sqlite/ext/wasm/api/sqlite3-api-glue.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 glues together disparate pieces of JS which are loaded in
  previous steps of the sqlite3-api.js bootstrapping process:
  sqlite3-api-prologue.js, whwasmutil.js, and jaccwabyt.js. It
  initializes the main API pieces so that the downstream components
  (e.g. sqlite3-api-oo1.js) have all that they need.
*/
self.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
  'use strict';
  const toss = (...args)=>{throw new Error(args.join(' '))};
  const toss3 = sqlite3.SQLite3Error.toss;
  const capi = sqlite3.capi, wasm = sqlite3.wasm, util = sqlite3.util;
  self.WhWasmUtilInstaller(wasm);
  delete self.WhWasmUtilInstaller;

  /**
     Install JS<->C struct bindings for the non-opaque struct types we
     need... */
  sqlite3.StructBinder = self.Jaccwabyt({
    heap: 0 ? wasm.memory : wasm.heap8u,
    alloc: wasm.alloc,
    dealloc: wasm.dealloc,
    functionTable: wasm.functionTable,
    bigIntEnabled: wasm.bigIntEnabled,
    memberPrefix: '$'
  });
  delete self.Jaccwabyt;

  if(0){
    /*  "The problem" is that the following isn't even remotely
        type-safe. OTOH, nothing about WASM pointers is. */
    const argPointer = wasm.xWrap.argAdapter('*');
    wasm.xWrap.argAdapter('StructType', (v)=>{
      if(v && v.constructor && v instanceof StructBinder.StructType){
        v = v.pointer;
      }
      return wasm.isPtr(v)
        ? argPointer(v)
        : toss("Invalid (object) type for StructType-type argument.");
    });
  }

  if(1){/* Convert Arrays and certain TypedArrays to strings for
           'flexible-string'-type arguments */
    const xString = wasm.xWrap.argAdapter('string');
    wasm.xWrap.argAdapter(
      'flexible-string', (v)=>xString(util.flexibleString(v))
    );
  }
  
  if(1){// WhWasmUtil.xWrap() bindings...
    /**
       Add some descriptive xWrap() aliases for '*' intended to (A)
       initially improve readability/correctness of capi.signatures
       and (B) eventually perhaps provide automatic conversion from
       higher-level representations, e.g. capi.sqlite3_vfs to
       `sqlite3_vfs*` via capi.sqlite3_vfs.pointer.
    */
    const aPtr = wasm.xWrap.argAdapter('*');
    wasm.xWrap.argAdapter('sqlite3*', aPtr)
    ('sqlite3_stmt*', aPtr)
    ('sqlite3_context*', aPtr)
    ('sqlite3_value*', aPtr)
    ('sqlite3_vfs*', aPtr)
    ('void*', aPtr);
    wasm.xWrap.resultAdapter('sqlite3*', aPtr)
    ('sqlite3_context*', aPtr)
    ('sqlite3_stmt*', aPtr)
    ('sqlite3_vfs*', aPtr)
    ('void*', aPtr);

    /**
       Populate api object with sqlite3_...() by binding the "raw" wasm
       exports into type-converting proxies using wasm.xWrap().
    */
    for(const e of wasm.bindingSignatures){
      capi[e[0]] = wasm.xWrap.apply(null, e);
    }
    for(const e of wasm.bindingSignatures.wasm){
      wasm[e[0]] = wasm.xWrap.apply(null, e);
    }

    /* For C API functions which cannot work properly unless
       wasm.bigIntEnabled is true, install a bogus impl which
       throws if called when bigIntEnabled is false. */
    const fI64Disabled = function(fname){
      return ()=>toss(fname+"() disabled due to lack",
                      "of BigInt support in this build.");
    };
    for(const e of wasm.bindingSignatures.int64){
      capi[e[0]] = wasm.bigIntEnabled
        ? wasm.xWrap.apply(null, e)
        : fI64Disabled(e[0]);
    }

    /* There's no(?) need to expose bindingSignatures to clients,
       implicitly making it part of the public interface. */
    delete wasm.bindingSignatures;

    if(wasm.exports.sqlite3_wasm_db_error){
      util.sqlite3_wasm_db_error = wasm.xWrap(
        'sqlite3_wasm_db_error', 'int', 'sqlite3*', 'int', 'string'
      );
    }else{
      util.sqlite3_wasm_db_error = function(pDb,errCode,msg){
        console.warn("sqlite3_wasm_db_error() is not exported.",arguments);
        return errCode;
      };
    }

  }/*xWrap() bindings*/;

  /**
     When registering a VFS and its related components it may be
     necessary to ensure that JS keeps a reference to them to keep
     them from getting garbage collected. Simply pass each such value
     to this function and a reference will be held to it for the life
     of the app.
  */
  capi.sqlite3_vfs_register.addReference = function f(...args){
    if(!f._) f._ = [];
    f._.push(...args);
  };

  /**
     Internal helper to assist in validating call argument counts in
     the hand-written sqlite3_xyz() wrappers. We do this only for
     consistency with non-special-case wrappings.
  */
  const __dbArgcMismatch = (pDb,f,n)=>{
    return sqlite3.util.sqlite3_wasm_db_error(pDb, capi.SQLITE_MISUSE,
                                              f+"() requires "+n+" argument"+
                                              (1===n?'':'s')+".");
  };

  /**
     Helper for flexible-string conversions which require a
     byte-length counterpart argument. Passed a value and its
     ostensible length, this function returns [V,N], where V
     is either v or a transformed copy of v and N is either n,
     -1, or the byte length of v (if it's a byte array).
  */
  const __flexiString = function(v,n){
    if('string'===typeof v){
      n = -1;
    }else if(util.isSQLableTypedArray(v)){
      n = v.byteLength;
      v = util.typedArrayToString(v);
    }else if(Array.isArray(v)){
      v = v.join('');
      n = -1;
    }
    return [v, n];
  };

  if(1){/* Special-case handling of sqlite3_exec() */
    const __exec = wasm.xWrap("sqlite3_exec", "int",
                              ["sqlite3*", "flexible-string", "*", "*", "**"]);
    /* Documented in the api object's initializer. */
    capi.sqlite3_exec = function f(pDb, sql, callback, pVoid, pErrMsg){
      if(f.length!==arguments.length){
        return __dbArgcMismatch(pDb,"sqlite3_exec",f.length);
      }else if('function' !== typeof callback){
        return __exec(pDb, sql, callback, pVoid, pErrMsg);
      }
      /* Wrap the callback in a WASM-bound function and convert the callback's
         `(char**)` arguments to arrays of strings... */
      const cbwrap = function(pVoid, nCols, pColVals, pColNames){
        let rc = capi.SQLITE_ERROR;
        try {
          let aVals = [], aNames = [], i = 0, offset = 0;
          for( ; i < nCols; offset += (wasm.ptrSizeof * ++i) ){
            aVals.push( wasm.cstringToJs(wasm.getPtrValue(pColVals + offset)) );
            aNames.push( wasm.cstringToJs(wasm.getPtrValue(pColNames + offset)) );
          }
          rc = callback(pVoid, nCols, aVals, aNames) | 0;
          /* The first 2 args of the callback are useless for JS but
             we want the JS mapping of the C API to be as close to the
             C API as possible. */
        }catch(e){
          /* If we set the db error state here, the higher-level exec() call
             replaces it with its own, so we have no way of reporting the
             exception message except the console. We must not propagate
             exceptions through the C API. */
        }
        return rc;
      };
      let pFunc, rc;
      try{
        pFunc = wasm.installFunction("ipipp", cbwrap);
        rc = __exec(pDb, sql, pFunc, pVoid, pErrMsg);
      }catch(e){
        rc = util.sqlite3_wasm_db_error(pDb, capi.SQLITE_ERROR,
                                        "Error running exec(): "+e.message);
      }finally{
        if(pFunc) wasm.uninstallFunction(pFunc);
      }
      return rc;
    };
  }/*sqlite3_exec() proxy*/;

  if(1){/* Special-case handling of sqlite3_create_function_v2()
           and sqlite3_create_window_function() */
    const sqlite3CreateFunction = wasm.xWrap(
      "sqlite3_create_function_v2", "int",
      ["sqlite3*", "string"/*funcName*/, "int"/*nArg*/,
       "int"/*eTextRep*/, "*"/*pApp*/,
       "*"/*xStep*/,"*"/*xFinal*/, "*"/*xValue*/, "*"/*xDestroy*/]
    );
    const sqlite3CreateWindowFunction = wasm.xWrap(
      "sqlite3_create_window_function", "int",
      ["sqlite3*", "string"/*funcName*/, "int"/*nArg*/,
       "int"/*eTextRep*/, "*"/*pApp*/,
       "*"/*xStep*/,"*"/*xFinal*/, "*"/*xValue*/,
       "*"/*xInverse*/, "*"/*xDestroy*/]
    );

    const __udfSetResult = function(pCtx, val){
      //console.warn("udfSetResult",typeof val, val);
      switch(typeof val) {
          case 'undefined':
            /* Assume that the client already called sqlite3_result_xxx(). */
            break;
          case 'boolean':
            capi.sqlite3_result_int(pCtx, val ? 1 : 0);
            break;
          case 'bigint':
            if(wasm.bigIntEnabled){
              if(util.bigIntFits64(val)) capi.sqlite3_result_int64(pCtx, val);
              else toss3("BigInt value",val.toString(),"is too BigInt for int64.");
            }else if(util.bigIntFits32(val)){
              capi.sqlite3_result_int(pCtx, Number(val));
            }else if(util.bigIntFitsDouble(val)){
              capi.sqlite3_result_double(pCtx, Number(val));
            }else{
              toss3("BigInt value",val.toString(),"is too BigInt.");
            }
            break;
          case 'number': {
            (util.isInt32(val)
             ? capi.sqlite3_result_int
             : capi.sqlite3_result_double)(pCtx, val);
            break;
          }
          case 'string':
            capi.sqlite3_result_text(pCtx, val, -1, capi.SQLITE_TRANSIENT);
            break;
          case 'object':
            if(null===val/*yes, typeof null === 'object'*/) {
              capi.sqlite3_result_null(pCtx);
              break;
            }else if(util.isBindableTypedArray(val)){
              const pBlob = wasm.allocFromTypedArray(val);
              capi.sqlite3_result_blob(
                pCtx, pBlob, val.byteLength,
                wasm.exports[sqlite3.config.deallocExportName]
              );
              break;
            }
            // else fall through
          default:
          toss3("Don't not how to handle this UDF result value:",(typeof val), val);
      };
    }/*__udfSetResult()*/;

    const __udfConvertArgs = function(argc, pArgv){
      let i, pVal, valType, arg;
      const tgt = [];
      for(i = 0; i < argc; ++i){
        pVal = wasm.getPtrValue(pArgv + (wasm.ptrSizeof * i));
        /**
           Curiously: despite ostensibly requiring 8-byte
           alignment, the pArgv array is parcelled into chunks of
           4 bytes (1 pointer each). The values those point to
           have 8-byte alignment but the individual argv entries
           do not.
        */            
        valType = capi.sqlite3_value_type(pVal);
        switch(valType){
            case capi.SQLITE_INTEGER:
              if(wasm.bigIntEnabled){
                arg = capi.sqlite3_value_int64(pVal);
                if(util.bigIntFitsDouble(arg)) arg = Number(arg);
              }
              else arg = capi.sqlite3_value_double(pVal)/*yes, double, for larger integers*/;
              break;
            case capi.SQLITE_FLOAT:
              arg = capi.sqlite3_value_double(pVal);
              break;
            case capi.SQLITE_TEXT:
              arg = capi.sqlite3_value_text(pVal);
              break;
            case capi.SQLITE_BLOB:{
              const n = capi.sqlite3_value_bytes(pVal);
              const pBlob = capi.sqlite3_value_blob(pVal);
              if(n && !pBlob) sqlite3.WasmAllocError.toss(
                "Cannot allocate memory for blob argument of",n,"byte(s)"
              );
              arg = n ? wasm.heap8u().slice(pBlob, pBlob + Number(n)) : null;
              break;
            }
            case capi.SQLITE_NULL:
              arg = null; break;
            default:
              toss3("Unhandled sqlite3_value_type()",valType,
                    "is possibly indicative of incorrect",
                    "pointer size assumption.");
        }
        tgt.push(arg);
      }
      return tgt;
    }/*__udfConvertArgs()*/;

    const __udfSetError = (pCtx, e)=>{
      if(e instanceof sqlite3.WasmAllocError){
        capi.sqlite3_result_error_nomem(pCtx);
      }else{
        const msg = ('string'===typeof e) ? e : e.message;
        capi.sqlite3_result_error(pCtx, msg, -1);
      }
    };

    const __xFunc = function(callback){
      return function(pCtx, argc, pArgv){
        try{ __udfSetResult(pCtx, callback(pCtx, ...__udfConvertArgs(argc, pArgv))) }
        catch(e){
          //console.error('xFunc() caught:',e);
          __udfSetError(pCtx, e);
        }
      };
    };

    const __xInverseAndStep = function(callback){
      return function(pCtx, argc, pArgv){
        try{ callback(pCtx, ...__udfConvertArgs(argc, pArgv)) }
        catch(e){ __udfSetError(pCtx, e) }
      };
    };

    const __xFinalAndValue = function(callback){
      return function(pCtx){
        try{ __udfSetResult(pCtx, callback(pCtx)) }
        catch(e){ __udfSetError(pCtx, e) }
      };
    };

    const __xDestroy = function(callback){
      return function(pVoid){
        try{ callback(pVoid) }
        catch(e){ console.error("UDF xDestroy method threw:",e) }
      };
    };

    const __xMap = Object.assign(Object.create(null), {
      xFunc:    {sig:'v(pip)', f:__xFunc},
      xStep:    {sig:'v(pip)', f:__xInverseAndStep},
      xInverse: {sig:'v(pip)', f:__xInverseAndStep},
      xFinal:   {sig:'v(p)',   f:__xFinalAndValue},
      xValue:   {sig:'v(p)',   f:__xFinalAndValue},
      xDestroy: {sig:'v(p)',   f:__xDestroy}
    });

    const __xWrapFuncs = function(theFuncs, tgtUninst){
      const rc = []
      let k;
      for(k in theFuncs){
        let fArg = theFuncs[k];
        if('function'===typeof fArg){
          const w = __xMap[k];
          fArg = wasm.installFunction(w.sig, w.f(fArg));
          tgtUninst.push(fArg);
        }
        rc.push(fArg);
      }
      return rc;
    };

    /* Documented in the api object's initializer. */
    capi.sqlite3_create_function_v2 = function f(
      pDb, funcName, nArg, eTextRep, pApp,
      xFunc,   //void (*xFunc)(sqlite3_context*,int,sqlite3_value**)
      xStep,   //void (*xStep)(sqlite3_context*,int,sqlite3_value**)
      xFinal,  //void (*xFinal)(sqlite3_context*)
      xDestroy //void (*xDestroy)(void*)
    ){
      if(f.length!==arguments.length){
        return __dbArgcMismatch(pDb,"sqlite3_create_function_v2",f.length);
      }
      /* Wrap the callbacks in a WASM-bound functions... */
      const uninstall = [/*funcs to uninstall on error*/];
      let rc;
      try{
        const funcArgs =  __xWrapFuncs({xFunc, xStep, xFinal, xDestroy},
                                       uninstall);
        rc = sqlite3CreateFunction(pDb, funcName, nArg, eTextRep,
                                   pApp, ...funcArgs);
      }catch(e){
        console.error("sqlite3_create_function_v2() setup threw:",e);
        for(let v of uninstall){
          wasm.uninstallFunction(v);
        }
        rc = util.sqlite3_wasm_db_error(pDb, capi.SQLITE_ERROR,
                                        "Creation of UDF threw: "+e.message);
      }
      return rc;
    };

    capi.sqlite3_create_function = function f(
      pDb, funcName, nArg, eTextRep, pApp,
      xFunc, xStep, xFinal
    ){
      return (f.length===arguments.length)
        ? capi.sqlite3_create_function_v2(pDb, funcName, nArg, eTextRep,
                                          pApp, xFunc, xStep, xFinal, 0)
        : __dbArgcMismatch(pDb,"sqlite3_create_function",f.length);
    };

    /* Documented in the api object's initializer. */
    capi.sqlite3_create_window_function = function f(
      pDb, funcName, nArg, eTextRep, pApp,
      xStep,   //void (*xStep)(sqlite3_context*,int,sqlite3_value**)
      xFinal,  //void (*xFinal)(sqlite3_context*)
      xValue,  //void (*xFinal)(sqlite3_context*)
      xInverse,//void (*xStep)(sqlite3_context*,int,sqlite3_value**)
      xDestroy //void (*xDestroy)(void*)
    ){
      if(f.length!==arguments.length){
        return __dbArgcMismatch(pDb,"sqlite3_create_window_function",f.length);
      }
      /* Wrap the callbacks in a WASM-bound functions... */
      const uninstall = [/*funcs to uninstall on error*/];
      let rc;
      try{
        const funcArgs = __xWrapFuncs({xStep, xFinal, xValue, xInverse, xDestroy},
                                      uninstall);
        rc = sqlite3CreateWindowFunction(pDb, funcName, nArg, eTextRep,
                                         pApp, ...funcArgs);
      }catch(e){
        console.error("sqlite3_create_window_function() setup threw:",e);
        for(let v of uninstall){
          wasm.uninstallFunction(v);
        }
        rc = util.sqlite3_wasm_db_error(pDb, capi.SQLITE_ERROR,
                                        "Creation of UDF threw: "+e.message);
      }
      return rc;
    };
    /**
       A helper for UDFs implemented in JS and bound to WASM by the
       client. Given a JS value, udfSetResult(pCtx,X) calls one of the
       sqlite3_result_xyz(pCtx,...)  routines, depending on X's data
       type:

       - `null`: sqlite3_result_null()
       - `boolean`: sqlite3_result_int()
       - `number`: sqlite3_result_int() or sqlite3_result_double()
       - `string`: sqlite3_result_text()
       - Uint8Array or Int8Array: sqlite3_result_blob()
       - `undefined`: indicates that the UDF called one of the
         `sqlite3_result_xyz()` routines on its own, making this
         function a no-op. Results are _undefined_ if this function is
         passed the `undefined` value but did _not_ call one of the
         `sqlite3_result_xyz()` routines.

       Anything else triggers sqlite3_result_error().
    */
    capi.sqlite3_create_function_v2.udfSetResult =
      capi.sqlite3_create_function.udfSetResult =
      capi.sqlite3_create_window_function.udfSetResult = __udfSetResult;

    /**
       A helper for UDFs implemented in JS and bound to WASM by the
       client. When passed the
       (argc,argv) values from the UDF-related functions which receive
       them (xFunc, xStep, xInverse), it creates a JS array
       representing those arguments, converting each to JS in a manner
       appropriate to its data type: numeric, text, blob
       (Uint8Array), or null.

       Results are undefined if it's passed anything other than those
       two arguments from those specific contexts.

       Thus an argc of 4 will result in a length-4 array containing
       the converted values from the corresponding argv.

       The conversion will throw only on allocation error or an internal
       error.
    */
    capi.sqlite3_create_function_v2.udfConvertArgs =
      capi.sqlite3_create_function.udfConvertArgs =
      capi.sqlite3_create_window_function.udfConvertArgs = __udfConvertArgs;

    /**
       A helper for UDFs implemented in JS and bound to WASM by the
       client. It expects to be a passed `(sqlite3_context*, Error)`
       (an exception object or message string). And it sets the
       current UDF's result to sqlite3_result_error_nomem() or
       sqlite3_result_error(), depending on whether the 2nd argument
       is a sqlite3.WasmAllocError object or not.
    */
    capi.sqlite3_create_function_v2.udfSetError =
      capi.sqlite3_create_function.udfSetError =
      capi.sqlite3_create_window_function.udfSetError = __udfSetError;

  }/*sqlite3_create_function_v2() and sqlite3_create_window_function() proxies*/;

  if(1){/* Special-case handling of sqlite3_prepare_v2() and
           sqlite3_prepare_v3() */
    /**
       Scope-local holder of the two impls of sqlite3_prepare_v2/v3().
    */
    const __prepare = Object.create(null);
    /**
       This binding expects a JS string as its 2nd argument and
       null as its final argument. In order to compile multiple
       statements from a single string, the "full" impl (see
       below) must be used.
    */
    __prepare.basic = wasm.xWrap('sqlite3_prepare_v3',
                                 "int", ["sqlite3*", "string",
                                         "int"/*ignored for this impl!*/,
                                         "int", "**",
                                         "**"/*MUST be 0 or null or undefined!*/]);
    /**
       Impl which requires that the 2nd argument be a pointer
       to the SQL string, instead of being converted to a
       string. This variant is necessary for cases where we
       require a non-NULL value for the final argument
       (exec()'ing multiple statements from one input
       string). For simpler cases, where only the first
       statement in the SQL string is required, the wrapper
       named sqlite3_prepare_v2() is sufficient and easier to
       use because it doesn't require dealing with pointers.
    */
    __prepare.full = wasm.xWrap('sqlite3_prepare_v3',
                                "int", ["sqlite3*", "*", "int", "int",
                                        "**", "**"]);

    /* Documented in the api object's initializer. */
    capi.sqlite3_prepare_v3 = function f(pDb, sql, sqlLen, prepFlags, ppStmt, pzTail){
      if(f.length!==arguments.length){
        return __dbArgcMismatch(pDb,"sqlite3_prepare_v3",f.length);
      }
      const [xSql, xSqlLen] = __flexiString(sql, sqlLen);
      switch(typeof xSql){
          case 'string': return __prepare.basic(pDb, xSql, xSqlLen, prepFlags, ppStmt, null);
          case 'number': return __prepare.full(pDb, xSql, xSqlLen, prepFlags, ppStmt, pzTail);
          default:
            return util.sqlite3_wasm_db_error(
              pDb, capi.SQLITE_MISUSE,
              "Invalid SQL argument type for sqlite3_prepare_v2/v3()."
            );
      }
    };

    /* Documented in the api object's initializer. */
    capi.sqlite3_prepare_v2 = function f(pDb, sql, sqlLen, ppStmt, pzTail){
      return (f.length===arguments.length)
        ? capi.sqlite3_prepare_v3(pDb, sql, sqlLen, 0, ppStmt, pzTail)
        : __dbArgcMismatch(pDb,"sqlite3_prepare_v2",f.length);
    };
  }/*sqlite3_prepare_v2/v3()*/;

  {/* Import C-level constants and structs... */
    const cJson = wasm.xCall('sqlite3_wasm_enum_json');
    if(!cJson){
      toss("Maintenance required: increase sqlite3_wasm_enum_json()'s",
           "static buffer size!");
    }
    wasm.ctype = JSON.parse(wasm.cstringToJs(cJson));
    //console.debug('wasm.ctype length =',wasm.cstrlen(cJson));
    for(const t of ['access', 'blobFinalizers', 'dataTypes',
                    'encodings', 'fcntl', 'flock', 'ioCap',
                    'openFlags', 'prepareFlags', 'resultCodes',
                    'serialize', 'syncFlags', 'trace', 'udfFlags',
                    'version'
                   ]){
      for(const e of Object.entries(wasm.ctype[t])){
        // ^^^ [k,v] there triggers a buggy code transormation via one
        // of the Emscripten-driven optimizers.
        capi[e[0]] = e[1];
      }
    }
    const __rcMap = Object.create(null);
    for(const t of ['resultCodes']){
      for(const e of Object.entries(wasm.ctype[t])){
        __rcMap[e[1]] = e[0];
      }
    }
    /**
       For the given integer, returns the SQLITE_xxx result code as a
       string, or undefined if no such mapping is found.
    */
    capi.sqlite3_js_rc_str = (rc)=>__rcMap[rc];
    /* Bind all registered C-side structs... */
    const notThese = Object.assign(Object.create(null),{
      // Structs NOT to register
      WasmTestStruct: true
    });
    if(!util.isUIThread()){
      /* We remove the kvvfs VFS from Worker threads below. */
      notThese.sqlite3_kvvfs_methods = true;
    }
    for(const s of wasm.ctype.structs){
      if(!notThese[s.name]){
        capi[s.name] = sqlite3.StructBinder(s);
      }
    }
  }/*end C constant imports*/

  const pKvvfs = capi.sqlite3_vfs_find("kvvfs");
  if( pKvvfs ){/* kvvfs-specific glue */
    if(util.isUIThread()){
      const kvvfsMethods = new capi.sqlite3_kvvfs_methods(
        wasm.exports.sqlite3_wasm_kvvfs_methods()
      );
      delete capi.sqlite3_kvvfs_methods;

      const kvvfsMakeKey = wasm.exports.sqlite3_wasm_kvvfsMakeKeyOnPstack,
            pstack = wasm.pstack,
            pAllocRaw = wasm.exports.sqlite3_wasm_pstack_alloc;

      const kvvfsStorage = (zClass)=>
            ((115/*=='s'*/===wasm.getMemValue(zClass))
             ? sessionStorage : localStorage);
      
      const kvvfsImpls = {
        xRead: (zClass, zKey, zBuf, nBuf)=>{
          const stack = pstack.pointer,
                astack = wasm.scopedAllocPush();
          try {
            const zXKey = kvvfsMakeKey(zClass,zKey);
            if(!zXKey) return -3/*OOM*/;
            const jKey = wasm.cstringToJs(zXKey);
            const jV = kvvfsStorage(zClass).getItem(jKey);
            if(!jV) return -1;
            const nV = jV.length /* Note that we are relying 100% on v being
                                    ASCII so that jV.length is equal to the
                                    C-string's byte length. */;
            if(nBuf<=0) return nV;
            else if(1===nBuf){
              wasm.setMemValue(zBuf, 0);
              return nV;
            }
            const zV = wasm.scopedAllocCString(jV);
            if(nBuf > nV + 1) nBuf = nV + 1;
            wasm.heap8u().copyWithin(zBuf, zV, zV + nBuf - 1);
            wasm.setMemValue(zBuf + nBuf - 1, 0);
            return nBuf - 1;
          }catch(e){
            console.error("kvstorageRead()",e);
            return -2;
          }finally{
            pstack.restore(stack);
            wasm.scopedAllocPop(astack);
          }
        },
        xWrite: (zClass, zKey, zData)=>{
          const stack = pstack.pointer;
          try {
            const zXKey = kvvfsMakeKey(zClass,zKey);
            if(!zXKey) return 1/*OOM*/;
            const jKey = wasm.cstringToJs(zXKey);
            kvvfsStorage(zClass).setItem(jKey, wasm.cstringToJs(zData));
            return 0;
          }catch(e){
            console.error("kvstorageWrite()",e);
            return capi.SQLITE_IOERR;
          }finally{
            pstack.restore(stack);
          }
        },
        xDelete: (zClass, zKey)=>{
          const stack = pstack.pointer;
          try {
            const zXKey = kvvfsMakeKey(zClass,zKey);
            if(!zXKey) return 1/*OOM*/;
            kvvfsStorage(zClass).removeItem(wasm.cstringToJs(zXKey));
            return 0;
          }catch(e){
            console.error("kvstorageDelete()",e);
            return capi.SQLITE_IOERR;
          }finally{
            pstack.restore(stack);
          }
        }
      }/*kvvfsImpls*/;
      for(let k of Object.keys(kvvfsImpls)){
        kvvfsMethods[kvvfsMethods.memberKey(k)] =
          wasm.installFunction(
            kvvfsMethods.memberSignature(k),
            kvvfsImpls[k]
          );
      }
    }else{
      /* Worker thread: unregister kvvfs to avoid it being used
         for anything other than local/sessionStorage. It "can"
         be used that way but it's not really intended to be. */
      capi.sqlite3_vfs_unregister(pKvvfs);
    }
  }/*pKvvfs*/

});