from math import ceil
import base64
import io
import traceback
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, include_wire_type=False):
'''Returns a dict mapping field numbers to values
data is the protobuf structure, which must not be b64-encoded'''
if include_wire_type:
return {field_number: [wire_type, value]
for wire_type, field_number, value in read_protobuf(data)}
return {field_number: value
for _, field_number, value in read_protobuf(data)}
base64_enc_funcs = {
'base64': base64.urlsafe_b64encode,
'base64s': unpadded_b64encode,
'base64p': percent_b64encode,
}
def _make_protobuf(data):
'''
Input: Recursive list of protobuf objects or base-64 encodings
Output: Protobuf bytestring
Each protobuf object takes the form [wire_type, field_number, field_data]
If a string protobuf has a list/tuple of length 2, this has the form
(base64 type, data)
The base64 types are
- base64 means a base64 encode with equals sign paddings
- base64s means a base64 encode without padding
- base64p means a url base64 encode with equals signs replaced with %3D
'''
# must be dict mapping field_number to [wire_type, value]
if isinstance(data, dict):
new_data = []
for field_num, (wire_type, value) in sorted(data.items()):
new_data.append((wire_type, field_num, value))
data = new_data
if isinstance(data, str):
return data.encode('utf-8')
elif len(data) == 2 and data[0] in list(base64_enc_funcs.keys()):
return base64_enc_funcs[data[0]](_make_protobuf(data[1]))
elif isinstance(data, list):
result = b''
for field in data:
if field[0] == 0:
result += uint(field[1], field[2])
elif field[0] == 2:
result += string(field[1], _make_protobuf(field[2]))
else:
raise NotImplementedError('Wire type ' + str(field[0])
+ ' not implemented')
return result
return data
def make_protobuf(data):
return _make_protobuf(data).decode('ascii')
def _set_protobuf_value(data, *path, value):
if not path:
return value
op = path[0]
if op in base64_enc_funcs:
inner_data = b64_to_bytes(data)
return base64_enc_funcs[op](
_set_protobuf_value(inner_data, *path[1:], value=value)
)
pb_dict = parse(data, include_wire_type=True)
pb_dict[op][1] = _set_protobuf_value(
pb_dict[op][1], *path[1:], value=value
)
return _make_protobuf(pb_dict)
def set_protobuf_value(data, *path, value):
'''Set a field's value in a raw protobuf structure
path is a list of field numbers and/or base64 encoding directives
The directives are
base64: normal base64 encoding with equal signs padding
base64s ("stripped"): no padding
base64p: %3D instead of = for padding
return new_protobuf, err'''
try:
new_protobuf = _set_protobuf_value(data, *path, value=value)
return new_protobuf.decode('ascii'), None
except Exception:
return None, traceback.format_exc()
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))
