wasm/api/sqlite3-api-oo1.js

/*
  2022-07-22

  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 contains the so-called OO #1 API wrapper for the sqlite3
  WASM build. It requires that sqlite3-api-glue.js has already run
  and it installs its deliverable as self.sqlite3.oo1.
*/
self.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
  const toss = (...args)=>{throw new Error(args.join(' '))};
  const toss3 = (...args)=>{throw new sqlite3.SQLite3Error(...args)};

  const capi = sqlite3.capi, wasm = capi.wasm, util = capi.util;
  /* What follows is colloquially known as "OO API #1". It is a
     binding of the sqlite3 API which is designed to be run within
     the same thread (main or worker) as the one in which the
     sqlite3 WASM binding was initialized. This wrapper cannot use
     the sqlite3 binding if, e.g., the wrapper is in the main thread
     and the sqlite3 API is in a worker. */

  /**
     In order to keep clients from manipulating, perhaps
     inadvertently, the underlying pointer values of DB and Stmt
     instances, we'll gate access to them via the `pointer` property
     accessor and store their real values in this map. Keys = DB/Stmt
     objects, values = pointer values. This also unifies how those are
     accessed, for potential use downstream via custom
     wasm.xWrap() function signatures which know how to extract
     it.
  */
  const __ptrMap = new WeakMap();
  /**
     Map of DB instances to objects, each object being a map of Stmt
     wasm pointers to Stmt objects.
  */
  const __stmtMap = new WeakMap();

  /** If object opts has _its own_ property named p then that
      property's value is returned, else dflt is returned. */
  const getOwnOption = (opts, p, dflt)=>{
    const d = Object.getOwnPropertyDescriptor(opts,p);
    return d ? d.value : dflt;
  };

  // Documented in DB.checkRc()
  const checkSqlite3Rc = function(dbPtr, sqliteResultCode){
    if(sqliteResultCode){
      if(dbPtr instanceof DB) dbPtr = dbPtr.pointer;
      toss3(
        "sqlite result code",sqliteResultCode+":",
        (dbPtr
         ? capi.sqlite3_errmsg(dbPtr)
         : capi.sqlite3_errstr(sqliteResultCode))
      );
    }
  };

  /**
     sqlite3_trace_v2() callback which gets installed by the DB ctor
     if its open-flags contain "t".
  */
  const __dbTraceToConsole =
        wasm.installFunction('i(ippp)', function(t,c,p,x){
          if(capi.SQLITE_TRACE_STMT===t){
            // x == SQL, p == sqlite3_stmt*
            console.log("SQL TRACE #"+(++this.counter),
                        wasm.cstringToJs(x));
          }
        }.bind({counter: 0}));

  /**
     A map of sqlite3_vfs pointers to SQL code to run when the DB
     constructor opens a database with the given VFS.
  */
  const __vfsPostOpenSql = Object.create(null);

  /**
     A proxy for DB class constructors. It must be called with the
     being-construct DB object as its "this". See the DB constructor
     for the argument docs. This is split into a separate function
     in order to enable simple creation of special-case DB constructors,
     e.g. JsStorageDB and OpfsDB.

     Expects to be passed a configuration object with the following
     properties:

     - `.filename`: the db filename. It may be a special name like ":memory:"
       or "".

     - `.flags`: as documented in the DB constructor.

     - `.vfs`: as documented in the DB constructor.

     It also accepts those as the first 3 arguments.
  */
  const dbCtorHelper = function ctor(...args){
    if(!ctor._name2vfs){
      /**
         Map special filenames which we handle here (instead of in C)
         to some helpful metadata...

         As of 2022-09-20, the C API supports the names :localStorage:
         and :sessionStorage: for kvvfs. However, C code cannot
         determine (without embedded JS code, e.g. via Emscripten's
         EM_JS()) whether the kvvfs is legal in the current browser
         context (namely the main UI thread). In order to help client
         code fail early on, instead of it being delayed until they
         try to read or write a kvvfs-backed db, we'll check for those
         names here and throw if they're not legal in the current
         context.
      */
      ctor._name2vfs = Object.create(null);
      const isWorkerThread = ('function'===typeof importScripts/*===running in worker thread*/)
            ? (n)=>toss3("The VFS for",n,"is only available in the main window thread.")
            : false;
      ctor._name2vfs[':localStorage:'] = {
        vfs: 'kvvfs', filename: isWorkerThread || (()=>'local')
      };
      ctor._name2vfs[':sessionStorage:'] = {
        vfs: 'kvvfs', filename: isWorkerThread || (()=>'session')
      };
    }
    const opt = ctor.normalizeArgs(...args);
    let fn = opt.filename, vfsName = opt.vfs, flagsStr = opt.flags;
    if(('string'!==typeof fn && 'number'!==typeof fn)
       || 'string'!==typeof flagsStr
       || (vfsName && ('string'!==typeof vfsName && 'number'!==typeof vfsName))){
      console.error("Invalid DB ctor args",opt,arguments);
      toss3("Invalid arguments for DB constructor.");
    }
    let fnJs = ('number'===typeof fn) ? wasm.cstringToJs(fn) : fn;
    const vfsCheck = ctor._name2vfs[fnJs];
    if(vfsCheck){
      vfsName = vfsCheck.vfs;
      fn = fnJs = vfsCheck.filename(fnJs);
    }
    let pDb, oflags = 0;
    if( flagsStr.indexOf('c')>=0 ){
      oflags |= capi.SQLITE_OPEN_CREATE | capi.SQLITE_OPEN_READWRITE;
    }
    if( flagsStr.indexOf('w')>=0 ) oflags |= capi.SQLITE_OPEN_READWRITE;
    if( 0===oflags ) oflags |= capi.SQLITE_OPEN_READONLY;
    oflags |= capi.SQLITE_OPEN_EXRESCODE;
    const scope = wasm.scopedAllocPush();
    try {
      const pPtr = wasm.allocPtr() /* output (sqlite3**) arg */;
      const pVfsName = vfsName ? (
        ('number'===typeof vfsName ? vfsName : wasm.scopedAllocCString(vfsName))
      ): 0;
      let rc = capi.sqlite3_open_v2(fn, pPtr, oflags, pVfsName);
      pDb = wasm.getPtrValue(pPtr);
      checkSqlite3Rc(pDb, rc);
      if(flagsStr.indexOf('t')>=0){
        capi.sqlite3_trace_v2(pDb, capi.SQLITE_TRACE_STMT,
                              __dbTraceToConsole, 0);
      }
      // Check for per-VFS post-open SQL...
      wasm.setPtrValue(pPtr, 0);
      if(0===capi.sqlite3_file_control(
        pDb, "main", capi.SQLITE_FCNTL_VFS_POINTER, pPtr
      )){
        const postInitSql = __vfsPostOpenSql[wasm.getPtrValue(pPtr)];
        if(postInitSql){
          rc = capi.sqlite3_exec(pDb, postInitSql, 0, 0, 0);
          checkSqlite3Rc(pDb, rc);
        }
      }
    }catch( e ){
      if( pDb ) capi.sqlite3_close_v2(pDb);
      throw e;
    }finally{
      wasm.scopedAllocPop(scope);
    }
    this.filename = fnJs;
    __ptrMap.set(this, pDb);
    __stmtMap.set(this, Object.create(null));
  };

  /**
     Sets SQL which should be exec()'d on a DB instance after it is
     opened with the given VFS pointer. This is intended only for use
     by DB subclasses or sqlite3_vfs implementations.
  */
  dbCtorHelper.setVfsPostOpenSql = function(pVfs, sql){
    __vfsPostOpenSql[pVfs] = sql;
  };

  /**
     A helper for DB constructors. It accepts either a single
     config-style object or up to 3 arguments (filename, dbOpenFlags,
     dbVfsName). It returns a new object containing:

     { filename: ..., flags: ..., vfs: ... }

     If passed an object, any additional properties it has are copied
     as-is into the new object.
  */
  dbCtorHelper.normalizeArgs = function(filename=':memory:',flags = 'c',vfs = null){
    const arg = {};
    if(1===arguments.length && 'object'===typeof arguments[0]){
      const x = arguments[0];
      Object.keys(x).forEach((k)=>arg[k] = x[k]);
      if(undefined===arg.flags) arg.flags = 'c';
      if(undefined===arg.vfs) arg.vfs = null;
      if(undefined===arg.filename) arg.filename = ':memory:';
    }else{
      arg.filename = filename;
      arg.flags = flags;
      arg.vfs = vfs;
    }
    return arg;
  };
  /**
     The DB class provides a high-level OO wrapper around an sqlite3
     db handle.

     The given db filename must be resolvable using whatever
     filesystem layer (virtual or otherwise) is set up for the default
     sqlite3 VFS.

     Note that the special sqlite3 db names ":memory:" and ""
     (temporary db) have their normal special meanings here and need
     not resolve to real filenames, but "" uses an on-storage
     temporary database and requires that the VFS support that.

     The second argument specifies the open/create mode for the
     database. It must be string containing a sequence of letters (in
     any order, but case sensitive) specifying the mode:

     - "c": create if it does not exist, else fail if it does not
       exist. Implies the "w" flag.

     - "w": write. Implies "r": a db cannot be write-only.

     - "r": read-only if neither "w" nor "c" are provided, else it
       is ignored.

     - "t": enable tracing of SQL executed on this database handle,
       sending it to `console.log()`. To disable it later, call
       `sqlite3.capi.sqlite3_trace_v2(thisDb.pointer, 0, 0, 0)`.

     If "w" is not provided, the db is implicitly read-only, noting
     that "rc" is meaningless

     Any other letters are currently ignored. The default is
     "c". These modes are ignored for the special ":memory:" and ""
     names and _may_ be ignored altogether for certain VFSes.

     The final argument is analogous to the final argument of
     sqlite3_open_v2(): the name of an sqlite3 VFS. Pass a falsy value,
     or none at all, to use the default. If passed a value, it must
     be the string name of a VFS.

     The constructor optionally (and preferably) takes its arguments
     in the form of a single configuration object with the following
     properties:

     - `.filename`: database file name
     - `.flags`: open-mode flags
     - `.vfs`: the VFS fname

     The `filename` and `vfs` arguments may be either JS strings or
     C-strings allocated via WASM. `flags` is required to be a JS
     string (because it's specific to this API, which is specific
     to JS).

     For purposes of passing a DB instance to C-style sqlite3
     functions, the DB object's read-only `pointer` property holds its
     `sqlite3*` pointer value. That property can also be used to check
     whether this DB instance is still open.

     In the main window thread, the filenames `":localStorage:"` and
     `":sessionStorage:"` are special: they cause the db to use either
     localStorage or sessionStorage for storing the database using
     the kvvfs. If one of these names are used, they trump
     any vfs name set in the arguments.
  */
  const DB = function(...args){
    dbCtorHelper.apply(this, args);
  };

  /**
     Internal-use enum for mapping JS types to DB-bindable types.
     These do not (and need not) line up with the SQLITE_type
     values. All values in this enum must be truthy and distinct
     but they need not be numbers.
  */
  const BindTypes = {
    null: 1,
    number: 2,
    string: 3,
    boolean: 4,
    blob: 5
  };
  BindTypes['undefined'] == BindTypes.null;
  if(wasm.bigIntEnabled){
    BindTypes.bigint = BindTypes.number;
  }

  /**
     This class wraps sqlite3_stmt. Calling this constructor
     directly will trigger an exception. Use DB.prepare() to create
     new instances.

     For purposes of passing a Stmt instance to C-style sqlite3
     functions, its read-only `pointer` property holds its `sqlite3_stmt*`
     pointer value.

     Other non-function properties include:

     - `db`: the DB object which created the statement.

     - `columnCount`: the number of result columns in the query, or 0 for
     queries which cannot return results.

     - `parameterCount`: the number of bindable paramters in the query.
  */
  const Stmt = function(){
    if(BindTypes!==arguments[2]){
      toss3("Do not call the Stmt constructor directly. Use DB.prepare().");
    }
    this.db = arguments[0];
    __ptrMap.set(this, arguments[1]);
    this.columnCount = capi.sqlite3_column_count(this.pointer);
    this.parameterCount = capi.sqlite3_bind_parameter_count(this.pointer);
  };

  /** Throws if the given DB has been closed, else it is returned. */
  const affirmDbOpen = function(db){
    if(!db.pointer) toss3("DB has been closed.");
    return db;
  };

  /** Throws if ndx is not an integer or if it is out of range
      for stmt.columnCount, else returns stmt.

      Reminder: this will also fail after the statement is finalized
      but the resulting error will be about an out-of-bounds column
      index rather than a statement-is-finalized error.
  */
  const affirmColIndex = function(stmt,ndx){
    if((ndx !== (ndx|0)) || ndx<0 || ndx>=stmt.columnCount){
      toss3("Column index",ndx,"is out of range.");
    }
    return stmt;
  };

  /**
     Expects to be passed the `arguments` object from DB.exec(). Does
     the argument processing/validation, throws on error, and returns
     a new object on success:

     { sql: the SQL, opt: optionsObj, cbArg: function}

     The opt object is a normalized copy of any passed to this
     function. The sql will be converted to a string if it is provided
     in one of the supported non-string formats.

     cbArg is only set if the opt.callback or opt.resultRows are set,
     in which case it's a function which expects to be passed the
     current Stmt and returns the callback argument of the type
     indicated by the input arguments.
  */
  const parseExecArgs = function(args){
    const out = Object.create(null);
    out.opt = Object.create(null);
    switch(args.length){
        case 1:
          if('string'===typeof args[0] || util.isSQLableTypedArray(args[0])){
            out.sql = args[0];
          }else if(args[0] && 'object'===typeof args[0]){
            out.opt = args[0];
            out.sql = out.opt.sql;
          }else if(Array.isArray(args[0])){
            out.sql = args[0];
          }
          break;
        case 2:
          out.sql = args[0];
          out.opt = args[1];
          break;
        default: toss3("Invalid argument count for exec().");
    };
    if(util.isSQLableTypedArray(out.sql)){
      out.sql = util.typedArrayToString(out.sql);
    }else if(Array.isArray(out.sql)){
      out.sql = out.sql.join('');
    }else if('string'!==typeof out.sql){
      toss3("Missing SQL argument.");
    }
    if(out.opt.callback || out.opt.resultRows){
      switch((undefined===out.opt.rowMode)
             ? 'array' : out.opt.rowMode) {
          case 'object': out.cbArg = (stmt)=>stmt.get(Object.create(null)); break;
          case 'array': out.cbArg = (stmt)=>stmt.get([]); break;
          case 'stmt':
            if(Array.isArray(out.opt.resultRows)){
              toss3("exec(): invalid rowMode for a resultRows array: must",
                    "be one of 'array', 'object',",
                    "a result column number, or column name reference.");
            }
            out.cbArg = (stmt)=>stmt;
            break;
          default:
            if(util.isInt32(out.opt.rowMode)){
              out.cbArg = (stmt)=>stmt.get(out.opt.rowMode);
              break;
            }else if('string'===typeof out.opt.rowMode && out.opt.rowMode.length>1){
              /* "$X", ":X", and "@X" fetch column named "X" (case-sensitive!) */
              const prefix = out.opt.rowMode[0];
              if(':'===prefix || '@'===prefix || '$'===prefix){
                out.cbArg = function(stmt){
                  const rc = stmt.get(this.obj)[this.colName];
                  return (undefined===rc) ? toss3("exec(): unknown result column:",this.colName) : rc;
                }.bind({
                  obj:Object.create(null),
                  colName: out.opt.rowMode.substr(1)
                });
                break;
              }
            }
            toss3("Invalid rowMode:",out.opt.rowMode);
      }
    }
    return out;
  };

  /**
     Expects to be given a DB instance or an `sqlite3*` pointer (may
     be null) and an sqlite3 API result code. If the result code is
     not falsy, this function throws an SQLite3Error with an error
     message from sqlite3_errmsg(), using dbPtr as the db handle, or
     sqlite3_errstr() if dbPtr is falsy. Note that if it's passed a
     non-error code like SQLITE_ROW or SQLITE_DONE, it will still
     throw but the error string might be "Not an error."  The various
     non-0 non-error codes need to be checked for in
     client code where they are expected.
  */
  DB.checkRc = checkSqlite3Rc;

  DB.prototype = {
    /** Returns true if this db handle is open, else false. */
    isOpen: function(){
      return !!this.pointer;
    },
    /** Throws if this given DB has been closed, else returns `this`. */
    affirmOpen: function(){
      return affirmDbOpen(this);
    },
    /**
       Finalizes all open statements and closes this database
       connection. This is a no-op if the db has already been
       closed. After calling close(), `this.pointer` will resolve to
       `undefined`, so that can be used to check whether the db
       instance is still opened.

       If this.onclose.before is a function then it is called before
       any close-related cleanup.

       If this.onclose.after is a function then it is called after the
       db is closed but before auxiliary state like this.filename is
       cleared.

       Both onclose handlers are passed this object. If this db is not
       opened, neither of the handlers are called. Any exceptions the
       handlers throw are ignored because "destructors must not
       throw."

       Note that garbage collection of a db handle, if it happens at
       all, will never trigger close(), so onclose handlers are not a
       reliable way to implement close-time cleanup or maintenance of
       a db.
    */
    close: function(){
      if(this.pointer){
        if(this.onclose && (this.onclose.before instanceof Function)){
          try{this.onclose.before(this)}
          catch(e){/*ignore*/}
        }
        const pDb = this.pointer;
        Object.keys(__stmtMap.get(this)).forEach((k,s)=>{
          if(s && s.pointer) s.finalize();
        });
        __ptrMap.delete(this);
        __stmtMap.delete(this);
        capi.sqlite3_close_v2(pDb);
        if(this.onclose && (this.onclose.after instanceof Function)){
          try{this.onclose.after(this)}
          catch(e){/*ignore*/}
        }
        delete this.filename;
      }
    },
    /**
       Returns the number of changes, as per sqlite3_changes()
       (if the first argument is false) or sqlite3_total_changes()
       (if it's true). If the 2nd argument is true, it uses
       sqlite3_changes64() or sqlite3_total_changes64(), which
       will trigger an exception if this build does not have
       BigInt support enabled.
    */
    changes: function(total=false,sixtyFour=false){
      const p = affirmDbOpen(this).pointer;
      if(total){
        return sixtyFour
          ? capi.sqlite3_total_changes64(p)
          : capi.sqlite3_total_changes(p);
      }else{
        return sixtyFour
          ? capi.sqlite3_changes64(p)
          : capi.sqlite3_changes(p);
      }
    },
    /**
       Similar to the this.filename property but will return a falsy
       value for special names like ":memory:". Throws if the DB has
       been closed. If passed an argument it then it will return the
       filename of the ATTACHEd db with that name, else it assumes a
       name of `main`. The argument may be either a JS string or
       a pointer to a WASM-allocated C-string.
    */
    getFilename: function(dbName='main'){
      return capi.sqlite3_db_filename(affirmDbOpen(this).pointer, dbName);
    },
    /**
       Returns true if this db instance has a name which resolves to a
       file. If the name is "" or starts with ":", it resolves to false.
       Note that it is not aware of the peculiarities of URI-style
       names and a URI-style name for a ":memory:" db will fool it.
       Returns false if this db is closed.
    */
    hasFilename: function(){
      return this.filename && ':'!==this.filename[0];
    },
    /**
       Returns the name of the given 0-based db number, as documented
       for sqlite3_db_name().
    */
    dbName: function(dbNumber=0){
      return capi.sqlite3_db_name(affirmDbOpen(this).pointer, dbNumber);
    },
    /**
       Compiles the given SQL and returns a prepared Stmt. This is
       the only way to create new Stmt objects. Throws on error.

       The given SQL must be a string, a Uint8Array holding SQL, a
       WASM pointer to memory holding the NUL-terminated SQL string,
       or an array of strings. In the latter case, the array is
       concatenated together, with no separators, to form the SQL
       string (arrays are often a convenient way to formulate long
       statements).  If the SQL contains no statements, an
       SQLite3Error is thrown.

       Design note: the C API permits empty SQL, reporting it as a 0
       result code and a NULL stmt pointer. Supporting that case here
       would cause extra work for all clients: any use of the Stmt API
       on such a statement will necessarily throw, so clients would be
       required to check `stmt.pointer` after calling `prepare()` in
       order to determine whether the Stmt instance is empty or not.
       Long-time practice (with other sqlite3 script bindings)
       suggests that the empty-prepare case is sufficiently rare that
       supporting it here would simply hurt overall usability.
    */
    prepare: function(sql){
      affirmDbOpen(this);
      const stack = wasm.pstack.pointer;
      let ppStmt, pStmt;
      try{
        ppStmt = wasm.pstack.alloc(8)/* output (sqlite3_stmt**) arg */;
        DB.checkRc(this, capi.sqlite3_prepare_v2(this.pointer, sql, -1, ppStmt, null));
        pStmt = wasm.getPtrValue(ppStmt);
      }
      finally {
        wasm.pstack.restore(stack);
      }
      if(!pStmt) toss3("Cannot prepare empty SQL.");
      const stmt = new Stmt(this, pStmt, BindTypes);
      __stmtMap.get(this)[pStmt] = stmt;
      return stmt;
    },
    /**
       Executes one or more SQL statements in the form of a single
       string. Its arguments must be either (sql,optionsObject) or
       (optionsObject). In the latter case, optionsObject.sql
       must contain the SQL to execute. Returns this
       object. Throws on error.

       If no SQL is provided, or a non-string is provided, an
       exception is triggered. Empty SQL, on the other hand, is
       simply a no-op.

       The optional options object may contain any of the following
       properties:

       - `.sql` = the SQL to run (unless it's provided as the first
       argument). This must be of type string, Uint8Array, or an array
       of strings. In the latter case they're concatenated together
       as-is, _with no separator_ between elements, before evaluation.
       The array form is often simpler for long hand-written queries.

       - `.bind` = a single value valid as an argument for
       Stmt.bind(). This is _only_ applied to the _first_ non-empty
       statement in the SQL which has any bindable parameters. (Empty
       statements are skipped entirely.)

       - `.saveSql` = an optional array. If set, the SQL of each
       executed statement is appended to this array before the
       statement is executed (but after it is prepared - we don't have
       the string until after that). Empty SQL statements are elided.

       ==================================================================
       The following options apply _only_ to the _first_ statement
       which has a non-zero result column count, regardless of whether
       the statement actually produces any result rows.
       ==================================================================

       - `.columnNames`: if this is an array, the column names of the
       result set are stored in this array before the callback (if
       any) is triggered (regardless of whether the query produces any
       result rows). If no statement has result columns, this value is
       unchanged. Achtung: an SQL result may have multiple columns
       with identical names.

       - `.callback` = a function which gets called for each row of
       the result set, but only if that statement has any result
       _rows_. The callback's "this" is the options object, noting
       that this function synthesizes one if the caller does not pass
       one to exec(). The second argument passed to the callback is
       always the current Stmt object, as it's needed if the caller
       wants to fetch the column names or some such (noting that they
       could also be fetched via `this.columnNames`, if the client
       provides the `columnNames` option).

       ACHTUNG: The callback MUST NOT modify the Stmt object. Calling
       any of the Stmt.get() variants, Stmt.getColumnName(), or
       similar, is legal, but calling step() or finalize() is
       not. Member methods which are illegal in this context will
       trigger an exception.

       The first argument passed to the callback defaults to an array of
       values from the current result row but may be changed with ...

       - `.rowMode` = specifies the type of he callback's first argument.
       It may be any of...

       A) A string describing what type of argument should be passed
       as the first argument to the callback:

         A.1) `'array'` (the default) causes the results of
         `stmt.get([])` to be passed to the `callback` and/or appended
         to `resultRows`.

         A.2) `'object'` causes the results of
         `stmt.get(Object.create(null))` to be passed to the
         `callback` and/or appended to `resultRows`.  Achtung: an SQL
         result may have multiple columns with identical names. In
         that case, the right-most column will be the one set in this
         object!

         A.3) `'stmt'` causes the current Stmt to be passed to the
         callback, but this mode will trigger an exception if
         `resultRows` is an array because appending the statement to
         the array would be downright unhelpful.

       B) An integer, indicating a zero-based column in the result
       row. Only that one single value will be passed on.

       C) A string with a minimum length of 2 and leading character of
       ':', '$', or '@' will fetch the row as an object, extract that
       one field, and pass that field's value to the callback. Note
       that these keys are case-sensitive so must match the case used
       in the SQL. e.g. `"select a A from t"` with a `rowMode` of
       `'$A'` would work but `'$a'` would not. A reference to a column
       not in the result set will trigger an exception on the first
       row (as the check is not performed until rows are fetched).
       Note also that `$` is a legal identifier character in JS so
       need not be quoted. (Design note: those 3 characters were
       chosen because they are the characters support for naming bound
       parameters.)

       Any other `rowMode` value triggers an exception.

       - `.resultRows`: if this is an array, it functions similarly to
       the `callback` option: each row of the result set (if any),
       with the exception that the `rowMode` 'stmt' is not legal. It
       is legal to use both `resultRows` and `callback`, but
       `resultRows` is likely much simpler to use for small data sets
       and can be used over a WebWorker-style message interface.
       exec() throws if `resultRows` is set and `rowMode` is 'stmt'.


       Potential TODOs:

       - `.bind`: permit an array of arrays/objects to bind. The first
       sub-array would act on the first statement which has bindable
       parameters (as it does now). The 2nd would act on the next such
       statement, etc.

       - `.callback` and `.resultRows`: permit an array entries with
       semantics similar to those described for `.bind` above.

    */
    exec: function(/*(sql [,obj]) || (obj)*/){
      affirmDbOpen(this);
      const wasm = capi.wasm;
      const arg = parseExecArgs(arguments);
      if(!arg.sql){
        return (''===arg.sql) ? this : toss3("exec() requires an SQL string.");
      }
      const opt = arg.opt;
      const callback = opt.callback;
      let resultRows = (Array.isArray(opt.resultRows)
                          ? opt.resultRows : undefined);
      let stmt;
      let bind = opt.bind;
      let evalFirstResult = !!(arg.cbArg || opt.columnNames) /* true to evaluate the first result-returning query */;
      const stack = wasm.scopedAllocPush();
      try{
        const isTA = util.isSQLableTypedArray(arg.sql)
        /* Optimization: if the SQL is a TypedArray we can save some string
           conversion costs. */;
        /* Allocate the two output pointers (ppStmt, pzTail) and heap
           space for the SQL (pSql). When prepare_v2() returns, pzTail
           will point to somewhere in pSql. */
        let sqlByteLen = isTA ? arg.sql.byteLength : wasm.jstrlen(arg.sql);
        const ppStmt  = wasm.scopedAlloc(/* output (sqlite3_stmt**) arg and pzTail */
          (2 * wasm.ptrSizeof)
          + (sqlByteLen + 1/* SQL + NUL */));
        const pzTail = ppStmt + wasm.ptrSizeof /* final arg to sqlite3_prepare_v2() */;
        let pSql = pzTail + wasm.ptrSizeof;
        const pSqlEnd = pSql + sqlByteLen;
        if(isTA) wasm.heap8().set(arg.sql, pSql);
        else wasm.jstrcpy(arg.sql, wasm.heap8(), pSql, sqlByteLen, false);
        wasm.setMemValue(pSql + sqlByteLen, 0/*NUL terminator*/);
        while(pSql && wasm.getMemValue(pSql, 'i8')
              /* Maintenance reminder:^^^ _must_ be 'i8' or else we
                 will very likely cause an endless loop. What that's
                 doing is checking for a terminating NUL byte. If we
                 use i32 or similar then we read 4 bytes, read stuff
                 around the NUL terminator, and get stuck in and
                 endless loop at the end of the SQL, endlessly
                 re-preparing an empty statement. */ ){
          wasm.setPtrValue(ppStmt, 0);
          wasm.setPtrValue(pzTail, 0);
          DB.checkRc(this, capi.sqlite3_prepare_v3(
            this.pointer, pSql, sqlByteLen, 0, ppStmt, pzTail
          ));
          const pStmt = wasm.getPtrValue(ppStmt);
          pSql = wasm.getPtrValue(pzTail);
          sqlByteLen = pSqlEnd - pSql;
          if(!pStmt) continue;
          if(Array.isArray(opt.saveSql)){
            opt.saveSql.push(capi.sqlite3_sql(pStmt).trim());
          }
          stmt = new Stmt(this, pStmt, BindTypes);
          if(bind && stmt.parameterCount){
            stmt.bind(bind);
            bind = null;
          }
          if(evalFirstResult && stmt.columnCount){
            /* Only forward SELECT results for the FIRST query
               in the SQL which potentially has them. */
            evalFirstResult = false;
            if(Array.isArray(opt.columnNames)){
              stmt.getColumnNames(opt.columnNames);
            }
            while(!!arg.cbArg && stmt.step()){
              stmt._isLocked = true;
              const row = arg.cbArg(stmt);
              if(resultRows) resultRows.push(row);
              if(callback) callback.apply(opt,[row,stmt]);
              stmt._isLocked = false;
            }
          }else{
            stmt.step();
          }
          stmt.finalize();
          stmt = null;
        }
      }/*catch(e){
        console.warn("DB.exec() is propagating exception",opt,e);
        throw e;
      }*/finally{
        if(stmt){
          delete stmt._isLocked;
          stmt.finalize();
        }
        wasm.scopedAllocPop(stack);
      }
      return this;
    }/*exec()*/,
    /**
       Creates a new scalar UDF (User-Defined Function) which is
       accessible via SQL code. This function may be called in any
       of the following forms:

       - (name, function)
       - (name, function, optionsObject)
       - (name, optionsObject)
       - (optionsObject)

       In the final two cases, the function must be defined as the
       `callback` property of the options object (optionally called
       `xFunc` to align with the C API documentation). In the final
       case, the function's name must be the 'name' property.

       The first two call forms can only be used for creating scalar
       functions. Creating an aggregate function requires the
       options-object form (see below for details).

       UDFs cannot currently be removed from a DB handle after they're
       added. More correctly, they can be removed as documented for
       sqlite3_create_function_v2(), but doing so will "leak" the
       JS-created WASM binding of those functions.

       On success, returns this object. Throws on error.

       When called from SQL arguments to the UDF, and its result,
       will be converted between JS and SQL with as much fidelity as
       is feasible, triggering an exception if a type conversion
       cannot be determined. The docs for sqlite3_create_function_v2()
       describe the conversions in more detail.

       The values set in the options object differ for scalar and
       aggregate functions:

       - Scalar: set the `xFunc` function-type property to the UDF
         function.

       - Aggregate: set the `xStep` and `xFinal` function-type
         properties to the "step" and "final" callbacks for the
         aggregate. Do not set the `xFunc` property.

       The options object may optionally have an `xDestroy`
       function-type property, as per
       sqlite3_create_function_v2(). Its argument will be the
       WASM-pointer-type value of the `pApp` property, and this
       function will throw if `pApp` is defined but is not null,
       undefined, or a numeric (WASM pointer) value.

       The optional options object may contain flags to modify how
       the function is defined:

       - `arity`: the number of arguments which SQL calls to this
       function expect or require. The default value is `xFunc.length`
       or `xStep.length` (i.e. the number of declared parameters it
       has) **MINUS 1** (see below for why). As a special case, if the
       `length` is 0, its arity is also 0 instead of -1. A negative
       arity value means that the function is variadic and may accept
       any number of arguments, up to sqlite3's compile-time
       limits. sqlite3 will enforce the argument count if is zero or
       greater.

       The callback always receives a pointer to an `sqlite3_context`
       object as its first argument. Any arguments after that are from
       SQL code. The leading context argument does _not_ count towards
       the function's arity. See the docs for
       sqlite3.capi.sqlite3_create_function_v2() for why that argument
       is needed in the interface.

       The following properties correspond to flags documented at:

       https://sqlite.org/c3ref/create_function.html

       - .deterministic = SQLITE_DETERMINISTIC
       - .directOnly = SQLITE_DIRECTONLY
       - .innocuous = SQLITE_INNOCUOUS
    */
    createFunction: function f(name, xFunc, opt){
      let xStep, xFinal;
      const isFunc = (f)=>(f instanceof Function);
      switch(arguments.length){
          case 1: /* (optionsObject) */
            opt = name;
            name = opt.name;
            xFunc = opt.xFunc;
            break;
          case 2: /* (name, callback|optionsObject) */
            if(!isFunc(xFunc)){
              opt = xFunc;
              xFunc = opt.xFunc;
            }
            break;
          case 3: /* name, xFunc, opt */
            break;
          default: break;
      }
      if(!opt) opt = {};
      if('string' !== typeof name){
        toss3("Invalid arguments: missing function name.");
      }
      xStep = opt.xStep;
      xFinal = opt.xFinal;
      if(isFunc(xFunc)){
        if(isFunc(xStep) || isFunc(xFinal)){
          toss3("Ambiguous arguments: scalar or aggregate?");
        }
        xStep = xFinal = null;
      }else if(isFunc(xStep)){
        if(!isFunc(xFinal)){
          toss3("Missing xFinal() callback for aggregate UDF.");
        }
        xFunc = null;
      }else if(isFunc(xFinal)){
        toss3("Missing xStep() callback for aggregate UDF.");
      }else{
        toss3("Missing function-type properties.");
      }
      const pApp = opt.pApp;
      if(undefined!==pApp && (('number'!==typeof pApp)
                              || !capi.util.isInt32(pApp))){
        toss3("Invalid value for pApp property. Must be a legal WASM pointer value.");
      }
      const xDestroy = opt.xDestroy;
      if(xDestroy && !isFunc(xDestroy)){
        toss3("xDestroy property must be a function.");
      }
      let fFlags = 0 /*flags for sqlite3_create_function_v2()*/;
      if(getOwnOption(opt, 'deterministic')) fFlags |= capi.SQLITE_DETERMINISTIC;
      if(getOwnOption(opt, 'directOnly')) fFlags |= capi.SQLITE_DIRECTONLY;
      if(getOwnOption(opt, 'innocuous')) fFlags |= capi.SQLITE_INNOCUOUS;
      name = name.toLowerCase();
      const xArity = xFunc || xStep;
      const arity = getOwnOption(opt, 'arity');
      DB.checkRc(this, capi.sqlite3_create_function_v2(
        this.pointer, name,
        ('number'===typeof arity
         ? arity
         : (xArity.length ? xArity.length-1/*for pCtx arg*/ : 0)),
        capi.SQLITE_UTF8 | fFlags, pApp,
        xFunc, xStep, xFinal, xDestroy));
      return this;
    }/*createFunction()*/,
    /**
       Prepares the given SQL, step()s it one time, and returns
       the value of the first result column. If it has no results,
       undefined is returned.

       If passed a second argument, it is treated like an argument
       to Stmt.bind(), so may be any type supported by that
       function. Passing the undefined value is the same as passing
       no value, which is useful when...

       If passed a 3rd argument, it is expected to be one of the
       SQLITE_{typename} constants. Passing the undefined value is
       the same as not passing a value.

       Throws on error (e.g. malformed SQL).
    */
    selectValue: function(sql,bind,asType){
      let stmt, rc;
      try {
        stmt = this.prepare(sql).bind(bind);
        if(stmt.step()) rc = stmt.get(0,asType);
      }finally{
        if(stmt) stmt.finalize();
      }
      return rc;
    },

    /**
       Returns the number of currently-opened Stmt handles for this db
       handle, or 0 if this DB instance is closed.
    */
    openStatementCount: function(){
      return this.pointer ? Object.keys(__stmtMap.get(this)).length : 0;
    },

    /**
       Starts a transaction, calls the given callback, and then either
       rolls back or commits the savepoint, depending on whether the
       callback throws. The callback is passed this db object as its
       only argument. On success, returns the result of the
       callback. Throws on error.

       Note that transactions may not be nested, so this will throw if
       it is called recursively. For nested transactions, use the
       savepoint() method or manually manage SAVEPOINTs using exec().
     */
    transaction: function(callback){
      affirmDbOpen(this).exec("BEGIN");
      try {
        const rc = callback(this);
        this.exec("COMMIT");
        return rc;
      }catch(e){
        this.exec("ROLLBACK");
        throw e;
      }
    },

    /**
       This works similarly to transaction() but uses sqlite3's SAVEPOINT
       feature. This function starts a savepoint (with an unspecified name)
       and calls the given callback function, passing it this db object.
       If the callback returns, the savepoint is released (committed). If
       the callback throws, the savepoint is rolled back. If it does not
       throw, it returns the result of the callback.
    */
    savepoint: function(callback){
      affirmDbOpen(this).exec("SAVEPOINT oo1");
      try {
        const rc = callback(this);
        this.exec("RELEASE oo1");
        return rc;
      }catch(e){
        this.exec("ROLLBACK to SAVEPOINT oo1; RELEASE SAVEPOINT oo1");
        throw e;
      }
    }
  }/*DB.prototype*/;


  /** Throws if the given Stmt has been finalized, else stmt is
      returned. */
  const affirmStmtOpen = function(stmt){
    if(!stmt.pointer) toss3("Stmt has been closed.");
    return stmt;
  };

  /** Returns an opaque truthy value from the BindTypes
      enum if v's type is a valid bindable type, else
      returns a falsy value. As a special case, a value of
      undefined is treated as a bind type of null. */
  const isSupportedBindType = function(v){
    let t = BindTypes[(null===v||undefined===v) ? 'null' : typeof v];
    switch(t){
        case BindTypes.boolean:
        case BindTypes.null:
        case BindTypes.number:
        case BindTypes.string:
          return t;
        case BindTypes.bigint:
          if(wasm.bigIntEnabled) return t;
          /* else fall through */
        default:
          //console.log("isSupportedBindType",t,v);
          return util.isBindableTypedArray(v) ? BindTypes.blob : undefined;
    }
  };

  /**
     If isSupportedBindType(v) returns a truthy value, this
     function returns that value, else it throws.
  */
  const affirmSupportedBindType = function(v){
    //console.log('affirmSupportedBindType',v);
    return isSupportedBindType(v) || toss3("Unsupported bind() argument type:",typeof v);
  };

  /**
     If key is a number and within range of stmt's bound parameter
     count, key is returned.

     If key is not a number then it is checked against named
     parameters. If a match is found, its index is returned.

     Else it throws.
  */
  const affirmParamIndex = function(stmt,key){
    const n = ('number'===typeof key)
          ? key : capi.sqlite3_bind_parameter_index(stmt.pointer, key);
    if(0===n || !util.isInt32(n)){
      toss3("Invalid bind() parameter name: "+key);
    }
    else if(n<1 || n>stmt.parameterCount) toss3("Bind index",key,"is out of range.");
    return n;
  };

  /**
     If stmt._isLocked is truthy, this throws an exception
     complaining that the 2nd argument (an operation name,
     e.g. "bind()") is not legal while the statement is "locked".
     Locking happens before an exec()-like callback is passed a
     statement, to ensure that the callback does not mutate or
     finalize the statement. If it does not throw, it returns stmt.
  */
  const affirmUnlocked = function(stmt,currentOpName){
    if(stmt._isLocked){
      toss3("Operation is illegal when statement is locked:",currentOpName);
    }
    return stmt;
  };

  /**
     Binds a single bound parameter value on the given stmt at the
     given index (numeric or named) using the given bindType (see
     the BindTypes enum) and value. Throws on error. Returns stmt on
     success.
  */
  const bindOne = function f(stmt,ndx,bindType,val){
    affirmUnlocked(stmt, 'bind()');
    if(!f._){
      f._tooBigInt = (v)=>toss3(
        "BigInt value is too big to store without precision loss:", v
      );
      /* Reminder: when not in BigInt mode, it's impossible for
         JS to represent a number out of the range we can bind,
         so we have no range checking. */
      f._ = {
        string: function(stmt, ndx, val, asBlob){
          if(1){
            /* _Hypothetically_ more efficient than the impl in the 'else' block. */
            const stack = wasm.scopedAllocPush();
            try{
              const n = wasm.jstrlen(val);
              const pStr = wasm.scopedAlloc(n);
              wasm.jstrcpy(val, wasm.heap8u(), pStr, n, false);
              const f = asBlob ? capi.sqlite3_bind_blob : capi.sqlite3_bind_text;
              return f(stmt.pointer, ndx, pStr, n, capi.SQLITE_TRANSIENT);
            }finally{
              wasm.scopedAllocPop(stack);
            }
          }else{
            const bytes = wasm.jstrToUintArray(val,false);
            const pStr = wasm.alloc(bytes.length || 1);
            wasm.heap8u().set(bytes.length ? bytes : [0], pStr);
            try{
              const f = asBlob ? capi.sqlite3_bind_blob : capi.sqlite3_bind_text;
              return f(stmt.pointer, ndx, pStr, bytes.length, capi.SQLITE_TRANSIENT);
            }finally{
              wasm.dealloc(pStr);
            }
          }
        }
      };
    }/* static init */
    affirmSupportedBindType(val);
    ndx = affirmParamIndex(stmt,ndx);
    let rc = 0;
    switch((null===val || undefined===val) ? BindTypes.null : bindType){
        case BindTypes.null:
          rc = capi.sqlite3_bind_null(stmt.pointer, ndx);
          break;
        case BindTypes.string:
          rc = f._.string(stmt, ndx, val, false);
          break;
        case BindTypes.number: {
          let m;
          if(util.isInt32(val)) m = capi.sqlite3_bind_int;
          else if('bigint'===typeof val){
            if(!util.bigIntFits64(val)){
              f._tooBigInt(val);
            }else if(wasm.bigIntEnabled){
              m = capi.sqlite3_bind_int64;
            }else if(util.bigIntFitsDouble(val)){
              val = Number(val);
              m = capi.sqlite3_bind_double;
            }else{
              f._tooBigInt(val);
            }
          }else{ // !int32, !bigint
            val = Number(val);
            if(wasm.bigIntEnabled && Number.isInteger(val)){
              m = capi.sqlite3_bind_int64;
            }else{
              m = capi.sqlite3_bind_double;
            }
          }
          rc = m(stmt.pointer, ndx, val);
          break;
        }
        case BindTypes.boolean:
          rc = capi.sqlite3_bind_int(stmt.pointer, ndx, val ? 1 : 0);
          break;
        case BindTypes.blob: {
          if('string'===typeof val){
            rc = f._.string(stmt, ndx, val, true);
          }else if(!util.isBindableTypedArray(val)){
            toss3("Binding a value as a blob requires",
                  "that it be a string, Uint8Array, or Int8Array.");
          }else if(1){
            /* _Hypothetically_ more efficient than the impl in the 'else' block. */
            const stack = wasm.scopedAllocPush();
            try{
              const pBlob = wasm.scopedAlloc(val.byteLength || 1);
              wasm.heap8().set(val.byteLength ? val : [0], pBlob)
              rc = capi.sqlite3_bind_blob(stmt.pointer, ndx, pBlob, val.byteLength,
                                         capi.SQLITE_TRANSIENT);
            }finally{
              wasm.scopedAllocPop(stack);
            }
          }else{
            const pBlob = wasm.allocFromTypedArray(val);
            try{
              rc = capi.sqlite3_bind_blob(stmt.pointer, ndx, pBlob, val.byteLength,
                                         capi.SQLITE_TRANSIENT);
            }finally{
              wasm.dealloc(pBlob);
            }
          }
          break;
        }
        default:
          console.warn("Unsupported bind() argument type:",val);
          toss3("Unsupported bind() argument type: "+(typeof val));
    }
    if(rc) DB.checkRc(stmt.db.pointer, rc);
    return stmt;
  };

  Stmt.prototype = {
    /**
       "Finalizes" this statement. This is a no-op if the
       statement has already been finalizes. Returns
       undefined. Most methods in this class will throw if called
       after this is.
    */
    finalize: function(){
      if(this.pointer){
        affirmUnlocked(this,'finalize()');
        delete __stmtMap.get(this.db)[this.pointer];
        capi.sqlite3_finalize(this.pointer);
        __ptrMap.delete(this);
        delete this._mayGet;
        delete this.columnCount;
        delete this.parameterCount;
        delete this.db;
        delete this._isLocked;
      }
    },
    /** Clears all bound values. Returns this object.
        Throws if this statement has been finalized. */
    clearBindings: function(){
      affirmUnlocked(affirmStmtOpen(this), 'clearBindings()')
      capi.sqlite3_clear_bindings(this.pointer);
      this._mayGet = false;
      return this;
    },
    /**
       Resets this statement so that it may be step()ed again
       from the beginning. Returns this object. Throws if this
       statement has been finalized.

       If passed a truthy argument then this.clearBindings() is
       also called, otherwise any existing bindings, along with
       any memory allocated for them, are retained.
    */
    reset: function(alsoClearBinds){
      affirmUnlocked(this,'reset()');
      if(alsoClearBinds) this.clearBindings();
      capi.sqlite3_reset(affirmStmtOpen(this).pointer);
      this._mayGet = false;
      return this;
    },
    /**
       Binds one or more values to its bindable parameters. It
       accepts 1 or 2 arguments:

       If passed a single argument, it must be either an array, an
       object, or a value of a bindable type (see below).

       If passed 2 arguments, the first one is the 1-based bind
       index or bindable parameter name and the second one must be
       a value of a bindable type.

       Bindable value types:

       - null is bound as NULL.

       - undefined as a standalone value is a no-op intended to
         simplify certain client-side use cases: passing undefined as
         a value to this function will not actually bind anything and
         this function will skip confirmation that binding is even
         legal. (Those semantics simplify certain client-side uses.)
         Conversely, a value of undefined as an array or object
         property when binding an array/object (see below) is treated
         the same as null.

       - Numbers are bound as either doubles or integers: doubles if
         they are larger than 32 bits, else double or int32, depending
         on whether they have a fractional part. Booleans are bound as
         integer 0 or 1. It is not expected the distinction of binding
         doubles which have no fractional parts is integers is
         significant for the majority of clients due to sqlite3's data
         typing model. If [BigInt] support is enabled then this
         routine will bind BigInt values as 64-bit integers if they'll
         fit in 64 bits. If that support disabled, it will store the
         BigInt as an int32 or a double if it can do so without loss
         of precision. If the BigInt is _too BigInt_ then it will
         throw.

       - Strings are bound as strings (use bindAsBlob() to force
         blob binding).

       - Uint8Array and Int8Array instances are bound as blobs.
         (TODO: binding the other TypedArray types.)

       If passed an array, each element of the array is bound at
       the parameter index equal to the array index plus 1
       (because arrays are 0-based but binding is 1-based).

       If passed an object, each object key is treated as a
       bindable parameter name. The object keys _must_ match any
       bindable parameter names, including any `$`, `@`, or `:`
       prefix. Because `$` is a legal identifier chararacter in
       JavaScript, that is the suggested prefix for bindable
       parameters: `stmt.bind({$a: 1, $b: 2})`.

       It returns this object on success and throws on
       error. Errors include:

       - Any bind index is out of range, a named bind parameter
       does not match, or this statement has no bindable
       parameters.

       - Any value to bind is of an unsupported type.

       - Passed no arguments or more than two.

       - The statement has been finalized.
    */
    bind: function(/*[ndx,] arg*/){
      affirmStmtOpen(this);
      let ndx, arg;
      switch(arguments.length){
          case 1: ndx = 1; arg = arguments[0]; break;
          case 2: ndx = arguments[0]; arg = arguments[1]; break;
          default: toss3("Invalid bind() arguments.");
      }
      if(undefined===arg){
        /* It might seem intuitive to bind undefined as NULL
           but this approach simplifies certain client-side
           uses when passing on arguments between 2+ levels of
           functions. */
        return this;
      }else if(!this.parameterCount){
        toss3("This statement has no bindable parameters.");
      }
      this._mayGet = false;
      if(null===arg){
        /* bind NULL */
        return bindOne(this, ndx, BindTypes.null, arg);
      }
      else if(Array.isArray(arg)){
        /* bind each entry by index */
        if(1!==arguments.length){
          toss3("When binding an array, an index argument is not permitted.");
        }
        arg.forEach((v,i)=>bindOne(this, i+1, affirmSupportedBindType(v), v));
        return this;
      }
      else if('object'===typeof arg/*null was checked above*/
              && !util.isBindableTypedArray(arg)){
        /* Treat each property of arg as a named bound parameter. */
        if(1!==arguments.length){
          toss3("When binding an object, an index argument is not permitted.");
        }
        Object.keys(arg)
          .forEach(k=>bindOne(this, k,
                              affirmSupportedBindType(arg[k]),
                              arg[k]));
        return this;
      }else{
        return bindOne(this, ndx, affirmSupportedBindType(arg), arg);
      }
      toss3("Should not reach this point.");
    },
    /**
       Special case of bind() which binds the given value using the
       BLOB binding mechanism instead of the default selected one for
       the value. The ndx may be a numbered or named bind index. The
       value must be of type string, null/undefined (both get treated
       as null), or a TypedArray of a type supported by the bind()
       API.

       If passed a single argument, a bind index of 1 is assumed and
       the first argument is the value.
    */
    bindAsBlob: function(ndx,arg){
      affirmStmtOpen(this);
      if(1===arguments.length){
        arg = ndx;
        ndx = 1;
      }
      const t = affirmSupportedBindType(arg);
      if(BindTypes.string !== t && BindTypes.blob !== t
         && BindTypes.null !== t){
        toss3("Invalid value type for bindAsBlob()");
      }
      bindOne(this, ndx, BindTypes.blob, arg);
      this._mayGet = false;
      return this;
    },
    /**
       Steps the statement one time. If the result indicates that a
       row of data is available, a truthy value is returned.
       If no row of data is available, a falsy
       value is returned.  Throws on error.
    */
    step: function(){
      affirmUnlocked(this, 'step()');
      const rc = capi.sqlite3_step(affirmStmtOpen(this).pointer);
      switch(rc){
          case capi.SQLITE_DONE: return this._mayGet = false;
          case capi.SQLITE_ROW: return this._mayGet = true;
          default:
            this._mayGet = false;
            console.warn("sqlite3_step() rc=",rc,
                         capi.sqlite3_web_rc_str(rc),
                         "SQL =", capi.sqlite3_sql(this.pointer));
            DB.checkRc(this.db.pointer, rc);
      }
    },
    /**
       Functions exactly like step() except that...

       1) On success, it calls this.reset() and returns this object.
       2) On error, it throws and does not call reset().

       This is intended to simplify constructs like:

       ```
       for(...) {
         stmt.bind(...).stepReset();
       }
       ```

       Note that the reset() call makes it illegal to call this.get()
       after the step.
    */
    stepReset: function(){
      this.step();
      return this.reset();
    },
    /**
       Functions like step() except that it finalizes this statement
       immediately after stepping unless the step cannot be performed
       because the statement is locked. Throws on error, but any error
       other than the statement-is-locked case will also trigger
       finalization of this statement.

       On success, it returns true if the step indicated that a row of
       data was available, else it returns false.

       This is intended to simplify use cases such as:

       ```
       aDb.prepare("insert into foo(a) values(?)").bind(123).stepFinalize();
       ```
    */
    stepFinalize: function(){
      const rc = this.step();
      this.finalize();
      return rc;
    },
    /**
       Fetches the value from the given 0-based column index of
       the current data row, throwing if index is out of range.

       Requires that step() has just returned a truthy value, else
       an exception is thrown.

       By default it will determine the data type of the result
       automatically. If passed a second arugment, it must be one
       of the enumeration values for sqlite3 types, which are
       defined as members of the sqlite3 module: SQLITE_INTEGER,
       SQLITE_FLOAT, SQLITE_TEXT, SQLITE_BLOB. Any other value,
       except for undefined, will trigger an exception. Passing
       undefined is the same as not passing a value. It is legal
       to, e.g., fetch an integer value as a string, in which case
       sqlite3 will convert the value to a string.

       If ndx is an array, this function behaves a differently: it
       assigns the indexes of the array, from 0 to the number of
       result columns, to the values of the corresponding column,
       and returns that array.

       If ndx is a plain object, this function behaves even
       differentlier: it assigns the properties of the object to
       the values of their corresponding result columns.

       Blobs are returned as Uint8Array instances.

       Potential TODO: add type ID SQLITE_JSON, which fetches the
       result as a string and passes it (if it's not null) to
       JSON.parse(), returning the result of that. Until then,
       getJSON() can be used for that.
    */
    get: function(ndx,asType){
      if(!affirmStmtOpen(this)._mayGet){
        toss3("Stmt.step() has not (recently) returned true.");
      }
      if(Array.isArray(ndx)){
        let i = 0;
        while(i<this.columnCount){
          ndx[i] = this.get(i++);
        }
        return ndx;
      }else if(ndx && 'object'===typeof ndx){
        let i = 0;
        while(i<this.columnCount){
          ndx[capi.sqlite3_column_name(this.pointer,i)] = this.get(i++);
        }
        return ndx;
      }
      affirmColIndex(this, ndx);
      switch(undefined===asType
             ? capi.sqlite3_column_type(this.pointer, ndx)
             : asType){
          case capi.SQLITE_NULL: return null;
          case capi.SQLITE_INTEGER:{
            if(wasm.bigIntEnabled){
              const rc = capi.sqlite3_column_int64(this.pointer, ndx);
              if(rc>=Number.MIN_SAFE_INTEGER && rc<=Number.MAX_SAFE_INTEGER){
                /* Coerce "normal" number ranges to normal number values,
                   and only return BigInt-type values for numbers out of this
                   range. */
                return Number(rc).valueOf();
              }
              return rc;
            }else{
              const rc = capi.sqlite3_column_double(this.pointer, ndx);
              if(rc>Number.MAX_SAFE_INTEGER || rc<Number.MIN_SAFE_INTEGER){
                /* Throwing here is arguable but, since we're explicitly
                   extracting an SQLITE_INTEGER-type value, it seems fair to throw
                   if the extracted number is out of range for that type.
                   This policy may be laxened to simply pass on the number and
                   hope for the best, as the C API would do. */
                toss3("Integer is out of range for JS integer range: "+rc);
              }
              //console.log("get integer rc=",rc,isInt32(rc));
              return util.isInt32(rc) ? (rc | 0) : rc;
            }
          }
          case capi.SQLITE_FLOAT:
            return capi.sqlite3_column_double(this.pointer, ndx);
          case capi.SQLITE_TEXT:
            return capi.sqlite3_column_text(this.pointer, ndx);
          case capi.SQLITE_BLOB: {
            const n = capi.sqlite3_column_bytes(this.pointer, ndx),
                  ptr = capi.sqlite3_column_blob(this.pointer, ndx),
                  rc = new Uint8Array(n);
            //heap = n ? wasm.heap8() : false;
            if(n) rc.set(wasm.heap8u().slice(ptr, ptr+n), 0);
            //for(let i = 0; i < n; ++i) rc[i] = heap[ptr + i];
            if(n && this.db._blobXfer instanceof Array){
              /* This is an optimization soley for the
                 Worker-based API. These values will be
                 transfered to the main thread directly
                 instead of being copied. */
              this.db._blobXfer.push(rc.buffer);
            }
            return rc;
          }
          default: toss3("Don't know how to translate",
                         "type of result column #"+ndx+".");
      }
      toss3("Not reached.");
    },
    /** Equivalent to get(ndx) but coerces the result to an
        integer. */
    getInt: function(ndx){return this.get(ndx,capi.SQLITE_INTEGER)},
    /** Equivalent to get(ndx) but coerces the result to a
        float. */
    getFloat: function(ndx){return this.get(ndx,capi.SQLITE_FLOAT)},
    /** Equivalent to get(ndx) but coerces the result to a
        string. */
    getString: function(ndx){return this.get(ndx,capi.SQLITE_TEXT)},
    /** Equivalent to get(ndx) but coerces the result to a
        Uint8Array. */
    getBlob: function(ndx){return this.get(ndx,capi.SQLITE_BLOB)},
    /**
       A convenience wrapper around get() which fetches the value
       as a string and then, if it is not null, passes it to
       JSON.parse(), returning that result. Throws if parsing
       fails. If the result is null, null is returned. An empty
       string, on the other hand, will trigger an exception.
    */
    getJSON: function(ndx){
      const s = this.get(ndx, capi.SQLITE_STRING);
      return null===s ? s : JSON.parse(s);
    },
    // Design note: the only reason most of these getters have a 'get'
    // prefix is for consistency with getVALUE_TYPE().  The latter
    // arguably really need that prefix for API readability and the
    // rest arguably don't, but consistency is a powerful thing.
    /**
       Returns the result column name of the given index, or
       throws if index is out of bounds or this statement has been
       finalized. This can be used without having run step()
       first.
    */
    getColumnName: function(ndx){
      return capi.sqlite3_column_name(
        affirmColIndex(affirmStmtOpen(this),ndx).pointer, ndx
      );
    },
    /**
       If this statement potentially has result columns, this
       function returns an array of all such names. If passed an
       array, it is used as the target and all names are appended
       to it. Returns the target array. Throws if this statement
       cannot have result columns. This object's columnCount member
       holds the number of columns.
    */
    getColumnNames: function(tgt=[]){
      affirmColIndex(affirmStmtOpen(this),0);
      for(let i = 0; i < this.columnCount; ++i){
        tgt.push(capi.sqlite3_column_name(this.pointer, i));
      }
      return tgt;
    },
    /**
       If this statement has named bindable parameters and the
       given name matches one, its 1-based bind index is
       returned. If no match is found, 0 is returned. If it has no
       bindable parameters, the undefined value is returned.
    */
    getParamIndex: function(name){
      return (affirmStmtOpen(this).parameterCount
              ? capi.sqlite3_bind_parameter_index(this.pointer, name)
              : undefined);
    }
  }/*Stmt.prototype*/;

  {/* Add the `pointer` property to DB and Stmt. */
    const prop = {
      enumerable: true,
      get: function(){return __ptrMap.get(this)},
      set: ()=>toss3("The pointer property is read-only.")
    }
    Object.defineProperty(Stmt.prototype, 'pointer', prop);
    Object.defineProperty(DB.prototype, 'pointer', prop);
  }

  /** The OO API's public namespace. */
  sqlite3.oo1 = {
    version: {
      lib: capi.sqlite3_libversion(),
      ooApi: "0.1"
    },
    DB,
    Stmt,
    dbCtorHelper
  }/*oo1 object*/;

  if(util.isMainWindow()){
    /**
       Functionally equivalent to DB(storageName,'c','kvvfs') except
       that it throws if the given storage name is not one of 'local'
       or 'session'.
    */
    sqlite3.oo1.JsStorageDb = function(storageName='session'){
      if('session'!==storageName && 'local'!==storageName){
        toss3("JsStorageDb db name must be one of 'session' or 'local'.");
      }
      dbCtorHelper.call(this, {
        filename: storageName,
        flags: 'c',
        vfs: "kvvfs"
      });
    };
    const jdb = sqlite3.oo1.JsStorageDb;
    jdb.prototype = Object.create(DB.prototype);
    /** Equivalent to sqlite3_web_kvvfs_clear(). */
    jdb.clearStorage = capi.sqlite3_web_kvvfs_clear;
    /**
       Clears this database instance's storage or throws if this
       instance has been closed. Returns the number of
       database blocks which were cleaned up.
    */
    jdb.prototype.clearStorage = function(){
      return jdb.clearStorage(affirmDbOpen(this).filename);
    };
    /** Equivalent to sqlite3_web_kvvfs_size(). */
    jdb.storageSize = capi.sqlite3_web_kvvfs_size;
    /**
       Returns the _approximate_ number of bytes this database takes
       up in its storage or throws if this instance has been closed.
    */
    jdb.prototype.storageSize = function(){
      return jdb.storageSize(affirmDbOpen(this).filename);
    };
  }/*main-window-only bits*/

});