321 lines
9.0 KiB
C
321 lines
9.0 KiB
C
/*
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** 2018-04-19
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**
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** The author disclaims copyright to this source code. In place of
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** a legal notice, here is a blessing:
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**
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** May you do good and not evil.
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** May you find forgiveness for yourself and forgive others.
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** May you share freely, never taking more than you give.
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**
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*************************************************************************
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**
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** This file implements a table-valued function:
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**
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** prefixes('abcdefg')
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**
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** The function has a single (non-HIDDEN) column named prefix that takes
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** on all prefixes of the string in its argument, including an empty string
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** and the input string itself. The order of prefixes is from longest
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** to shortest.
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*/
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#if !defined(SQLITE_CORE) || !defined(SQLITE_OMIT_VIRTUALTABLE)
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#if !defined(SQLITEINT_H)
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#include "sqlite3ext.h"
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#endif
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SQLITE_EXTENSION_INIT1
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#include <string.h>
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#include <assert.h>
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/* prefixes_vtab is a subclass of sqlite3_vtab which is
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** underlying representation of the virtual table
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*/
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typedef struct prefixes_vtab prefixes_vtab;
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struct prefixes_vtab {
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sqlite3_vtab base; /* Base class - must be first */
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/* No additional fields are necessary */
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};
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/* prefixes_cursor is a subclass of sqlite3_vtab_cursor which will
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** serve as the underlying representation of a cursor that scans
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** over rows of the result
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*/
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typedef struct prefixes_cursor prefixes_cursor;
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struct prefixes_cursor {
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sqlite3_vtab_cursor base; /* Base class - must be first */
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sqlite3_int64 iRowid; /* The rowid */
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char *zStr; /* Original string to be prefixed */
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int nStr; /* Length of the string in bytes */
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};
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/*
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** The prefixesConnect() method is invoked to create a new
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** template virtual table.
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**
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** Think of this routine as the constructor for prefixes_vtab objects.
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**
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** All this routine needs to do is:
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**
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** (1) Allocate the prefixes_vtab object and initialize all fields.
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**
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** (2) Tell SQLite (via the sqlite3_declare_vtab() interface) what the
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** result set of queries against the virtual table will look like.
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*/
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static int prefixesConnect(
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sqlite3 *db,
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void *pAux,
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int argc, const char *const*argv,
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sqlite3_vtab **ppVtab,
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char **pzErr
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){
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prefixes_vtab *pNew;
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int rc;
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rc = sqlite3_declare_vtab(db,
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"CREATE TABLE prefixes(prefix TEXT, original_string TEXT HIDDEN)"
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);
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if( rc==SQLITE_OK ){
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pNew = sqlite3_malloc( sizeof(*pNew) );
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*ppVtab = (sqlite3_vtab*)pNew;
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if( pNew==0 ) return SQLITE_NOMEM;
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memset(pNew, 0, sizeof(*pNew));
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sqlite3_vtab_config(db, SQLITE_VTAB_INNOCUOUS);
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}
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return rc;
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}
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/*
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** This method is the destructor for prefixes_vtab objects.
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*/
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static int prefixesDisconnect(sqlite3_vtab *pVtab){
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prefixes_vtab *p = (prefixes_vtab*)pVtab;
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sqlite3_free(p);
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return SQLITE_OK;
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}
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/*
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** Constructor for a new prefixes_cursor object.
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*/
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static int prefixesOpen(sqlite3_vtab *p, sqlite3_vtab_cursor **ppCursor){
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prefixes_cursor *pCur;
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pCur = sqlite3_malloc( sizeof(*pCur) );
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if( pCur==0 ) return SQLITE_NOMEM;
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memset(pCur, 0, sizeof(*pCur));
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*ppCursor = &pCur->base;
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return SQLITE_OK;
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}
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/*
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** Destructor for a prefixes_cursor.
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*/
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static int prefixesClose(sqlite3_vtab_cursor *cur){
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prefixes_cursor *pCur = (prefixes_cursor*)cur;
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sqlite3_free(pCur->zStr);
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sqlite3_free(pCur);
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return SQLITE_OK;
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}
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/*
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** Advance a prefixes_cursor to its next row of output.
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*/
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static int prefixesNext(sqlite3_vtab_cursor *cur){
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prefixes_cursor *pCur = (prefixes_cursor*)cur;
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pCur->iRowid++;
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return SQLITE_OK;
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}
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/*
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** Return values of columns for the row at which the prefixes_cursor
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** is currently pointing.
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*/
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static int prefixesColumn(
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sqlite3_vtab_cursor *cur, /* The cursor */
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sqlite3_context *ctx, /* First argument to sqlite3_result_...() */
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int i /* Which column to return */
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){
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prefixes_cursor *pCur = (prefixes_cursor*)cur;
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switch( i ){
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case 0:
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sqlite3_result_text(ctx, pCur->zStr, pCur->nStr - (int)pCur->iRowid,
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0);
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break;
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default:
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sqlite3_result_text(ctx, pCur->zStr, pCur->nStr, 0);
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break;
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}
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return SQLITE_OK;
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}
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/*
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** Return the rowid for the current row. In this implementation, the
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** rowid is the same as the output value.
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*/
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static int prefixesRowid(sqlite3_vtab_cursor *cur, sqlite_int64 *pRowid){
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prefixes_cursor *pCur = (prefixes_cursor*)cur;
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*pRowid = pCur->iRowid;
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return SQLITE_OK;
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}
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/*
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** Return TRUE if the cursor has been moved off of the last
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** row of output.
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*/
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static int prefixesEof(sqlite3_vtab_cursor *cur){
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prefixes_cursor *pCur = (prefixes_cursor*)cur;
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return pCur->iRowid>pCur->nStr;
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}
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/*
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** This method is called to "rewind" the prefixes_cursor object back
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** to the first row of output. This method is always called at least
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** once prior to any call to prefixesColumn() or prefixesRowid() or
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** prefixesEof().
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*/
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static int prefixesFilter(
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sqlite3_vtab_cursor *pVtabCursor,
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int idxNum, const char *idxStr,
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int argc, sqlite3_value **argv
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){
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prefixes_cursor *pCur = (prefixes_cursor *)pVtabCursor;
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sqlite3_free(pCur->zStr);
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if( argc>0 ){
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pCur->zStr = sqlite3_mprintf("%s", sqlite3_value_text(argv[0]));
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pCur->nStr = pCur->zStr ? (int)strlen(pCur->zStr) : 0;
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}else{
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pCur->zStr = 0;
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pCur->nStr = 0;
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}
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pCur->iRowid = 0;
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return SQLITE_OK;
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}
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/*
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** SQLite will invoke this method one or more times while planning a query
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** that uses the virtual table. This routine needs to create
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** a query plan for each invocation and compute an estimated cost for that
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** plan.
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*/
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static int prefixesBestIndex(
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sqlite3_vtab *tab,
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sqlite3_index_info *pIdxInfo
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){
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/* Search for a usable equality constraint against column 1
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** (original_string) and use it if at all possible */
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int i;
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const struct sqlite3_index_constraint *p;
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for(i=0, p=pIdxInfo->aConstraint; i<pIdxInfo->nConstraint; i++, p++){
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if( p->iColumn!=1 ) continue;
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if( p->op!=SQLITE_INDEX_CONSTRAINT_EQ ) continue;
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if( !p->usable ) continue;
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pIdxInfo->aConstraintUsage[i].argvIndex = 1;
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pIdxInfo->aConstraintUsage[i].omit = 1;
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pIdxInfo->estimatedCost = (double)10;
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pIdxInfo->estimatedRows = 10;
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return SQLITE_OK;
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}
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pIdxInfo->estimatedCost = (double)1000000000;
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pIdxInfo->estimatedRows = 1000000000;
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return SQLITE_OK;
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}
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/*
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** This following structure defines all the methods for the
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** virtual table.
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*/
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static sqlite3_module prefixesModule = {
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/* iVersion */ 0,
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/* xCreate */ 0,
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/* xConnect */ prefixesConnect,
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/* xBestIndex */ prefixesBestIndex,
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/* xDisconnect */ prefixesDisconnect,
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/* xDestroy */ 0,
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/* xOpen */ prefixesOpen,
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/* xClose */ prefixesClose,
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/* xFilter */ prefixesFilter,
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/* xNext */ prefixesNext,
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/* xEof */ prefixesEof,
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/* xColumn */ prefixesColumn,
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/* xRowid */ prefixesRowid,
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/* xUpdate */ 0,
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/* xBegin */ 0,
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/* xSync */ 0,
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/* xCommit */ 0,
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/* xRollback */ 0,
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/* xFindMethod */ 0,
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/* xRename */ 0,
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/* xSavepoint */ 0,
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/* xRelease */ 0,
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/* xRollbackTo */ 0,
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/* xShadowName */ 0
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};
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/*
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** This is a copy of the SQLITE_SKIP_UTF8(zIn) macro in sqliteInt.h.
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**
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** Assuming zIn points to the first byte of a UTF-8 character,
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** advance zIn to point to the first byte of the next UTF-8 character.
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*/
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#define PREFIX_SKIP_UTF8(zIn) { \
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if( (*(zIn++))>=0xc0 ){ \
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while( (*zIn & 0xc0)==0x80 ){ zIn++; } \
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} \
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}
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/*
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** Implementation of function prefix_length(). This function accepts two
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** strings as arguments and returns the length in characters (not bytes),
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** of the longest prefix shared by the two strings. For example:
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**
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** prefix_length('abcdxxx', 'abcyy') == 3
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** prefix_length('abcdxxx', 'bcyyy') == 0
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** prefix_length('abcdxxx', 'ab') == 2
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** prefix_length('ab', 'abcd') == 2
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**
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** This function assumes the input is well-formed utf-8. If it is not,
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** it is possible for this function to return -1.
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*/
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static void prefixLengthFunc(
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sqlite3_context *ctx,
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int nVal,
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sqlite3_value **apVal
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){
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int nByte; /* Number of bytes to compare */
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int nRet = 0; /* Return value */
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const unsigned char *zL = sqlite3_value_text(apVal[0]);
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const unsigned char *zR = sqlite3_value_text(apVal[1]);
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int nL = sqlite3_value_bytes(apVal[0]);
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int nR = sqlite3_value_bytes(apVal[1]);
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int i;
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nByte = (nL > nR ? nL : nR);
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for(i=0; i<nByte; i++){
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if( zL[i]!=zR[i] ) break;
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if( (zL[i] & 0xC0)!=0x80 ) nRet++;
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}
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if( (zL[i] & 0xC0)==0x80 ) nRet--;
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sqlite3_result_int(ctx, nRet);
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}
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#ifdef _WIN32
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__declspec(dllexport)
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#endif
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int sqlite3_prefixes_init(
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sqlite3 *db,
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char **pzErrMsg,
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const sqlite3_api_routines *pApi
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){
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int rc = SQLITE_OK;
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SQLITE_EXTENSION_INIT2(pApi);
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rc = sqlite3_create_module(db, "prefixes", &prefixesModule, 0);
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if( rc==SQLITE_OK ){
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rc = sqlite3_create_function(
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db, "prefix_length", 2, SQLITE_UTF8, 0, prefixLengthFunc, 0, 0
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);
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}
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return rc;
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}
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#endif /* !defined(SQLITE_CORE) || !defined(SQLITE_OMIT_VIRTUALTABLE) */
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