fix: fix wrong length number write to packet

lib/packets/packet.js

@@ -831,11 +831,10 @@ class Packet {
     if (n === null) {
       return this.writeInt8(0xfb);
     }
-    // TODO: check that n is out of int precision
     this.writeInt8(0xfe);
-    this.buffer.writeUInt32LE(n, this.offset);
+    this.buffer.writeUInt32LE(n >>> 0, this.offset);
     this.offset += 4;
-    this.buffer.writeUInt32LE(n >> 32, this.offset);
+    this.buffer.writeUInt32LE(Math.floor(n / 0x100000000), this.offset);
     this.offset += 4;
     return this.offset;
   }

test/unit/packets/test-length-coded-number.test.mts

@@ -0,0 +1,41 @@
+import { assert, describe, it } from 'poku';
+import Packet from '../../../lib/packets/packet.js';
+
+describe('writeLengthCodedNumber / readLengthCodedNumber roundtrip', () => {
+  const roundtrip = (n: number): number | null => {
+    const size = 4 + Packet.lengthCodedNumberLength(n);
+    const buffer = Buffer.alloc(size);
+    const packet = new Packet(0, buffer, 0, size);
+
+    packet.writeLengthCodedNumber(n);
+    packet.offset = 4;
+
+    return packet.readLengthCodedNumber();
+  };
+
+  it('should roundtrip values in the 1-byte range', () => {
+    assert.strictEqual(roundtrip(0), 0);
+    assert.strictEqual(roundtrip(250), 250);
+  });
+
+  it('should roundtrip values in the 2-byte range (0xFC tag)', () => {
+    assert.strictEqual(roundtrip(251), 251);
+    assert.strictEqual(roundtrip(0xfffe), 0xfffe);
+  });
+
+  it('should roundtrip values in the 3-byte range (0xFD tag)', () => {
+    assert.strictEqual(roundtrip(0xffff), 0xffff);
+    assert.strictEqual(roundtrip(0xfffffe), 0xfffffe);
+  });
+
+  it('should roundtrip values >= 0xFFFFFF in the 8-byte range (0xFE tag)', () => {
+    assert.strictEqual(roundtrip(0xffffff), 0xffffff);
+    assert.strictEqual(roundtrip(0x2000000), 0x2000000); // 32MB: PR #3177
+    assert.strictEqual(roundtrip(0xffffffff), 0xffffffff);
+  });
+
+  it('should roundtrip values above 32-bit range', () => {
+    assert.strictEqual(roundtrip(0x100000001), 0x100000001);
+    assert.strictEqual(roundtrip(0x1ffffffffff), 2199023255551);
+  });
+});