createExif.ts

import {
    writeFile
} from "fs";

const stickerPackID = "com.snowcorp.stickerly.android.stickercontentprovider b5e7275f-f1de-4137-961f-57becfad34f2"; //not sure what this does
const googleLink = "https://play.google.com/store/apps/details?id=com.marsconstd.stickermakerforwhatsapp";
const appleLink = "https://itunes.apple.com/app/sticker-maker-studio/id1443326857";

export function createExif(packname: string, author: string, id: string) {
    const json = {
        "sticker-pack-id": stickerPackID,
        "sticker-pack-name": packname,
        "sticker-pack-publisher": author,
        "android-app-store-link": googleLink,
        "ios-app-store-link": appleLink
    };

    let length: any = JSON.stringify(json).length;
    const f = Buffer.from([0x49, 0x49, 0x2A, 0x00, 0x08, 0x00, 0x00, 0x00, 0x01, 0x00, 0x41, 0x57, 0x07, 0x00]);
    const code = [0x00,
        0x00,
        0x16,
        0x00,
        0x00,
        0x00];
    if (length > 256) {
        length = length - 256;
        code.unshift(0x01);
    } else {
        code.unshift(0x00);
    }
    const fff = Buffer.from(code);
    const ffff = Buffer.from(JSON.stringify(json));

    if (length < 16) {
        length = length.toString(16);
        length = "0" + length;
    } else {
        length = length.toString(16);
    }

    const ff = Buffer.from(length, "hex");
    const buffer = Buffer.concat([f, ff, fff, ffff]);
    writeFile(`${id}.exif`, buffer, function (err: Error) {
            if (err)
                return console.error(err);
        });
}