youtube fronendHEADmaster

1 files changed, 221 insertions, 0 deletions

diff --git a/youtube/proto.py b/youtube/proto.py
new file mode 100644
index 0000000..924e983
--- /dev/null
+++ b/youtube/proto.py
@@ -0,0 +1,221 @@
+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))