Frontend service: Update boot failure request to GET (#112603)

* update boot failure request to GET, add notes about why/how

* remove now unused function

* remove unneeded header

pkg/services/frontend/frontend_service.go

@@ -127,11 +127,6 @@ func (s *frontendService) routeGet(m *web.Mux, pattern string, h ...web.Handler)
 	m.Get(pattern, handlers...)
 }
 
-func (s *frontendService) routePost(m *web.Mux, pattern string, h ...web.Handler) {
-	handlers := append([]web.Handler{middleware.ProvideRouteOperationName(pattern)}, h...)
-	m.Post(pattern, handlers...)
-}
-
 // Apply the same middleware patterns as the main HTTP server
 func (s *frontendService) addMiddlewares(m *web.Mux) {
 	loggermiddleware := loggermw.Provide(s.cfg, s.features)
@@ -164,7 +159,9 @@ func (s *frontendService) registerRoutes(m *web.Mux) {
 	})
 
 	// Frontend boot error reporting endpoint
-	s.routePost(m, "/-/fe-boot-error", s.handleBootError)
+	// GET because all POST requests are passed to the backend, even though POST is more correct. The frontend
+	// uses cache busting to ensure requests aren't cached.
+	s.routeGet(m, "/-/fe-boot-error", s.handleBootError)
 
 	// All other requests return index.html
 	s.routeGet(m, "/*", s.index.HandleRequest)

pkg/services/frontend/index.html

@@ -174,15 +174,13 @@
           document.querySelector('.fs-variant-loader').classList.add('fs-hidden');
           document.querySelector('.fs-variant-error').classList.remove('fs-hidden');
 
-          // Report the error to the backend
-          const errorMessage = err ? err.message : 'Unknown error';
-
-          fetch('/-/fe-boot-error', {
-            method: 'POST',
-            headers: {
-              'Content-Type': 'application/json',
-            },
-            body: errorMessage,
+          // not a secure random value, but collisions are highly unlikely and 1/1000_000_000 lost requests
+          // doesn't make a difference.
+          fetch(`/-/fe-boot-error?ts=${Date.now()}${Math.random()}`, {
+            // This "should" be a POST request, but we must use GET to interact with the correct service.
+            // no-store and ?ts=_ are used to ensure the request isn't cached.
+            method: 'GET',
+            cache: "no-store",
           }).catch(err => {
             console.error('Failed to report boot error to backend: ', err);
           });