src/test_bestindex.c - external/github.com/pwnall/sqlite - Git at Google

 /*
 ** 2016-03-01
 **
 ** 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 testing the virtual table xBestIndex method and the query
 ** planner.
 */


 /*
 ** INSTRUCTIONS
 **
 ** This module exports a single tcl command - [register_tcl_module]. When
 ** invoked, it registers a special virtual table module with a database
 ** connection.
 **
 ** The virtual table is currently read-only. And always returns zero rows.
 ** It is created with a single argument - the name of a Tcl command - as
 ** follows:
 **
 **   CREATE VIRTUAL TABLE x1 USING tcl(tcl_command);
 **
 ** The command [tcl_command] is invoked when the table is first created (or
 ** connected), when the xBestIndex() method is invoked and when the xFilter()
 ** method is called. When it is created (or connected), it is invoked as
 ** follows:
 **
 **   tcl_command xConnect
 **
 ** In this case the return value of the script is passed to the
 ** sqlite3_declare_vtab() function to create the virtual table schema.
 **
 ** When the xBestIndex() method is called by SQLite, the Tcl command is
 ** invoked as:
 **
 **   tcl_command xBestIndex CONSTRAINTS ORDERBY MASK
 **
 ** where CONSTRAINTS is a tcl representation of the aConstraints[] array,
 ** ORDERBY is a representation of the contents of the aOrderBy[] array and
 ** MASK is a copy of sqlite3_index_info.colUsed. For example if the virtual
 ** table is declared as:
 **
 **   CREATE TABLE x1(a, b, c)
 **
 ** and the query is:
 **
 **   SELECT * FROM x1 WHERE a=? AND c<? ORDER BY b, c;
 **
 ** then the Tcl command is:
 **
 **   tcl_command xBestIndex                                  \
 **     {{op eq column 0 usable 1} {op lt column 2 usable 1}} \
 **     {{column 1 desc 0} {column 2 desc 0}}                 \
 **     7
 **
 ** The return value of the script is a list of key-value pairs used to
 ** populate the output fields of the sqlite3_index_info structure. Possible
 ** keys and the usage of the accompanying values are:
 **
 **   "orderby"          (value of orderByConsumed flag)
 **   "cost"             (value of estimatedCost field)
 **   "rows"             (value of estimatedRows field)
 **   "use"              (index of used constraint in aConstraint[])
 **   "omit"             (like "use", but also sets omit flag)
 **   "idxnum"           (value of idxNum field)
 **   "idxstr"           (value of idxStr field)
 **
 ** Refer to code below for further details.
 **
 ** When SQLite calls the xFilter() method, this module invokes the following
 ** Tcl script:
 **
 **   tcl_command xFilter IDXNUM IDXSTR ARGLIST
 **
 ** IDXNUM and IDXSTR are the values of the idxNum and idxStr parameters
 ** passed to xFilter. ARGLIST is a Tcl list containing each of the arguments
 ** passed to xFilter in text form.
 **
 ** As with xBestIndex(), the return value of the script is interpreted as a
 ** list of key-value pairs. There is currently only one key defined - "sql".
 ** The value must be the full text of an SQL statement that returns the data
 ** for the current scan. The leftmost column returned by the SELECT is assumed
 ** to contain the rowid. Other columns must follow, in order from left to
 ** right.
 */


 #include "sqliteInt.h"
 #if defined(INCLUDE_SQLITE_TCL_H)
 #  include "sqlite_tcl.h"
 #else
 #  include "tcl.h"
 #endif

 #ifndef SQLITE_OMIT_VIRTUALTABLE

 typedef struct tcl_vtab tcl_vtab;
 typedef struct tcl_cursor tcl_cursor;

 /*
 ** A fs virtual-table object
 */
 struct tcl_vtab {
   sqlite3_vtab base;
   Tcl_Interp *interp;
   Tcl_Obj *pCmd;
   sqlite3 *db;
 };

 /* A tcl cursor object */
 struct tcl_cursor {
   sqlite3_vtab_cursor base;
   sqlite3_stmt *pStmt;            /* Read data from here */
 };

 /*
 ** Dequote string z in place.
 */
 static void tclDequote(char *z){
   char q = z[0];

   /* Set stack variable q to the close-quote character */
   if( q=='[' || q=='\'' || q=='"' || q=='`' ){
     int iIn = 1;
     int iOut = 0;
     if( q=='[' ) q = ']';

     while( ALWAYS(z[iIn]) ){
       if( z[iIn]==q ){
         if( z[iIn+1]!=q ){
           /* Character iIn was the close quote. */
           iIn++;
           break;
         }else{
           /* Character iIn and iIn+1 form an escaped quote character. Skip
           ** the input cursor past both and copy a single quote character
           ** to the output buffer. */
           iIn += 2;
           z[iOut++] = q;
         }
       }else{
         z[iOut++] = z[iIn++];
       }
     }

     z[iOut] = '\0';
   }
 }

 /*
 ** This function is the implementation of both the xConnect and xCreate
 ** methods of the fs virtual table.
 **
 ** The argv[] array contains the following:
 **
 **   argv[0]   -> module name  ("fs")
 **   argv[1]   -> database name
 **   argv[2]   -> table name
 **   argv[...] -> other module argument fields.
 */
 static int tclConnect(
   sqlite3 *db,
   void *pAux,
   int argc, const char *const*argv,
   sqlite3_vtab **ppVtab,
   char **pzErr
 ){
   Tcl_Interp *interp = (Tcl_Interp*)pAux;
   tcl_vtab *pTab = 0;
   char *zCmd = 0;
   Tcl_Obj *pScript = 0;
   int rc = SQLITE_OK;

   if( argc!=4 ){
     *pzErr = sqlite3_mprintf("wrong number of arguments");
     return SQLITE_ERROR;
   }

   zCmd = sqlite3_malloc64(strlen(argv[3])+1);
   pTab = (tcl_vtab*)sqlite3_malloc64(sizeof(tcl_vtab));
   if( zCmd && pTab ){
     memcpy(zCmd, argv[3], strlen(argv[3])+1);
     tclDequote(zCmd);
     memset(pTab, 0, sizeof(tcl_vtab));

     pTab->pCmd = Tcl_NewStringObj(zCmd, -1);
     pTab->interp = interp;
     pTab->db = db;
     Tcl_IncrRefCount(pTab->pCmd);

     pScript = Tcl_DuplicateObj(pTab->pCmd);
     Tcl_IncrRefCount(pScript);
     Tcl_ListObjAppendElement(interp, pScript, Tcl_NewStringObj("xConnect", -1));

     rc = Tcl_EvalObjEx(interp, pScript, TCL_EVAL_GLOBAL);
     if( rc!=TCL_OK ){
       *pzErr = sqlite3_mprintf("%s", Tcl_GetStringResult(interp));
       rc = SQLITE_ERROR;
     }else{
       rc = sqlite3_declare_vtab(db, Tcl_GetStringResult(interp));
     }

     if( rc!=SQLITE_OK ){
       sqlite3_free(pTab);
       pTab = 0;
     }
   }else{
     rc = SQLITE_NOMEM;
   }

   sqlite3_free(zCmd);
   *ppVtab = &pTab->base;
   return rc;
 }

 /* The xDisconnect and xDestroy methods are also the same */
 static int tclDisconnect(sqlite3_vtab *pVtab){
   tcl_vtab *pTab = (tcl_vtab*)pVtab;
   Tcl_DecrRefCount(pTab->pCmd);
   sqlite3_free(pTab);
   return SQLITE_OK;
 }

 /*
 ** Open a new tcl cursor.
 */
 static int tclOpen(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCursor){
   tcl_cursor *pCur;
   pCur = sqlite3_malloc(sizeof(tcl_cursor));
   if( pCur==0 ) return SQLITE_NOMEM;
   memset(pCur, 0, sizeof(tcl_cursor));
   *ppCursor = &pCur->base;
   return SQLITE_OK;
 }

 /*
 ** Close a tcl cursor.
 */
 static int tclClose(sqlite3_vtab_cursor *cur){
   tcl_cursor *pCur = (tcl_cursor *)cur;
   if( pCur ){
     sqlite3_finalize(pCur->pStmt);
     sqlite3_free(pCur);
   }
   return SQLITE_OK;
 }

 static int tclNext(sqlite3_vtab_cursor *pVtabCursor){
   tcl_cursor *pCsr = (tcl_cursor*)pVtabCursor;
   if( pCsr->pStmt ){
     tcl_vtab *pTab = (tcl_vtab*)(pVtabCursor->pVtab);
     int rc = sqlite3_step(pCsr->pStmt);
     if( rc!=SQLITE_ROW ){
       const char *zErr;
       rc = sqlite3_finalize(pCsr->pStmt);
       pCsr->pStmt = 0;
       if( rc!=SQLITE_OK ){
         zErr = sqlite3_errmsg(pTab->db);
         pTab->base.zErrMsg = sqlite3_mprintf("%s", zErr);
       }
     }
   }
   return SQLITE_OK;
 }

 static int tclFilter(
   sqlite3_vtab_cursor *pVtabCursor,
   int idxNum, const char *idxStr,
   int argc, sqlite3_value **argv
 ){
   tcl_cursor *pCsr = (tcl_cursor*)pVtabCursor;
   tcl_vtab *pTab = (tcl_vtab*)(pVtabCursor->pVtab);
   Tcl_Interp *interp = pTab->interp;
   Tcl_Obj *pScript;
   Tcl_Obj *pArg;
   int ii;
   int rc;

   pScript = Tcl_DuplicateObj(pTab->pCmd);
   Tcl_IncrRefCount(pScript);
   Tcl_ListObjAppendElement(interp, pScript, Tcl_NewStringObj("xFilter", -1));
   Tcl_ListObjAppendElement(interp, pScript, Tcl_NewIntObj(idxNum));
   if( idxStr ){
     Tcl_ListObjAppendElement(interp, pScript, Tcl_NewStringObj(idxStr, -1));
   }else{
     Tcl_ListObjAppendElement(interp, pScript, Tcl_NewStringObj("", -1));
   }

   pArg = Tcl_NewObj();
   Tcl_IncrRefCount(pArg);
   for(ii=0; ii<argc; ii++){
     const char *zVal = (const char*)sqlite3_value_text(argv[ii]);
     Tcl_Obj *pVal;
     if( zVal==0 ){
       pVal = Tcl_NewObj();
     }else{
       pVal = Tcl_NewStringObj(zVal, -1);
     }
     Tcl_ListObjAppendElement(interp, pArg, pVal);
   }
   Tcl_ListObjAppendElement(interp, pScript, pArg);
   Tcl_DecrRefCount(pArg);

   rc = Tcl_EvalObjEx(interp, pScript, TCL_EVAL_GLOBAL);
   if( rc!=TCL_OK ){
     const char *zErr = Tcl_GetStringResult(interp);
     rc = SQLITE_ERROR;
     pTab->base.zErrMsg = sqlite3_mprintf("%s", zErr);
   }else{
     /* Analyze the scripts return value. The return value should be a tcl
     ** list object with an even number of elements. The first element of each
     ** pair must be one of:
     **
     **   "sql"          (SQL statement to return data)
     */
     Tcl_Obj *pRes = Tcl_GetObjResult(interp);
     Tcl_Obj **apElem = 0;
     int nElem;
     rc = Tcl_ListObjGetElements(interp, pRes, &nElem, &apElem);
     if( rc!=TCL_OK ){
       const char *zErr = Tcl_GetStringResult(interp);
       rc = SQLITE_ERROR;
       pTab->base.zErrMsg = sqlite3_mprintf("%s", zErr);
     }else{
       for(ii=0; rc==SQLITE_OK && ii<nElem; ii+=2){
         const char *zCmd = Tcl_GetString(apElem[ii]);
         Tcl_Obj *p = apElem[ii+1];
         if( sqlite3_stricmp("sql", zCmd)==0 ){
           const char *zSql = Tcl_GetString(p);
           rc = sqlite3_prepare_v2(pTab->db, zSql, -1, &pCsr->pStmt, 0);
           if( rc!=SQLITE_OK ){
             const char *zErr = sqlite3_errmsg(pTab->db);
             pTab->base.zErrMsg = sqlite3_mprintf("unexpected: %s", zErr);
           }
         }else{
           rc = SQLITE_ERROR;
           pTab->base.zErrMsg = sqlite3_mprintf("unexpected: %s", zCmd);
         }
       }
     }
   }

   if( rc==SQLITE_OK ){
     rc = tclNext(pVtabCursor);
   }
   return rc;
 }

 static int tclColumn(
   sqlite3_vtab_cursor *pVtabCursor,
   sqlite3_context *ctx,
   int i
 ){
   tcl_cursor *pCsr = (tcl_cursor*)pVtabCursor;
   sqlite3_result_value(ctx, sqlite3_column_value(pCsr->pStmt, i+1));
   return SQLITE_OK;
 }

 static int tclRowid(sqlite3_vtab_cursor *pVtabCursor, sqlite_int64 *pRowid){
   tcl_cursor *pCsr = (tcl_cursor*)pVtabCursor;
   *pRowid = sqlite3_column_int64(pCsr->pStmt, 0);
   return SQLITE_OK;
 }

 static int tclEof(sqlite3_vtab_cursor *pVtabCursor){
   tcl_cursor *pCsr = (tcl_cursor*)pVtabCursor;
   return (pCsr->pStmt==0);
 }

 static int tclBestIndex(sqlite3_vtab *tab, sqlite3_index_info *pIdxInfo){
   tcl_vtab *pTab = (tcl_vtab*)tab;
   Tcl_Interp *interp = pTab->interp;
   Tcl_Obj *pArg;
   Tcl_Obj *pScript;
   int ii;
   int rc = SQLITE_OK;

   pScript = Tcl_DuplicateObj(pTab->pCmd);
   Tcl_IncrRefCount(pScript);
   Tcl_ListObjAppendElement(interp, pScript, Tcl_NewStringObj("xBestIndex", -1));

   pArg = Tcl_NewObj();
   Tcl_IncrRefCount(pArg);
   for(ii=0; ii<pIdxInfo->nConstraint; ii++){
     struct sqlite3_index_constraint const *pCons = &pIdxInfo->aConstraint[ii];
     Tcl_Obj *pElem = Tcl_NewObj();
     const char *zOp = "?";

     Tcl_IncrRefCount(pElem);

     switch( pCons->op ){
       case SQLITE_INDEX_CONSTRAINT_EQ:
         zOp = "eq"; break;
       case SQLITE_INDEX_CONSTRAINT_GT:
         zOp = "gt"; break;
       case SQLITE_INDEX_CONSTRAINT_LE:
         zOp = "le"; break;
       case SQLITE_INDEX_CONSTRAINT_LT:
         zOp = "lt"; break;
       case SQLITE_INDEX_CONSTRAINT_GE:
         zOp = "ge"; break;
       case SQLITE_INDEX_CONSTRAINT_MATCH:
         zOp = "match"; break;
       case SQLITE_INDEX_CONSTRAINT_LIKE:
         zOp = "like"; break;
       case SQLITE_INDEX_CONSTRAINT_GLOB:
         zOp = "glob"; break;
       case SQLITE_INDEX_CONSTRAINT_REGEXP:
         zOp = "regexp"; break;
       case SQLITE_INDEX_CONSTRAINT_NE:
         zOp = "ne"; break;
       case SQLITE_INDEX_CONSTRAINT_ISNOT:
         zOp = "isnot"; break;
       case SQLITE_INDEX_CONSTRAINT_ISNOTNULL:
         zOp = "isnotnull"; break;
       case SQLITE_INDEX_CONSTRAINT_ISNULL:
         zOp = "isnull"; break;
       case SQLITE_INDEX_CONSTRAINT_IS:
         zOp = "is"; break;
     }

     Tcl_ListObjAppendElement(0, pElem, Tcl_NewStringObj("op", -1));
     Tcl_ListObjAppendElement(0, pElem, Tcl_NewStringObj(zOp, -1));
     Tcl_ListObjAppendElement(0, pElem, Tcl_NewStringObj("column", -1));
     Tcl_ListObjAppendElement(0, pElem, Tcl_NewIntObj(pCons->iColumn));
     Tcl_ListObjAppendElement(0, pElem, Tcl_NewStringObj("usable", -1));
     Tcl_ListObjAppendElement(0, pElem, Tcl_NewIntObj(pCons->usable));

     Tcl_ListObjAppendElement(0, pArg, pElem);
     Tcl_DecrRefCount(pElem);
   }

   Tcl_ListObjAppendElement(0, pScript, pArg);
   Tcl_DecrRefCount(pArg);

   pArg = Tcl_NewObj();
   Tcl_IncrRefCount(pArg);
   for(ii=0; ii<pIdxInfo->nOrderBy; ii++){
     struct sqlite3_index_orderby const *pOrder = &pIdxInfo->aOrderBy[ii];
     Tcl_Obj *pElem = Tcl_NewObj();
     Tcl_IncrRefCount(pElem);

     Tcl_ListObjAppendElement(0, pElem, Tcl_NewStringObj("column", -1));
     Tcl_ListObjAppendElement(0, pElem, Tcl_NewIntObj(pOrder->iColumn));
     Tcl_ListObjAppendElement(0, pElem, Tcl_NewStringObj("desc", -1));
     Tcl_ListObjAppendElement(0, pElem, Tcl_NewIntObj(pOrder->desc));

     Tcl_ListObjAppendElement(0, pArg, pElem);
     Tcl_DecrRefCount(pElem);
   }

   Tcl_ListObjAppendElement(0, pScript, pArg);
   Tcl_DecrRefCount(pArg);

   Tcl_ListObjAppendElement(0, pScript, Tcl_NewWideIntObj(pIdxInfo->colUsed));

   rc = Tcl_EvalObjEx(interp, pScript, TCL_EVAL_GLOBAL);
   Tcl_DecrRefCount(pScript);
   if( rc!=TCL_OK ){
     const char *zErr = Tcl_GetStringResult(interp);
     rc = SQLITE_ERROR;
     pTab->base.zErrMsg = sqlite3_mprintf("%s", zErr);
   }else{
     /* Analyze the scripts return value. The return value should be a tcl
     ** list object with an even number of elements. The first element of each
     ** pair must be one of:
     **
     **   "orderby"          (value of orderByConsumed flag)
     **   "cost"             (value of estimatedCost field)
     **   "rows"             (value of estimatedRows field)
     **   "use"              (index of used constraint in aConstraint[])
     **   "idxnum"           (value of idxNum field)
     **   "idxstr"           (value of idxStr field)
     **   "omit"             (index of omitted constraint in aConstraint[])
     */
     Tcl_Obj *pRes = Tcl_GetObjResult(interp);
     Tcl_Obj **apElem = 0;
     int nElem;
     rc = Tcl_ListObjGetElements(interp, pRes, &nElem, &apElem);
     if( rc!=TCL_OK ){
       const char *zErr = Tcl_GetStringResult(interp);
       rc = SQLITE_ERROR;
       pTab->base.zErrMsg = sqlite3_mprintf("%s", zErr);
     }else{
       int iArgv = 1;
       for(ii=0; rc==SQLITE_OK && ii<nElem; ii+=2){
         const char *zCmd = Tcl_GetString(apElem[ii]);
         Tcl_Obj *p = apElem[ii+1];
         if( sqlite3_stricmp("cost", zCmd)==0 ){
           rc = Tcl_GetDoubleFromObj(interp, p, &pIdxInfo->estimatedCost);
         }else
         if( sqlite3_stricmp("orderby", zCmd)==0 ){
           rc = Tcl_GetIntFromObj(interp, p, &pIdxInfo->orderByConsumed);
         }else
         if( sqlite3_stricmp("idxnum", zCmd)==0 ){
           rc = Tcl_GetIntFromObj(interp, p, &pIdxInfo->idxNum);
         }else
         if( sqlite3_stricmp("idxstr", zCmd)==0 ){
           sqlite3_free(pIdxInfo->idxStr);
           pIdxInfo->idxStr = sqlite3_mprintf("%s", Tcl_GetString(p));
           pIdxInfo->needToFreeIdxStr = 1;
         }else
         if( sqlite3_stricmp("rows", zCmd)==0 ){
           Tcl_WideInt x = 0;
           rc = Tcl_GetWideIntFromObj(interp, p, &x);
           pIdxInfo->estimatedRows = (tRowcnt)x;
         }else
         if( sqlite3_stricmp("use", zCmd)==0
          || sqlite3_stricmp("omit", zCmd)==0
         ){
           int iCons;
           rc = Tcl_GetIntFromObj(interp, p, &iCons);
           if( rc==SQLITE_OK ){
             if( iCons<0 || iCons>=pIdxInfo->nConstraint ){
               rc = SQLITE_ERROR;
               pTab->base.zErrMsg = sqlite3_mprintf("unexpected: %d", iCons);
             }else{
               int bOmit = (zCmd[0]=='o' || zCmd[0]=='O');
               pIdxInfo->aConstraintUsage[iCons].argvIndex = iArgv++;
               pIdxInfo->aConstraintUsage[iCons].omit = bOmit;
             }
           }
         }else{
           rc = SQLITE_ERROR;
           pTab->base.zErrMsg = sqlite3_mprintf("unexpected: %s", zCmd);
         }
         if( rc!=SQLITE_OK && pTab->base.zErrMsg==0 ){
           const char *zErr = Tcl_GetStringResult(interp);
           pTab->base.zErrMsg = sqlite3_mprintf("%s", zErr);
         }
       }
     }
   }

   return rc;
 }

 /*
 ** A virtual table module that provides read-only access to a
 ** Tcl global variable namespace.
 */
 static sqlite3_module tclModule = {
   0,                         /* iVersion */
   tclConnect,
   tclConnect,
   tclBestIndex,
   tclDisconnect,
   tclDisconnect,
   tclOpen,                      /* xOpen - open a cursor */
   tclClose,                     /* xClose - close a cursor */
   tclFilter,                    /* xFilter - configure scan constraints */
   tclNext,                      /* xNext - advance a cursor */
   tclEof,                       /* xEof - check for end of scan */
   tclColumn,                    /* xColumn - read data */
   tclRowid,                     /* xRowid - read data */
   0,                           /* xUpdate */
   0,                           /* xBegin */
   0,                           /* xSync */
   0,                           /* xCommit */
   0,                           /* xRollback */
   0,                           /* xFindMethod */
   0,                           /* xRename */
 };

 /*
 ** 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 SQLITE_TCLAPI register_tcl_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;
 #ifndef SQLITE_OMIT_VIRTUALTABLE
   sqlite3_create_module(db, "tcl", &tclModule, (void *)interp);
 #endif
   return TCL_OK;
 }

 #endif


 /*
 ** Register commands with the TCL interpreter.
 */
 int Sqlitetesttcl_Init(Tcl_Interp *interp){
 #ifndef SQLITE_OMIT_VIRTUALTABLE
   static struct {
      char *zName;
      Tcl_ObjCmdProc *xProc;
      void *clientData;
   } aObjCmd[] = {
      { "register_tcl_module",   register_tcl_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);
   }
 #endif
   return TCL_OK;
 }
	/*
	** 2016-03-01
	**
	** 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 testing the virtual table xBestIndex method and the query
	** planner.
	*/


	/*
	** INSTRUCTIONS
	**
	** This module exports a single tcl command - [register_tcl_module]. When
	** invoked, it registers a special virtual table module with a database
	** connection.
	**
	** The virtual table is currently read-only. And always returns zero rows.
	** It is created with a single argument - the name of a Tcl command - as
	** follows:
	**
	** CREATE VIRTUAL TABLE x1 USING tcl(tcl_command);
	**
	** The command [tcl_command] is invoked when the table is first created (or
	** connected), when the xBestIndex() method is invoked and when the xFilter()
	** method is called. When it is created (or connected), it is invoked as
	** follows:
	**
	** tcl_command xConnect
	**
	** In this case the return value of the script is passed to the
	** sqlite3_declare_vtab() function to create the virtual table schema.
	**
	** When the xBestIndex() method is called by SQLite, the Tcl command is
	** invoked as:
	**
	** tcl_command xBestIndex CONSTRAINTS ORDERBY MASK
	**
	** where CONSTRAINTS is a tcl representation of the aConstraints[] array,
	** ORDERBY is a representation of the contents of the aOrderBy[] array and
	** MASK is a copy of sqlite3_index_info.colUsed. For example if the virtual
	** table is declared as:
	**
	** CREATE TABLE x1(a, b, c)
	**
	** and the query is:
	**
	** SELECT * FROM x1 WHERE a=? AND c<? ORDER BY b, c;
	**
	** then the Tcl command is:
	**
	** tcl_command xBestIndex \
	** {{op eq column 0 usable 1} {op lt column 2 usable 1}} \
	** {{column 1 desc 0} {column 2 desc 0}} \
	** 7
	**
	** The return value of the script is a list of key-value pairs used to
	** populate the output fields of the sqlite3_index_info structure. Possible
	** keys and the usage of the accompanying values are:
	**
	** "orderby" (value of orderByConsumed flag)
	** "cost" (value of estimatedCost field)
	** "rows" (value of estimatedRows field)
	** "use" (index of used constraint in aConstraint[])
	** "omit" (like "use", but also sets omit flag)
	** "idxnum" (value of idxNum field)
	** "idxstr" (value of idxStr field)
	**
	** Refer to code below for further details.
	**
	** When SQLite calls the xFilter() method, this module invokes the following
	** Tcl script:
	**
	** tcl_command xFilter IDXNUM IDXSTR ARGLIST
	**
	** IDXNUM and IDXSTR are the values of the idxNum and idxStr parameters
	** passed to xFilter. ARGLIST is a Tcl list containing each of the arguments
	** passed to xFilter in text form.
	**
	** As with xBestIndex(), the return value of the script is interpreted as a
	** list of key-value pairs. There is currently only one key defined - "sql".
	** The value must be the full text of an SQL statement that returns the data
	** for the current scan. The leftmost column returned by the SELECT is assumed
	** to contain the rowid. Other columns must follow, in order from left to
	** right.
	*/


	#include "sqliteInt.h"
	#if defined(INCLUDE_SQLITE_TCL_H)
	# include "sqlite_tcl.h"
	#else
	# include "tcl.h"
	#endif

	#ifndef SQLITE_OMIT_VIRTUALTABLE

	typedef struct tcl_vtab tcl_vtab;
	typedef struct tcl_cursor tcl_cursor;

	/*
	** A fs virtual-table object
	*/
	struct tcl_vtab {
	sqlite3_vtab base;
	Tcl_Interp *interp;
	Tcl_Obj *pCmd;
	sqlite3 *db;
	};

	/* A tcl cursor object */
	struct tcl_cursor {
	sqlite3_vtab_cursor base;
	sqlite3_stmt pStmt; / Read data from here */
	};

	/*
	** Dequote string z in place.
	*/
	static void tclDequote(char *z){
	char q = z[0];

	/* Set stack variable q to the close-quote character */
	if( q=='[' \|\| q=='\'' \|\| q=='"' \|\| q=='`' ){
	int iIn = 1;
	int iOut = 0;
	if( q=='[' ) q = ']';

	while( ALWAYS(z[iIn]) ){
	if( z[iIn]==q ){
	if( z[iIn+1]!=q ){
	/* Character iIn was the close quote. */
	iIn++;
	break;
	}else{
	/* Character iIn and iIn+1 form an escaped quote character. Skip
	** the input cursor past both and copy a single quote character
	** to the output buffer. */
	iIn += 2;
	z[iOut++] = q;
	}
	}else{
	z[iOut++] = z[iIn++];
	}
	}

	z[iOut] = '\0';
	}
	}

	/*
	** This function is the implementation of both the xConnect and xCreate
	** methods of the fs virtual table.
	**
	** The argv[] array contains the following:
	**
	** argv[0] -> module name ("fs")
	** argv[1] -> database name
	** argv[2] -> table name
	** argv[...] -> other module argument fields.
	*/
	static int tclConnect(
	sqlite3 *db,
	void *pAux,
	int argc, const char constargv,
	sqlite3_vtab **ppVtab,
	char **pzErr
	){
	Tcl_Interp interp = (Tcl_Interp)pAux;
	tcl_vtab *pTab = 0;
	char *zCmd = 0;
	Tcl_Obj *pScript = 0;
	int rc = SQLITE_OK;

	if( argc!=4 ){
	*pzErr = sqlite3_mprintf("wrong number of arguments");
	return SQLITE_ERROR;
	}

	zCmd = sqlite3_malloc64(strlen(argv[3])+1);
	pTab = (tcl_vtab*)sqlite3_malloc64(sizeof(tcl_vtab));
	if( zCmd && pTab ){
	memcpy(zCmd, argv[3], strlen(argv[3])+1);
	tclDequote(zCmd);
	memset(pTab, 0, sizeof(tcl_vtab));

	pTab->pCmd = Tcl_NewStringObj(zCmd, -1);
	pTab->interp = interp;
	pTab->db = db;
	Tcl_IncrRefCount(pTab->pCmd);

	pScript = Tcl_DuplicateObj(pTab->pCmd);
	Tcl_IncrRefCount(pScript);
	Tcl_ListObjAppendElement(interp, pScript, Tcl_NewStringObj("xConnect", -1));

	rc = Tcl_EvalObjEx(interp, pScript, TCL_EVAL_GLOBAL);
	if( rc!=TCL_OK ){
	*pzErr = sqlite3_mprintf("%s", Tcl_GetStringResult(interp));
	rc = SQLITE_ERROR;
	}else{
	rc = sqlite3_declare_vtab(db, Tcl_GetStringResult(interp));
	}

	if( rc!=SQLITE_OK ){
	sqlite3_free(pTab);
	pTab = 0;
	}
	}else{
	rc = SQLITE_NOMEM;
	}

	sqlite3_free(zCmd);
	*ppVtab = &pTab->base;
	return rc;
	}

	/* The xDisconnect and xDestroy methods are also the same */
	static int tclDisconnect(sqlite3_vtab *pVtab){
	tcl_vtab pTab = (tcl_vtab)pVtab;
	Tcl_DecrRefCount(pTab->pCmd);
	sqlite3_free(pTab);
	return SQLITE_OK;
	}

	/*
	** Open a new tcl cursor.
	*/
	static int tclOpen(sqlite3_vtab pVTab, sqlite3_vtab_cursor *ppCursor){
	tcl_cursor *pCur;
	pCur = sqlite3_malloc(sizeof(tcl_cursor));
	if( pCur==0 ) return SQLITE_NOMEM;
	memset(pCur, 0, sizeof(tcl_cursor));
	*ppCursor = &pCur->base;
	return SQLITE_OK;
	}

	/*
	** Close a tcl cursor.
	*/
	static int tclClose(sqlite3_vtab_cursor *cur){
	tcl_cursor pCur = (tcl_cursor )cur;
	if( pCur ){
	sqlite3_finalize(pCur->pStmt);
	sqlite3_free(pCur);
	}
	return SQLITE_OK;
	}

	static int tclNext(sqlite3_vtab_cursor *pVtabCursor){
	tcl_cursor pCsr = (tcl_cursor)pVtabCursor;
	if( pCsr->pStmt ){
	tcl_vtab pTab = (tcl_vtab)(pVtabCursor->pVtab);
	int rc = sqlite3_step(pCsr->pStmt);
	if( rc!=SQLITE_ROW ){
	const char *zErr;
	rc = sqlite3_finalize(pCsr->pStmt);
	pCsr->pStmt = 0;
	if( rc!=SQLITE_OK ){
	zErr = sqlite3_errmsg(pTab->db);
	pTab->base.zErrMsg = sqlite3_mprintf("%s", zErr);
	}
	}
	}
	return SQLITE_OK;
	}

	static int tclFilter(
	sqlite3_vtab_cursor *pVtabCursor,
	int idxNum, const char *idxStr,
	int argc, sqlite3_value **argv
	){
	tcl_cursor pCsr = (tcl_cursor)pVtabCursor;
	tcl_vtab pTab = (tcl_vtab)(pVtabCursor->pVtab);
	Tcl_Interp *interp = pTab->interp;
	Tcl_Obj *pScript;
	Tcl_Obj *pArg;
	int ii;
	int rc;

	pScript = Tcl_DuplicateObj(pTab->pCmd);
	Tcl_IncrRefCount(pScript);
	Tcl_ListObjAppendElement(interp, pScript, Tcl_NewStringObj("xFilter", -1));
	Tcl_ListObjAppendElement(interp, pScript, Tcl_NewIntObj(idxNum));
	if( idxStr ){
	Tcl_ListObjAppendElement(interp, pScript, Tcl_NewStringObj(idxStr, -1));
	}else{
	Tcl_ListObjAppendElement(interp, pScript, Tcl_NewStringObj("", -1));
	}

	pArg = Tcl_NewObj();
	Tcl_IncrRefCount(pArg);
	for(ii=0; ii<argc; ii++){
	const char zVal = (const char)sqlite3_value_text(argv[ii]);
	Tcl_Obj *pVal;
	if( zVal==0 ){
	pVal = Tcl_NewObj();
	}else{
	pVal = Tcl_NewStringObj(zVal, -1);
	}
	Tcl_ListObjAppendElement(interp, pArg, pVal);
	}
	Tcl_ListObjAppendElement(interp, pScript, pArg);
	Tcl_DecrRefCount(pArg);

	rc = Tcl_EvalObjEx(interp, pScript, TCL_EVAL_GLOBAL);
	if( rc!=TCL_OK ){
	const char *zErr = Tcl_GetStringResult(interp);
	rc = SQLITE_ERROR;
	pTab->base.zErrMsg = sqlite3_mprintf("%s", zErr);
	}else{
	/* Analyze the scripts return value. The return value should be a tcl
	** list object with an even number of elements. The first element of each
	** pair must be one of:
	**
	** "sql" (SQL statement to return data)
	*/
	Tcl_Obj *pRes = Tcl_GetObjResult(interp);
	Tcl_Obj **apElem = 0;
	int nElem;
	rc = Tcl_ListObjGetElements(interp, pRes, &nElem, &apElem);
	if( rc!=TCL_OK ){
	const char *zErr = Tcl_GetStringResult(interp);
	rc = SQLITE_ERROR;
	pTab->base.zErrMsg = sqlite3_mprintf("%s", zErr);
	}else{
	for(ii=0; rc==SQLITE_OK && ii<nElem; ii+=2){
	const char *zCmd = Tcl_GetString(apElem[ii]);
	Tcl_Obj *p = apElem[ii+1];
	if( sqlite3_stricmp("sql", zCmd)==0 ){
	const char *zSql = Tcl_GetString(p);
	rc = sqlite3_prepare_v2(pTab->db, zSql, -1, &pCsr->pStmt, 0);
	if( rc!=SQLITE_OK ){
	const char *zErr = sqlite3_errmsg(pTab->db);
	pTab->base.zErrMsg = sqlite3_mprintf("unexpected: %s", zErr);
	}
	}else{
	rc = SQLITE_ERROR;
	pTab->base.zErrMsg = sqlite3_mprintf("unexpected: %s", zCmd);
	}
	}
	}
	}

	if( rc==SQLITE_OK ){
	rc = tclNext(pVtabCursor);
	}
	return rc;
	}

	static int tclColumn(
	sqlite3_vtab_cursor *pVtabCursor,
	sqlite3_context *ctx,
	int i
	){
	tcl_cursor pCsr = (tcl_cursor)pVtabCursor;
	sqlite3_result_value(ctx, sqlite3_column_value(pCsr->pStmt, i+1));
	return SQLITE_OK;
	}

	static int tclRowid(sqlite3_vtab_cursor pVtabCursor, sqlite_int64 pRowid){
	tcl_cursor pCsr = (tcl_cursor)pVtabCursor;
	*pRowid = sqlite3_column_int64(pCsr->pStmt, 0);
	return SQLITE_OK;
	}

	static int tclEof(sqlite3_vtab_cursor *pVtabCursor){
	tcl_cursor pCsr = (tcl_cursor)pVtabCursor;
	return (pCsr->pStmt==0);
	}

	static int tclBestIndex(sqlite3_vtab tab, sqlite3_index_info pIdxInfo){
	tcl_vtab pTab = (tcl_vtab)tab;
	Tcl_Interp *interp = pTab->interp;
	Tcl_Obj *pArg;
	Tcl_Obj *pScript;
	int ii;
	int rc = SQLITE_OK;

	pScript = Tcl_DuplicateObj(pTab->pCmd);
	Tcl_IncrRefCount(pScript);
	Tcl_ListObjAppendElement(interp, pScript, Tcl_NewStringObj("xBestIndex", -1));

	pArg = Tcl_NewObj();
	Tcl_IncrRefCount(pArg);
	for(ii=0; ii<pIdxInfo->nConstraint; ii++){
	struct sqlite3_index_constraint const *pCons = &pIdxInfo->aConstraint[ii];
	Tcl_Obj *pElem = Tcl_NewObj();
	const char *zOp = "?";

	Tcl_IncrRefCount(pElem);

	switch( pCons->op ){
	case SQLITE_INDEX_CONSTRAINT_EQ:
	zOp = "eq"; break;
	case SQLITE_INDEX_CONSTRAINT_GT:
	zOp = "gt"; break;
	case SQLITE_INDEX_CONSTRAINT_LE:
	zOp = "le"; break;
	case SQLITE_INDEX_CONSTRAINT_LT:
	zOp = "lt"; break;
	case SQLITE_INDEX_CONSTRAINT_GE:
	zOp = "ge"; break;
	case SQLITE_INDEX_CONSTRAINT_MATCH:
	zOp = "match"; break;
	case SQLITE_INDEX_CONSTRAINT_LIKE:
	zOp = "like"; break;
	case SQLITE_INDEX_CONSTRAINT_GLOB:
	zOp = "glob"; break;
	case SQLITE_INDEX_CONSTRAINT_REGEXP:
	zOp = "regexp"; break;
	case SQLITE_INDEX_CONSTRAINT_NE:
	zOp = "ne"; break;
	case SQLITE_INDEX_CONSTRAINT_ISNOT:
	zOp = "isnot"; break;
	case SQLITE_INDEX_CONSTRAINT_ISNOTNULL:
	zOp = "isnotnull"; break;
	case SQLITE_INDEX_CONSTRAINT_ISNULL:
	zOp = "isnull"; break;
	case SQLITE_INDEX_CONSTRAINT_IS:
	zOp = "is"; break;
	}

	Tcl_ListObjAppendElement(0, pElem, Tcl_NewStringObj("op", -1));
	Tcl_ListObjAppendElement(0, pElem, Tcl_NewStringObj(zOp, -1));
	Tcl_ListObjAppendElement(0, pElem, Tcl_NewStringObj("column", -1));
	Tcl_ListObjAppendElement(0, pElem, Tcl_NewIntObj(pCons->iColumn));
	Tcl_ListObjAppendElement(0, pElem, Tcl_NewStringObj("usable", -1));
	Tcl_ListObjAppendElement(0, pElem, Tcl_NewIntObj(pCons->usable));

	Tcl_ListObjAppendElement(0, pArg, pElem);
	Tcl_DecrRefCount(pElem);
	}

	Tcl_ListObjAppendElement(0, pScript, pArg);
	Tcl_DecrRefCount(pArg);

	pArg = Tcl_NewObj();
	Tcl_IncrRefCount(pArg);
	for(ii=0; ii<pIdxInfo->nOrderBy; ii++){
	struct sqlite3_index_orderby const *pOrder = &pIdxInfo->aOrderBy[ii];
	Tcl_Obj *pElem = Tcl_NewObj();
	Tcl_IncrRefCount(pElem);

	Tcl_ListObjAppendElement(0, pElem, Tcl_NewStringObj("column", -1));
	Tcl_ListObjAppendElement(0, pElem, Tcl_NewIntObj(pOrder->iColumn));
	Tcl_ListObjAppendElement(0, pElem, Tcl_NewStringObj("desc", -1));
	Tcl_ListObjAppendElement(0, pElem, Tcl_NewIntObj(pOrder->desc));

	Tcl_ListObjAppendElement(0, pArg, pElem);
	Tcl_DecrRefCount(pElem);
	}

	Tcl_ListObjAppendElement(0, pScript, pArg);
	Tcl_DecrRefCount(pArg);

	Tcl_ListObjAppendElement(0, pScript, Tcl_NewWideIntObj(pIdxInfo->colUsed));

	rc = Tcl_EvalObjEx(interp, pScript, TCL_EVAL_GLOBAL);
	Tcl_DecrRefCount(pScript);
	if( rc!=TCL_OK ){
	const char *zErr = Tcl_GetStringResult(interp);
	rc = SQLITE_ERROR;
	pTab->base.zErrMsg = sqlite3_mprintf("%s", zErr);
	}else{
	/* Analyze the scripts return value. The return value should be a tcl
	** list object with an even number of elements. The first element of each
	** pair must be one of:
	**
	** "orderby" (value of orderByConsumed flag)
	** "cost" (value of estimatedCost field)
	** "rows" (value of estimatedRows field)
	** "use" (index of used constraint in aConstraint[])
	** "idxnum" (value of idxNum field)
	** "idxstr" (value of idxStr field)
	** "omit" (index of omitted constraint in aConstraint[])
	*/
	Tcl_Obj *pRes = Tcl_GetObjResult(interp);
	Tcl_Obj **apElem = 0;
	int nElem;
	rc = Tcl_ListObjGetElements(interp, pRes, &nElem, &apElem);
	if( rc!=TCL_OK ){
	const char *zErr = Tcl_GetStringResult(interp);
	rc = SQLITE_ERROR;
	pTab->base.zErrMsg = sqlite3_mprintf("%s", zErr);
	}else{
	int iArgv = 1;
	for(ii=0; rc==SQLITE_OK && ii<nElem; ii+=2){
	const char *zCmd = Tcl_GetString(apElem[ii]);
	Tcl_Obj *p = apElem[ii+1];
	if( sqlite3_stricmp("cost", zCmd)==0 ){
	rc = Tcl_GetDoubleFromObj(interp, p, &pIdxInfo->estimatedCost);
	}else
	if( sqlite3_stricmp("orderby", zCmd)==0 ){
	rc = Tcl_GetIntFromObj(interp, p, &pIdxInfo->orderByConsumed);
	}else
	if( sqlite3_stricmp("idxnum", zCmd)==0 ){
	rc = Tcl_GetIntFromObj(interp, p, &pIdxInfo->idxNum);
	}else
	if( sqlite3_stricmp("idxstr", zCmd)==0 ){
	sqlite3_free(pIdxInfo->idxStr);
	pIdxInfo->idxStr = sqlite3_mprintf("%s", Tcl_GetString(p));
	pIdxInfo->needToFreeIdxStr = 1;
	}else
	if( sqlite3_stricmp("rows", zCmd)==0 ){
	Tcl_WideInt x = 0;
	rc = Tcl_GetWideIntFromObj(interp, p, &x);
	pIdxInfo->estimatedRows = (tRowcnt)x;
	}else
	if( sqlite3_stricmp("use", zCmd)==0
	\|\| sqlite3_stricmp("omit", zCmd)==0
	){
	int iCons;
	rc = Tcl_GetIntFromObj(interp, p, &iCons);
	if( rc==SQLITE_OK ){
	if( iCons<0 \|\| iCons>=pIdxInfo->nConstraint ){
	rc = SQLITE_ERROR;
	pTab->base.zErrMsg = sqlite3_mprintf("unexpected: %d", iCons);
	}else{
	int bOmit = (zCmd[0]=='o' \|\| zCmd[0]=='O');
	pIdxInfo->aConstraintUsage[iCons].argvIndex = iArgv++;
	pIdxInfo->aConstraintUsage[iCons].omit = bOmit;
	}
	}
	}else{
	rc = SQLITE_ERROR;
	pTab->base.zErrMsg = sqlite3_mprintf("unexpected: %s", zCmd);
	}
	if( rc!=SQLITE_OK && pTab->base.zErrMsg==0 ){
	const char *zErr = Tcl_GetStringResult(interp);
	pTab->base.zErrMsg = sqlite3_mprintf("%s", zErr);
	}
	}
	}
	}

	return rc;
	}

	/*
	** A virtual table module that provides read-only access to a
	** Tcl global variable namespace.
	*/
	static sqlite3_module tclModule = {
	0, /* iVersion */
	tclConnect,
	tclConnect,
	tclBestIndex,
	tclDisconnect,
	tclDisconnect,
	tclOpen, /* xOpen - open a cursor */
	tclClose, /* xClose - close a cursor */
	tclFilter, /* xFilter - configure scan constraints */
	tclNext, /* xNext - advance a cursor */
	tclEof, /* xEof - check for end of scan */
	tclColumn, /* xColumn - read data */
	tclRowid, /* xRowid - read data */
	0, /* xUpdate */
	0, /* xBegin */
	0, /* xSync */
	0, /* xCommit */
	0, /* xRollback */
	0, /* xFindMethod */
	0, /* xRename */
	};

	/*
	** 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 SQLITE_TCLAPI register_tcl_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;
	#ifndef SQLITE_OMIT_VIRTUALTABLE
	sqlite3_create_module(db, "tcl", &tclModule, (void *)interp);
	#endif
	return TCL_OK;
	}

	#endif


	/*
	** Register commands with the TCL interpreter.
	*/
	int Sqlitetesttcl_Init(Tcl_Interp *interp){
	#ifndef SQLITE_OMIT_VIRTUALTABLE
	static struct {
	char *zName;
	Tcl_ObjCmdProc *xProc;
	void *clientData;
	} aObjCmd[] = {
	{ "register_tcl_module", register_tcl_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);
	}
	#endif
	return TCL_OK;
	}