| # 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 | |