reverse-engineering-anything/src/native/AppleDispatchMetadata.test.ts

import { describe, expect, it } from "vitest";
import { decodeAppleDispatchMetadata } from "./AppleDispatchMetadata.js";

const base = 0x100000000n;
const fixture = (relative = false) => {
  const bytes = Buffer.alloc(2048);
  const u32 = (offset: number, value: number) =>
    bytes.writeUInt32LE(value, offset);
  const ptr = (offset: number, target: number) =>
    bytes.writeBigUInt64LE(base + BigInt(target), offset);
  u32(0, 0xfeedfacf);
  u32(4, 0x0100000c);
  u32(16, 1);
  u32(20, 152);
  u32(32, 0x19);
  u32(36, 152);
  bytes.write("__DATA", 40);
  ptr(56, 0);
  bytes.writeBigUInt64LE(2048n, 64);
  bytes.writeBigUInt64LE(2048n, 80);
  u32(92, 5);
  u32(96, 1);
  bytes.write("__objc_classlist", 104);
  bytes.write("__DATA", 120);
  ptr(136, 0x180);
  bytes.writeBigUInt64LE(8n, 144);
  u32(152, 0x180);
  ptr(0x180, 0x200);
  ptr(0x200, 0x280);
  ptr(0x220, 0x300);
  ptr(0x2a0, 0x380);
  u32(0x308, 16);
  ptr(0x318, 0x450);
  ptr(0x320, 0x480);
  ptr(0x330, 0x500);
  u32(0x380, 1);
  ptr(0x398, 0x450);
  bytes.write("Fixture\0", 0x450);
  bytes.write("performAction:\0", 0x460);
  u32(0x480, relative ? 0xc000000c : 24);
  u32(0x484, 1);
  if (relative) {
    bytes.writeInt32LE(0x460 - 0x488, 0x488);
    bytes.writeInt32LE(0x5c0 - 0x48c, 0x48c);
    bytes.writeInt32LE(0x700 - 0x490, 0x490);
  } else {
    ptr(0x488, 0x460);
    ptr(0x490, 0x5c0);
    ptr(0x498, 0x700);
  }
  u32(0x500, 32);
  u32(0x504, 1);
  ptr(0x508, 0x580);
  ptr(0x510, 0x5a0);
  ptr(0x518, 0x5c0);
  u32(0x580, 8);
  bytes.write("state\0", 0x5a0);
  bytes.write("i\0", 0x5c0);
  return bytes;
};
const provenance = { path: "/fixture/app", sha256: "a".repeat(64) };
describe("Apple dispatch binary metadata", () => {
  it.each([false, true])(
    "decodes stripped absolute/relative method lists (relative=%s) with exact offsets",
    (relative) => {
      const result = decodeAppleDispatchMetadata(
        fixture(relative),
        100,
        provenance,
      );
      expect(result.objc_classes).toMatchObject([
        {
          name: "Fixture",
          instance_size: 16,
          location: { address: "0x100000200", file_offset: 512 },
        },
        { name: "Fixture", is_meta_class: true },
      ]);
      expect(result.objc_dispatch_implementations).toMatchObject([
        {
          selector: "performAction:",
          implementation_address: "0x100000700",
          location: { file_offset: 0x488 },
          decode: { status: "decoded" },
        },
      ]);
      expect(result.objc_ivars).toMatchObject([
        {
          name: "state",
          type_encoding: "i",
          offset: 8,
          location: { file_offset: 0x508 },
        },
      ]);
    },
  );
  it("keeps unsupported pointers and record truncation explicit", () => {
    const bytes = fixture();
    bytes.writeBigUInt64LE(0xffffffffffffffffn, 0x498);
    const result = decodeAppleDispatchMetadata(bytes, 100, provenance);
    expect(result.objc_dispatch_implementations[0]).toMatchObject({
      implementation_address: null,
      decode: { status: "partial" },
    });
    expect(
      decodeAppleDispatchMetadata(fixture(), 1, provenance).coverage[0]?.reason,
    ).toContain("max_records_reached");
  });
  it("rejects malformed command and section boundaries", () => {
    const bytes = fixture();
    bytes.writeUInt32LE(7, 36);
    expect(() => decodeAppleDispatchMetadata(bytes, 100, provenance)).toThrow(
      "command size",
    );
    expect(() =>
      decodeAppleDispatchMetadata(Buffer.alloc(10), 100, provenance),
    ).toThrow("Truncated");
  });
});