tests(sync): Change the way the websocket server is run in the tests

Using [pytest-xprocess](https://pytest-xprocess.readthedocs.io/) proved
not being as useful as I thought at first, because it was causing
intermitent failures when starting the process.

The code now directly uses `subprocess.popen` calls to start the server.
The tests are grouped together using the following decorator:

`@pytest.mark.xdist_group(name="websockets")`

Tests now need to be run with the `pytest --dist loadgroup` so that all
tests of the same group happen on the same process.

More details on this blogpost:

  https://blog.notmyidea.org/start-a-process-when-using-pytest-xdist.html

Makefile

@@ -58,10 +58,10 @@ publish: ## Publish the Python package to Pypi
 test: testpy testjs
 
 testpy:
-	pytest -vv umap/tests/
+	pytest -vv umap/tests/ --dist=loadgroup
 
 test-integration:
-	pytest -xv umap/tests/integration/
+	pytest -xv umap/tests/integration/ --dist=loadgroup
 
 clean:
 	rm -f dist/*

pyproject.toml

@@ -62,7 +62,6 @@ test = [
   "pytest-django==4.8.0",
   "pytest-playwright==0.5.0",
   "pytest-xdist>=3.5.0,<4",
-  "pytest-xprocess>=1.0.1",
 ]
 docker = [
   "uwsgi==2.0.25.1",

umap/tests/integration/conftest.py

@@ -1,9 +1,10 @@
 import os
+import subprocess
+import time
 from pathlib import Path
 
 import pytest
 from playwright.sync_api import expect
-from xprocess import ProcessStarter
 
 
 @pytest.fixture(autouse=True)
@@ -37,19 +38,23 @@ def do_login(user):
     return do_login
 
 
-@pytest.fixture()
-def websocket_server(xprocess):
-    class Starter(ProcessStarter):
-        settings_path = (
-            (Path(__file__).parent.parent / "settings.py").absolute().as_posix()
-        )
-        os.environ["UMAP_SETTINGS"] = settings_path
-        # env = {"UMAP_SETTINGS": settings_path}
-        pattern = "Waiting for connections*"
-        args = ["python", "-m", "umap.ws"]
-        timeout = 1
-        terminate_on_interrupt = True
-
-    xprocess.ensure("websocket_server", Starter)
-    yield
-    xprocess.getinfo("websocket_server").terminate()
+@pytest.fixture
+def websocket_server():
+    # Find the test-settings, and put them in the current environment
+    settings_path = (Path(__file__).parent.parent / "settings.py").absolute().as_posix()
+    os.environ["UMAP_SETTINGS"] = settings_path
+
+    ds_proc = subprocess.Popen(
+        [
+            "umap",
+            "run_websocket_server",
+        ],
+        stdout=subprocess.PIPE,
+        stderr=subprocess.STDOUT,
+    )
+    time.sleep(2)
+    # Ensure it started properly before yielding
+    assert not ds_proc.poll(), ds_proc.stdout.read().decode("utf-8")
+    yield ds_proc
+    # Shut it down at the end of the pytest session
+    ds_proc.terminate()

umap/tests/integration/test_websocket_sync.py

@@ -1,5 +1,6 @@
 import re
 
+import pytest
 from playwright.sync_api import expect
 
 from umap.models import Map
@@ -9,6 +10,7 @@
 DATALAYER_UPDATE = re.compile(r".*/datalayer/update/.*")
 
 
+@pytest.mark.xdist_group(name="websockets")
 def test_websocket_connection_can_sync_markers(
     context, live_server, websocket_server, tilelayer
 ):
@@ -73,6 +75,7 @@ def test_websocket_connection_can_sync_markers(
     expect(b_marker_pane).to_have_count(1)
 
 
+@pytest.mark.xdist_group(name="websockets")
 def test_websocket_connection_can_sync_polygons(
     context, live_server, websocket_server, tilelayer
 ):
@@ -156,6 +159,7 @@ def test_websocket_connection_can_sync_polygons(
     expect(b_polygons).to_have_count(0)
 
 
+@pytest.mark.xdist_group(name="websockets")
 def test_websocket_connection_can_sync_map_properties(
     context, live_server, websocket_server, tilelayer
 ):
@@ -187,6 +191,7 @@ def test_websocket_connection_can_sync_map_properties(
     expect(peerA.locator(".leaflet-control-zoom")).to_be_hidden()
 
 
+@pytest.mark.xdist_group(name="websockets")
 def test_websocket_connection_can_sync_datalayer_properties(
     context, live_server, websocket_server, tilelayer
 ):
@@ -215,6 +220,7 @@ def test_websocket_connection_can_sync_datalayer_properties(
     expect(peerB.get_by_role("combobox")).to_have_value("Choropleth")
 
 
+@pytest.mark.xdist_group(name="websockets")
 def test_websocket_connection_can_sync_cloned_polygons(
     context, live_server, websocket_server, tilelayer
 ):

umap/tests/test_datalayer_views.py

@@ -1,5 +1,4 @@
 import json
-import time
 from copy import deepcopy
 from pathlib import Path
 

umap/websocket_server.py

@@ -0,0 +1,92 @@
+#!/usr/bin/env python
+
+import asyncio
+from collections import defaultdict
+from typing import Literal, Optional
+
+import websockets
+from django.conf import settings
+from django.core.signing import TimestampSigner
+from pydantic import BaseModel, ValidationError
+from websockets import WebSocketClientProtocol
+from websockets.server import serve
+
+from umap.models import Map, User  # NOQA
+
+# Contains the list of websocket connections handled by this process.
+# It's a mapping of map_id to a set of the active websocket connections
+CONNECTIONS = defaultdict(set)
+
+
+class JoinMessage(BaseModel):
+    kind: str = "join"
+    token: str
+
+
+class OperationMessage(BaseModel):
+    kind: str = "operation"
+    verb: str = Literal["upsert", "update", "delete"]
+    subject: str = Literal["map", "layer", "feature"]
+    metadata: Optional[dict] = None
+    key: Optional[str] = None
+
+
+async def join_and_listen(
+    map_id: int, permissions: list, user: str | int, websocket: WebSocketClientProtocol
+):
+    """Join a "room" whith other connected peers.
+
+    New messages will be broadcasted to other connected peers.
+    """
+    print(f"{user} joined room #{map_id}")
+    CONNECTIONS[map_id].add(websocket)
+    try:
+        async for raw_message in websocket:
+            # recompute the peers-list at the time of message-sending.
+            # as doing so beforehand would miss new connections
+            peers = CONNECTIONS[map_id] - {websocket}
+            # Only relay valid "operation" messages
+            try:
+                OperationMessage.model_validate_json(raw_message)
+                websockets.broadcast(peers, raw_message)
+            except ValidationError as e:
+                error = f"An error occurred when receiving this message: {raw_message}"
+                print(error, e)
+    finally:
+        CONNECTIONS[map_id].remove(websocket)
+
+
+async def handler(websocket):
+    """Main WebSocket handler.
+
+    If permissions are granted, let the peer enter a room.
+    """
+    raw_message = await websocket.recv()
+
+    # The first event should always be 'join'
+    message: JoinMessage = JoinMessage.model_validate_json(raw_message)
+    signed = TimestampSigner().unsign_object(message.token, max_age=30)
+    user, map_id, permissions = signed.values()
+
+    # Check if permissions for this map have been granted by the server
+    if "edit" in signed["permissions"]:
+        await join_and_listen(map_id, permissions, user, websocket)
+
+
+def run(host, port):
+    if not settings.WEBSOCKET_ENABLED:
+        msg = (
+            "WEBSOCKET_ENABLED should be set to True to run the WebSocket Server. "
+            "See the documentation at "
+            "https://docs.umap-project.org/en/stable/config/settings/#websocket_enabled "
+            "for more information."
+        )
+        print(msg)
+        exit(1)
+
+    async def _serve():
+        async with serve(handler, host, port):
+            print(f"Waiting for connections on {host}:{port}")
+            await asyncio.Future()  # run forever
+
+    asyncio.run(_serve())