wehub-resource-sync
310 lines
12 KiB
Python
310 lines
12 KiB
Python
"""Unit tests for bin/fetch-widevine.py — CRX3/protobuf parsing, app-id pinning,
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signature verification, the integrity-install policy, and zip extraction.
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All offline: the network (`_resolve_crx`/`_download`) is mocked, and a minimal
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CRX3 is synthesized in-process with a throwaway RSA key (with ``APP_ID``
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monkeypatched to that key's derived id) so the real verify path is exercised
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without Google's signing key.
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"""
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import hashlib
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import importlib.util
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import io
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import os
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import struct
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import zipfile
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from pathlib import Path
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import pytest
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# bin/fetch-widevine.py isn't importable by name (hyphen + bin/ not a package).
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_FW_PATH = Path(__file__).resolve().parent.parent / "bin" / "fetch-widevine.py"
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_spec = importlib.util.spec_from_file_location("fetch_widevine", _FW_PATH)
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fw = importlib.util.module_from_spec(_spec)
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_spec.loader.exec_module(fw)
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crypto = pytest.importorskip("cryptography")
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from cryptography.hazmat.primitives import hashes, serialization # noqa: E402
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from cryptography.hazmat.primitives.asymmetric import padding, rsa # noqa: E402
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# ---------------------------------------------------------------------------
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# protobuf primitives
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# ---------------------------------------------------------------------------
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def _encode_varint(n):
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out = bytearray()
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while True:
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b = n & 0x7F
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n >>= 7
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out.append(b | (0x80 if n else 0))
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if not n:
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return bytes(out)
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def _encode_ld(field, data):
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"""Encode one length-delimited (wire type 2) protobuf field."""
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return _encode_varint((field << 3) | 2) + _encode_varint(len(data)) + data
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class TestReadVarint:
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def test_single_byte(self):
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assert fw._read_varint(b"\x00", 0) == (0, 1)
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assert fw._read_varint(b"\x7f", 0) == (127, 1)
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def test_multi_byte(self):
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# 300 = 0b100101100 -> 0xAC 0x02
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assert fw._read_varint(b"\xac\x02", 0) == (300, 2)
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def test_resumes_at_offset(self):
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buf = b"\xff" + _encode_varint(16384)
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val, i = fw._read_varint(buf, 1)
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assert val == 16384 and i == len(buf)
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def test_truncated_raises(self):
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with pytest.raises(ValueError, match="truncated"):
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fw._read_varint(b"\x80\x80", 0) # continuation bit set, runs off end
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def test_too_long_raises(self):
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with pytest.raises(ValueError, match="too long"):
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fw._read_varint(b"\x80" * 12 + b"\x01", 0)
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class TestParsePb:
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def test_length_delimited_collected_repeated(self):
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blob = _encode_ld(2, b"aa") + _encode_ld(2, b"bb") + _encode_ld(1, b"c")
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out = fw._parse_pb(blob)
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assert out[2] == [b"aa", b"bb"]
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assert out[1] == [b"c"]
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def test_skips_varint_and_fixed_fields(self):
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# field 3 varint, field 4 fixed64, field 5 fixed32, then field 1 LD
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blob = (
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_encode_varint((3 << 3) | 0) + _encode_varint(99)
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+ _encode_varint((4 << 3) | 1) + b"\x00" * 8
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+ _encode_varint((5 << 3) | 5) + b"\x00" * 4
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+ _encode_ld(1, b"x")
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)
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out = fw._parse_pb(blob)
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assert out[1] == [b"x"]
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assert 3 not in out # varint values aren't retained
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class TestArch:
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@pytest.mark.parametrize("machine", ["x86_64", "amd64", "AMD64", "x64"])
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def test_x86_64_supported(self, machine, monkeypatch):
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monkeypatch.setattr(fw.platform, "machine", lambda: machine)
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assert fw._arch() == "x64"
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@pytest.mark.parametrize("machine", ["aarch64", "arm64", "arm"])
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def test_arm_rejected_clearly(self, machine, monkeypatch):
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# Google publishes the Linux CDM for x86-64 only; arm must fail loudly.
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monkeypatch.setattr(fw.platform, "machine", lambda: machine)
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with pytest.raises(SystemExit, match="not published for linux arm64"):
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fw._arch()
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def test_unsupported_raises(self, monkeypatch):
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monkeypatch.setattr(fw.platform, "machine", lambda: "mips")
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with pytest.raises(SystemExit, match="unsupported architecture"):
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fw._arch()
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class TestAppId:
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def test_constant_is_the_real_widevine_id(self):
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# Trust anchor: a typo here would silently accept the wrong publisher.
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# This exact id is what the live component server signs against (verified
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# end-to-end against update.googleapis.com).
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assert fw.APP_ID == "oimompecagnajdejgnnjijobebaeigek"
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class TestCrxAppId:
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def test_matches_independent_computation(self):
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pub = b"some-der-bytes"
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digest = hashlib.sha256(pub).digest()[:16]
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expected = "".join(
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chr(0x61 + (b >> 4)) + chr(0x61 + (b & 0xF)) for b in digest
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)
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appid, digest16 = fw._crx_appid(pub)
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assert appid == expected
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assert digest16 == digest
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assert len(appid) == 32 # 16 bytes -> 32 chars, alphabet a..p
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assert all("a" <= c <= "p" for c in appid)
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# ---------------------------------------------------------------------------
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# CRX3 signature verification
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# ---------------------------------------------------------------------------
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def _build_crx3(privkey, archive=b"PK\x03\x04zip", *, crx_id=None, tamper=False):
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"""Synthesize a minimal, validly-signed CRX3 for the given private key."""
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pub_der = privkey.public_key().public_bytes(
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serialization.Encoding.DER,
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serialization.PublicFormat.SubjectPublicKeyInfo,
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)
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if crx_id is None:
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crx_id = hashlib.sha256(pub_der).digest()[:16]
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signed_header = _encode_ld(1, crx_id) # SignedData.crx_id
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payload = (
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b"CRX3 SignedData\x00"
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+ struct.pack("<I", len(signed_header))
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+ signed_header
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+ archive
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)
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sig = privkey.sign(payload, padding.PKCS1v15(), hashes.SHA256())
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if tamper:
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archive = archive + b"X" # invalidate the signature
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proof = _encode_ld(1, pub_der) + _encode_ld(2, sig)
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header = _encode_ld(2, proof) + _encode_ld(10000, signed_header)
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return b"Cr24" + struct.pack("<I", 3) + struct.pack("<I", len(header)) + header + archive
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@pytest.fixture(scope="module")
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def rsa_key():
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return rsa.generate_private_key(public_exponent=65537, key_size=2048)
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class TestVerifyCrx3:
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def _pin(self, monkeypatch, privkey):
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pub_der = privkey.public_key().public_bytes(
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serialization.Encoding.DER,
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serialization.PublicFormat.SubjectPublicKeyInfo,
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)
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monkeypatch.setattr(fw, "APP_ID", fw._crx_appid(pub_der)[0])
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def test_valid_signature_accepts(self, rsa_key, monkeypatch):
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self._pin(monkeypatch, rsa_key)
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assert fw._verify_crx3(_build_crx3(rsa_key)) is True
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def test_tampered_archive_rejected(self, rsa_key, monkeypatch):
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self._pin(monkeypatch, rsa_key)
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with pytest.raises(SystemExit, match="INVALID"):
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fw._verify_crx3(_build_crx3(rsa_key, tamper=True))
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def test_wrong_publisher_key_rejected(self, rsa_key, monkeypatch):
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# APP_ID pinned to a DIFFERENT key than the one that signed.
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other = rsa.generate_private_key(public_exponent=65537, key_size=2048)
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self._pin(monkeypatch, other)
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with pytest.raises(SystemExit, match="expected Widevine publisher key"):
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fw._verify_crx3(_build_crx3(rsa_key))
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def test_crx_id_mismatch_rejected(self, rsa_key, monkeypatch):
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self._pin(monkeypatch, rsa_key)
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with pytest.raises(SystemExit, match="crx_id"):
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fw._verify_crx3(_build_crx3(rsa_key, crx_id=b"\x00" * 16))
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def test_bad_magic_rejected(self, rsa_key, monkeypatch):
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self._pin(monkeypatch, rsa_key)
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with pytest.raises(SystemExit, match="bad magic"):
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fw._verify_crx3(b"NOPE" + _build_crx3(rsa_key)[4:])
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def test_too_short_rejected(self):
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# < 12 bytes: clean SystemExit, not a raw struct.error.
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with pytest.raises(SystemExit, match="too short"):
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fw._verify_crx3(b"Cr24")
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def test_returns_false_without_cryptography(self, monkeypatch):
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# Force the inner `from cryptography...` import to fail.
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import builtins
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real_import = builtins.__import__
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def fake_import(name, *a, **k):
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if name.startswith("cryptography"):
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raise ImportError("blocked for test")
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return real_import(name, *a, **k)
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monkeypatch.setattr(builtins, "__import__", fake_import)
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assert fw._verify_crx3(b"Cr24anything") is False
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# ---------------------------------------------------------------------------
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# Integrity-install policy (main): refuse only when NOTHING is verifiable
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# ---------------------------------------------------------------------------
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class TestIntegrityPolicy:
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@pytest.mark.parametrize("sig_ok,sha,should_install", [
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(True, "deadbeef", True), # Docker normal
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(True, None, True), # server omitted sha; sig still verified
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(False, "deadbeef", True), # no crypto, but sha present
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(False, None, False), # no crypto AND no sha -> REFUSE
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])
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def test_branches(self, sig_ok, sha, should_install, monkeypatch, tmp_path):
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monkeypatch.setattr(fw.platform, "system", lambda: "Linux")
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monkeypatch.setattr(fw, "_arch", lambda: "x64")
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monkeypatch.setattr(fw, "_resolve_crx", lambda arch: ("9.9.9", "https://x/crx", sha))
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monkeypatch.setattr(fw, "_download", lambda url, s: b"BLOB")
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monkeypatch.setattr(fw, "_verify_crx3", lambda blob: sig_ok)
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extracted = {}
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monkeypatch.setattr(fw, "_extract", lambda blob, arch, out: extracted.setdefault("out", out))
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out = tmp_path / "WidevineCdm"
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if should_install:
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assert fw.main(["--out", str(out), "--quiet"]) == 0
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assert extracted["out"] == os.path.abspath(str(out))
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else:
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with pytest.raises(SystemExit, match="refusing to install"):
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fw.main(["--out", str(out), "--quiet"])
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assert "out" not in extracted # never reached extraction
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def test_cache_hit_skips_download(self, monkeypatch, tmp_path):
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monkeypatch.setattr(fw.platform, "system", lambda: "Linux")
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out = tmp_path / "WidevineCdm"
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out.mkdir()
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(out / "manifest.json").write_text("{}")
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called = {"n": 0}
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monkeypatch.setattr(fw, "_resolve_crx", lambda arch: called.__setitem__("n", called["n"] + 1))
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assert fw.main(["--out", str(out), "--quiet"]) == 0
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assert called["n"] == 0 # short-circuited before any network
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def test_non_linux_refuses(self, monkeypatch, tmp_path):
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monkeypatch.setattr(fw.platform, "system", lambda: "Darwin")
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with pytest.raises(SystemExit, match="Linux-only"):
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fw.main(["--out", str(tmp_path / "WidevineCdm"), "--quiet"])
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# ---------------------------------------------------------------------------
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# zip extraction — only the two expected members land; missing members fail
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# ---------------------------------------------------------------------------
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def _crx_with_zip(members):
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buf = io.BytesIO()
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with zipfile.ZipFile(buf, "w") as zf:
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for name, data in members.items():
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zf.writestr(name, data)
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# _extract reads the zip from the end, so a raw CRX prefix isn't required.
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return buf.getvalue()
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class TestExtract:
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def test_extracts_only_expected_members(self, tmp_path):
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so = "_platform_specific/linux_x64/libwidevinecdm.so"
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crx = _crx_with_zip({
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"manifest.json": b"{}",
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so: b"\x7fELF-fake",
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"evil/../../escape.txt": b"x", # extra member must be ignored
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})
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out = tmp_path / "WidevineCdm"
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fw._extract(crx, "x64", str(out))
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assert (out / "manifest.json").is_file()
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assert (out / so).is_file()
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assert not (tmp_path / "escape.txt").exists()
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assert not (out / "evil").exists()
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def test_missing_member_raises(self, tmp_path):
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crx = _crx_with_zip({"manifest.json": b"{}"}) # no .so
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with pytest.raises(SystemExit, match="missing expected members"):
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fw._extract(crx, "x64", str(tmp_path / "WidevineCdm"))
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def test_atomic_replace_of_existing_dir(self, tmp_path):
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out = tmp_path / "WidevineCdm"
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out.mkdir()
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(out / "stale").write_text("old")
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so = "_platform_specific/linux_x64/libwidevinecdm.so"
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crx = _crx_with_zip({"manifest.json": b"{}", so: b"new"})
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fw._extract(crx, "x64", str(out))
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assert (out / "manifest.json").is_file()
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assert not (out / "stale").exists() # old contents fully replaced
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