koa中当你使用不正确使用next时会造成的404 Not Found问题.【附带koa源码解释】

const userRouter = new Router({
  prefix: "/user",
});

userRouter.get("/profile", ValidTokenMiddleware, async (ctx: any) => {
  const user_id = MiddlewareGetHeaderUserId(ctx);
  console.log("user id: ", user_id);
  const user = await UserModel.findById(user_id);
  console.log("user: ", user);
  ctx.body = new LTNetResponse(LTNetErrorCode.Success, user, "");
});

...
    const user_id_of_header = decoded.userId;
    if (userId != user_id_of_header + "") {
      ctx.body = new LTNetResponse(
        LTNetErrorCode.ParamError,
        null,
        String_Token_Error
      );
      return;
    }
    next();
...

// Middleware normally takes two parameters (ctx, next), ctx is the context for one request,
// next is a function that is invoked to execute the downstream middleware. It returns a Promise with a then function for running code after completion.

app.use((ctx, next) => {
  const start = Date.now();
  return next().then(() => {
    const ms = Date.now() - start;
    console.log(`${ctx.method} ${ctx.url} - ${ms}ms`);
  });
});

/**
   * Shorthand for:
   *
   *    http.createServer(app.callback()).listen(...)
   *
   * @param {Mixed} ...
   * @return {Server}
   * @api public
   */

  listen(...args) {
    debug('listen');
    const server = http.createServer(this.callback());
    return server.listen(...args);
  }

import http from 'node:http';

// Create a local server to receive data from
const server = http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify({
    data: 'Hello World!',
  }));
});

/**
   * Return a request handler callback
   * for node's native http server.
   *
   * @return {Function}
   * @api public
   */

  callback() {
    const fn = compose(this.middleware);

    if (!this.listenerCount('error')) this.on('error', this.onerror);

    const handleRequest = (req, res) => {
      const ctx = this.createContext(req, res);
      if (!this.ctxStorage) {
        return this.handleRequest(ctx, fn);
      }
      return this.ctxStorage.run(ctx, async() => {
        return await this.handleRequest(ctx, fn);
      });
    };

    return handleRequest;
  }

/**
 * Compose `middleware` returning
 * a fully valid middleware comprised
 * of all those which are passed.
 *
 * @param {Array} middleware
 * @return {Function}
 * @api public
 */

function compose (middleware) {
  if (!Array.isArray(middleware)) throw new TypeError('Middleware stack must be an array!')
  for (const fn of middleware) {
    if (typeof fn !== 'function') throw new TypeError('Middleware must be composed of functions!')
  }

  /**
   * @param {Object} context
   * @return {Promise}
   * @api public
   */

  return function (context, next) {
    // last called middleware #
    let index = -1
    return dispatch(0)
    function dispatch (i) {
      if (i <= index) return Promise.reject(new Error('next() called multiple times'))
      index = i
      let fn = middleware[i]
      if (i === middleware.length) fn = next
      if (!fn) return Promise.resolve()
      try {
        return Promise.resolve(fn(context, dispatch.bind(null, i + 1)));
      } catch (err) {
        return Promise.reject(err)
      }
    }
  }
}