Started to implement server

vendor/deno.land/x/oak@v12.1.0/middleware.ts

@@ -0,0 +1,46 @@
+// Copyright 2018-2022 the oak authors. All rights reserved. MIT license.
+
+// deno-lint-ignore-file
+
+import type { State } from "./application.ts";
+import type { Context } from "./context.ts";
+
+/** Middleware are functions which are chained together to deal with requests. */
+export interface Middleware<
+  S extends State = Record<string, any>,
+  T extends Context = Context<S>,
+> {
+  (context: T, next: () => Promise<unknown>): Promise<unknown> | unknown;
+}
+
+/** Compose multiple middleware functions into a single middleware function. */
+export function compose<
+  S extends State = Record<string, any>,
+  T extends Context = Context<S>,
+>(
+  middleware: Middleware<S, T>[],
+): (context: T, next?: () => Promise<unknown>) => Promise<unknown> {
+  return function composedMiddleware(
+    context: T,
+    next?: () => Promise<unknown>,
+  ): Promise<unknown> {
+    let index = -1;
+
+    async function dispatch(i: number): Promise<void> {
+      if (i <= index) {
+        throw new Error("next() called multiple times.");
+      }
+      index = i;
+      let fn: Middleware<S, T> | undefined = middleware[i];
+      if (i === middleware.length) {
+        fn = next;
+      }
+      if (!fn) {
+        return;
+      }
+      await fn(context, dispatch.bind(null, i + 1));
+    }
+
+    return dispatch(0);
+  };
+}