passport 的序列化解析

// serializeUser 執(zhí)行在 passport 的 認證階段。
Authenticator.prototype.serializeUser = function(fn, req, done) {
  if (typeof fn === 'function') {
    return this._serializers.push(fn);
  }
  
  // private implementation that traverses the chain of serializers, attempting
  // to serialize a user
  var user = fn;

  // For backwards compatibility
  if (typeof req === 'function') {
    done = req;
    req = undefined;
  }
  
  var stack = this._serializers;
  (function pass(i, err, obj) {
    // serializers use 'pass' as an error to skip processing
    if ('pass' === err) {
      err = undefined;
    }
    // an error or serialized object was obtained, done
    if (err || obj || obj === 0) { return done(err, obj); }
    
    var layer = stack[i];
    if (!layer) {
      return done(new Error('Failed to serialize user into session'));
    }
    
    
    function serialized(e, o) {
      pass(i + 1, e, o);
    }
    
    try {
      var arity = layer.length;
      if (arity == 3) {
        layer(req, user, serialized);
      } else {
        layer(user, serialized);
      }
    } catch(e) {
      return done(e);
    }
  })(0);
};

源碼
通過自執(zhí)行函數(shù)，注入0嗡呼。 每次循環(huán)執(zhí)行之前壓入的執(zhí)行序列化函數(shù) layer施戴。
分離了 執(zhí)行序列化 和 序列化函數(shù)反浓。這樣避免了變量的污染。

// 以下代碼 通過 session  獲取到 session 信息的時候赞哗，會執(zhí)行 deserializeUser
// refactor passport session with koa middleware for performance
// https://github.com/jaredhanson/passport/blob/master/lib/strategies/session.js
function session() {
  return async function passportSession(ctx, next) {
    const req = ctx.req;
    let sessionUser;
    if (req._passport.session) {
      sessionUser = req._passport.session.user;
    }

    if (sessionUser || sessionUser === 0) {
      const user = await ctx.app.passport.deserializeUser(ctx, sessionUser);
      if (!user) {
        req._passport.session.user = undefined;
      } else {
        req[ctx.app.passport._userProperty] = user;
      }
    }

    return next();
  };
}