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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.
- from __future__ import annotations
- import struct
- # Z85CHARS is the base 85 symbol table
- Z85CHARS = b"0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ.-:+=^!/*?&<>()[]{}@%$#"
- # Z85MAP maps integers in [0,84] to the appropriate character in Z85CHARS
- Z85MAP = {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(f"length must be multiple of 4, not {len(rawbytes)}")
- nvalues = len(rawbytes) // 4
- values = struct.unpack(f'>{nvalues:d}I', rawbytes)
- encoded = []
- for v in values:
- for offset in _85s:
- encoded.append(Z85CHARS[(v // offset) % 85])
- return bytes(encoded)
- def decode(z85bytes):
- """decode Z85 bytes to raw bytes, accepts ASCII string"""
- if 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(f"Z85 length must be multiple of 5, not {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(f'>{nvalues:d}I', *values)
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