44 lines
1.6 KiB
Python
44 lines
1.6 KiB
Python
# Copyright 2017 Google Inc. All rights reserved.
|
|
#
|
|
# Licensed under the Apache License, Version 2.0 (the "License");
|
|
# you may not use this file except in compliance with the License.
|
|
# You may obtain a copy of the License at
|
|
#
|
|
# http://www.apache.org/licenses/LICENSE-2.0
|
|
#
|
|
# Unless required by applicable law or agreed to in writing, software
|
|
# distributed under the License is distributed on an "AS IS" BASIS,
|
|
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
# See the License for the specific language governing permissions and
|
|
# limitations under the License.
|
|
|
|
from . import encode
|
|
from . import number_types
|
|
from . import packer
|
|
|
|
def GetSizePrefix(buf, offset):
|
|
"""Extract the size prefix from a buffer."""
|
|
return encode.Get(packer.int32, buf, offset)
|
|
|
|
def GetBufferIdentifier(buf, offset, size_prefixed=False):
|
|
"""Extract the file_identifier from a buffer"""
|
|
if size_prefixed:
|
|
# increase offset by size of UOffsetTFlags
|
|
offset += number_types.UOffsetTFlags.bytewidth
|
|
# increase offset by size of root table pointer
|
|
offset += number_types.UOffsetTFlags.bytewidth
|
|
# end of FILE_IDENTIFIER
|
|
end = offset + encode.FILE_IDENTIFIER_LENGTH
|
|
return buf[offset:end]
|
|
|
|
def BufferHasIdentifier(buf, offset, file_identifier, size_prefixed=False):
|
|
got = GetBufferIdentifier(buf, offset, size_prefixed=size_prefixed)
|
|
return got == file_identifier
|
|
|
|
def RemoveSizePrefix(buf, offset):
|
|
"""
|
|
Create a slice of a size-prefixed buffer that has
|
|
its position advanced just past the size prefix.
|
|
"""
|
|
return buf, offset + number_types.Int32Flags.bytewidth
|