Netcatty/scripts/afterPackMacUuid.test.cjs

const test = require("node:test");
const assert = require("node:assert/strict");

const {
  deriveUuid,
  patchMachOBuffer,
} = require("./afterPackMacUuid.cjs");

const LC_UUID = 0x1b;
const LC_OTHER = 0x19;
const MH_MAGIC_64 = 0xfeedfacf;

// Build a minimal thin little-endian 64-bit Mach-O with two load commands:
// one dummy command and one LC_UUID carrying `uuidBytes`.
function buildThinMachO(uuidBytes) {
  const header = Buffer.alloc(32);
  header.writeUInt32LE(MH_MAGIC_64, 0); // magic
  header.writeUInt32LE(0x0100000c, 4); // cputype arm64 (value irrelevant)
  header.writeUInt32LE(0, 8); // cpusubtype
  header.writeUInt32LE(2, 12); // filetype
  header.writeUInt32LE(2, 16); // ncmds
  header.writeUInt32LE(16 + 24, 20); // sizeofcmds
  header.writeUInt32LE(0, 24); // flags
  header.writeUInt32LE(0, 28); // reserved

  const dummy = Buffer.alloc(16);
  dummy.writeUInt32LE(LC_OTHER, 0); // cmd
  dummy.writeUInt32LE(16, 4); // cmdsize
  dummy.fill(0xab, 8); // payload sentinel

  const uuidCmd = Buffer.alloc(24);
  uuidCmd.writeUInt32LE(LC_UUID, 0); // cmd
  uuidCmd.writeUInt32LE(24, 4); // cmdsize
  uuidBytes.copy(uuidCmd, 8);

  return Buffer.concat([header, dummy, uuidCmd]);
}

// Wrap one or more thin slices in a big-endian 32-bit fat binary.
function buildFatMachO(slices) {
  const headerSize = 8 + slices.length * 20;
  const header = Buffer.alloc(headerSize);
  header.writeUInt32BE(0xcafebabe, 0); // FAT_MAGIC
  header.writeUInt32BE(slices.length, 4);

  let offset = headerSize;
  const offsets = [];
  for (let i = 0; i < slices.length; i += 1) {
    const archOff = 8 + i * 20;
    header.writeUInt32BE(0x0100000c, archOff); // cputype
    header.writeUInt32BE(0, archOff + 4); // cpusubtype
    header.writeUInt32BE(offset, archOff + 8); // offset
    header.writeUInt32BE(slices[i].length, archOff + 12); // size
    header.writeUInt32BE(0, archOff + 16); // align
    offsets.push(offset);
    offset += slices[i].length;
  }

  return Buffer.concat([header, ...slices]);
}

test("deriveUuid is deterministic and 16 bytes", () => {
  const a = deriveUuid("com.netcatty.app");
  const b = deriveUuid("com.netcatty.app");
  assert.equal(a.length, 16);
  assert.ok(a.equals(b));
});

test("deriveUuid differs per appId and sets version/variant bits", () => {
  const a = deriveUuid("com.netcatty.app");
  const b = deriveUuid("com.example.other");
  assert.ok(!a.equals(b));
  assert.equal(a[6] & 0xf0, 0x50); // version 5
  assert.equal(a[8] & 0xc0, 0x80); // RFC 4122 variant
});

test("patchMachOBuffer rewrites LC_UUID in a thin Mach-O and leaves the rest intact", () => {
  const original = Buffer.alloc(16, 0x11);
  const buf = buildThinMachO(original);
  const uuid = deriveUuid("com.netcatty.app");

  const { patched, oldUuids } = patchMachOBuffer(buf, uuid);

  assert.equal(patched, 1);
  assert.equal(oldUuids[0], original.toString("hex"));
  // LC_UUID payload is now our derived uuid (uuid command starts at byte 48).
  assert.ok(buf.subarray(48 + 8, 48 + 24).equals(uuid));
  // Header magic + the dummy command's payload are untouched.
  assert.equal(buf.readUInt32LE(0), MH_MAGIC_64);
  assert.equal(buf.readUInt32LE(32), LC_OTHER);
  assert.ok(buf.subarray(32 + 8, 32 + 16).equals(Buffer.alloc(8, 0xab)));
});

test("patchMachOBuffer patches every slice of a fat binary", () => {
  const slice1 = buildThinMachO(Buffer.alloc(16, 0x22));
  const slice2 = buildThinMachO(Buffer.alloc(16, 0x33));
  const fat = buildFatMachO([slice1, slice2]);
  const uuid = deriveUuid("com.netcatty.app");

  const { patched } = patchMachOBuffer(fat, uuid);

  assert.equal(patched, 2);
});

test("patchMachOBuffer reports zero when there is no LC_UUID", () => {
  // A thin Mach-O whose single command is not LC_UUID.
  const header = Buffer.alloc(32);
  header.writeUInt32LE(MH_MAGIC_64, 0);
  header.writeUInt32LE(1, 16); // ncmds
  const cmd = Buffer.alloc(16);
  cmd.writeUInt32LE(LC_OTHER, 0);
  cmd.writeUInt32LE(16, 4);
  const buf = Buffer.concat([header, cmd]);

  const { patched } = patchMachOBuffer(buf, deriveUuid("com.netcatty.app"));
  assert.equal(patched, 0);
});