Moved warning about missing ws library only in upgrade case (#1370)

scripts/coverage

@@ -8,4 +8,4 @@ export SOURCE_FILES="uvicorn tests"
 
 set -x
 
-${PREFIX}coverage report --show-missing --skip-covered --fail-under=96.93
+${PREFIX}coverage report --show-missing --skip-covered --fail-under=96.87

uvicorn/protocols/http/h11_impl.py

@@ -225,6 +225,11 @@ def handle_upgrade(self, event):
         if upgrade_value != b"websocket" or self.ws_protocol_class is None:
             msg = "Unsupported upgrade request."
             self.logger.warning(msg)
+            from uvicorn.protocols.websockets.auto import AutoWebSocketsProtocol
+
+            if AutoWebSocketsProtocol is None:  # pragma: no cover
+                msg = "No supported WebSocket library detected. Please use 'pip install uvicorn[standard]', or install 'websockets' or 'wsproto' manually."  # noqa: E501
+                self.logger.warning(msg)
             self.send_400_response(msg)
             return
 
@@ -246,12 +251,6 @@ def handle_upgrade(self, event):
 
     def send_400_response(self, msg: str):
 
-        from uvicorn.protocols.websockets.auto import AutoWebSocketsProtocol
-
-        if AutoWebSocketsProtocol is None:
-            msg = "No supported WebSocket library detected. Please use 'pip install uvicorn[standard]', or install 'websockets' or 'wsproto' manually."  # noqa: E501
-            self.logger.warning(msg)
-
         reason = STATUS_PHRASES[400]
         headers = [
             (b"content-type", b"text/plain; charset=utf-8"),

uvicorn/protocols/http/httptools_impl.py

@@ -140,6 +140,11 @@ def handle_upgrade(self):
         if upgrade_value != b"websocket" or self.ws_protocol_class is None:
             msg = "Unsupported upgrade request."
             self.logger.warning(msg)
+            from uvicorn.protocols.websockets.auto import AutoWebSocketsProtocol
+
+            if AutoWebSocketsProtocol is None:  # pragma: no cover
+                msg = "No supported WebSocket library detected. Please use 'pip install uvicorn[standard]', or install 'websockets' or 'wsproto' manually."  # noqa: E501
+                self.logger.warning(msg)
             self.send_400_response(msg)
             return
 
@@ -162,12 +167,6 @@ def handle_upgrade(self):
 
     def send_400_response(self, msg: str):
 
-        from uvicorn.protocols.websockets.auto import AutoWebSocketsProtocol
-
-        if AutoWebSocketsProtocol is None:
-            msg = "No supported WebSocket library detected. Please use 'pip install uvicorn[standard]', or install 'websockets' or 'wsproto' manually."  # noqa: E501
-            self.logger.warning(msg)
-
         content = [STATUS_LINE[400]]
         for name, value in self.default_headers:
             content.extend([name, b": ", value, b"\r\n"])