sqlite引入的fts5扩展功能，会创建table_content/table_data等数据表，其中_data中是索引数据，可以尝试解析还原出很多有趣的内容。
至于数据结构后面有心情了再补充，直接贴代码。
此代码为C++类。
#pragma once
#include <string>
#include <vector>
#include <map>
#define _fts5GetVarint32(a,b) Fts5GetVarint32((const unsigned char*)a,(uint32_t*)&b)
#define _fts5GetVarint(a,b) Fts5GetVarint((const unsigned char*)a,b)
#define _fts5FastGetVarint32(a, iOff, nVal) { \
nVal = (a)[iOff++]; \
if( nVal & 0x80 ){ \
iOff--; \
iOff += _fts5GetVarint32(&(a)[iOff], nVal); \
} \
}
class FTS5DataHandler
{
public:
FTS5DataHandler() = default;
#define FTS5_DATA_ID_B 16 /* Max seg id number 65535 */
#define FTS5_DATA_DLI_B 1 /* Doclist-index flag (1 bit) */
#define FTS5_DATA_HEIGHT_B 5 /* Max dlidx tree height of 32 */
#define FTS5_DATA_PAGE_B 31 /* Max page number of 2147483648 */
static void fts5DecodeRowid(
int64_t iRowid, /* Rowid from %_data table */
int* piSegid, /* OUT: Segment id */
int* pbDlidx, /* OUT: Dlidx flag */
int* piHeight, /* OUT: Height */
int* piPgno /* OUT: Page number */
) {
*piPgno = (int)(iRowid & (((int64_t)1 << FTS5_DATA_PAGE_B) - 1));
iRowid >>= FTS5_DATA_PAGE_B;
*piHeight = (int)(iRowid & (((int64_t)1 << FTS5_DATA_HEIGHT_B) - 1));
iRowid >>= FTS5_DATA_HEIGHT_B;
*pbDlidx = (int)(iRowid & 0x0001);
iRowid >>= FTS5_DATA_DLI_B;
*piSegid = (int)(iRowid & (((int64_t)1 << FTS5_DATA_ID_B) - 1));
}
static std::pair<std::string, bool> ParserFts5BlockOverData(const std::string& block)
{
int nDataLen = (int)block.length();
if (nDataLen < 4)
return {};
const char* pData = block.c_str();
int iRowidOff = fts5GetU16((const unsigned char*)&pData[0]);
int iPgidx = fts5GetU16((const unsigned char*)&pData[2]); //词条数据总长度
if (iPgidx > nDataLen)
return {};
if (iPgidx == nDataLen)
return { block.substr(4, iPgidx - 4), true };
int iOverdataLen = 0;
_fts5GetVarint32(&pData[iPgidx], iOverdataLen);
if (iOverdataLen <= 4)
return {};
if (iOverdataLen >= nDataLen)
return {};
return { block.substr(4, iOverdataLen - 4), false };
}
void ParserFts5BlockData(const std::string& block, const std::vector<std::string>& overdatas)
{
if (block.length() < 4)
return;
const char* pData = block.data();
int nDataSize = (int)block.length();
int iRowidOff = fts5GetU16((const unsigned char*)&pData[0]); //上一条数据的pos list的over data len + 4
int iPgidx = fts5GetU16((const unsigned char*)&pData[2]); //词条数据总长度
if (iPgidx >= nDataSize)
return;
int iTermOff = 0;
int iPgidxOff = iPgidx;
iPgidxOff += _fts5GetVarint32(&pData[iPgidxOff], iTermOff); //上一条数据的doclist的over data
assert(iTermOff);
std::string last_block;
int iLastTermLen = 0;
std::vector<int> overdataLens;
//解析词条数据
bool bFirst = true;
std::string word;
while (true)
{
int nTermLen;
if (iPgidxOff < nDataSize)
{
iPgidxOff += _fts5GetVarint32(&pData[iPgidxOff], nTermLen);
}
else if (iTermOff < iPgidx)
{
//末尾块
nTermLen = iPgidx - iTermOff;
if (!overdatas.empty())
{
std::string overdata;
for (const auto& data : overdatas)
{
overdata.append(data);
overdataLens.emplace_back((int)data.length());
}
last_block = block.substr(iTermOff, nTermLen);
last_block.append(overdata);
//修正变量
iLastTermLen = nTermLen; //用于重置overdata的rowid索引
nTermLen += (int)overdata.length();
iPgidx = nTermLen;
iTermOff = 0;
pData = last_block.data();
}
}
else
{
//数据解析到头了
break;
}
if (iTermOff + nTermLen > iPgidx)
break;
int iTermEnd = iTermOff + nTermLen;
//fmtlog("term len:{}, offset:0x{:x}", nTermLen, iTermOff);
//读取词条keep
int iWordKeep = 0;
if (!bFirst)
{
_fts5FastGetVarint32(pData, iTermOff, iWordKeep);
if (iWordKeep <= 0)
break;
iWordKeep--;
}
//读取词条长度
int nWordLen;
_fts5FastGetVarint32(pData, iTermOff, nWordLen);
if (nWordLen <= 0)
break;
if (iTermOff + nWordLen >= iPgidx)
break;
//读取词条
if (bFirst && nWordLen > 1)
{
//跳过一个字节
if (nWordLen > 1)
word.assign(&pData[iTermOff + 1], nWordLen - 1);
else
word.assign(&pData[iTermOff], nWordLen); //理论上不应该到这里
bFirst = false;
}
else
{
if (iWordKeep)
{
if (iWordKeep > (int)word.length())
break;
word.assign(word, 0, iWordKeep);
word.append(&pData[iTermOff], nWordLen);
}
else
{
word.assign(&pData[iTermOff], nWordLen);
}
}
iTermOff += nWordLen;
//fmtlog("word:{}({}), keep:{}", Utf82GBK(word), String2Hex(word), iWordKeep);
// if (word == "j")
// int b = 0;
//解析docList
int nRowID = 0;
while (iTermOff < iTermEnd)
{
if (iLastTermLen && iTermOff >= iLastTermLen)
{
//重置rowid
nRowID = 0;
if (!overdataLens.empty())
{
iLastTermLen += overdataLens[0];
overdataLens.erase(overdataLens.begin());
}
else
{
iLastTermLen = 0;
}
}
//读取rowid(docid)
int nRowidTmp = 0;
iTermOff += _fts5GetVarint32(&pData[iTermOff], nRowidTmp);
//增量
nRowID += nRowidTmp;
//fmtlog(" rowid:{}", nRowID);
//读取pos list len
int nPosListSize = 0;
iTermOff += _fts5GetVarint32(&pData[iTermOff], nPosListSize);
if (nPosListSize < 0)
break;
nPosListSize /= 2;
//fmtlog(" pos list size:{}", nPosListSize);
if (iTermOff + nPosListSize > iTermEnd)
break;
if (nPosListSize == 0)
continue;
//读取pos list
auto poslist = fts5DecodePosList(&pData[iTermOff], nPosListSize);
if (m_rowidsFilter.empty() || !m_rowidsFilter.HasKey(nRowID))
{
//printf("word:%s(%s), keep:%d \n", Utf82GBK(word).c_str(), String2Hex(word).c_str(), iWordKeep);
//printf(" rowid:%d \n", nRowID);
//printf(" pos list size:%d \n", nPosListSize);
//fmtlog(" pos list:{}", poslist);
for (const auto& posinfo : poslist)
{
for (const auto& pos : posinfo.second)
{
m_result[nRowID][posinfo.first].emplace(pos, word);
//auto ret = m_result[nRowID][posinfo.first].emplace(pos, word);
// if (!ret.second)
// printf("break;\n");
}
}
}
iTermOff += nPosListSize;
}
}
}
inline void SetRowidFilter(int nRowid)
{
m_rowidsFilter.emplace(nRowid);
}
inline void ClearRowidFilter()
{
m_rowidsFilter.clear();
}
std::map<int, std::map<int, std::string>> GetResult()
{
//整理词语转为真正的句子
//std::map<int, std::map<int, std::vector<std::pair<std::string, std::vector<int>>>>> m_result;
// rowid colid content
std::map<int, std::map<int, std::string>> ret;
for (auto& kv : m_result)
{
int nRowid = kv.first;
for (auto& rowinfo : kv.second)
{
int nColid = rowinfo.first;
//合并字符串
std::string content;
std::for_each(rowinfo.second.begin(), rowinfo.second.end(), [&content](const std::pair<int, std::string> &p) {
content.append(p.second);
});
ret[nRowid][nColid] = content;
//ret[nRowid][nColid] = Utf82GBK(content);
}
}
#ifdef _DEBUG
//fmtlog("ret:{}", ret);
#endif // _DEBUG
return ret;
}
private:
FKeySet<int> m_rowidsFilter;
//结果集
// rowid colid index word
std::map<int, std::map<int, std::map<int, std::string, std::less<>>>> m_result;
//列id-pos list
// col pos list
static std::map<int, std::vector<int>> fts5DecodePosList(const char* pData, int nPosListSize)
{
std::map<int, std::vector<int>> ret;
int nPos = 0;
int nDocOff = 0;
int nColID = 0;
int nPosID = 0;
while (nDocOff < nPosListSize)
{
int nPos;
_fts5FastGetVarint32(pData, nDocOff, nPos);
if (nPos <= 0)
break;
if (nPos == 1)
{
//列切换
int nColOff;
_fts5FastGetVarint32(pData, nDocOff, nColOff);
if (nColOff <= 0)
break;
nColID += nColOff;
nPosID = 0;
continue;
}
nPosID += nPos - 2;
ret[nColID].emplace_back(nPosID);
}
return ret;
}
#define SLOT_2_0 0x001fc07f
#define SLOT_4_2_0 0xf01fc07f
static uint16_t fts5GetU16(const unsigned char* aIn)
{
return ((uint16_t)aIn[0] << 8) + aIn[1];
}
static uint8_t Fts5GetVarint(const unsigned char* p, uint64_t* v) {
uint32_t a, b, s;
a = *p;
/* a: p0 (unmasked) */
if (!(a & 0x80))
{
*v = a;
return 1;
}
p++;
b = *p;
/* b: p1 (unmasked) */
if (!(b & 0x80))
{
a &= 0x7f;
a = a << 7;
a |= b;
*v = a;
return 2;
}
/* Verify that constants are precomputed correctly */
assert(SLOT_2_0 == ((0x7f << 14) | (0x7f)));
assert(SLOT_4_2_0 == ((0xfU << 28) | (0x7f << 14) | (0x7f)));
p++;
a = a << 14;
a |= *p;
/* a: p0<<14 | p2 (unmasked) */
if (!(a & 0x80))
{
a &= SLOT_2_0;
b &= 0x7f;
b = b << 7;
a |= b;
*v = a;
return 3;
}
/* CSE1 from below */
a &= SLOT_2_0;
p++;
b = b << 14;
b |= *p;
/* b: p1<<14 | p3 (unmasked) */
if (!(b & 0x80))
{
b &= SLOT_2_0;
/* moved CSE1 up */
/* a &= (0x7f<<14)|(0x7f); */
a = a << 7;
a |= b;
*v = a;
return 4;
}
/* a: p0<<14 | p2 (masked) */
/* b: p1<<14 | p3 (unmasked) */
/* 1:save off p0<<21 | p1<<14 | p2<<7 | p3 (masked) */
/* moved CSE1 up */
/* a &= (0x7f<<14)|(0x7f); */
b &= SLOT_2_0;
s = a;
/* s: p0<<14 | p2 (masked) */
p++;
a = a << 14;
a |= *p;
/* a: p0<<28 | p2<<14 | p4 (unmasked) */
if (!(a & 0x80))
{
/* we can skip these cause they were (effectively) done above in calc'ing s */
/* a &= (0x7f<<28)|(0x7f<<14)|(0x7f); */
/* b &= (0x7f<<14)|(0x7f); */
b = b << 7;
a |= b;
s = s >> 18;
*v = ((uint64_t)s) << 32 | a;
return 5;
}
/* 2:save off p0<<21 | p1<<14 | p2<<7 | p3 (masked) */
s = s << 7;
s |= b;
/* s: p0<<21 | p1<<14 | p2<<7 | p3 (masked) */
p++;
b = b << 14;
b |= *p;
/* b: p1<<28 | p3<<14 | p5 (unmasked) */
if (!(b & 0x80))
{
/* we can skip this cause it was (effectively) done above in calc'ing s */
/* b &= (0x7f<<28)|(0x7f<<14)|(0x7f); */
a &= SLOT_2_0;
a = a << 7;
a |= b;
s = s >> 18;
*v = ((uint64_t)s) << 32 | a;
return 6;
}
p++;
a = a << 14;
a |= *p;
/* a: p2<<28 | p4<<14 | p6 (unmasked) */
if (!(a & 0x80))
{
a &= SLOT_4_2_0;
b &= SLOT_2_0;
b = b << 7;
a |= b;
s = s >> 11;
*v = ((uint64_t)s) << 32 | a;
return 7;
}
/* CSE2 from below */
a &= SLOT_2_0;
p++;
b = b << 14;
b |= *p;
/* b: p3<<28 | p5<<14 | p7 (unmasked) */
if (!(b & 0x80))
{
b &= SLOT_4_2_0;
/* moved CSE2 up */
/* a &= (0x7f<<14)|(0x7f); */
a = a << 7;
a |= b;
s = s >> 4;
*v = ((uint64_t)s) << 32 | a;
return 8;
}
p++;
a = a << 15;
a |= *p;
/* a: p4<<29 | p6<<15 | p8 (unmasked) */
/* moved CSE2 up */
/* a &= (0x7f<<29)|(0x7f<<15)|(0xff); */
b &= SLOT_2_0;
b = b << 8;
a |= b;
s = s << 4;
b = p[-4];
b &= 0x7f;
b = b >> 3;
s |= b;
*v = ((uint64_t)s) << 32 | a;
return 9;
}
static int Fts5GetVarint32(const unsigned char* p, uint32_t* v) {
uint32_t a, b;
/* The 1-byte case. Overwhelmingly the most common. */
a = *p;
/* a: p0 (unmasked) */
if (!(a & 0x80))
{
/* Values between 0 and 127 */
*v = a;
return 1;
}
/* The 2-byte case */
p++;
b = *p;
/* b: p1 (unmasked) */
if (!(b & 0x80))
{
/* Values between 128 and 16383 */
a &= 0x7f;
a = a << 7;
*v = a | b;
return 2;
}
/* The 3-byte case */
p++;
a = a << 14;
a |= *p;
/* a: p0<<14 | p2 (unmasked) */
if (!(a & 0x80))
{
/* Values between 16384 and 2097151 */
a &= (0x7f << 14) | (0x7f);
b &= 0x7f;
b = b << 7;
*v = a | b;
return 3;
}
/* A 32-bit varint is used to store size information in btrees.
** Objects are rarely larger than 2MiB limit of a 3-byte varint.
** A 3-byte varint is sufficient, for example, to record the size
** of a 1048569-byte BLOB or string.
**
** We only unroll the first 1-, 2-, and 3- byte cases. The very
** rare larger cases can be handled by the slower 64-bit varint
** routine.
*/
{
uint64_t v64;
uint8_t n;
p -= 2;
n = Fts5GetVarint(p, &v64);
*v = ((uint32_t)v64) & 0x7FFFFFFF;
assert(n > 3 && n <= 9);
return n;
}
}
};