الـ Buffers والبيانات الـ binary: الـ bytes من جُوّه

const buf = Buffer.from("Hi مُنى", "utf8");

console.log(buf);
console.log(buf.length, "bytes", [..."Hi مُنى"].length, "characters");
console.log(buf[0], buf[0].toString(2).padStart(8, "0"), String.fromCharCode(buf[0]));

console.log(buf.toString("hex"));
console.log(buf.toString("base64"));
console.log(Buffer.from("a+b/c?", "utf8").toString("base64url"));
console.log(Buffer.from(buf.toString("base64"), "base64").toString("utf8"));

$ node main.js
<Buffer 48 69 20 d9 85 d9 8f d9 86 d9 89>
11 bytes 7 characters
72 01001000 H
486920d985d98fd986d989
SGkg2YXZj9mG2Yk=
YStiL2M_
Hi مُنى

const original = Buffer.from("secret-token");
const view = original.subarray(0, 6);
const copy = Buffer.from(original.subarray(0, 6));

view[0] = 0x53; // S
console.log(original.toString(), "| view:", view.toString(), "| copy:", copy.toString());

// alloc بتصفّر، allocUnsafe ممكن يكون فيها بيانات قديمة
console.log(Buffer.alloc(4), Buffer.alloc(4, 0xff));

$ node main.js
Secret-token | view: Secret | copy: secret
<Buffer 00 00 00 00> <Buffer ff ff ff ff>

const text = "أهلًا";
const bytes = Buffer.from(text);
// الشبكة ممكن تقسم الكلام في نص حرف
const chunks = [bytes.subarray(0, 3), bytes.subarray(3)];

let wrong = "";
for (const c of chunks) wrong += c.toString();
console.log("غلط:", wrong);

console.log("صح:", Buffer.concat(chunks).toString());

const decoder = new TextDecoder("utf-8");
let streamed = "";
for (const c of chunks) streamed += decoder.decode(c, { stream: true });
streamed += decoder.decode();
console.log("صح (stream):", streamed);

$ node main.js
غلط: أ��لًا
صح: أهلًا
صح (stream): أهلًا

// رسالة binary: [نوع 1 byte][طول 4 bytes][البيانات]
function encode(type, payload) {
  const body = Buffer.from(JSON.stringify(payload));
  const header = Buffer.alloc(5);
  header.writeUInt8(type, 0);
  header.writeUInt32BE(body.length, 1);
  return Buffer.concat([header, body]);
}

function decode(buf) {
  const type = buf.readUInt8(0);
  const length = buf.readUInt32BE(1);
  const payload = JSON.parse(buf.subarray(5, 5 + length).toString());
  return { type, length, payload };
}

const msg = encode(2, { event: "order.paid", id: 7 });
console.log(msg.subarray(0, 5));
console.log(decode(msg));

$ node main.js
<Buffer 02 00 00 00 1d>
{ type: 2, length: 29, payload: { event: 'order.paid', id: 7 } }

// أول bytes في أي ملف بتقول نوعه الحقيقي (magic numbers)
const uploads = [
  { name: "avatar.png", data: Buffer.from("89504e470d0a1a0a0000000d49484452", "hex") },
  { name: "photo.jpg", data: Buffer.from("ffd8ffe000104a464946", "hex") },
  { name: "cv.pdf", data: Buffer.from("%PDF-1.7\n%...") },
  { name: "cat.png", data: Buffer.from("<?php system($_GET['c']); ?>") },
  { name: "tiny.png", data: Buffer.from([0x89, 0x50]) },
];


import path from "node:path";

const SIGNATURES = {
  png: Buffer.from("89504e470d0a1a0a", "hex"),
  jpg: Buffer.from("ffd8ff", "hex"),
  pdf: Buffer.from("25504446", "hex"),
};

function sniff(buf) {
  for (const [type, sig] of Object.entries(SIGNATURES)) {
    if (buf.subarray(0, sig.length).equals(sig)) return type;
  }
  return null;
}

function check(file) {
  let ext = path.extname(file.name).slice(1).toLowerCase();
  if (ext === "jpeg") ext = "jpg";
  const real = sniff(file.data);
  return real === ext ? "ok" : `رفض (النوع الحقيقي: ${real})`;
}

for (const f of uploads) console.log(f.name, "←", check(f));

$ node main.js
avatar.png ← ok
photo.jpg ← ok
cv.pdf ← ok
cat.png ← رفض (النوع الحقيقي: null)
tiny.png ← رفض (النوع الحقيقي: null)