refactor: consolidate health-check HTTP logic in pool

Extract _http_check() to deduplicate identical HTTP GET + status
parsing between _test_proxy and _test_chain.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/s5p/pool.py

@@ -233,16 +233,13 @@ class ProxyPool:
 
     # -- health testing ------------------------------------------------------
 
-    async def _test_proxy(self, key: str, entry: ProxyEntry) -> bool:
+    async def _http_check(self, chain: list[ChainHop]) -> bool:
-        """Test a single proxy by building the full chain and sending HTTP GET."""
+        """Send an HTTP GET through *chain* and return True on 2xx."""
         parsed = urlparse(self._cfg.test_url)
         host = parsed.hostname or "httpbin.org"
         port = parsed.port or 80
         path = parsed.path or "/"
 
-        chain = self._chain + [entry.hop]
-        entry.last_test = time.time()
-        entry.tests += 1
         try:
             reader, writer = await build_chain(
                 chain, host, port, timeout=self._cfg.test_timeout,
@@ -267,39 +264,17 @@ class ProxyPool:
             except OSError:
                 pass
 
+    async def _test_proxy(self, key: str, entry: ProxyEntry) -> bool:
+        """Test a single proxy by building the full chain and sending HTTP GET."""
+        entry.last_test = time.time()
+        entry.tests += 1
+        return await self._http_check(self._chain + [entry.hop])
+
     async def _test_chain(self) -> bool:
         """Test the static chain without any pool proxy."""
         if not self._chain:
             return True
-
+        return await self._http_check(self._chain)
-        parsed = urlparse(self._cfg.test_url)
-        host = parsed.hostname or "httpbin.org"
-        port = parsed.port or 80
-        path = parsed.path or "/"
-
-        try:
-            reader, writer = await build_chain(
-                self._chain, host, port, timeout=self._cfg.test_timeout,
-            )
-        except (ProtoError, TimeoutError, ConnectionError, OSError, EOFError):
-            return False
-
-        try:
-            request = f"GET {path} HTTP/1.1\r\nHost: {host}\r\nConnection: close\r\n\r\n"
-            writer.write(request.encode())
-            await writer.drain()
-
-            line = await asyncio.wait_for(reader.readline(), timeout=self._cfg.test_timeout)
-            parts = line.decode("utf-8", errors="replace").split(None, 2)
-            return len(parts) >= 2 and parts[1].startswith("2")
-        except (TimeoutError, ConnectionError, OSError, EOFError):
-            return False
-        finally:
-            try:
-                writer.close()
-                await writer.wait_closed()
-            except OSError:
-                pass
 
     async def _run_health_tests(self, keys: list[str] | None = None) -> None:
         """Test proxies with bounded concurrency.