2.2.14 ABF_TRAILER_LENGTH Structure
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LengthOfTrailer |
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LengthOfTrailer (4 bytes): A 32-bit unsigned number that is the length of either the ABF_FULL_TRAILER or ABF_DELTA_TRAILER structure that precedes this structure. Additional information MAY be added to the file format. If additional information is added, it MUST be placed after the ABF_FULL_TRAILER or ABF_DELTA_TRAILER structure and before the ABF_TRAILER_LENGTH structure. To access the trailer structure, readers of the file seek to the end of the file less the size of the ABF_TRAILER_LENGTH structure to read the length of the trailer structure. Once the LengthOfTrailer field has been read, readers of the file can seek from the end of the file less LengthOfTrailer less 4 (the size of the ABF_TRAILER_LENGTH structure) to get to the beginning of the trailer structure. This allows future versions of the file format to contain more information if necessary. If more information is added to the file, the LengthOfTrailer MUST include the length of the added information. Using this mechanism prevents breaking old clients using the existing file format.