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from math import ceil
import base64
import io
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('utf-8')
return value
def read_varint(data):
result = 0
i = 0
while True:
try:
byte = data.read(1)[0]
except IndexError:
if i == 0:
raise EOFError()
raise Exception('Unterminated varint starting at ' + str(data.tell() - i))
result |= (byte & 127) << 7*i
if not byte & 128:
break
i += 1
return result
def read_group(data, end_sequence):
start = data.tell()
index = data.original.find(end_sequence, start)
if index == -1:
raise Exception('Unterminated group')
data.seek(index + len(end_sequence))
return data.original[start:index]
def read_protobuf(data):
data_original = data
data = io.BytesIO(data)
data.original = data_original
while True:
try:
tag = read_varint(data)
except EOFError:
break
wire_type = tag & 7
field_number = tag >> 3
if wire_type == 0:
value = read_varint(data)
elif wire_type == 1:
value = data.read(8)
elif wire_type == 2:
length = read_varint(data)
value = data.read(length)
elif wire_type == 3:
end_bytes = encode_varint((field_number << 3) | 4)
value = read_group(data, end_bytes)
elif wire_type == 5:
value = data.read(4)
else:
raise Exception("Unknown wire type: " + str(wire_type) + ", Tag: " + bytes_to_hex(succinct_encode(tag)) + ", at position " + str(data.tell()))
yield (wire_type, field_number, value)
def parse(data):
return {field_number: value for _, field_number, value in read_protobuf(data)}
def b64_to_bytes(data):
if isinstance(data, bytes):
data = data.decode('ascii')
data = data.replace("%3D", "=")
return base64.urlsafe_b64decode(data + "="*((4 - len(data)%4)%4))
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