fix: preserve resumable downloads across retries

py/services/downloader.py

@@ -138,7 +138,7 @@ class Downloader:
         self.chunk_size = (
             16 * 1024 * 1024
         )  # 16MB chunks to balance I/O reduction and memory usage
-        self.max_retries = 5
+        self.max_retries = self._resolve_max_retries()
         self.base_delay = 2.0  # Base delay for exponential backoff
         self.session_timeout = 300  # 5 minutes
         self.stall_timeout = self._resolve_stall_timeout()
@@ -192,6 +192,18 @@ class Downloader:
 
         return max(30.0, timeout_value)
 
+    def _resolve_max_retries(self) -> int:
+        """Determine max retry count from environment while preserving defaults."""
+        default_retries = 5
+        raw_value = os.environ.get("COMFYUI_DOWNLOAD_MAX_RETRIES")
+
+        try:
+            retries = int(raw_value)
+        except (TypeError, ValueError):
+            retries = default_retries
+
+        return max(0, retries)
+
     def _should_refresh_session(self) -> bool:
         """Check if session should be refreshed"""
         if self._session is None:
@@ -334,6 +346,7 @@ class Downloader:
             logger.info(f"Resuming download from offset {resume_offset} bytes")
 
         total_size = 0
+        range_redirect_retry_urls: set[str] = set()
 
         while retry_count <= self.max_retries:
             try:
@@ -372,6 +385,23 @@ class Downloader:
                     if response.status == 200:
                         # Full content response
                         if resume_offset > 0:
+                            redirected_url = str(response.url)
+                            if (
+                                allow_resume
+                                and response.history
+                                and redirected_url
+                                and redirected_url != url
+                                and redirected_url not in range_redirect_retry_urls
+                            ):
+                                range_redirect_retry_urls.add(redirected_url)
+                                logger.info(
+                                    "Range request was not honored after redirect; retrying final URL directly: %s",
+                                    redirected_url,
+                                )
+                                url = redirected_url
+                                response.release()
+                                continue
+
                             # Server doesn't support ranges, restart from beginning
                             logger.warning(
                                 "Server doesn't support range requests, restarting download"
@@ -571,37 +601,53 @@ class Downloader:
                     expected_size = total_size if total_size > 0 else None
 
                     integrity_error: Optional[str] = None
+                    resumable_incomplete = False
                     if final_size <= 0:
                         integrity_error = "Downloaded file is empty"
                     elif expected_size is not None and final_size != expected_size:
                         integrity_error = f"File size mismatch. Expected: {expected_size}, Got: {final_size}"
+                        resumable_incomplete = (
+                            allow_resume
+                            and part_path != save_path
+                            and final_size > 0
+                            and final_size < expected_size
+                        )
 
                     if integrity_error is not None:
-                        logger.error(
+                        log_fn = logger.warning if resumable_incomplete else logger.error
+                        log_fn(
                             "Download integrity check failed for %s: %s",
                             save_path,
                             integrity_error,
                         )
 
-                        # Remove the corrupted payload so future attempts start fresh
+                        if resumable_incomplete:
-                        if os.path.exists(part_path):
+                            logger.info(
-                            try:
+                                "Preserving incomplete download for resume: %s (%s/%s bytes)",
-                                os.remove(part_path)
+                                part_path,
-                            except OSError as remove_error:
+                                final_size,
-                                logger.warning(
+                                expected_size,
-                                    "Failed to delete corrupted download %s: %s",
+                            )
-                                    part_path,
+                        else:
-                                    remove_error,
+                            # Remove corrupted payloads that cannot be safely resumed.
-                                )
+                            if os.path.exists(part_path):
-                        if part_path != save_path and os.path.exists(save_path):
+                                try:
-                            try:
+                                    os.remove(part_path)
-                                os.remove(save_path)
+                                except OSError as remove_error:
-                            except OSError as remove_error:
+                                    logger.warning(
-                                logger.warning(
+                                        "Failed to delete corrupted download %s: %s",
-                                    "Failed to delete target file %s after integrity error: %s",
+                                        part_path,
-                                    save_path,
+                                        remove_error,
-                                    remove_error,
+                                    )
-                                )
+                            if part_path != save_path and os.path.exists(save_path):
+                                try:
+                                    os.remove(save_path)
+                                except OSError as remove_error:
+                                    logger.warning(
+                                        "Failed to delete target file %s after integrity error: %s",
+                                        save_path,
+                                        remove_error,
+                                    )
 
                         retry_count += 1
                         if retry_count <= self.max_retries:
@@ -611,8 +657,16 @@ class Downloader:
                                 delay,
                             )
                             await asyncio.sleep(delay)
-                            resume_offset = 0
+                            if resumable_incomplete and os.path.exists(part_path):
-                            total_size = 0
+                                resume_offset = os.path.getsize(part_path)
+                                total_size = expected_size or 0
+                                logger.info(
+                                    "Will resume incomplete download from byte %s",
+                                    resume_offset,
+                                )
+                            else:
+                                resume_offset = 0
+                                total_size = 0
                             await self._create_session()
                             continue
 

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-"