fix(downloader): harden ranged reads, teardown and multiprocess sessions

Validates the 206 range end, bounds the DASH collapse, and preserves cookie domains and pool size in spawned children.

tests/core/test_retry_after.py

@@ -0,0 +1,69 @@
+"""RnetSession.get_sleep_time must survive hostile or malformed Retry-After headers."""
+
+from datetime import datetime, timedelta, timezone
+from email.utils import format_datetime
+from types import SimpleNamespace
+
+import pytest
+
+from unshackle.core.session import RnetSession
+
+
+@pytest.fixture
+def session():
+    return RnetSession()
+
+
+def response(retry_after=None):
+    headers = {} if retry_after is None else {"Retry-After": retry_after}
+    return SimpleNamespace(headers=headers)
+
+
+def test_numeric_retry_after_passes_through(session):
+    assert session.get_sleep_time(response("3"), 1) == 3.0
+
+
+def test_huge_numeric_retry_after_is_clamped(session):
+    assert session.get_sleep_time(response("86400"), 1) == session.max_backoff
+
+
+def test_huge_numeric_retry_after_respects_session_cap():
+    session = RnetSession(max_backoff=5.0)
+    assert session.get_sleep_time(response("86400"), 1) == 5.0
+
+
+def test_http_date_retry_after_honoured(session):
+    when = format_datetime(datetime.now(timezone.utc) + timedelta(seconds=10), usegmt=True)
+    assert 5 <= session.get_sleep_time(response(when), 1) <= 10
+
+
+def test_naive_http_date_does_not_raise(session):
+    # "-0000" makes parsedate_to_datetime return a naive datetime
+    when = format_datetime(datetime.now(timezone.utc) + timedelta(seconds=10)).replace("+0000", "-0000")
+    assert 5 <= session.get_sleep_time(response(when), 1) <= 10
+
+
+def test_past_http_date_yields_no_sleep(session):
+    when = format_datetime(datetime.now(timezone.utc) - timedelta(seconds=30), usegmt=True)
+    assert session.get_sleep_time(response(when), 1) <= 0
+
+
+def test_malformed_retry_after_falls_back_to_backoff(session):
+    value = session.get_sleep_time(response("not-a-date"), 1)
+    assert 0 < value <= session.max_backoff
+
+
+def test_empty_retry_after_falls_back_to_backoff(session):
+    value = session.get_sleep_time(response(""), 1)
+    assert 0 < value <= session.max_backoff
+
+
+def test_exponential_backoff_without_retry_after(session):
+    assert session.get_sleep_time(response(), 0) == 0.0
+    base = session.backoff_factor * 4
+    assert base * 0.9 <= session.get_sleep_time(response(), 3) <= base * 1.1
+    assert session.get_sleep_time(response(), 30) == session.max_backoff
+
+
+def test_no_response_still_backs_off(session):
+    assert session.get_sleep_time(None, 30) == session.max_backoff