koa源码阅读之context.js/koa-convert/is-generator-functi

摘要：老伙计今天我们来讲一下的还有一些自己写的库吧。我们常用来在中间件发出一些错误状态码。从而使得上级中间件可以这个错误从而响应默认的一个错误处理如果不是实例。看完全文都是好样的源码链接文档链接

"use strict";
const createError = require("http-errors");
const httpAssert = require("http-assert");
const delegate = require("delegates");
const statuses = require("statuses");

const proto = module.exports = {

    //前面文章有讲过这个了，这里不描述了
  inspect() {
    if (this === proto) return this;
    return this.toJSON();
  },

  toJSON() {
    return {
      request: this.request.toJSON(),//实际上调用request.js的toJSON(下同)
      response: this.response.toJSON(),
      app: this.app.toJSON(),
      originalUrl: this.originalUrl,
      req: "",
      res: "",
      socket: ""
    };
  },

  /**
   * Similar to .throw(), adds assertion.
   *
   *    this.assert(this.user, 401, "Please login!");
   *
   * See: https://github.com/jshttp/http-assert
   *
   * @param {Mixed} test
   * @param {Number} status
   * @param {String} message
   * @api public
   */

  assert: httpAssert,

  /**
   * Throw an error with `msg` and optional `status`
   * defaulting to 500. Note that these are user-level
   * errors, and the message may be exposed to the client.
   *
   *    this.throw(403)
   *    this.throw("name required", 400)
   *    this.throw(400, "name required")
   *    this.throw("something exploded")
   *    this.throw(new Error("invalid"), 400);
   *    this.throw(400, new Error("invalid"));
   *
   * See: https://github.com/jshttp/http-errors
   *
   * @param {String|Number|Error} err, msg or status
   * @param {String|Number|Error} [err, msg or status]
   * @param {Object} [props]
   * @api public
   */
    //throw方法。上面是使用的方法。我们 常用来在中间件throw发出一些错误状态码。
    //从而使得上级中间件可以try catch这个错误从而响应
    //createError([status], [message], [properties])
    //properties - custom properties to attach to the object
  throw(...args) {
    throw createError(...args);
  },
    //默认的一个错误处理
  onerror(err) {
    // don"t do anything if there is no error.
    // this allows you to pass `this.onerror`
    // to node-style callbacks.
    if (null == err) return;
    // 如果error不是Error实例。此时生成一个错误实例给下文处理
    if (!(err instanceof Error)) err = new Error(`non-error thrown: ${err}`);

    let headerSent = false;
    //当然需要可写且没有被发送
    if (this.headerSent || !this.writable) {
      headerSent = err.headerSent = true;
    }

    //触发事件
    this.app.emit("error", err, this);

    //发送了肯定啥都不能干了
    if (headerSent) {
      return;
    }

    const { res } = this;
    //解构一下获得response
    
    //兼容咯
    //首次清除所有的headers
    if (typeof res.getHeaderNames === "function") {
      res.getHeaderNames().forEach(name => res.removeHeader(name));
    } else {
      res._headers = {}; // Node < 7.7
    }

    // 然后设置为错误的headers标识
    this.set(err.headers);

    //强制text/plain
    this.type = "text";

    // 支持ENOENT 
    if ("ENOENT" == err.code) err.status = 404;

    // 默认转换成500状态码
    if ("number" != typeof err.status || !statuses[err.status]) err.status = 500;

    //响应
    const code = statuses[err.status];
    const msg = err.expose ? err.message : code;
    this.status = err.status;
    this.length = Buffer.byteLength(msg);
    this.res.end(msg);
    //跟原生的一样嘛。
    //给我们一个提示。我们要使一个连接关闭。那么ctx.res.end(msg);
  }
};

/**
 * Response delegation.
 */
//委托到这个上下文对象里
//委托方法 与属性的getter或者setter
delegate(proto, "response")
  .method("attachment")
  .method("redirect")
  .method("remove")
  .method("vary")
  .method("set")
  .method("append")
  .method("flushHeaders")
  .access("status")
  .access("message")
  .access("body")
  .access("length")
  .access("type")
  .access("lastModified")
  .access("etag")
  .getter("headerSent")
  .getter("writable");

/**
 * Request delegation.
 */

delegate(proto, "request")
  .method("acceptsLanguages")
  .method("acceptsEncodings")
  .method("acceptsCharsets")
  .method("accepts")
  .method("get")
  .method("is")
  .access("querystring")
  .access("idempotent")
  .access("socket")
  .access("search")
  .access("method")
  .access("query")
  .access("path")
  .access("url")
  .getter("origin")
  .getter("href")
  .getter("subdomains")
  .getter("protocol")
  .getter("host")
  .getter("hostname")
  .getter("URL")
  .getter("header")
  .getter("headers")
  .getter("secure")
  .getter("stale")
  .getter("fresh")
  .getter("ips")
  .getter("ip");

因为下一个篇幅准备将最重要的application.js
所以这个接下来准备说几个引入的库源码

"use strict"

const co = require("co")
//引入co
const compose = require("koa-compose")

module.exports = convert

function convert (mw) {
    //进行判断
  if (typeof mw !== "function") {
    throw new TypeError("middleware must be a function")
  }
  if (mw.constructor.name !== "GeneratorFunction") {
    // assume it"s Promise-based middleware
    return mw
  }
  const converted = function (ctx, next) {
    return co.call(ctx, mw.call(ctx, createGenerator(next)))
  }
  converted._name = mw._name || mw.name
  return converted
}

function * createGenerator (next) {
  return yield next()
}

// convert.compose(mw, mw, mw)
// convert.compose([mw, mw, mw])
// koa-compose 日后再说嘻嘻^v^
convert.compose = function (arr) {
  if (!Array.isArray(arr)) {
    arr = Array.from(arguments)
  }
  return compose(arr.map(convert))
}
//我的天啊。这个疯子还支持回退
//回退方法很是精妙啊
convert.back = function (mw) {
  if (typeof mw !== "function") {
    throw new TypeError("middleware must be a function")
  }
  if (mw.constructor.name === "GeneratorFunction") {
    // assume it"s generator middleware
    return mw
  }
  const converted = function * (next) {
    let ctx = this
    let called = false
    // no need try...catch here, it"s ok even `mw()` throw exception
    yield Promise.resolve(mw(ctx, function () {
        //使得next仅仅被调用一次
      if (called) {
        // guard against multiple next() calls
        // https://github.com/koajs/compose/blob/4e3e96baf58b817d71bd44a8c0d78bb42623aa95/index.js#L36
        return Promise.reject(new Error("next() called multiple times"))
      }
      called = true
      return co.call(ctx, next)
    }))
  }
  converted._name = mw._name || mw.name
  return converted
}

"use strict";
//减少查找引用，常见的优化方法
var toStr = Object.prototype.toString;
var fnToStr = Function.prototype.toString;
//这个正则匹配function *但是好像有点bug
//* function(){}也会受到判定true
var isFnRegex = /^s*(?:function)?*/;

var hasToStringTag = typeof Symbol === "function" && typeof Symbol.toStringTag === "symbol";
var getProto = Object.getPrototypeOf;
var getGeneratorFunc = function () { // eslint-disable-line consistent-return
    if (!hasToStringTag) {
        return false;
    }
    try {
        return Function("return function*() {}")();
    } catch (e) {
    }
};
var generatorFunc = getGeneratorFunc();
var GeneratorFunction = generatorFunc ? getProto(generatorFunc) : {};

//主要从三点看。
//一点是function toString
//一点是[object GeneratorFunction] Object toString
//一点是从原型看(内部[[Prototype]]属性的值)
module.exports = function isGeneratorFunction(fn) {
    if (typeof fn !== "function") {
        return false;
    }
    if (isFnRegex.test(fnToStr.call(fn))) {
        return true;
    }
    if (!hasToStringTag) {
        var str = toStr.call(fn);
        return str === "[object GeneratorFunction]";
    }
    return getProto(fn) === GeneratorFunction;
};

这次写的好粗糙啊= =
希望在结尾部分能写好。
sry sry sry

看完全文都是好样的！！

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