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#!/usr/bin/env python
##
# Licensed to the Apache Software Foundation (ASF) under one
# or more contributor license agreements. See the NOTICE file
# distributed with this work for additional information
# regarding copyright ownership. The ASF licenses this file
# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License. You may obtain a copy of the License at
#
# https://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.
"""
Contains Codecs for Python Avro.
Note that the word "codecs" means "compression/decompression algorithms" in the
Avro world (https://avro.apache.org/docs/current/spec.html#Object+Container+Files),
so don't confuse it with the Python's "codecs", which is a package mainly for
converting charsets (https://docs.python.org/3/library/codecs.html).
"""
from __future__ import absolute_import, division, print_function
import io
import struct
import sys
import zlib
from abc import ABCMeta, abstractmethod
from binascii import crc32
from struct import Struct
import avro.io
from avro.schema import AvroException
#
# Constants
#
STRUCT_CRC32 = Struct('>I') # big-endian unsigned int
try:
import bz2
has_bzip2 = True
except ImportError:
has_bzip2 = False
try:
import snappy
has_snappy = True
except ImportError:
has_snappy = False
try:
import zstandard as zstd
has_zstandard = True
except ImportError:
has_zstandard = False
class Codec:
"""Abstract base class for all Avro codec classes."""
__metaclass__ = ABCMeta
@abstractmethod
def compress(self, data):
"""Compress the passed data.
:param data: a byte string to be compressed
:type data: str
:rtype: tuple
:return: compressed data and its length
"""
pass
@abstractmethod
def decompress(self, readers_decoder):
"""Read compressed data via the passed BinaryDecoder and decompress it.
:param readers_decoder: a BinaryDecoder object currently being used for
reading an object container file
:type readers_decoder: avro.io.BinaryDecoder
:rtype: avro.io.BinaryDecoder
:return: a newly instantiated BinaryDecoder object that contains the
decompressed data which is wrapped by a StringIO
"""
pass
class NullCodec(Codec):
def compress(self, data):
return data, len(data)
def decompress(self, readers_decoder):
readers_decoder.skip_long()
return readers_decoder
class DeflateCodec(Codec):
def compress(self, data):
# The first two characters and last character are zlib
# wrappers around deflate data.
compressed_data = zlib.compress(data)[2:-1]
return compressed_data, len(compressed_data)
def decompress(self, readers_decoder):
# Compressed data is stored as (length, data), which
# corresponds to how the "bytes" type is encoded.
data = readers_decoder.read_bytes()
# -15 is the log of the window size; negative indicates
# "raw" (no zlib headers) decompression. See zlib.h.
uncompressed = zlib.decompress(data, -15)
return avro.io.BinaryDecoder(io.BytesIO(uncompressed))
if has_bzip2:
class BZip2Codec(Codec):
def compress(self, data):
compressed_data = bz2.compress(data)
return compressed_data, len(compressed_data)
def decompress(self, readers_decoder):
length = readers_decoder.read_long()
data = readers_decoder.read(length)
uncompressed = bz2.decompress(data)
return avro.io.BinaryDecoder(io.BytesIO(uncompressed))
if has_snappy:
class SnappyCodec(Codec):
def compress(self, data):
compressed_data = snappy.compress(data)
# A 4-byte, big-endian CRC32 checksum
compressed_data += STRUCT_CRC32.pack(crc32(data) & 0xffffffff)
return compressed_data, len(compressed_data)
def decompress(self, readers_decoder):
# Compressed data includes a 4-byte CRC32 checksum
length = readers_decoder.read_long()
data = readers_decoder.read(length - 4)
uncompressed = snappy.decompress(data)
checksum = readers_decoder.read(4)
self.check_crc32(uncompressed, checksum)
return avro.io.BinaryDecoder(io.BytesIO(uncompressed))
def check_crc32(self, bytes, checksum):
checksum = STRUCT_CRC32.unpack(checksum)[0]
if crc32(bytes) & 0xffffffff != checksum:
raise schema.AvroException("Checksum failure")
if has_zstandard:
class ZstandardCodec(Codec):
def compress(self, data):
compressed_data = zstd.ZstdCompressor().compress(data)
return compressed_data, len(compressed_data)
def decompress(self, readers_decoder):
length = readers_decoder.read_long()
data = readers_decoder.read(length)
uncompressed = bytearray()
dctx = zstd.ZstdDecompressor()
with dctx.stream_reader(io.BytesIO(data)) as reader:
while True:
chunk = reader.read(16384)
if not chunk:
break
uncompressed.extend(chunk)
return avro.io.BinaryDecoder(io.BytesIO(uncompressed))
class Codecs(object):
@staticmethod
def get_codec(codec_name):
codec_name = codec_name.lower()
if codec_name == "null":
return NullCodec()
elif codec_name == "deflate":
return DeflateCodec()
elif codec_name == "bzip2" and has_bzip2:
return BZip2Codec()
elif codec_name == "snappy" and has_snappy:
return SnappyCodec()
elif codec_name == "zstandard" and has_zstandard:
return ZstandardCodec()
else:
raise ValueError("Unsupported codec: %r" % codec_name)
@staticmethod
def supported_codec_names():
codec_names = ['null', 'deflate']
if has_bzip2:
codec_names.append('bzip2')
if has_snappy:
codec_names.append('snappy')
if has_zstandard:
codec_names.append('zstandard')
return codec_names
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