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