python-awips/thrift/transport/TZlibTransport.py

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"""TZlibTransport provides a compressed transport and transport factory
class, using the python standard library zlib module to implement
data compression.
"""


import zlib
from io 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