中间软件

用于发电机和电效应操作的型式安全堆肥中件

Middleware 允许您将任何功能用可以被截取的链条包裹 检查参数,转换返回值,或完全执行短路. 这个 combine() 函数将一组中间软件编成单个 中间软件,执行从左到右.

因为中间软件在返回类型上是通用的,生成器函数会编曲 结束 combine() 和普通功能一样 这意味着你可以建造 中间软件管道,每层设置效果资源,建立 上下文, 或管理清理, 而堆栈中的所有下方都继承 上下文自动.

快速启动

import { combine } from "@effectionx/middleware";
import type { Middleware } from "@effectionx/middleware";
import type { Operation } from "effection";
import { createContext } from "effection";

type Handler = Middleware<[Request], Operation<Response>>;

const DatabaseConnection = createContext<Connection>("database");

// Each middleware is a generator — it's still running while inner layers execute
const withDatabase: Handler = function* (args, next) {
  const conn = yield* connect(process.env.DATABASE_URL);
  yield* DatabaseConnection.set(conn);
  try {
    return yield* next(...args);
  } finally {
    yield* conn.close();
  }
};

const withTransaction: Handler = function* (args, next) {
  const conn = yield* DatabaseConnection.expect();
  const tx = yield* conn.begin();
  try {
    const response = yield* next(...args);
    yield* tx.commit();
    return response;
  } catch (error) {
    yield* tx.rollback();
    throw error;
  }
};

核心处理器使用由中件设置的上下文——但从未收到任何上下文 作为参数:

function* handleRequest(request: Request): Operation<Response> {
  const conn = yield* DatabaseConnection.expect();
  const posts = yield* conn.query("SELECT * FROM posts");
  return Response.json(posts);
}

拼凑起来:

const handle = combine([withDatabase, withTransaction]);

function* processRequest(request: Request): Operation<Response> {
  return yield* handle([request], handleRequest);
}

何时 handleRequest 返回(或丢出,或被取消),堆栈会打开风窗 倒转 : withTransaction (承诺或回滚) • withDatabase (关闭) 连接). 结构货币保证资源不会泄漏,即使 请求取消.

普通函数

Middleware也具有平面同步功能——没有Effection 依赖性。 这对论证、记录或结果有用 转换 :

import { combine } from "@effectionx/middleware";
import type { Middleware } from "@effectionx/middleware";

const logger: Middleware<[number, number], number> = (args, next) => {
  console.log("adding", args);
  const result = next(...args);
  console.log("result", result);
  return result;
};

const doubler: Middleware<[number, number], number> = (args, next) =>
  next(...args) * 2;

const add = combine([logger, doubler]);

add([3, 4], (a, b) => a + b);
// adding [3, 4]
// result 14
// => 14

API 密码

Middleware<TArgs, TReturn>

单个中件函数的类型 。 它接受的论点是一团糟 (单位:千美元) next 函数以授权给下一个中间软件(或核心职能).

import type { Middleware } from "@effectionx/middleware";

const timer: Middleware<[string], string> = (args, next) => {
  const start = performance.now();
  const result = next(...args);
  console.log(`took ${performance.now() - start}ms`);
  return result;
};

中间软件可以:

• 通过: 调用 next(...args) 并返回结果
• 变换参数: 调用 next() 有不同论据
• 转换返回值: 修改什么 next() 返回时
• 短路: 返回一个不调用值 next() 完全没有

combine(middlewares)

将一组中相软件编成单个中相软件. 执行中间软件 左到右:数组中第一个运行最外侧.

import { combine } from "@effectionx/middleware";

const composed = combine([logger, validator, retry]);
const result = composed(["hello"], coreFn);
// Execution: logger → validator → retry → coreFn

返回的值本身是一个 Middleware这样它就可以在其它地方筑巢 combine() 呼叫或通过任何中间软件.