65 lines
2.1 KiB
Python
65 lines
2.1 KiB
Python
from math import ceil
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import base64
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def byte(n):
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return bytes((n,))
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def varint_encode(offset):
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'''In this encoding system, for each 8-bit byte, the first bit is 1 if there are more bytes, and 0 is this is the last one.
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The next 7 bits are data. These 7-bit sections represent the data in Little endian order. For example, suppose the data is
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aaaaaaabbbbbbbccccccc (each of these sections is 7 bits). It will be encoded as:
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1ccccccc 1bbbbbbb 0aaaaaaa
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This encoding is used in youtube parameters to encode offsets and to encode the length for length-prefixed data.
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See https://developers.google.com/protocol-buffers/docs/encoding#varints for more info.'''
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needed_bytes = ceil(offset.bit_length()/7) or 1 # (0).bit_length() returns 0, but we need 1 in that case.
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encoded_bytes = bytearray(needed_bytes)
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for i in range(0, needed_bytes - 1):
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encoded_bytes[i] = (offset & 127) | 128 # 7 least significant bits
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offset = offset >> 7
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encoded_bytes[-1] = offset & 127 # leave first bit as zero for last byte
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return bytes(encoded_bytes)
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def varint_decode(encoded):
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decoded = 0
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for i, byte in enumerate(encoded):
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decoded |= (byte & 127) << 7*i
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if not (byte & 128):
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break
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return decoded
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def string(field_number, data):
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data = as_bytes(data)
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return _proto_field(2, field_number, varint_encode(len(data)) + data)
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nested = string
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def uint(field_number, value):
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return _proto_field(0, field_number, varint_encode(value))
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def _proto_field(wire_type, field_number, data):
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''' See https://developers.google.com/protocol-buffers/docs/encoding#structure '''
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return varint_encode( (field_number << 3) | wire_type) + data
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def percent_b64encode(data):
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return base64.urlsafe_b64encode(data).replace(b'=', b'%3D')
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def unpadded_b64encode(data):
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return base64.urlsafe_b64encode(data).replace(b'=', b'')
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def as_bytes(value):
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if isinstance(value, str):
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return value.encode('ascii')
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return value
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