checksum.h File Reference

On-disk layout definitions for the checksum block (BlockType::ChecksumBlock). More...

#include <stdint.h>

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Data Structures
struct	ChecksumHeader
	Header that precedes the sequence of checksum entries for a checksum block. More...
struct	ChecksumEntry
	Per-checksum metadata immediately followed by the digest / signature bytes. More...

Typedefs
typedef struct ChecksumHeader	ChecksumHeader
typedef struct ChecksumEntry	ChecksumEntry

Detailed Description

On-disk layout definitions for the checksum block (BlockType::ChecksumBlock).

A checksum block stores one or more whole-image (user data) checksums. For optical media the user data definition follows the format's raw sector rules (e.g. 2352-byte raw sector when available).

Binary layout (all integers are little-endian, structure is packed):

+---------------------------—+----------------------------—+ | Field | Size (bytes) | +==============================+===============================+ | ChecksumHeader | sizeof(ChecksumHeader)=9 | | identifier | 4 (BlockType::ChecksumBlock) | | length | 4 (payload bytes that follow)| | entries | 1 (number of checksum entries)| +---------------------------—+----------------------------—+ | Repeated for each entry: | | ChecksumEntry | sizeof(ChecksumEntry)=5 | | type | 1 (ChecksumAlgorithm) | | length | 4 (digest length) | | digest bytes | length | +---------------------------—+----------------------------—+

Thus, the payload size (ChecksumHeader.length) MUST equal the sum over all entries of: sizeof(ChecksumEntry) + entry.length.

Typical digest lengths:

• Md5: 16 bytes
• Sha1: 20 bytes
• Sha256: 32 bytes
• SpamSum: variable length ASCII, NOT null-terminated on disk (a terminating '\0' may be appended in memory).

Warning

The structures are packed; never rely on host compiler default padding or directly casting from a buffer without ensuring correct endianness if porting to big-endian systems (current implementation assumes LE).

See also

BlockType

ChecksumAlgorithm

Definition in file checksum.h.

Typedef Documentation

ChecksumEntry

typedef struct ChecksumEntry ChecksumEntry

ChecksumHeader

typedef struct ChecksumHeader ChecksumHeader