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SQLite training in Houston TX on 2019-11-05 (details)
Part of the 2019 Tcl Conference

• File src/test_fuzzer.c — part of check-in [a6a81d4f] at 2011-04-01 20:28:31 on branch word-fuzzer — Add additional test data and documentation to the fuzzer virtual table. (user: drh size: 27588) [more...]

``````/*
** 2011 March 24
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** Code for demonstartion virtual table that generates variations
** on an input word at increasing edit distances from the original.
**
** A fuzzer virtual table is created like this:
**
**     CREATE VIRTUAL TABLE temp.f USING fuzzer;
**
** The name of the new virtual table in the example above is "f".
** Note that all fuzzer virtual tables must be TEMP tables.  The
** "temp." prefix in front of the table name is required when the
** table is being created.  The "temp." prefix can be omitted when
** using the table as long as the name is unambiguous.
**
** Before being used, the fuzzer needs to be programmed by giving it
** character transformations and a cost associated with each transformation.
** Examples:
**
**    INSERT INTO f(cFrom,cTo,Cost) VALUES('','a',100);
**
** The above statement says that the cost of inserting a letter 'a' is
** 100.  (All costs are integers.  We recommend that costs be scaled so
** that the average cost is around 100.)
**
**    INSERT INTO f(cFrom,cTo,Cost) VALUES('b','',87);
**
** The above statement says that the cost of deleting a single letter
** 'b' is 87.
**
**    INSERT INTO f(cFrom,cTo,Cost) VALUES('o','oe',38);
**    INSERT INTO f(cFrom,cTo,Cost) VALUES('oe','o',40);
**
** This third example says that the cost of transforming the single
** letter "o" into the two-letter sequence "oe" is 38 and that the
** cost of transforming "oe" back into "o" is 40.
**
** After all the transformation costs have been set, the fuzzer table
** can be queried as follows:
**
**    SELECT word, distance FROM f
**     WHERE word MATCH 'abcdefg'
**       AND distance<200;
**
** This first query outputs the string "abcdefg" and all strings that
** can be derived from that string by appling the specified transformations.
** The strings are output together with their total transformation cost
** (called "distance") and appear in order of increasing cost.  No string
** is output more than once.  If there are multiple ways to transform the
** target string into the output string then the lowest cost transform is
** the one that is returned.  In the example, the search is limited to
** strings with a total distance of less than 200.
**
** It is important to put some kind of a limit on the fuzzer output.  This
** can be either in the form of a LIMIT clause at the end of the query,
** or better, a "distance<NNN" constraint where NNN is some number.  The
** running time and memory requirement is exponential in the value of NNN
** so you want to make sure that NNN is not too big.  A value of NNN that
** is about twice the average transformation cost seems to give good results.
**
** The fuzzer table can be useful for tasks such as spelling correction.
** Suppose there is a second table vocabulary(w) where the w column contains
** all correctly spelled words.   Let \$word be a word you want to look up.
**
**   SELECT vocabulary.w FROM f, vocabulary
**    WHERE f.word MATCH \$word
**      AND f.distance<=200
**      AND f.word=vocabulary.w
**    LIMIT 20
**
** The query above gives the 20 closest words to the \$word being tested.
** (Note that for good performance, the vocubulary.w column should be
** indexed.)
**
** A similar query can be used to find all words in the dictionary that
** begin with some prefix \$prefix:
**
**   SELECT vocabulary.w FROM f, vocabulary
**    WHERE f.word MATCH \$prefix
**      AND f.distance<=200
**      AND vocabulary.w BETWEEN f.word AND (f.word || x'F7BFBFBF')
**    LIMIT 50
**
** This last query will show up to 50 words out of the vocabulary that
** match or nearly match the \$prefix.
*/
#include "sqlite3.h"
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <stdio.h>

#ifndef SQLITE_OMIT_VIRTUALTABLE

/*
** Forward declaration of objects used by this implementation
*/
typedef struct fuzzer_vtab fuzzer_vtab;
typedef struct fuzzer_cursor fuzzer_cursor;
typedef struct fuzzer_rule fuzzer_rule;
typedef struct fuzzer_seen fuzzer_seen;
typedef struct fuzzer_stem fuzzer_stem;

/*
** Type of the "cost" of an edit operation.  Might be changed to
** "float" or "double" or "sqlite3_int64" in the future.
*/
typedef int fuzzer_cost;

/*
** Each transformation rule is stored as an instance of this object.
** All rules are kept on a linked list sorted by rCost.
*/
struct fuzzer_rule {
fuzzer_rule *pNext;        /* Next rule in order of increasing rCost */
fuzzer_cost rCost;         /* Cost of this transformation */
int nFrom, nTo;            /* Length of the zFrom and zTo strings */
char *zFrom;               /* Transform from */
char zTo[4];               /* Transform to (extra space appended) */
};

/*
** A stem object is used to generate variants.  It is also used to record
** previously generated outputs.
**
** Every stem is added to a hash table as it is output.  Generation of
** duplicate stems is suppressed.
**
** Active stems (those that might generate new outputs) are kepts on a linked
** list sorted by increasing cost.  The cost is the sum of rBaseCost and
** pRule->rCost.
*/
struct fuzzer_stem {
char *zBasis;              /* Word being fuzzed */
int nBasis;                /* Length of the zBasis string */
const fuzzer_rule *pRule;  /* Current rule to apply */
int n;                     /* Apply pRule at this character offset */
fuzzer_cost rBaseCost;     /* Base cost of getting to zBasis */
fuzzer_cost rCostX;        /* Precomputed rBaseCost + pRule->rCost */
fuzzer_stem *pNext;        /* Next stem in rCost order */
fuzzer_stem *pHash;        /* Next stem with same hash on zBasis */
};

/*
** A fuzzer virtual-table object
*/
struct fuzzer_vtab {
sqlite3_vtab base;         /* Base class - must be first */
char *zClassName;          /* Name of this class.  Default: "fuzzer" */
fuzzer_rule *pRule;        /* All active rules in this fuzzer */
fuzzer_rule *pNewRule;     /* New rules to add when last cursor expires */
int nCursor;               /* Number of active cursors */
};

#define FUZZER_HASH  4001    /* Hash table size */
#define FUZZER_NQUEUE  20    /* Number of slots on the stem queue */

/* A fuzzer cursor object */
struct fuzzer_cursor {
sqlite3_vtab_cursor base;  /* Base class - must be first */
sqlite3_int64 iRowid;      /* The rowid of the current word */
fuzzer_vtab *pVtab;        /* The virtual table this cursor belongs to */
fuzzer_cost rLimit;        /* Maximum cost of any term */
fuzzer_stem *pStem;        /* Stem with smallest rCostX */
fuzzer_stem *pDone;        /* Stems already processed to completion */
fuzzer_stem *aQueue[FUZZER_NQUEUE];  /* Queue of stems with higher rCostX */
int mxQueue;               /* Largest used index in aQueue[] */
char *zBuf;                /* Temporary use buffer */
int nBuf;                  /* Bytes allocated for zBuf */
int nStem;                 /* Number of stems allocated */
fuzzer_rule nullRule;      /* Null rule used first */
fuzzer_stem *apHash[FUZZER_HASH]; /* Hash of previously generated terms */
};

/* Methods for the fuzzer module */
static int fuzzerConnect(
sqlite3 *db,
void *pAux,
int argc, const char *const*argv,
sqlite3_vtab **ppVtab,
char **pzErr
){
fuzzer_vtab *pNew;
int n;
if( strcmp(argv[1],"temp")!=0 ){
*pzErr = sqlite3_mprintf("%s virtual tables must be TEMP", argv[0]);
return SQLITE_ERROR;
}
n = strlen(argv[0]) + 1;
pNew = sqlite3_malloc( sizeof(*pNew) + n );
if( pNew==0 ) return SQLITE_NOMEM;
pNew->zClassName = (char*)&pNew[1];
memcpy(pNew->zClassName, argv[0], n);
sqlite3_declare_vtab(db, "CREATE TABLE x(word,distance,cFrom,cTo,cost)");
memset(pNew, 0, sizeof(*pNew));
*ppVtab = &pNew->base;
return SQLITE_OK;
}
/* Note that for this virtual table, the xCreate and xConnect
** methods are identical. */

static int fuzzerDisconnect(sqlite3_vtab *pVtab){
fuzzer_vtab *p = (fuzzer_vtab*)pVtab;
assert( p->nCursor==0 );
do{
while( p->pRule ){
fuzzer_rule *pRule = p->pRule;
p->pRule = pRule->pNext;
sqlite3_free(pRule);
}
p->pRule = p->pNewRule;
p->pNewRule = 0;
}while( p->pRule );
sqlite3_free(p);
return SQLITE_OK;
}
/* The xDisconnect and xDestroy methods are also the same */

/*
** The two input rule lists are both sorted in order of increasing
** cost.  Merge them together into a single list, sorted by cost, and
** return a pointer to the head of that list.
*/
static fuzzer_rule *fuzzerMergeRules(fuzzer_rule *pA, fuzzer_rule *pB){
fuzzer_rule *pTail;

while( pA && pB ){
if( pA->rCost<=pB->rCost ){
pTail->pNext = pA;
pTail = pA;
pA = pA->pNext;
}else{
pTail->pNext = pB;
pTail = pB;
pB = pB->pNext;
}
}
if( pA==0 ){
pTail->pNext = pB;
}else{
pTail->pNext = pA;
}
}

/*
** Open a new fuzzer cursor.
*/
static int fuzzerOpen(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCursor){
fuzzer_vtab *p = (fuzzer_vtab*)pVTab;
fuzzer_cursor *pCur;
pCur = sqlite3_malloc( sizeof(*pCur) );
if( pCur==0 ) return SQLITE_NOMEM;
memset(pCur, 0, sizeof(*pCur));
pCur->pVtab = p;
*ppCursor = &pCur->base;
if( p->nCursor==0 && p->pNewRule ){
unsigned int i;
fuzzer_rule *pX;
fuzzer_rule *a[15];
for(i=0; i<sizeof(a)/sizeof(a[0]); i++) a[i] = 0;
while( (pX = p->pNewRule)!=0 ){
p->pNewRule = pX->pNext;
pX->pNext = 0;
for(i=0; a[i] && i<sizeof(a)/sizeof(a[0])-1; i++){
pX = fuzzerMergeRules(a[i], pX);
a[i] = 0;
}
a[i] = fuzzerMergeRules(a[i], pX);
}
for(pX=a[0], i=1; i<sizeof(a)/sizeof(a[0]); i++){
pX = fuzzerMergeRules(a[i], pX);
}
p->pRule = fuzzerMergeRules(p->pRule, pX);
}
p->nCursor++;
return SQLITE_OK;
}

/*
** Free all stems in a list.
*/
static void fuzzerClearStemList(fuzzer_stem *pStem){
while( pStem ){
fuzzer_stem *pNext = pStem->pNext;
sqlite3_free(pStem);
pStem = pNext;
}
}

/*
** Free up all the memory allocated by a cursor.  Set it rLimit to 0
** to indicate that it is at EOF.
*/
static void fuzzerClearCursor(fuzzer_cursor *pCur, int clearHash){
int i;
fuzzerClearStemList(pCur->pStem);
fuzzerClearStemList(pCur->pDone);
for(i=0; i<FUZZER_NQUEUE; i++) fuzzerClearStemList(pCur->aQueue[i]);
pCur->rLimit = (fuzzer_cost)0;
if( clearHash && pCur->nStem ){
pCur->mxQueue = 0;
pCur->pStem = 0;
pCur->pDone = 0;
memset(pCur->aQueue, 0, sizeof(pCur->aQueue));
memset(pCur->apHash, 0, sizeof(pCur->apHash));
}
pCur->nStem = 0;
}

/*
** Close a fuzzer cursor.
*/
static int fuzzerClose(sqlite3_vtab_cursor *cur){
fuzzer_cursor *pCur = (fuzzer_cursor *)cur;
fuzzerClearCursor(pCur, 0);
sqlite3_free(pCur->zBuf);
pCur->pVtab->nCursor--;
sqlite3_free(pCur);
return SQLITE_OK;
}

/*
** Compute the current output term for a fuzzer_stem.
*/
static int fuzzerRender(
fuzzer_stem *pStem,   /* The stem to be rendered */
char **pzBuf,         /* Write results into this buffer.  realloc if needed */
int *pnBuf            /* Size of the buffer */
){
const fuzzer_rule *pRule = pStem->pRule;
int n;
char *z;

n = pStem->nBasis + pRule->nTo - pRule->nFrom;
if( (*pnBuf)<n+1 ){
(*pzBuf) = sqlite3_realloc((*pzBuf), n+100);
if( (*pzBuf)==0 ) return SQLITE_NOMEM;
(*pnBuf) = n+100;
}
n = pStem->n;
z = *pzBuf;
if( n<0 ){
memcpy(z, pStem->zBasis, pStem->nBasis+1);
}else{
memcpy(z, pStem->zBasis, n);
memcpy(&z[n], pRule->zTo, pRule->nTo);
memcpy(&z[n+pRule->nTo], &pStem->zBasis[n+pRule->nFrom],
pStem->nBasis-n-pRule->nFrom+1);
}
return SQLITE_OK;
}

/*
** Compute a hash on zBasis.
*/
static unsigned int fuzzerHash(const char *z){
unsigned int h = 0;
while( *z ){ h = (h<<3) ^ (h>>29) ^ *(z++); }
return h % FUZZER_HASH;
}

/*
** Current cost of a stem
*/
static fuzzer_cost fuzzerCost(fuzzer_stem *pStem){
return pStem->rCostX = pStem->rBaseCost + pStem->pRule->rCost;
}

#if 0
/*
** Print a description of a fuzzer_stem on stderr.
*/
static void fuzzerStemPrint(
const char *zPrefix,
fuzzer_stem *pStem,
const char *zSuffix
){
if( pStem->n<0 ){
fprintf(stderr, "%s[%s](%d)-->self%s",
zPrefix,
pStem->zBasis, pStem->rBaseCost,
zSuffix
);
}else{
char *zBuf = 0;
int nBuf = 0;
if( fuzzerRender(pStem, &zBuf, &nBuf)!=SQLITE_OK ) return;
fprintf(stderr, "%s[%s](%d)-->{%s}(%d)%s",
zPrefix,
pStem->zBasis, pStem->rBaseCost, zBuf, pStem->,
zSuffix
);
sqlite3_free(zBuf);
}
}
#endif

/*
** Return 1 if the string to which the cursor is point has already
** been emitted.  Return 0 if not.  Return -1 on a memory allocation
** failures.
*/
static int fuzzerSeen(fuzzer_cursor *pCur, fuzzer_stem *pStem){
unsigned int h;
fuzzer_stem *pLookup;

if( fuzzerRender(pStem, &pCur->zBuf, &pCur->nBuf)==SQLITE_NOMEM ){
return -1;
}
h = fuzzerHash(pCur->zBuf);
pLookup = pCur->apHash[h];
while( pLookup && strcmp(pLookup->zBasis, pCur->zBuf)!=0 ){
pLookup = pLookup->pHash;
}
return pLookup!=0;
}

/*
** Advance a fuzzer_stem to its next value.   Return 0 if there are
** no more values that can be generated by this fuzzer_stem.  Return
** -1 on a memory allocation failure.
*/
static int fuzzerAdvance(fuzzer_cursor *pCur, fuzzer_stem *pStem){
const fuzzer_rule *pRule;
while( (pRule = pStem->pRule)!=0 ){
while( pStem->n < pStem->nBasis - pRule->nFrom ){
pStem->n++;
if( pRule->nFrom==0
|| memcmp(&pStem->zBasis[pStem->n], pRule->zFrom, pRule->nFrom)==0
){
/* Found a rewrite case.  Make sure it is not a duplicate */
int rc = fuzzerSeen(pCur, pStem);
if( rc<0 ) return -1;
if( rc==0 ){
fuzzerCost(pStem);
return 1;
}
}
}
pStem->n = -1;
pStem->pRule = pRule->pNext;
if( pStem->pRule && fuzzerCost(pStem)>pCur->rLimit ) pStem->pRule = 0;
}
return 0;
}

/*
** The two input stem lists are both sorted in order of increasing
** rCostX.  Merge them together into a single list, sorted by rCostX, and
** return a pointer to the head of that new list.
*/
static fuzzer_stem *fuzzerMergeStems(fuzzer_stem *pA, fuzzer_stem *pB){
fuzzer_stem *pTail;

while( pA && pB ){
if( pA->rCostX<=pB->rCostX ){
pTail->pNext = pA;
pTail = pA;
pA = pA->pNext;
}else{
pTail->pNext = pB;
pTail = pB;
pB = pB->pNext;
}
}
if( pA==0 ){
pTail->pNext = pB;
}else{
pTail->pNext = pA;
}
}

/*
** Load pCur->pStem with the lowest-cost stem.  Return a pointer
** to the lowest-cost stem.
*/
static fuzzer_stem *fuzzerLowestCostStem(fuzzer_cursor *pCur){
fuzzer_stem *pBest, *pX;
int iBest;
int i;

if( pCur->pStem==0 ){
iBest = -1;
pBest = 0;
for(i=0; i<=pCur->mxQueue; i++){
pX = pCur->aQueue[i];
if( pX==0 ) continue;
if( pBest==0 || pBest->rCostX>pX->rCostX ){
pBest = pX;
iBest = i;
}
}
if( pBest ){
pCur->aQueue[iBest] = pBest->pNext;
pBest->pNext = 0;
pCur->pStem = pBest;
}
}
return pCur->pStem;
}

/*
** Insert pNew into queue of pending stems.  Then find the stem
** with the lowest rCostX and move it into pCur->pStem.
** list.  The insert is done such the pNew is in the correct order
** according to fuzzer_stem.zBaseCost+fuzzer_stem.pRule->rCost.
*/
static fuzzer_stem *fuzzerInsert(fuzzer_cursor *pCur, fuzzer_stem *pNew){
fuzzer_stem *pX;
int i;

/* If pCur->pStem exists and is greater than pNew, then make pNew
** the new pCur->pStem and insert the old pCur->pStem instead.
*/
if( (pX = pCur->pStem)!=0 && pX->rCostX>pNew->rCostX ){
pNew->pNext = 0;
pCur->pStem = pNew;
pNew = pX;
}

/* Insert the new value */
pNew->pNext = 0;
pX = pNew;
for(i=0; i<=pCur->mxQueue; i++){
if( pCur->aQueue[i] ){
pX = fuzzerMergeStems(pX, pCur->aQueue[i]);
pCur->aQueue[i] = 0;
}else{
pCur->aQueue[i] = pX;
break;
}
}
if( i>pCur->mxQueue ){
if( i<FUZZER_NQUEUE ){
pCur->mxQueue = i;
pCur->aQueue[i] = pX;
}else{
assert( pCur->mxQueue==FUZZER_NQUEUE-1 );
pX = fuzzerMergeStems(pX, pCur->aQueue[FUZZER_NQUEUE-1]);
pCur->aQueue[FUZZER_NQUEUE-1] = pX;
}
}

return fuzzerLowestCostStem(pCur);
}

/*
** Allocate a new fuzzer_stem.  Add it to the hash table but do not
** link it into either the pCur->pStem or pCur->pDone lists.
*/
static fuzzer_stem *fuzzerNewStem(
fuzzer_cursor *pCur,
const char *zWord,
fuzzer_cost rBaseCost
){
fuzzer_stem *pNew;
unsigned int h;

pNew = sqlite3_malloc( sizeof(*pNew) + strlen(zWord) + 1 );
if( pNew==0 ) return 0;
memset(pNew, 0, sizeof(*pNew));
pNew->zBasis = (char*)&pNew[1];
pNew->nBasis = strlen(zWord);
memcpy(pNew->zBasis, zWord, pNew->nBasis+1);
pNew->pRule = pCur->pVtab->pRule;
pNew->n = -1;
pNew->rBaseCost = pNew->rCostX = rBaseCost;
h = fuzzerHash(pNew->zBasis);
pNew->pHash = pCur->apHash[h];
pCur->apHash[h] = pNew;
pCur->nStem++;
return pNew;
}

/*
** Advance a cursor to its next row of output
*/
static int fuzzerNext(sqlite3_vtab_cursor *cur){
fuzzer_cursor *pCur = (fuzzer_cursor*)cur;
int rc;
fuzzer_stem *pStem, *pNew;

pCur->iRowid++;

/* Use the element the cursor is currently point to to create
** a new stem and insert the new stem into the priority queue.
*/
pStem = pCur->pStem;
if( pStem->rCostX>0 ){
rc = fuzzerRender(pStem, &pCur->zBuf, &pCur->nBuf);
if( rc==SQLITE_NOMEM ) return SQLITE_NOMEM;
pNew = fuzzerNewStem(pCur, pCur->zBuf, pStem->rCostX);
if( pNew ){
pNew->pNext = pCur->pDone;
pCur->pDone = pNew;
}else{
if( fuzzerInsert(pCur, pNew)==pNew ){
return SQLITE_OK;
}
}
}else{
return SQLITE_NOMEM;
}
}

/* Adjust the priority queue so that the first element of the
** stem list is the next lowest cost word.
*/
while( (pStem = pCur->pStem)!=0 ){
pCur->pStem = 0;
pStem = fuzzerInsert(pCur, pStem);
if( (rc = fuzzerSeen(pCur, pStem))!=0 ){
if( rc<0 ) return SQLITE_NOMEM;
continue;
}
return SQLITE_OK;  /* New word found */
}
pCur->pStem = 0;
pStem->pNext = pCur->pDone;
pCur->pDone = pStem;
if( fuzzerLowestCostStem(pCur) ){
rc = fuzzerSeen(pCur, pCur->pStem);
if( rc<0 ) return SQLITE_NOMEM;
if( rc==0 ){
return SQLITE_OK;
}
}
}

/* Reach this point only if queue has been exhausted and there is
** nothing left to be output. */
pCur->rLimit = (fuzzer_cost)0;
return SQLITE_OK;
}

/*
** Called to "rewind" a cursor back to the beginning so that
** it starts its output over again.  Always called at least once
** prior to any fuzzerColumn, fuzzerRowid, or fuzzerEof call.
*/
static int fuzzerFilter(
sqlite3_vtab_cursor *pVtabCursor,
int idxNum, const char *idxStr,
int argc, sqlite3_value **argv
){
fuzzer_cursor *pCur = (fuzzer_cursor *)pVtabCursor;
const char *zWord = 0;
fuzzer_stem *pStem;

fuzzerClearCursor(pCur, 1);
pCur->rLimit = 2147483647;
if( idxNum==1 ){
zWord = (const char*)sqlite3_value_text(argv[0]);
}else if( idxNum==2 ){
pCur->rLimit = (fuzzer_cost)sqlite3_value_int(argv[0]);
}else if( idxNum==3 ){
zWord = (const char*)sqlite3_value_text(argv[0]);
pCur->rLimit = (fuzzer_cost)sqlite3_value_int(argv[1]);
}
if( zWord==0 ) zWord = "";
pCur->pStem = pStem = fuzzerNewStem(pCur, zWord, (fuzzer_cost)0);
if( pStem==0 ) return SQLITE_NOMEM;
pCur->nullRule.pNext = pCur->pVtab->pRule;
pCur->nullRule.rCost = 0;
pCur->nullRule.nFrom = 0;
pCur->nullRule.nTo = 0;
pCur->nullRule.zFrom = "";
pStem->pRule = &pCur->nullRule;
pStem->n = pStem->nBasis;
pCur->iRowid = 1;
return SQLITE_OK;
}

/*
** Only the word and distance columns have values.  All other columns
** return NULL
*/
static int fuzzerColumn(sqlite3_vtab_cursor *cur, sqlite3_context *ctx, int i){
fuzzer_cursor *pCur = (fuzzer_cursor*)cur;
if( i==0 ){
/* the "word" column */
if( fuzzerRender(pCur->pStem, &pCur->zBuf, &pCur->nBuf)==SQLITE_NOMEM ){
return SQLITE_NOMEM;
}
sqlite3_result_text(ctx, pCur->zBuf, -1, SQLITE_TRANSIENT);
}else if( i==1 ){
/* the "distance" column */
sqlite3_result_int(ctx, pCur->pStem->rCostX);
}else{
/* All other columns are NULL */
sqlite3_result_null(ctx);
}
return SQLITE_OK;
}

/*
** The rowid.
*/
static int fuzzerRowid(sqlite3_vtab_cursor *cur, sqlite_int64 *pRowid){
fuzzer_cursor *pCur = (fuzzer_cursor*)cur;
*pRowid = pCur->iRowid;
return SQLITE_OK;
}

/*
** When the fuzzer_cursor.rLimit value is 0 or less, that is a signal
** that the cursor has nothing more to output.
*/
static int fuzzerEof(sqlite3_vtab_cursor *cur){
fuzzer_cursor *pCur = (fuzzer_cursor*)cur;
return pCur->rLimit<=(fuzzer_cost)0;
}

/*
** Search for terms of these forms:
**
**       word MATCH \$str
**       distance < \$value
**       distance <= \$value
**
** The distance< and distance<= are both treated as distance<=.
** The query plan number is as follows:
**
**   0:    None of the terms above are found
**   1:    There is a "word MATCH" term with \$str in filter.argv[0].
**   2:    There is a "distance<" term with \$value in filter.argv[0].
**   3:    Both "word MATCH" and "distance<" with \$str in argv[0] and
**         \$value in argv[1].
*/
static int fuzzerBestIndex(sqlite3_vtab *tab, sqlite3_index_info *pIdxInfo){
int iPlan = 0;
int iDistTerm = -1;
int i;
const struct sqlite3_index_constraint *pConstraint;
pConstraint = pIdxInfo->aConstraint;
for(i=0; i<pIdxInfo->nConstraint; i++, pConstraint++){
if( pConstraint->usable==0 ) continue;
if( (iPlan & 1)==0
&& pConstraint->iColumn==0
&& pConstraint->op==SQLITE_INDEX_CONSTRAINT_MATCH
){
iPlan |= 1;
pIdxInfo->aConstraintUsage[i].argvIndex = 1;
pIdxInfo->aConstraintUsage[i].omit = 1;
}
if( (iPlan & 2)==0
&& pConstraint->iColumn==1
&& (pConstraint->op==SQLITE_INDEX_CONSTRAINT_LT
|| pConstraint->op==SQLITE_INDEX_CONSTRAINT_LE)
){
iPlan |= 2;
iDistTerm = i;
}
}
if( iPlan==2 ){
pIdxInfo->aConstraintUsage[iDistTerm].argvIndex = 1;
}else if( iPlan==3 ){
pIdxInfo->aConstraintUsage[iDistTerm].argvIndex = 2;
}
pIdxInfo->idxNum = iPlan;
if( pIdxInfo->nOrderBy==1
&& pIdxInfo->aOrderBy[0].iColumn==1
&& pIdxInfo->aOrderBy[0].desc==0
){
pIdxInfo->orderByConsumed = 1;
}
pIdxInfo->estimatedCost = (double)10000;

return SQLITE_OK;
}

/*
** Disallow all attempts to DELETE or UPDATE.  Only INSERTs are allowed.
**
** On an insert, the cFrom, cTo, and cost columns are used to construct
** a new rule.   All other columns are ignored.  The rule is ignored
** if cFrom and cTo are identical.  A NULL value for cFrom or cTo is
** interpreted as an empty string.  The cost must be positive.
*/
static int fuzzerUpdate(
sqlite3_vtab *pVTab,
int argc,
sqlite3_value **argv,
sqlite_int64 *pRowid
){
fuzzer_vtab *p = (fuzzer_vtab*)pVTab;
fuzzer_rule *pRule;
const char *zFrom;
int nFrom;
const char *zTo;
int nTo;
fuzzer_cost rCost;
if( argc!=7 ){
sqlite3_free(pVTab->zErrMsg);
pVTab->zErrMsg = sqlite3_mprintf("cannot delete from a %s virtual table",
p->zClassName);
return SQLITE_CONSTRAINT;
}
if( sqlite3_value_type(argv[0])!=SQLITE_NULL ){
sqlite3_free(pVTab->zErrMsg);
pVTab->zErrMsg = sqlite3_mprintf("cannot update a %s virtual table",
p->zClassName);
return SQLITE_CONSTRAINT;
}
zFrom = (char*)sqlite3_value_text(argv[4]);
if( zFrom==0 ) zFrom = "";
zTo = (char*)sqlite3_value_text(argv[5]);
if( zTo==0 ) zTo = "";
if( strcmp(zFrom,zTo)==0 ){
/* Silently ignore null transformations */
return SQLITE_OK;
}
rCost = sqlite3_value_int(argv[6]);
if( rCost<=0 ){
sqlite3_free(pVTab->zErrMsg);
pVTab->zErrMsg = sqlite3_mprintf("cost must be positive");
return SQLITE_CONSTRAINT;
}
nFrom = strlen(zFrom);
nTo = strlen(zTo);
pRule = sqlite3_malloc( sizeof(*pRule) + nFrom + nTo );
if( pRule==0 ){
return SQLITE_NOMEM;
}
pRule->zFrom = &pRule->zTo[nTo+1];
pRule->nFrom = nFrom;
memcpy(pRule->zFrom, zFrom, nFrom+1);
memcpy(pRule->zTo, zTo, nTo+1);
pRule->nTo = nTo;
pRule->rCost = rCost;
pRule->pNext = p->pNewRule;
p->pNewRule = pRule;
return SQLITE_OK;
}

/*
** Tcl global variable namespace.
*/
static sqlite3_module fuzzerModule = {
0,                           /* iVersion */
fuzzerConnect,
fuzzerConnect,
fuzzerBestIndex,
fuzzerDisconnect,
fuzzerDisconnect,
fuzzerOpen,                  /* xOpen - open a cursor */
fuzzerClose,                 /* xClose - close a cursor */
fuzzerFilter,                /* xFilter - configure scan constraints */
fuzzerNext,                  /* xNext - advance a cursor */
fuzzerEof,                   /* xEof - check for end of scan */
fuzzerColumn,                /* xColumn - read data */
fuzzerRowid,                 /* xRowid - read data */
fuzzerUpdate,                /* xUpdate - INSERT */
0,                           /* xBegin */
0,                           /* xSync */
0,                           /* xCommit */
0,                           /* xRollback */
0,                           /* xFindMethod */
0,                           /* xRename */
};

#endif /* SQLITE_OMIT_VIRTUALTABLE */

/*
** Register the fuzzer virtual table
*/
int fuzzer_register(sqlite3 *db){
int rc = SQLITE_OK;
#ifndef SQLITE_OMIT_VIRTUALTABLE
rc = sqlite3_create_module(db, "fuzzer", &fuzzerModule, 0);
#endif
return rc;
}

#ifdef SQLITE_TEST
#include <tcl.h>
/*
** Decode a pointer to an sqlite3 object.
*/
extern int getDbPointer(Tcl_Interp *interp, const char *zA, sqlite3 **ppDb);

/*
** Register the echo virtual table module.
*/
static int register_fuzzer_module(
ClientData clientData, /* Pointer to sqlite3_enable_XXX function */
Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
int objc,              /* Number of arguments */
Tcl_Obj *CONST objv[]  /* Command arguments */
){
sqlite3 *db;
if( objc!=2 ){
Tcl_WrongNumArgs(interp, 1, objv, "DB");
return TCL_ERROR;
}
if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;
fuzzer_register(db);
return TCL_OK;
}

/*
** Register commands with the TCL interpreter.
*/
int Sqlitetestfuzzer_Init(Tcl_Interp *interp){
static struct {
char *zName;
Tcl_ObjCmdProc *xProc;
void *clientData;
} aObjCmd[] = {
{ "register_fuzzer_module",   register_fuzzer_module, 0 },
};
int i;
for(i=0; i<sizeof(aObjCmd)/sizeof(aObjCmd[0]); i++){
Tcl_CreateObjCommand(interp, aObjCmd[i].zName,
aObjCmd[i].xProc, aObjCmd[i].clientData, 0);
}
return TCL_OK;
}

#endif /* SQLITE_TEST */
```
```