Switch to sansio websockets back-end

Uvicorn uses the now deprecated `websockets.legacy` back end by default. It also supports the newer `sansio` interface. As far as I can tell, either works, so I'm not sure why legacy is the default: backwards compatibility I guess.

I'd like to switch to the newer implementation now, before we are using websockets in anger, as it feels wrong to start out with deprecation warnings in the test suite!

Author: rwb27

src/labthings_fastapi/server/cli.py

@@ -161,7 +161,7 @@ def serve_from_cli(
         server = ThingServer.from_config(config, True if args.debug else False)
         if dry_run:
             return server
-        uvicorn.run(server.app, host=args.host, port=args.port)
+        uvicorn.run(server.app, host=args.host, port=args.port, ws="websockets-sansio")
     except BaseException as e:
         if args.fallback:
             print(f"Error: {e}")
@@ -174,7 +174,7 @@ def serve_from_cli(
                 )
             )
 
-            uvicorn.run(app, host=args.host, port=args.port)
+            uvicorn.run(app, host=args.host, port=args.port, ws="websockets-sansio")
         else:
             if isinstance(e, (ValidationError, ThingImportFailure)):
                 print(f"Error reading LabThings configuration:\n{e}")

tests/test_fallback.py

@@ -170,7 +170,7 @@ def test_actual_server_fallback():
 
     # Starting the server is a SystemExit
     with pytest.raises(SystemExit, match="3") as excinfo:
-        uvicorn.run(server.app, port=5000)
+        uvicorn.run(server.app, port=5000, ws="websockets-sansio")
     server_error = excinfo.value
     assert server.startup_failure is not None
     assert server.startup_failure["thing"] == "bad_thing"

tests/test_mjpeg_stream.py

@@ -78,4 +78,4 @@ def test_mjpeg_stream(client):
     assert isinstance(telly, Telly)
     telly.framerate = 6
     telly.frame_limit = -1
-    uvicorn.run(server.app, port=5000)
+    uvicorn.run(server.app, port=5000, ws="websockets-sansio")