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#!/usr/bin/env python3
##
# 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).
"""
import abc
import binascii
import io
import struct
import zlib
from typing import Dict, Tuple, Type
import avro.errors
import avro.io
#
# Constants
#
STRUCT_CRC32 = struct.Struct(">I") # big-endian unsigned int
def _check_crc32(bytes_: bytes, checksum: bytes) -> None:
if binascii.crc32(bytes_) & 0xFFFFFFFF != STRUCT_CRC32.unpack(checksum)[0]:
raise avro.errors.AvroException("Checksum failure")
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(abc.ABC):
"""Abstract base class for all Avro codec classes."""
@staticmethod
@abc.abstractmethod
def compress(data: bytes) -> Tuple[bytes, int]:
"""Compress the passed data.
:param data: a byte string to be compressed
:type data: str
:rtype: tuple
:return: compressed data and its length
"""
@staticmethod
@abc.abstractmethod
def decompress(readers_decoder: avro.io.BinaryDecoder) -> avro.io.BinaryDecoder:
"""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
"""
class NullCodec(Codec):
@staticmethod
def compress(data: bytes) -> Tuple[bytes, int]:
return data, len(data)
@staticmethod
def decompress(readers_decoder: avro.io.BinaryDecoder) -> avro.io.BinaryDecoder:
readers_decoder.skip_long()
return readers_decoder
class DeflateCodec(Codec):
@staticmethod
def compress(data: bytes) -> Tuple[bytes, int]:
# 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)
@staticmethod
def decompress(readers_decoder: avro.io.BinaryDecoder) -> avro.io.BinaryDecoder:
# 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):
@staticmethod
def compress(data: bytes) -> Tuple[bytes, int]:
compressed_data = bz2.compress(data)
return compressed_data, len(compressed_data)
@staticmethod
def decompress(readers_decoder: avro.io.BinaryDecoder) -> avro.io.BinaryDecoder:
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):
@staticmethod
def compress(data: bytes) -> Tuple[bytes, int]:
compressed_data = snappy.compress(data)
# A 4-byte, big-endian CRC32 checksum
compressed_data += STRUCT_CRC32.pack(binascii.crc32(data) & 0xFFFFFFFF)
return compressed_data, len(compressed_data)
@staticmethod
def decompress(readers_decoder: avro.io.BinaryDecoder) -> avro.io.BinaryDecoder:
# 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)
_check_crc32(uncompressed, checksum)
return avro.io.BinaryDecoder(io.BytesIO(uncompressed))
if has_zstandard:
class ZstandardCodec(Codec):
@staticmethod
def compress(data: bytes) -> Tuple[bytes, int]:
compressed_data = zstd.ZstdCompressor().compress(data)
return compressed_data, len(compressed_data)
@staticmethod
def decompress(readers_decoder: avro.io.BinaryDecoder) -> avro.io.BinaryDecoder:
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))
KNOWN_CODECS: Dict[str, Type[Codec]] = {
name[:-5].lower(): class_
for name, class_ in globals().items()
if class_ != Codec and name.endswith("Codec") and isinstance(class_, type) and issubclass(class_, Codec)
}
def get_codec(codec_name: str) -> Type[Codec]:
try:
return KNOWN_CODECS[codec_name]
except KeyError:
raise avro.errors.UnsupportedCodec(f"Unsupported codec: {codec_name}. (Is it installed?)")
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