restringer/src/modules/safe/resolveProxyCalls.js

Deobfuscate Javascript with emphasis on reconstructing strings

/**
 * Remove redundant call expressions which only pass the arguments to other call expression.
 * E.g.
 * function call1(a, b) {
 *   return a + b;
 * }
 * function call2(c, d) {
 *   return call1(c, d);        // will be changed to call1(c, d);
 * }
 * function call3(e, f) {
 *   return call2(e, f);        // will be changed to call1(e, f);
 * }
 * const three = call3(1, 2);   // will be changed to call1(1, 2);
 * @param {Arborist} arb
 * @param {Function} candidateFilter (optional) a filter to apply on the candidates list
 * @return {Arborist}
 */
function resolveProxyCalls(arb, candidateFilter = () => true) {
	const relevantNodes = [
		...(arb.ast[0].typeMap.FunctionDeclaration || []),
	];
	for (let i = 0; i < relevantNodes.length; i++) {
		const n = relevantNodes[i];
		if (n?.body?.body?.[0]?.type === 'ReturnStatement' &&
		n.body.body[0].argument?.type === 'CallExpression' &&
		n.body.body[0].argument.arguments?.length === n.params?.length &&
		n.body.body[0].argument.callee.type === 'Identifier' &&
		candidateFilter(n)) {
			const funcName = n.id;
			const ret = n.body.body[0].argument;
			let transitiveArguments = true;
			try {
				for (let j = 0; j < n.params.length; j++) {
					if (n.params[j]?.name !== ret?.arguments[j]?.name) {
						transitiveArguments = false;
						break;
					}
				}
			} catch {
				transitiveArguments = false;
			}
			if (transitiveArguments) {
				for (const ref of funcName.references || []) {
					arb.markNode(ref, ret.callee);
				}
			}
		}
	}
	return arb;
}

export default resolveProxyCalls;