Add auto follow instances index support

shared/extra-utils/instances-index/mock-instances-index.ts

@@ -0,0 +1,38 @@
+import * as express from 'express'
+
+export class MockInstancesIndex {
+  private indexInstances: { host: string, createdAt: string }[] = []
+
+  initialize () {
+    return new Promise(res => {
+      const app = express()
+
+      app.use('/', (req: express.Request, res: express.Response, next: express.NextFunction) => {
+        if (process.env.DEBUG) console.log('Receiving request on mocked server %s.', req.url)
+
+        return next()
+      })
+
+      app.get('/api/v1/instances/hosts', (req: express.Request, res: express.Response) => {
+        const since = req.query.since
+
+        const filtered = this.indexInstances.filter(i => {
+          if (!since) return true
+
+          return i.createdAt > since
+        })
+
+        return res.json({
+          total: filtered.length,
+          data: filtered
+        })
+      })
+
+      app.listen(42100, () => res())
+    })
+  }
+
+  addInstance (host: string) {
+    this.indexInstances.push({ host, createdAt: new Date().toISOString() })
+  }
+}