
self.strbuf = ''
return
buf.prune()
if self.overflowed:
sz = len(buf)
if sz < self.overflow:
# Revert to a faster buffer.
self._set_small_buffer()
def getfile(self):
buf = self.buf
if buf is None:
buf = self._create_buffer()
return buf.getfile()