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