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"""

Utility functions for decoding response bodies.

"""

import codecs

import collections

from io import BytesIO

import gzip

import zlib

import brotli

from typing import Union, Optional, AnyStr # noqa

# We have a shared single-element cache for encoding and decoding.

# This is quite useful in practice, e.g.

# flow.request.content = flow.request.content.replace(b"foo", b"bar")

# does not require an .encode() call if content does not contain b"foo"

CachedDecode = collections.namedtuple(

"CachedDecode", "encoded encoding errors decoded"

)

_cache = CachedDecode(None, None, None, None)

def decode(

encoded: Optional[bytes], encoding: str, errors: str='strict'

) -> Optional[AnyStr]:

"""

Decode the given input object

Returns:

The decoded value

Raises:

ValueError, if decoding fails.

"""

if encoded is None:

return None

global _cache

cached = (

isinstance(encoded, bytes) and

_cache.encoded == encoded and

_cache.encoding == encoding and

_cache.errors == errors

)

if cached:

return _cache.decoded

try:

try:

decoded = custom_decode[encoding](encoded)

except KeyError:

decoded = codecs.decode(encoded, encoding, errors)

if encoding in ("gzip", "deflate", "br"):

_cache = CachedDecode(encoded, encoding, errors, decoded)

return decoded

except TypeError:

raise

except Exception as e:

raise ValueError("{} when decoding {} with {}: {}".format(

type(e).__name__,

repr(encoded)[:10],

repr(encoding),

repr(e),

))

def encode(decoded: Optional[str], encoding: str, errors: str='strict') -> Optional[AnyStr]:

"""

Encode the given input object

Returns:

The encoded value

Raises:

ValueError, if encoding fails.

"""

if decoded is None:

return None

global _cache

cached = (

isinstance(decoded, bytes) and

_cache.decoded == decoded and

_cache.encoding == encoding and

_cache.errors == errors

)

if cached:

return _cache.encoded

try:

try:

encoded = custom_encode[encoding](decoded)

except KeyError:

encoded = codecs.encode(decoded, encoding, errors)

if encoding in ("gzip", "deflate", "br"):

_cache = CachedDecode(encoded, encoding, errors, decoded)

return encoded

except TypeError:

raise

except Exception as e:

raise ValueError("{} when encoding {} with {}: {}".format(

type(e).__name__,

repr(decoded)[:10],

repr(encoding),

repr(e),

))

def identity(content):

"""

Returns content unchanged. Identity is the default value of

Accept-Encoding headers.

"""

return content

def decode_gzip(content: bytes) -> bytes:

if not content:

return b""

gfile = gzip.GzipFile(fileobj=BytesIO(content))

return gfile.read()

def encode_gzip(content: bytes) -> bytes:

s = BytesIO()

gf = gzip.GzipFile(fileobj=s, mode='wb')

gf.write(content)

gf.close()

return s.getvalue()

def decode_brotli(content: bytes) -> bytes:

if not content:

return b""

return brotli.decompress(content)

def encode_brotli(content: bytes) -> bytes:

return brotli.compress(content)

def decode_deflate(content: bytes) -> bytes:

"""

Returns decompressed data for DEFLATE. Some servers may respond with

compressed data without a zlib header or checksum. An undocumented

feature of zlib permits the lenient decompression of data missing both

values.

http://bugs.python.org/issue5784

"""

if not content:

return b""

try:

return zlib.decompress(content)

except zlib.error:

return zlib.decompress(content, -15)

def encode_deflate(content: bytes) -> bytes:

"""

Returns compressed content, always including zlib header and checksum.

"""

return zlib.compress(content)

custom_decode = {

"none": identity,

"identity": identity,

"gzip": decode_gzip,

"deflate": decode_deflate,

"br": decode_brotli,

}

custom_encode = {

"none": identity,

"identity": identity,

"gzip": encode_gzip,

"deflate": encode_deflate,

"br": encode_brotli,

}

__all__ = ["encode", "decode"]