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/* eslint-disable no-bitwise -- Convenient */
import jsep from 'jsep';
import jsepRegex from '@jsep-plugin/regex';
import jsepAssignment from '@jsep-plugin/assignment';
// register plugins
jsep.plugins.register(jsepRegex, jsepAssignment);
jsep.addUnaryOp('typeof');
jsep.addUnaryOp('void');
jsep.addLiteral('null', null);
jsep.addLiteral('undefined', undefined);
const BLOCKED_PROTO_PROPERTIES = new Set([
'constructor',
'__proto__',
'__defineGetter__',
'__defineSetter__',
'__lookupGetter__',
'__lookupSetter__'
]);
const SafeEval = {
/**
* @param {jsep.Expression} ast
* @param {Record<string, any>} subs
*/
evalAst (ast, subs) {
switch (ast.type) {
case 'BinaryExpression':
case 'LogicalExpression':
return SafeEval.evalBinaryExpression(ast, subs);
case 'Compound':
return SafeEval.evalCompound(ast, subs);
case 'ConditionalExpression':
return SafeEval.evalConditionalExpression(ast, subs);
case 'Identifier':
return SafeEval.evalIdentifier(ast, subs);
case 'Literal':
return SafeEval.evalLiteral(ast, subs);
case 'MemberExpression':
return SafeEval.evalMemberExpression(ast, subs);
case 'UnaryExpression':
return SafeEval.evalUnaryExpression(ast, subs);
case 'ArrayExpression':
return SafeEval.evalArrayExpression(ast, subs);
case 'CallExpression':
return SafeEval.evalCallExpression(ast, subs);
case 'AssignmentExpression':
return SafeEval.evalAssignmentExpression(ast, subs);
default:
throw SyntaxError('Unexpected expression', ast);
}
},
evalBinaryExpression (ast, subs) {
const result = {
'||': (a, b) => a || b(),
'&&': (a, b) => a && b(),
'|': (a, b) => a | b(),
'^': (a, b) => a ^ b(),
'&': (a, b) => a & b(),
// eslint-disable-next-line eqeqeq -- API
'==': (a, b) => a == b(),
// eslint-disable-next-line eqeqeq -- API
'!=': (a, b) => a != b(),
'===': (a, b) => a === b(),
'!==': (a, b) => a !== b(),
'<': (a, b) => a < b(),
'>': (a, b) => a > b(),
'<=': (a, b) => a <= b(),
'>=': (a, b) => a >= b(),
'<<': (a, b) => a << b(),
'>>': (a, b) => a >> b(),
'>>>': (a, b) => a >>> b(),
'+': (a, b) => a + b(),
'-': (a, b) => a - b(),
'*': (a, b) => a * b(),
'/': (a, b) => a / b(),
'%': (a, b) => a % b()
}[ast.operator](
SafeEval.evalAst(ast.left, subs),
() => SafeEval.evalAst(ast.right, subs)
);
return result;
},
evalCompound (ast, subs) {
let last;
for (let i = 0; i < ast.body.length; i++) {
if (
ast.body[i].type === 'Identifier' &&
['var', 'let', 'const'].includes(ast.body[i].name) &&
ast.body[i + 1] &&
ast.body[i + 1].type === 'AssignmentExpression'
) {
// var x=2; is detected as
// [{Identifier var}, {AssignmentExpression x=2}]
// eslint-disable-next-line @stylistic/max-len -- Long
// eslint-disable-next-line sonarjs/updated-loop-counter -- Convenient
i += 1;
}
const expr = ast.body[i];
last = SafeEval.evalAst(expr, subs);
}
return last;
},
evalConditionalExpression (ast, subs) {
if (SafeEval.evalAst(ast.test, subs)) {
return SafeEval.evalAst(ast.consequent, subs);
}
return SafeEval.evalAst(ast.alternate, subs);
},
evalIdentifier (ast, subs) {
if (Object.hasOwn(subs, ast.name)) {
return subs[ast.name];
}
throw ReferenceError(`${ast.name} is not defined`);
},
evalLiteral (ast) {
return ast.value;
},
evalMemberExpression (ast, subs) {
const prop = String(
// NOTE: `String(value)` throws error when
// value has overwritten the toString method to return non-string
// i.e. `value = {toString: () => []}`
ast.computed
? SafeEval.evalAst(ast.property) // `object[property]`
: ast.property.name // `object.property` property is Identifier
);
const obj = SafeEval.evalAst(ast.object, subs);
if (obj === undefined || obj === null) {
throw TypeError(
`Cannot read properties of ${obj} (reading '${prop}')`
);
}
if (!Object.hasOwn(obj, prop) && BLOCKED_PROTO_PROPERTIES.has(prop)) {
throw TypeError(
`Cannot read properties of ${obj} (reading '${prop}')`
);
}
const result = obj[prop];
if (typeof result === 'function') {
return result.bind(obj); // arrow functions aren't affected by bind.
}
return result;
},
evalUnaryExpression (ast, subs) {
const result = {
'-': (a) => -SafeEval.evalAst(a, subs),
'!': (a) => !SafeEval.evalAst(a, subs),
'~': (a) => ~SafeEval.evalAst(a, subs),
// eslint-disable-next-line no-implicit-coercion -- API
'+': (a) => +SafeEval.evalAst(a, subs),
typeof: (a) => typeof SafeEval.evalAst(a, subs),
// eslint-disable-next-line no-void, sonarjs/void-use -- feature
void: (a) => void SafeEval.evalAst(a, subs)
}[ast.operator](ast.argument);
return result;
},
evalArrayExpression (ast, subs) {
return ast.elements.map((el) => SafeEval.evalAst(el, subs));
},
evalCallExpression (ast, subs) {
const args = ast.arguments.map((arg) => SafeEval.evalAst(arg, subs));
const func = SafeEval.evalAst(ast.callee, subs);
/* c8 ignore start */
if (func === Function) {
// unreachable since BLOCKED_PROTO_PROPERTIES includes 'constructor'
throw new Error('Function constructor is disabled');
}
/* c8 ignore end */
return func(...args);
},
evalAssignmentExpression (ast, subs) {
if (ast.left.type !== 'Identifier') {
throw SyntaxError('Invalid left-hand side in assignment');
}
const id = ast.left.name;
const value = SafeEval.evalAst(ast.right, subs);
subs[id] = value;
return subs[id];
}
};
/**
* A replacement for NodeJS' VM.Script which is also {@link https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP | Content Security Policy} friendly.
*/
class SafeScript {
/**
* @param {string} expr Expression to evaluate
*/
constructor (expr) {
this.code = expr;
this.ast = jsep(this.code);
}
/**
* @param {object} context Object whose items will be added
* to evaluation
* @returns {EvaluatedResult} Result of evaluated code
*/
runInNewContext (context) {
// `Object.create(null)` creates a prototypeless object
const keyMap = Object.assign(Object.create(null), context);
return SafeEval.evalAst(this.ast, keyMap);
}
}
export {SafeScript};