| Austin Schuh | e89fa2d | 2019-08-14 20:24:23 -0700 | [diff] [blame^] | 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 | |
| 15 | from . import encode |
| 16 | from . import number_types |
| 17 | from . import packer |
| 18 | |
| 19 | def GetSizePrefix(buf, offset): |
| 20 | """Extract the size prefix from a buffer.""" |
| 21 | return encode.Get(packer.int32, buf, offset) |
| 22 | |
| 23 | def 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 | |
| 34 | def BufferHasIdentifier(buf, offset, file_identifier, size_prefixed=False): |
| 35 | got = GetBufferIdentifier(buf, offset, size_prefixed=size_prefixed) |
| 36 | return got == file_identifier |
| 37 | |
| 38 | def 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 |