Remove fallback to getservbyname in _get_default_port (#1076)

CHANGES/1076.breaking.rst

@@ -0,0 +1,3 @@
+Removed support :rfc:`3986#section-3.2.3` port normalization when the scheme is not one of ``http``, ``https``, ``wss``, or ``ws`` -- by :user:`bdraco`.
+
+Support for port normalization was recently added in :issue:`1033` and contained code that would do blocking I/O if the scheme was not one of the four listed above. The code has been removed because this library is intended to be safe for usage with ``asyncio``.

yarl/_url.py

@@ -1,6 +1,5 @@
 import functools
 import math
-import socket
 import warnings
 from collections.abc import Mapping, Sequence
 from contextlib import suppress
@@ -423,16 +422,10 @@ def raw_authority(self):
         return self._val.netloc
 
     def _get_default_port(self) -> Union[int, None]:
-        if not self.scheme:
+        scheme = self.scheme
+        if not scheme:
             return None
-
-        with suppress(KeyError):
-            return DEFAULT_PORTS[self.scheme]
-
-        with suppress(OSError):
-            return socket.getservbyname(self.scheme)
-
-        return None
+        return DEFAULT_PORTS.get(scheme)
 
     def _get_port(self) -> Union[int, None]:
         """Port or None if default port"""