valia/src/testers/utils.ts

A runtime data validator in TypeScript with advanced type inference, built-in validation functions, and seamless integration for server and client environments.

import { LooseAutocomplete } from "../types";
import { StandardTags } from "./types";

const supportWeakRef = typeof WeakRef !== 'undefined';
export function lazy<T extends object>(callback: () => T): () => T {
	let cache: any;
    return () => {
		if (supportWeakRef) {
			if (!cache?.deref()) {
				cache = new WeakRef(callback());
			}
			return (cache?.deref());
		} else if (!cache) {
			cache = callback();
		}
        return (cache);
    };
}

export function hasTag(x: unknown, tag: LooseAutocomplete<StandardTags>): boolean {
	return (Object.prototype.toString.call(x).slice(8, -1) === tag);
}

/**
 * @see https://www.garykessler.net/library/file_sigs.html
 * @see https://en.wikipedia.org/wiki/List_of_file_signatures
 */
const signatures = [
	// Image
	{ ext: "png" as const, offset: 0, flags: ["89504E470D0A1A0A"]},
	{ ext: "jpg" as const, offset: 0, flags: ["FFD8FFE0"]},
	{ ext: "jp2" as const, offset: 0, flags: ["0000000C6A5020200D0A870A"]},
	{ ext: "gif" as const, offset: 0, flags: ["474946383761", "474946383961"]},
	{ ext: "webp" as const, offset: 0, flags: ["52494646????????57454250"]},
	// Audio
	{ ext: "mp3" as const, offset: 0, flags: ["FFFB", "FFF3", "FFF2", "494433"]},
	{ ext: "mp4" as const, offset: 4, flags: ["6674797069736F6D", "667479704D534E56"]},
	// 3D
	{ ext: "stl" as const, offset: 4, flags: ["736F6C6964"]}
];

export function hasFileSignature(hex: string, extensions: Array<(typeof signatures)[number]['ext']>) {
	for (let i = 0; i < extensions.length; i++) {
		const { offset, flags } = signatures.find(({ ext }) => ext === extensions[i])!;

		for (let i = 0; i < flags.length; i++) {
			const flag = flags[i];
			let j = (flag.length - 1) + offset;

			if (j >= hex.length) continue;
			while (j >= 0) {
				if (flag[j] !== "?" && hex[j] !== flag[j]) break;
				j--;
			}
			if (j === 0) return (true);
		}
	}
}