#
# Licensed to the Apache Software Foundation (ASF) under one
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# regarding copyright ownership. The ASF licenses this file
# to you under the Apache License, Version 2.0 (the
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# with the License. You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing,
# software distributed under the License is distributed on an
# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
# KIND, either express or implied. See the License for the
# specific language governing permissions and limitations
# under the License.
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'''
TZlibTransport provides a compressed transport and transport factory
class, using the python standard library zlib module to implement
data compression.
'''
from __future__ import division
import zlib
from cStringIO import StringIO
from TTransport import TTransportBase, CReadableTransport
class TZlibTransportFactory(object):
'''
Factory transport that builds zlib compressed transports.
This factory caches the last single client/transport that it was passed
and returns the same TZlibTransport object that was created.
This caching means the TServer class will get the _same_ transport
object for both input and output transports from this factory.
(For non-threaded scenarios only, since the cache only holds one object)
The purpose of this caching is to allocate only one TZlibTransport where
only one is really needed (since it must have separate read/write buffers),
and makes the statistics from getCompSavings() and getCompRatio()
easier to understand.
'''
# class scoped cache of last transport given and zlibtransport returned
_last_trans = None
_last_z = None
def getTransport(self, trans, compresslevel=9):
'''Wrap a transport , trans, with the TZlibTransport
compressed transport class, returning a new
transport to the caller.
@param compresslevel: The zlib compression level, ranging
from 0 (no compression) to 9 (best compression). Defaults to 9.
@type compresslevel: int
This method returns a TZlibTransport which wraps the
passed C{trans} TTransport derived instance.
'''
if trans == self._last_trans:
return self._last_z
ztrans = TZlibTransport(trans, compresslevel)
self._last_trans = trans
self._last_z = ztrans
return ztrans
class TZlibTransport(TTransportBase, CReadableTransport):
'''
Class that wraps a transport with zlib, compressing writes
and decompresses reads, using the python standard
library zlib module.
'''
# Read buffer size for the python fastbinary C extension,
# the TBinaryProtocolAccelerated class.
DEFAULT_BUFFSIZE = 4096
def __init__(self, trans, compresslevel=9):
'''
Create a new TZlibTransport, wrapping C{trans}, another
TTransport derived object.
@param trans: A thrift transport object, i.e. a TSocket() object.
@type trans: TTransport
@param compresslevel: The zlib compression level, ranging
from 0 (no compression) to 9 (best compression). Default is 9.
@type compresslevel: int
'''
self.__trans = trans
self.compresslevel = compresslevel
self.__rbuf = StringIO()
self.__wbuf = StringIO()
self._init_zlib()
self._init_stats()
def _reinit_buffers(self):
'''
Internal method to initialize/reset the internal StringIO objects
for read and write buffers.
'''
self.__rbuf = StringIO()
self.__wbuf = StringIO()
def _init_stats(self):
'''
Internal method to reset the internal statistics counters
for compression ratios and bandwidth savings.
'''
self.bytes_in = 0
self.bytes_out = 0
self.bytes_in_comp = 0
self.bytes_out_comp = 0
def _init_zlib(self):
'''
Internal method for setting up the zlib compression and
decompression objects.
'''
self._zcomp_read = zlib.decompressobj()
self._zcomp_write = zlib.compressobj(self.compresslevel)
def getCompRatio(self):
'''
Get the current measured compression ratios (in,out) from
this transport.
Returns a tuple of:
(inbound_compression_ratio, outbound_compression_ratio)
The compression ratios are computed as:
compressed / uncompressed
E.g., data that compresses by 10x will have a ratio of: 0.10
and data that compresses to half of ts original size will
have a ratio of 0.5
None is returned if no bytes have yet been processed in
a particular direction.
'''
r_percent, w_percent = (None, None)
if self.bytes_in > 0:
r_percent = self.bytes_in_comp / self.bytes_in
if self.bytes_out > 0:
w_percent = self.bytes_out_comp / self.bytes_out
return (r_percent, w_percent)
def getCompSavings(self):
'''
Get the current count of saved bytes due to data
compression.
Returns a tuple of:
(inbound_saved_bytes, outbound_saved_bytes)
Note: if compression is actually expanding your
data (only likely with very tiny thrift objects), then
the values returned will be negative.
'''
r_saved = self.bytes_in - self.bytes_in_comp
w_saved = self.bytes_out - self.bytes_out_comp
return (r_saved, w_saved)
def isOpen(self):
'''Return the underlying transport's open status'''
return self.__trans.isOpen()
def open(self):
"""Open the underlying transport"""
self._init_stats()
return self.__trans.open()
def listen(self):
'''Invoke the underlying transport's listen() method'''
self.__trans.listen()
def accept(self):
'''Accept connections on the underlying transport'''
return self.__trans.accept()
def close(self):
'''Close the underlying transport,'''
self._reinit_buffers()
self._init_zlib()
return self.__trans.close()
def read(self, sz):
'''
Read up to sz bytes from the decompressed bytes buffer, and
read from the underlying transport if the decompression
buffer is empty.
'''
ret = self.__rbuf.read(sz)
if len(ret) > 0:
return ret
# keep reading from transport until something comes back
while True:
if self.readComp(sz):
break
ret = self.__rbuf.read(sz)
return ret
def readComp(self, sz):
'''
Read compressed data from the underlying transport, then
decompress it and append it to the internal StringIO read buffer
'''
zbuf = self.__trans.read(sz)
zbuf = self._zcomp_read.unconsumed_tail + zbuf
buf = self._zcomp_read.decompress(zbuf)
self.bytes_in += len(zbuf)
self.bytes_in_comp += len(buf)
old = self.__rbuf.read()
self.__rbuf = StringIO(old + buf)
if len(old) + len(buf) == 0:
return False
return True
def write(self, buf):
'''
Write some bytes, putting them into the internal write
buffer for eventual compression.
'''
self.__wbuf.write(buf)
def flush(self):
'''
Flush any queued up data in the write buffer and ensure the
compression buffer is flushed out to the underlying transport
'''
wout = self.__wbuf.getvalue()
if len(wout) > 0:
zbuf = self._zcomp_write.compress(wout)
self.bytes_out += len(wout)
self.bytes_out_comp += len(zbuf)
else:
zbuf = ''
ztail = self._zcomp_write.flush(zlib.Z_SYNC_FLUSH)
self.bytes_out_comp += len(ztail)
if (len(zbuf) + len(ztail)) > 0:
self.__wbuf = StringIO()
self.__trans.write(zbuf + ztail)
self.__trans.flush()
@property
def cstringio_buf(self):
'''Implement the CReadableTransport interface'''
return self.__rbuf
def cstringio_refill(self, partialread, reqlen):
'''Implement the CReadableTransport interface for refill'''
retstring = partialread
if reqlen < self.DEFAULT_BUFFSIZE:
retstring += self.read(self.DEFAULT_BUFFSIZE)
while len(retstring) < reqlen:
retstring += self.read(reqlen - len(retstring))
self.__rbuf = StringIO(retstring)
return self.__rbuf