Merge pull request #899 from Phinease/fix/resumable-download-retries

fix: preserve resumable downloads across retries

tests/services/test_downloader.py

@@ -30,10 +30,21 @@ class FakeStream:
 
 
 class FakeResponse:
-    def __init__(self, status, headers, chunks):
+    def __init__(
+        self,
+        status,
+        headers,
+        chunks,
+        *,
+        url="https://example.com/file",
+        history=None,
+    ):
         self.status = status
         self.headers = headers
         self.content = FakeStream(chunks)
+        self.url = url
+        self.history = history or []
+        self.released = False
 
     async def __aenter__(self):
         return self
@@ -41,14 +52,25 @@ class FakeResponse:
     async def __aexit__(self, exc_type, exc, tb):
         return False
 
+    def release(self):
+        self.released = True
+
 
 class FakeSession:
     def __init__(self, responses):
         self._responses = list(responses)
         self._get_calls = 0
+        self.requests = []
 
     def get(self, url, headers=None, allow_redirects=True, proxy=None):  # noqa: D401 - signature mirrors aiohttp
-        del url, headers, allow_redirects, proxy
+        self.requests.append(
+            {
+                "url": url,
+                "headers": headers or {},
+                "allow_redirects": allow_redirects,
+                "proxy": proxy,
+            }
+        )
         response_factory = self._responses[self._get_calls]
         self._get_calls += 1
         return response_factory()
@@ -75,7 +97,7 @@ def _build_downloader(responses, *, max_retries=0):
 
 
 @pytest.mark.asyncio
-async def test_download_file_fails_when_size_mismatch(tmp_path):
+async def test_download_file_preserves_incomplete_part_when_size_mismatch(tmp_path):
     target_path = tmp_path / "model" / "file.bin"
     target_path.parent.mkdir()
 
@@ -94,7 +116,7 @@ async def test_download_file_fails_when_size_mismatch(tmp_path):
     assert success is False
     assert "mismatch" in message.lower()
     assert not target_path.exists()
-    assert not Path(str(target_path) + ".part").exists()
+    assert Path(str(target_path) + ".part").read_bytes() == b"abc"
 
 
 @pytest.mark.asyncio
@@ -136,7 +158,9 @@ async def test_download_file_succeeds_when_sizes_match(tmp_path):
 
     downloader = _build_downloader(responses)
 
-    success, result_path = await downloader.download_file("https://example.com/file", str(target_path))
+    success, result_path = await downloader.download_file(
+        "https://example.com/file", str(target_path)
+    )
 
     assert success is True
     assert Path(result_path).read_bytes() == payload
@@ -166,9 +190,77 @@ async def test_download_file_recovers_from_stall(tmp_path):
     downloader = _build_downloader(responses, max_retries=1)
     downloader.stall_timeout = 0.05
 
-    success, result_path = await downloader.download_file("https://example.com/file", str(target_path))
+    success, result_path = await downloader.download_file(
+        "https://example.com/file", str(target_path)
+    )
 
     assert success is True
     assert Path(result_path).read_bytes() == payload
     assert downloader._session._get_calls == 2
     assert not Path(str(target_path) + ".part").exists()
+
+
+@pytest.mark.asyncio
+async def test_download_file_resumes_after_incomplete_integrity_check(tmp_path):
+    target_path = tmp_path / "model" / "file.bin"
+    target_path.parent.mkdir()
+
+    responses = [
+        lambda: FakeResponse(
+            status=200,
+            headers={"content-length": "6"},
+            chunks=[b"abc"],
+        ),
+        lambda: FakeResponse(
+            status=206,
+            headers={"content-length": "3", "Content-Range": "bytes 3-5/6"},
+            chunks=[b"def"],
+        ),
+    ]
+
+    downloader = _build_downloader(responses, max_retries=1)
+
+    success, result_path = await downloader.download_file("https://example.com/file", str(target_path))
+
+    assert success is True
+    assert Path(result_path).read_bytes() == b"abcdef"
+    assert downloader._session._get_calls == 2
+    assert downloader._session.requests[1]["headers"]["Range"] == "bytes=3-"
+    assert not Path(str(target_path) + ".part").exists()
+
+
+@pytest.mark.asyncio
+async def test_download_file_retries_redirected_url_when_range_not_honored(tmp_path):
+    target_path = tmp_path / "model" / "file.bin"
+    target_path.parent.mkdir()
+    Path(str(target_path) + ".part").write_bytes(b"abc")
+
+    redirected_url = "https://download.example.com/file.bin"
+    first_response = FakeResponse(
+        status=200,
+        headers={"content-length": "6"},
+        chunks=[],
+        url=redirected_url,
+        history=[object()],
+    )
+
+    responses = [
+        lambda: first_response,
+        lambda: FakeResponse(
+            status=206,
+            headers={"content-length": "3", "Content-Range": "bytes 3-5/6"},
+            chunks=[b"def"],
+            url=redirected_url,
+        ),
+    ]
+
+    downloader = _build_downloader(responses, max_retries=0)
+
+    success, result_path = await downloader.download_file("https://example.com/file", str(target_path))
+
+    assert success is True
+    assert Path(result_path).read_bytes() == b"abcdef"
+    assert first_response.released is True
+    assert downloader._session.requests[0]["headers"]["Range"] == "bytes=3-"
+    assert downloader._session.requests[1]["url"] == redirected_url
+    assert downloader._session.requests[1]["headers"]["Range"] == "bytes=3-"