Add CORS middleware and a identification route to the fallback app

src/labthings_fastapi/server/fallback.py

@@ -16,6 +16,7 @@
 from typing import Any, TYPE_CHECKING
 
 from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import HTMLResponse
 from jinja2 import Environment, BaseLoader, select_autoescape
 from starlette.responses import RedirectResponse
@@ -149,6 +150,15 @@ def fallback_page(self) -> HTMLResponse:
 
 app = FallbackApp()
 
+# Add middleware so contacting the the fallback server doesn't throw CORS errors.
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["*"],
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
 
 @app.get("/")
 async def root() -> HTMLResponse:
@@ -159,6 +169,17 @@ async def root() -> HTMLResponse:
     return app.fallback_page()
 
 
+@app.get("/labthings_fallback")
+async def fallback_route() -> bool:
+    """Return True, this is a LabThings Fallback Server.
+
+    Use this to check over the API if this is a LabThings Fallback Server.
+
+    :return: returns True. This is a LabThings Fallback Server.
+    """
+    return True
+
+
 def _format_error_and_traceback(context: FallbackContext) -> tuple[str, str]:
     """Format the error and traceback.
 

tests/test_fallback.py

@@ -158,6 +158,14 @@ def test_fallback_with_log():
         assert "Fake log content" in html
 
 
+def test_fallback_identification():
+    """Test the server identifies as a fallback server."""
+    app.set_context(FallbackContext())
+    with TestClient(app) as client:
+        response = client.get("/labthings_fallback")
+        assert response.json() is True
+
+
 def test_actual_server_fallback():
     """Test that the the server configures its startup failure correctly.