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