wal.cpp

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// Copyright (C) 2026 Douglas Quigg (dstroy0) <dquigg123@gmail.com>
// SPDX-License-Identifier: AGPL-3.0-or-later
 
/**
 * @file wal.cpp
 * @brief Write-ahead journal record framing + crash-recovery replay (see wal.h).
 */
 
#include "services/wal/wal.h"
 
#if DETWS_ENABLE_WAL
 
#include <string.h>
 
namespace
{
// CRC-32 (IEEE 802.3, reflected, poly 0xEDB88320) byte lookup table. A table-driven step is several times
// faster than the bit-by-bit form on the ESP32-S3, where the WAL write path is CRC-bound (~4.4 MB/s ->
// table; see docs/FEATURE_PERFORMANCE.md section 4). 1 KiB of rodata.
const uint32_t CRC32_TABLE[256] = {
    0x00000000u, 0x77073096u, 0xee0e612cu, 0x990951bau, 0x076dc419u, 0x706af48fu, 0xe963a535u, 0x9e6495a3u, 0x0edb8832u,
    0x79dcb8a4u, 0xe0d5e91eu, 0x97d2d988u, 0x09b64c2bu, 0x7eb17cbdu, 0xe7b82d07u, 0x90bf1d91u, 0x1db71064u, 0x6ab020f2u,
    0xf3b97148u, 0x84be41deu, 0x1adad47du, 0x6ddde4ebu, 0xf4d4b551u, 0x83d385c7u, 0x136c9856u, 0x646ba8c0u, 0xfd62f97au,
    0x8a65c9ecu, 0x14015c4fu, 0x63066cd9u, 0xfa0f3d63u, 0x8d080df5u, 0x3b6e20c8u, 0x4c69105eu, 0xd56041e4u, 0xa2677172u,
    0x3c03e4d1u, 0x4b04d447u, 0xd20d85fdu, 0xa50ab56bu, 0x35b5a8fau, 0x42b2986cu, 0xdbbbc9d6u, 0xacbcf940u, 0x32d86ce3u,
    0x45df5c75u, 0xdcd60dcfu, 0xabd13d59u, 0x26d930acu, 0x51de003au, 0xc8d75180u, 0xbfd06116u, 0x21b4f4b5u, 0x56b3c423u,
    0xcfba9599u, 0xb8bda50fu, 0x2802b89eu, 0x5f058808u, 0xc60cd9b2u, 0xb10be924u, 0x2f6f7c87u, 0x58684c11u, 0xc1611dabu,
    0xb6662d3du, 0x76dc4190u, 0x01db7106u, 0x98d220bcu, 0xefd5102au, 0x71b18589u, 0x06b6b51fu, 0x9fbfe4a5u, 0xe8b8d433u,
    0x7807c9a2u, 0x0f00f934u, 0x9609a88eu, 0xe10e9818u, 0x7f6a0dbbu, 0x086d3d2du, 0x91646c97u, 0xe6635c01u, 0x6b6b51f4u,
    0x1c6c6162u, 0x856530d8u, 0xf262004eu, 0x6c0695edu, 0x1b01a57bu, 0x8208f4c1u, 0xf50fc457u, 0x65b0d9c6u, 0x12b7e950u,
    0x8bbeb8eau, 0xfcb9887cu, 0x62dd1ddfu, 0x15da2d49u, 0x8cd37cf3u, 0xfbd44c65u, 0x4db26158u, 0x3ab551ceu, 0xa3bc0074u,
    0xd4bb30e2u, 0x4adfa541u, 0x3dd895d7u, 0xa4d1c46du, 0xd3d6f4fbu, 0x4369e96au, 0x346ed9fcu, 0xad678846u, 0xda60b8d0u,
    0x44042d73u, 0x33031de5u, 0xaa0a4c5fu, 0xdd0d7cc9u, 0x5005713cu, 0x270241aau, 0xbe0b1010u, 0xc90c2086u, 0x5768b525u,
    0x206f85b3u, 0xb966d409u, 0xce61e49fu, 0x5edef90eu, 0x29d9c998u, 0xb0d09822u, 0xc7d7a8b4u, 0x59b33d17u, 0x2eb40d81u,
    0xb7bd5c3bu, 0xc0ba6cadu, 0xedb88320u, 0x9abfb3b6u, 0x03b6e20cu, 0x74b1d29au, 0xead54739u, 0x9dd277afu, 0x04db2615u,
    0x73dc1683u, 0xe3630b12u, 0x94643b84u, 0x0d6d6a3eu, 0x7a6a5aa8u, 0xe40ecf0bu, 0x9309ff9du, 0x0a00ae27u, 0x7d079eb1u,
    0xf00f9344u, 0x8708a3d2u, 0x1e01f268u, 0x6906c2feu, 0xf762575du, 0x806567cbu, 0x196c3671u, 0x6e6b06e7u, 0xfed41b76u,
    0x89d32be0u, 0x10da7a5au, 0x67dd4accu, 0xf9b9df6fu, 0x8ebeeff9u, 0x17b7be43u, 0x60b08ed5u, 0xd6d6a3e8u, 0xa1d1937eu,
    0x38d8c2c4u, 0x4fdff252u, 0xd1bb67f1u, 0xa6bc5767u, 0x3fb506ddu, 0x48b2364bu, 0xd80d2bdau, 0xaf0a1b4cu, 0x36034af6u,
    0x41047a60u, 0xdf60efc3u, 0xa867df55u, 0x316e8eefu, 0x4669be79u, 0xcb61b38cu, 0xbc66831au, 0x256fd2a0u, 0x5268e236u,
    0xcc0c7795u, 0xbb0b4703u, 0x220216b9u, 0x5505262fu, 0xc5ba3bbeu, 0xb2bd0b28u, 0x2bb45a92u, 0x5cb36a04u, 0xc2d7ffa7u,
    0xb5d0cf31u, 0x2cd99e8bu, 0x5bdeae1du, 0x9b64c2b0u, 0xec63f226u, 0x756aa39cu, 0x026d930au, 0x9c0906a9u, 0xeb0e363fu,
    0x72076785u, 0x05005713u, 0x95bf4a82u, 0xe2b87a14u, 0x7bb12baeu, 0x0cb61b38u, 0x92d28e9bu, 0xe5d5be0du, 0x7cdcefb7u,
    0x0bdbdf21u, 0x86d3d2d4u, 0xf1d4e242u, 0x68ddb3f8u, 0x1fda836eu, 0x81be16cdu, 0xf6b9265bu, 0x6fb077e1u, 0x18b74777u,
    0x88085ae6u, 0xff0f6a70u, 0x66063bcau, 0x11010b5cu, 0x8f659effu, 0xf862ae69u, 0x616bffd3u, 0x166ccf45u, 0xa00ae278u,
    0xd70dd2eeu, 0x4e048354u, 0x3903b3c2u, 0xa7672661u, 0xd06016f7u, 0x4969474du, 0x3e6e77dbu, 0xaed16a4au, 0xd9d65adcu,
    0x40df0b66u, 0x37d83bf0u, 0xa9bcae53u, 0xdebb9ec5u, 0x47b2cf7fu, 0x30b5ffe9u, 0xbdbdf21cu, 0xcabac28au, 0x53b39330u,
    0x24b4a3a6u, 0xbad03605u, 0xcdd70693u, 0x54de5729u, 0x23d967bfu, 0xb3667a2eu, 0xc4614ab8u, 0x5d681b02u, 0x2a6f2b94u,
    0xb40bbe37u, 0xc30c8ea1u, 0x5a05df1bu, 0x2d02ef8du,
};
 
// CRC-32 core with no init/final xor, so it composes across a header + payload in two steps.
uint32_t crc32_step(uint32_t crc, const uint8_t *d, size_t n)
{
    for (size_t i = 0; i < n; i++)
        crc = CRC32_TABLE[(crc ^ d[i]) & 0xFFu] ^ (crc >> 8);
    return crc;
}
 
void put_u32(uint8_t *p, uint32_t v)
{
    p[0] = (uint8_t)v;
    p[1] = (uint8_t)(v >> 8);
    p[2] = (uint8_t)(v >> 16);
    p[3] = (uint8_t)(v >> 24);
}
void put_u64(uint8_t *p, uint64_t v)
{
    for (int i = 0; i < 8; i++)
        p[i] = (uint8_t)(v >> (8 * i));
}
uint32_t get_u32(const uint8_t *p)
{
    return (uint32_t)p[0] | ((uint32_t)p[1] << 8) | ((uint32_t)p[2] << 16) | ((uint32_t)p[3] << 24);
}
uint64_t get_u64(const uint8_t *p)
{
    uint64_t v = 0;
    for (int i = 0; i < 8; i++)
        v |= (uint64_t)p[i] << (8 * i);
    return v;
}
} // namespace
 
uint32_t wal_crc32(const uint8_t *data, size_t len)
{
    return crc32_step(0xFFFFFFFFu, data, len) ^ 0xFFFFFFFFu;
}
 
uint32_t wal_crc32_init(void)
{
    return 0xFFFFFFFFu;
}
uint32_t wal_crc32_update(uint32_t crc, const uint8_t *d, size_t n)
{
    return crc32_step(crc, d, n);
}
uint32_t wal_crc32_final(uint32_t crc)
{
    return crc ^ 0xFFFFFFFFu;
}
 
size_t wal_record_encode(uint8_t *out, size_t cap, uint64_t seq, const uint8_t *payload, uint32_t len)
{
    size_t need = (size_t)WAL_RECORD_HEADER + len;
    if (out == nullptr || need > cap)
        return 0;
    put_u32(out + 0, WAL_MAGIC);
    put_u64(out + 4, seq);
    put_u32(out + 12, len);
    // crc over the 16 header bytes (magic+seq+len) then the payload
    uint32_t crc = crc32_step(0xFFFFFFFFu, out, 16);
    crc = crc32_step(crc, payload, len) ^ 0xFFFFFFFFu;
    put_u32(out + 16, crc);
    if (len)
        memcpy(out + WAL_RECORD_HEADER, payload, len);
    return need;
}
 
size_t wal_replay(const uint8_t *img, size_t len, WalRecordCb cb, void *ctx)
{
    size_t off = 0;
    while (off + WAL_RECORD_HEADER <= len)
    {
        const uint8_t *r = img + off;
        if (get_u32(r) != WAL_MAGIC)
            break; // not a record start (end of log or garbage)
        uint64_t seq = get_u64(r + 4);
        uint32_t plen = get_u32(r + 12);
        uint32_t crc_stored = get_u32(r + 16);
        if (off + (size_t)WAL_RECORD_HEADER + plen > len)
            break; // truncated tail (power loss mid-record)
        uint32_t crc = crc32_step(0xFFFFFFFFu, r, 16);
        crc = crc32_step(crc, r + WAL_RECORD_HEADER, plen) ^ 0xFFFFFFFFu;
        if (crc != crc_stored)
            break; // torn / corrupt record - stop here, this is the durable end
        if (cb)
            cb(seq, r + WAL_RECORD_HEADER, plen, ctx);
        off += (size_t)WAL_RECORD_HEADER + plen;
    }
    return off;
}
 
#endif // DETWS_ENABLE_WAL