/*
** 2018-04-19
**
** 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.
**
*************************************************************************
**
** This file implements a table-valued function:
**
** prefixes('abcdefg')
**
** The function has a single (non-HIDDEN) column named prefix that takes
** on all prefixes of the string in its argument, including an empty string
** and the input string itself. The order of prefixes is from longest
** to shortest.
*/
#if !defined(SQLITE_CORE) || !defined(SQLITE_OMIT_VIRTUALTABLE)
#if !defined(SQLITEINT_H)
#include "sqlite3ext.h"
#endif
SQLITE_EXTENSION_INIT1
#include <string.h>
#include <assert.h>
/* prefixes_vtab is a subclass of sqlite3_vtab which is
** underlying representation of the virtual table
*/
typedef struct prefixes_vtab prefixes_vtab;
struct prefixes_vtab {
sqlite3_vtab base; /* Base class - must be first */
/* No additional fields are necessary */
};
/* prefixes_cursor is a subclass of sqlite3_vtab_cursor which will
** serve as the underlying representation of a cursor that scans
** over rows of the result
*/
typedef struct prefixes_cursor prefixes_cursor;
struct prefixes_cursor {
sqlite3_vtab_cursor base; /* Base class - must be first */
sqlite3_int64 iRowid; /* The rowid */
char *zStr; /* Original string to be prefixed */
int nStr; /* Length of the string in bytes */
};
/*
** The prefixesConnect() method is invoked to create a new
** template virtual table.
**
** Think of this routine as the constructor for prefixes_vtab objects.
**
** All this routine needs to do is:
**
** (1) Allocate the prefixes_vtab object and initialize all fields.
**
** (2) Tell SQLite (via the sqlite3_declare_vtab() interface) what the
** result set of queries against the virtual table will look like.
*/
static int prefixesConnect(
sqlite3 *db,
void *pAux,
int argc, const char *const*argv,
sqlite3_vtab **ppVtab,
char **pzErr
){
prefixes_vtab *pNew;
int rc;
rc = sqlite3_declare_vtab(db,
"CREATE TABLE prefixes(prefix TEXT, original_string TEXT HIDDEN)"
);
if( rc==SQLITE_OK ){
pNew = sqlite3_malloc( sizeof(*pNew) );
*ppVtab = (sqlite3_vtab*)pNew;
if( pNew==0 ) return SQLITE_NOMEM;
memset(pNew, 0, sizeof(*pNew));
}
return rc;
}
/*
** This method is the destructor for prefixes_vtab objects.
*/
static int prefixesDisconnect(sqlite3_vtab *pVtab){
prefixes_vtab *p = (prefixes_vtab*)pVtab;
sqlite3_free(p);
return SQLITE_OK;
}
/*
** Constructor for a new prefixes_cursor object.
*/
static int prefixesOpen(sqlite3_vtab *p, sqlite3_vtab_cursor **ppCursor){
prefixes_cursor *pCur;
pCur = sqlite3_malloc( sizeof(*pCur) );
if( pCur==0 ) return SQLITE_NOMEM;
memset(pCur, 0, sizeof(*pCur));
*ppCursor = &pCur->base;
return SQLITE_OK;
}
/*
** Destructor for a prefixes_cursor.
*/
static int prefixesClose(sqlite3_vtab_cursor *cur){
prefixes_cursor *pCur = (prefixes_cursor*)cur;
sqlite3_free(pCur->zStr);
sqlite3_free(pCur);
return SQLITE_OK;
}
/*
** Advance a prefixes_cursor to its next row of output.
*/
static int prefixesNext(sqlite3_vtab_cursor *cur){
prefixes_cursor *pCur = (prefixes_cursor*)cur;
pCur->iRowid++;
return SQLITE_OK;
}
/*
** Return values of columns for the row at which the prefixes_cursor
** is currently pointing.
*/
static int prefixesColumn(
sqlite3_vtab_cursor *cur, /* The cursor */
sqlite3_context *ctx, /* First argument to sqlite3_result_...() */
int i /* Which column to return */
){
prefixes_cursor *pCur = (prefixes_cursor*)cur;
switch( i ){
case 0:
sqlite3_result_text(ctx, pCur->zStr, pCur->nStr - (int)pCur->iRowid,
0);
break;
default:
sqlite3_result_text(ctx, pCur->zStr, pCur->nStr, 0);
break;
}
return SQLITE_OK;
}
/*
** Return the rowid for the current row. In this implementation, the
** rowid is the same as the output value.
*/
static int prefixesRowid(sqlite3_vtab_cursor *cur, sqlite_int64 *pRowid){
prefixes_cursor *pCur = (prefixes_cursor*)cur;
*pRowid = pCur->iRowid;
return SQLITE_OK;
}
/*
** Return TRUE if the cursor has been moved off of the last
** row of output.
*/
static int prefixesEof(sqlite3_vtab_cursor *cur){
prefixes_cursor *pCur = (prefixes_cursor*)cur;
return pCur->iRowid>pCur->nStr;
}
/*
** This method is called to "rewind" the prefixes_cursor object back
** to the first row of output. This method is always called at least
** once prior to any call to prefixesColumn() or prefixesRowid() or
** prefixesEof().
*/
static int prefixesFilter(
sqlite3_vtab_cursor *pVtabCursor,
int idxNum, const char *idxStr,
int argc, sqlite3_value **argv
){
prefixes_cursor *pCur = (prefixes_cursor *)pVtabCursor;
sqlite3_free(pCur->zStr);
if( argc>0 ){
pCur->zStr = sqlite3_mprintf("%s", sqlite3_value_text(argv[0]));
pCur->nStr = pCur->zStr ? (int)strlen(pCur->zStr) : 0;
}else{
pCur->zStr = 0;
pCur->nStr = 0;
}
pCur->iRowid = 0;
return SQLITE_OK;
}
/*
** SQLite will invoke this method one or more times while planning a query
** that uses the virtual table. This routine needs to create
** a query plan for each invocation and compute an estimated cost for that
** plan.
*/
static int prefixesBestIndex(
sqlite3_vtab *tab,
sqlite3_index_info *pIdxInfo
){
/* Search for a usable equality constraint against column 1
** (original_string) and use it if at all possible */
int i;
const struct sqlite3_index_constraint *p;
for(i=0, p=pIdxInfo->aConstraint; i<pIdxInfo->nConstraint; i++, p++){
if( p->iColumn!=1 ) continue;
if( p->op!=SQLITE_INDEX_CONSTRAINT_EQ ) continue;
if( !p->usable ) continue;
pIdxInfo->aConstraintUsage[i].argvIndex = 1;
pIdxInfo->aConstraintUsage[i].omit = 1;
pIdxInfo->estimatedCost = (double)10;
pIdxInfo->estimatedRows = 10;
return SQLITE_OK;
}
pIdxInfo->estimatedCost = (double)1000000000;
pIdxInfo->estimatedRows = 1000000000;
return SQLITE_OK;
}
/*
** This following structure defines all the methods for the
** virtual table.
*/
static sqlite3_module prefixesModule = {
/* iVersion */ 0,
/* xCreate */ 0,
/* xConnect */ prefixesConnect,
/* xBestIndex */ prefixesBestIndex,
/* xDisconnect */ prefixesDisconnect,
/* xDestroy */ 0,
/* xOpen */ prefixesOpen,
/* xClose */ prefixesClose,
/* xFilter */ prefixesFilter,
/* xNext */ prefixesNext,
/* xEof */ prefixesEof,
/* xColumn */ prefixesColumn,
/* xRowid */ prefixesRowid,
/* xUpdate */ 0,
/* xBegin */ 0,
/* xSync */ 0,
/* xCommit */ 0,
/* xRollback */ 0,
/* xFindMethod */ 0,
/* xRename */ 0,
/* xSavepoint */ 0,
/* xRelease */ 0,
/* xRollbackTo */ 0,
/* xShadowName */ 0
};
/*
** This is a copy of the SQLITE_SKIP_UTF8(zIn) macro in sqliteInt.h.
**
** Assuming zIn points to the first byte of a UTF-8 character,
** advance zIn to point to the first byte of the next UTF-8 character.
*/
#define PREFIX_SKIP_UTF8(zIn) { \
if( (*(zIn++))>=0xc0 ){ \
while( (*zIn & 0xc0)==0x80 ){ zIn++; } \
} \
}
/*
** Implementation of function prefix_length(). This function accepts two
** strings as arguments and returns the length in characters (not bytes),
** of the longest prefix shared by the two strings. For example:
**
** prefix_length('abcdxxx', 'abcyy') == 3
** prefix_length('abcdxxx', 'bcyyy') == 0
** prefix_length('abcdxxx', 'ab') == 2
** prefix_length('ab', 'abcd') == 2
**
** This function assumes the input is well-formed utf-8. If it is not,
** it is possible for this function to return -1.
*/
static void prefixLengthFunc(
sqlite3_context *ctx,
int nVal,
sqlite3_value **apVal
){
int nByte; /* Number of bytes to compare */
int nRet = 0; /* Return value */
const unsigned char *zL = sqlite3_value_text(apVal[0]);
const unsigned char *zR = sqlite3_value_text(apVal[1]);
int nL = sqlite3_value_bytes(apVal[0]);
int nR = sqlite3_value_bytes(apVal[1]);
int i;
nByte = (nL > nR ? nL : nR);
for(i=0; i<nByte; i++){
if( zL[i]!=zR[i] ) break;
if( (zL[i] & 0xC0)!=0x80 ) nRet++;
}
if( (zL[i] & 0xC0)==0x80 ) nRet--;
sqlite3_result_int(ctx, nRet);
}
#ifdef _WIN32
__declspec(dllexport)
#endif
int sqlite3_prefixes_init(
sqlite3 *db,
char **pzErrMsg,
const sqlite3_api_routines *pApi
){
int rc = SQLITE_OK;
SQLITE_EXTENSION_INIT2(pApi);
rc = sqlite3_create_module(db, "prefixes", &prefixesModule, 0);
if( rc==SQLITE_OK ){
rc = sqlite3_create_function(
db, "prefix_length", 2, SQLITE_UTF8, 0, prefixLengthFunc, 0, 0
);
}
return rc;
}
#endif /* !defined(SQLITE_CORE) || !defined(SQLITE_OMIT_VIRTUALTABLE) */