feat(routes): diff desired vs current routes

src/server/utils/routes.ts

@@ -130,9 +130,29 @@ function parseDeviceRoutes(output: string): DeviceRoute[] {
   return result;
 }
 
+/**
+ * Compute which routes to add and which managed routes to remove. A desired
+ * route already present in any form (including a kernel route) is not re-added;
+ * only managed routes are removed.
+ */
+function diffRoutes(
+  desired: Set<string>,
+  current: DeviceRoute[]
+): { toAdd: string[]; toDel: string[] } {
+  const currentCidrs = new Set(current.map((route) => route.cidr));
+
+  const toAdd = [...desired].filter((cidr) => !currentCidrs.has(cidr));
+  const toDel = current
+    .filter((route) => route.managed && !desired.has(route.cidr))
+    .map((route) => route.cidr);
+
+  return { toAdd, toDel };
+}
+
 export const routesTestExports = {
   normalizeRoute,
   isManageable,
   collectDesiredRoutes,
   parseDeviceRoutes,
+  diffRoutes,
 };

src/test/unit/routes.spec.ts

@@ -7,6 +7,7 @@ const {
   isManageable,
   collectDesiredRoutes,
   parseDeviceRoutes,
+  diffRoutes,
 } = routesTestExports;
 
 describe('routes', () => {
@@ -144,4 +145,38 @@ describe('routes', () => {
       ]);
     });
   });
+
+  describe('diffRoutes', () => {
+    test('adds desired routes that are not present', () => {
+      const current = [{ cidr: '100.255.1.0/24', managed: false }];
+      const { toAdd, toDel } = diffRoutes(
+        new Set(['192.168.120.0/22']),
+        current
+      );
+      expect(toAdd).toEqual(['192.168.120.0/22']);
+      expect(toDel).toEqual([]);
+    });
+    test('removes stale managed routes', () => {
+      const current = [
+        { cidr: '192.168.120.0/22', managed: true },
+        { cidr: '10.10.0.0/24', managed: true },
+      ];
+      const { toAdd, toDel } = diffRoutes(
+        new Set(['192.168.120.0/22']),
+        current
+      );
+      expect(toAdd).toEqual([]);
+      expect(toDel).toEqual(['10.10.0.0/24']);
+    });
+    test('never removes unmanaged routes', () => {
+      const current = [{ cidr: '100.255.1.0/24', managed: false }];
+      const { toDel } = diffRoutes(new Set(), current);
+      expect(toDel).toEqual([]);
+    });
+    test('does not re-add a route already present as a kernel route', () => {
+      const current = [{ cidr: '100.255.1.0/24', managed: false }];
+      const { toAdd } = diffRoutes(new Set(['100.255.1.0/24']), current);
+      expect(toAdd).toEqual([]);
+    });
+  });
 });