1# Copyright 2017 Google Inc. All rights reserved.
2#
3# Licensed under the Apache License, Version 2.0 (the "License");
4# you may not use this file except in compliance with the License.
5# You may obtain a copy of the License at
6#
7#     http://www.apache.org/licenses/LICENSE-2.0
8#
9# Unless required by applicable law or agreed to in writing, software
10# distributed under the License is distributed on an "AS IS" BASIS,
11# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12# See the License for the specific language governing permissions and
13# limitations under the License.
14
15from . import encode
16from . import number_types
17from . import packer
18
19def GetSizePrefix(buf, offset):
20	"""Extract the size prefix from a buffer."""
21	return encode.Get(packer.int32, buf, offset)
22
23def GetBufferIdentifier(buf, offset, size_prefixed=False):
24        """Extract the file_identifier from a buffer"""
25        if size_prefixed:
26            # increase offset by size of UOffsetTFlags
27            offset += number_types.UOffsetTFlags.bytewidth
28        # increase offset by size of root table pointer
29        offset += number_types.UOffsetTFlags.bytewidth
30        # end of FILE_IDENTIFIER
31        end = offset + encode.FILE_IDENTIFIER_LENGTH
32        return buf[offset:end]
33
34def BufferHasIdentifier(buf, offset, file_identifier, size_prefixed=False):
35        got = GetBufferIdentifier(buf, offset, size_prefixed=size_prefixed)
36        return got == file_identifier
37
38def RemoveSizePrefix(buf, offset):
39	"""
40	Create a slice of a size-prefixed buffer that has
41	its position advanced just past the size prefix.
42	"""
43	return buf, offset + number_types.Int32Flags.bytewidth
44