koa-send源码解析

介绍

Simple session middleware for Koa. Defaults to cookie-based sessions and supports external stores.

意为，Koa 简单的中间件。默认基于 cookie 的会话存储，支持终端存储。

源码 koa-session 6.2.0

const debug = require("debug")("koa-session");
const ContextSession = require("./lib/context");
const util = require("./lib/util");
const assert = require("assert");
const uuid = require("uuid/v4");
const is = require("is-type-of");

const CONTEXT_SESSION = Symbol("context#contextSession");
const _CONTEXT_SESSION = Symbol("context#_contextSession");

module.exports = function (opts, app) {
  // 修正参数位置，类似session(app[, opts])
  if (opts && typeof opts.use === "function") {
    [app, opts] = [opts, app];
  }
  // app是必传参数
  if (!app || typeof app.use !== "function") {
    throw new TypeError("app instance required: `session(opts, app)`");
  }

  // 格式化参数
  opts = formatOpts(opts);
  // 扩展context
  extendContext(app.context, opts);

  return async function session(ctx, next) {
    const sess = ctx[CONTEXT_SESSION];
    if (sess.store) await sess.initFromExternal();
    try {
      await next();
    } catch (err) {
      throw err;
    } finally {
      if (opts.autoCommit) {
        await sess.commit();
      }
    }
  };
};

function formatOpts(opts) {
  // 初始化参数对象
  opts = opts || {};
  // 设置会话的cookie名，默认koa.sess
  opts.key = opts.key || "koa.sess";

  // 兼容maxage
  if (!("maxAge" in opts)) opts.maxAge = opts.maxage;

  // defaults
  if (opts.overwrite == null) opts.overwrite = true;
  if (opts.httpOnly == null) opts.httpOnly = true;
  // 删除 null sameSite配置
  if (opts.sameSite == null) delete opts.sameSite;
  if (opts.signed == null) opts.signed = true;
  if (opts.autoCommit == null) opts.autoCommit = true;

  debug("session options %j", opts);

  // 设置编码/解码函数
  if (typeof opts.encode !== "function") {
    opts.encode = util.encode;
  }
  if (typeof opts.decode !== "function") {
    opts.decode = util.decode;
  }

  // 下边都是assert判断函数类型
  const store = opts.store;
  if (store) {
    assert(is.function(store.get), "store.get must be function");
    assert(is.function(store.set), "store.set must be function");
    assert(is.function(store.destroy), "store.destroy must be function");
  }

  const externalKey = opts.externalKey;
  if (externalKey) {
    assert(is.function(externalKey.get), "externalKey.get must be function");
    assert(is.function(externalKey.set), "externalKey.set must be function");
  }

  const ContextStore = opts.ContextStore;
  if (ContextStore) {
    assert(is.class(ContextStore), "ContextStore must be a class");
    assert(
      is.function(ContextStore.prototype.get),
      "ContextStore.prototype.get must be function"
    );
    assert(
      is.function(ContextStore.prototype.set),
      "ContextStore.prototype.set must be function"
    );
    assert(
      is.function(ContextStore.prototype.destroy),
      "ContextStore.prototype.destroy must be function"
    );
  }

  // 生成一个唯一id
  if (!opts.genid) {
    if (opts.prefix) opts.genid = () => `${opts.prefix}${uuid()}`;
    else opts.genid = uuid;
  }

  return opts;
}

// 扩展context原型，增加session属性
function extendContext(context, opts) {
  // 如果存在返回
  if (context.hasOwnProperty(CONTEXT_SESSION)) {
    return;
  }
  Object.defineProperties(context, {
    // 向外暴露
    [CONTEXT_SESSION]: {
      get() {
        if (this[_CONTEXT_SESSION]) return this[_CONTEXT_SESSION];
        this[_CONTEXT_SESSION] = new ContextSession(this, opts);
        return this[_CONTEXT_SESSION];
      },
    },
    // 暴露session方法，用于获取和设置session
    session: {
      get() {
        return this[CONTEXT_SESSION].get();
      },
      set(val) {
        this[CONTEXT_SESSION].set(val);
      },
      configurable: true,
    },
    // 获取session上的opts参数，也就是传入时的参数
    sessionOptions: {
      get() {
        return this[CONTEXT_SESSION].opts;
      },
    },
  });
}

参考链接

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