feat: DoS prevention, #250

src/util/limiter.ts

@@ -0,0 +1,18 @@
+import { assert } from './assert'
+
+export class Limiter {
+  private message: string
+  private base = 0
+  private limit: number
+  constructor (resource: string, limit: number) {
+    this.message = `${resource} limit exceeded`
+    this.limit = limit
+  }
+  use (count: number) {
+    assert(this.base + count <= this.limit, this.message)
+    this.base += count
+  }
+  check (count: number) {
+    assert(count <= this.limit, this.message)
+  }
+}