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- """Python implementation of Z85 85-bit encoding
- Z85 encoding is a plaintext encoding for a bytestring interpreted as 32bit integers.
- Since the chunks are 32bit, a bytestring must be a multiple of 4 bytes.
- See ZMQ RFC 32 for details.
- """
- # Copyright (C) PyZMQ Developers
- # Distributed under the terms of the Modified BSD License.
- import sys
- import struct
- PY3 = sys.version_info[0] >= 3
- # Z85CHARS is the base 85 symbol table
- Z85CHARS = b"0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ.-:+=^!/*?&<>()[]{}@%$#"
- # Z85MAP maps integers in [0,84] to the appropriate character in Z85CHARS
- Z85MAP = dict([(c, idx) for idx, c in enumerate(Z85CHARS)])
- _85s = [ 85**i for i in range(5) ][::-1]
- def encode(rawbytes):
- """encode raw bytes into Z85"""
- # Accepts only byte arrays bounded to 4 bytes
- if len(rawbytes) % 4:
- raise ValueError("length must be multiple of 4, not %i" % len(rawbytes))
-
- nvalues = len(rawbytes) / 4
-
- values = struct.unpack('>%dI' % nvalues, rawbytes)
- encoded = []
- for v in values:
- for offset in _85s:
- encoded.append(Z85CHARS[(v // offset) % 85])
-
- # In Python 3, encoded is a list of integers (obviously?!)
- if PY3:
- return bytes(encoded)
- else:
- return b''.join(encoded)
- def decode(z85bytes):
- """decode Z85 bytes to raw bytes, accepts ASCII string"""
- if PY3 and isinstance(z85bytes, str):
- try:
- z85bytes = z85bytes.encode('ascii')
- except UnicodeEncodeError:
- raise ValueError('string argument should contain only ASCII characters')
- if len(z85bytes) % 5:
- raise ValueError("Z85 length must be multiple of 5, not %i" % len(z85bytes))
-
- nvalues = len(z85bytes) / 5
- values = []
- for i in range(0, len(z85bytes), 5):
- value = 0
- for j, offset in enumerate(_85s):
- value += Z85MAP[z85bytes[i+j]] * offset
- values.append(value)
- return struct.pack('>%dI' % nvalues, *values)
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