helper-tools/tests/helpers/random-limits-downloads.test.ts

import { describe, expect, it, vi } from "vitest";

import {
  HelperLimitError,
  assertBoundedBytes,
  assertBoundedItems,
  assertBoundedText,
  createObjectUrlLease,
  createSeededRandom,
  sanitizeDownloadFilename,
  secureRandomBytes,
  secureRandomInt,
  shuffleSeeded,
  triggerBlobDownload,
} from "../../src/helpers";

describe("shared ceilings and download safety", () => {
  it("reports actual and configured bounds", () => {
    expect(() => assertBoundedText("123", 2)).toThrow(HelperLimitError);
    expect(() => assertBoundedBytes(new Uint8Array(3), 2)).toThrow(/limit/u);
    expect(() => assertBoundedItems(3, 2)).toThrow(/limit/u);
    try {
      assertBoundedText("123", 2, "Sample");
    } catch (error) {
      expect(error).toMatchObject({ actual: 3, limit: 2 });
    }
  });

  it("sanitizes filenames and revokes object URLs exactly once", () => {
    expect(sanitizeDownloadFilename("../bad:\0name?.txt")).toBe(
      "_bad__name_.txt",
    );
    expect(sanitizeDownloadFilename("...", "../fallback?.txt")).toBe(
      "_fallback_.txt",
    );
    expect(sanitizeDownloadFilename("CON.txt")).toBe("_CON.txt");
    expect(sanitizeDownloadFilename("report\u202egnp.exe")).toBe(
      "report_gnp.exe",
    );
    const emojiBoundary = sanitizeDownloadFilename(
      `${"a".repeat(179)}😀.txt`,
      "fallback.txt",
      180,
    );
    expect(emojiBoundary).not.toMatch(/[\uD800-\uDBFF]$/u);
    expect(emojiBoundary.length).toBeLessThanOrEqual(180);
    expect(() => sanitizeDownloadFilename("x", "fallback", 0)).toThrow(
      /positive/u,
    );
    const createObjectURL = vi.fn(() => "blob:test");
    const revokeObjectURL = vi.fn();
    const lease = createObjectUrlLease(new Blob(["x"]), {
      createObjectURL,
      revokeObjectURL,
    });
    expect(lease).toMatchObject({ url: "blob:test", revoked: false });
    lease.revoke();
    lease.revoke();
    expect(lease.revoked).toBe(true);
    expect(revokeObjectURL).toHaveBeenCalledOnce();
  });

  it("removes download anchors and revokes their URL on the next task", () => {
    const originalUrl = globalThis.URL;
    const createObjectURL = vi.fn(() => "blob:download");
    const revokeObjectURL = vi.fn();
    const click = vi
      .spyOn(HTMLAnchorElement.prototype, "click")
      .mockImplementation(() => undefined);
    vi.stubGlobal("URL", { createObjectURL, revokeObjectURL });
    vi.useFakeTimers();
    try {
      const lease = triggerBlobDownload(new Blob(["local"]), "../safe?.txt");
      expect(click).toHaveBeenCalledOnce();
      expect(click.mock.instances[0]).toMatchObject({
        download: "_safe_.txt",
      });
      expect(document.querySelector('a[href="blob:download"]')).toBeNull();
      expect(lease.revoked).toBe(false);
      vi.runAllTimers();
      expect(lease.revoked).toBe(true);
      expect(revokeObjectURL).toHaveBeenCalledWith("blob:download");
    } finally {
      vi.useRealTimers();
      vi.stubGlobal("URL", originalUrl);
    }
  });
});

describe("secure and seeded randomness", () => {
  it("fills secure byte requests in Web Crypto-sized chunks", () => {
    const getRandomValues = vi.fn(<T extends ArrayBufferView>(array: T) => {
      new Uint8Array(array.buffer, array.byteOffset, array.byteLength).fill(7);
      return array;
    });
    const cryptoSource = { getRandomValues } as unknown as Pick<
      Crypto,
      "getRandomValues"
    >;
    expect(secureRandomBytes(70_000, cryptoSource)).toEqual(
      new Uint8Array(70_000).fill(7),
    );
    expect(getRandomValues).toHaveBeenCalledTimes(2);
    expect(() => secureRandomBytes(2, cryptoSource, 1)).toThrow(/exceeds/u);
  });

  it("uses rejection sampling for bounded secure integers", () => {
    const samples = [0xffffffff, 7];
    const getRandomValues = <T extends ArrayBufferView>(array: T): T => {
      new Uint32Array(array.buffer, array.byteOffset, 1)[0] =
        samples.shift() ?? 0;
      return array;
    };
    expect(secureRandomInt(10, 20, { getRandomValues })).toBe(17);
  });

  it("produces reproducible seeded primitives without mutating inputs", () => {
    const first = createSeededRandom("repeatable");
    const second = createSeededRandom("repeatable");
    expect(Array.from({ length: 8 }, () => first.nextUint32())).toEqual(
      Array.from({ length: 8 }, () => second.nextUint32()),
    );
    const input = [1, 2, 3, 4, 5];
    const shuffled = shuffleSeeded(input, 42);
    expect(shuffled).toEqual(shuffleSeeded(input, 42));
    expect(shuffled).not.toEqual(input);
    expect(input).toEqual([1, 2, 3, 4, 5]);
    expect(createSeededRandom("bytes").bytes(7)).toHaveLength(7);
    const value = createSeededRandom("float").nextFloat();
    expect(value).toBeGreaterThanOrEqual(0);
    expect(value).toBeLessThan(1);
  });
});