diff options
Diffstat (limited to 'youtube/proto.py')
| -rw-r--r-- | youtube/proto.py | 138 |
1 files changed, 115 insertions, 23 deletions
diff --git a/youtube/proto.py b/youtube/proto.py index 004375a..db83a06 100644 --- a/youtube/proto.py +++ b/youtube/proto.py @@ -1,17 +1,19 @@ 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. @@ -19,48 +21,49 @@ def varint_encode(offset): 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 - + 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 + 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.encode('utf-8') return value @@ -81,7 +84,7 @@ def read_varint(data): i += 1 return result - + def read_group(data, end_sequence): start = data.tell() index = data.original.find(end_sequence, start) @@ -101,7 +104,7 @@ def read_protobuf(data): break wire_type = tag & 7 field_number = tag >> 3 - + if wire_type == 0: value = read_varint(data) elif wire_type == 1: @@ -110,20 +113,109 @@ def read_protobuf(data): length = read_varint(data) value = data.read(length) elif wire_type == 3: - end_bytes = encode_varint((field_number << 3) | 4) + end_bytes = varint_encode((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())) + raise Exception("Unknown wire type: " + str(wire_type) + " 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 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) ) - + return base64.urlsafe_b64decode(data + "="*((4 - len(data) % 4) % 4)) |