feat: better retries

src/fastdownloader/downloader.py

@@ -8,8 +8,9 @@ import aiohttp
 from tqdm import tqdm
 
 CHUNK_READ_SIZE = 65536
-MAX_RETRIES = 3
-RETRY_DELAYS = [1, 2, 4]
+MAX_RETRIES = 5
+RETRY_DELAYS = [1, 2, 4, 8, 16]
+_RETRYABLE = (TimeoutError, OSError, aiohttp.ClientError)
 
 
 async def fetch_chunk(  # noqa: PLR0913
@@ -34,7 +35,7 @@ async def fetch_chunk(  # noqa: PLR0913
                         f.write(chunk)
                         bytes_written += len(chunk)
                         pbar.update(len(chunk))
-        except (TimeoutError, aiohttp.ClientError):
+        except _RETRYABLE:
             pbar.update(-bytes_written)
             if attempt < MAX_RETRIES - 1:
                 await asyncio.sleep(RETRY_DELAYS[attempt])
@@ -47,14 +48,26 @@ async def fetch_chunk(  # noqa: PLR0913
 async def fetch_single_stream(
     session: aiohttp.ClientSession, url: str, filepath: Path, pbar: tqdm,
 ) -> None:
-    async with session.get(url) as response:
-        with filepath.open("wb") as f:
-            while True:
-                chunk = await response.content.read(CHUNK_READ_SIZE)
-                if not chunk:
-                    break
-                f.write(chunk)
-                pbar.update(len(chunk))
+    for attempt in range(MAX_RETRIES):
+        bytes_written = 0
+        try:
+            async with session.get(url) as response:
+                with filepath.open("wb") as f:
+                    while True:
+                        chunk = await response.content.read(CHUNK_READ_SIZE)
+                        if not chunk:
+                            break
+                        f.write(chunk)
+                        bytes_written += len(chunk)
+                        pbar.update(len(chunk))
+        except _RETRYABLE:
+            pbar.update(-bytes_written)
+            if attempt < MAX_RETRIES - 1:
+                await asyncio.sleep(RETRY_DELAYS[attempt])
+            else:
+                raise
+        else:
+            return
 
 
 def get_filename(response: aiohttp.ClientResponse) -> str:
@@ -85,12 +98,31 @@ def get_filename(response: aiohttp.ClientResponse) -> str:
     return unquote(filename)
 
 
+async def _head_with_retry(
+    session: aiohttp.ClientSession, url: str,
+) -> tuple[str, str | None, str]:
+    for attempt in range(MAX_RETRIES):
+        try:
+            async with session.head(url, allow_redirects=True) as response:
+                return (
+                    get_filename(response),
+                    response.headers.get("Content-Length"),
+                    response.headers.get("Accept-Ranges", ""),
+                )
+        except _RETRYABLE:
+            if attempt < MAX_RETRIES - 1:
+                await asyncio.sleep(RETRY_DELAYS[attempt])
+            else:
+                raise
+    raise RuntimeError("unreachable")  # pragma: no cover
+
+
 async def download_file(url: str, num_parts: int = 20, *, position: int = 0) -> None:
-    async with aiohttp.ClientSession() as session:
-        async with session.head(url, allow_redirects=True) as response:
-            filename = get_filename(response)
-            content_length_str = response.headers.get("Content-Length")
-            accept_ranges = response.headers.get("Accept-Ranges", "")
+    timeout = aiohttp.ClientTimeout(total=None, connect=30, sock_read=60)
+    async with aiohttp.ClientSession(timeout=timeout) as session:
+        filename, content_length_str, accept_ranges = await _head_with_retry(
+            session, url,
+        )
 
         supports_ranges = accept_ranges == "bytes" and content_length_str is not None