big upgrade UwU

sticker_downloader/fetcher.py

@@ -0,0 +1,29 @@
+"""Fetching file bytes from Telegram's CDN."""
+
+from __future__ import annotations
+
+from typing import Protocol, runtime_checkable
+
+import aiohttp
+
+from sticker_downloader.errors import FetchError
+
+
+@runtime_checkable
+class Fetcher(Protocol):
+    """Minimal interface the downloader needs to read a file off the network."""
+
+    async def fetch(self, url: str) -> bytes: ...
+
+
+class AiohttpFetcher:
+    """A :class:`Fetcher` backed by a shared :class:`aiohttp.ClientSession`."""
+
+    def __init__(self, session: aiohttp.ClientSession) -> None:
+        self._session = session
+
+    async def fetch(self, url: str) -> bytes:
+        async with self._session.get(url) as response:
+            if response.status >= 400:
+                raise FetchError(url, response.status, response.reason or "")
+            return await response.read()