SailsJS用一个Controller动作调用两个Service方法

Question

我对学习全栈开发相当陌生，特别是后端，我试图弄清楚异步Nodejs的东西。

我有一些后端操作，我需要在提交忘记密码表单时完成。基本上控制器动作看起来像这样(我知道这肯定是错误的方式):

forgot: function (req, res) {
    var token = "febfoebfoui38383303cnc";
    var userEmail = req.body.email;
    var host = req.headers.host;
    AuthService.saveResetPasswordValues(token, userEmail, function (err, savedRecord) {
        if (err) { return res.send(404, 'nnerror occurrednn'); }
        return res.json(savedRecord);
    });
    AuthService.sendForgotPasswordEmail(token, userEmail, host, function (err, message) {
        if (err) { return res.send(404, 'nnerror occurrednn'); }
        return res.json(message);
    });
},

每个服务都做一些事情来帮助发送密码重置电子邮件。

saveResetPasswordValues: function (token, userEmail, cb) {
    var expiration = Date.now() + 3600000; // 1 hour
    User.update({ email: userEmail },
        { resetPasswordToken: token,
            resetPasswordExpires: expiration})
        .exec(function (err, user) {
            if (err) { return cb({ status: 404, message: 'Could not find user with that email address' }); }
            return cb(err, user);
        });
},
sendForgotPasswordEmail: function (token, userEmail, host, cb) {
    var htmlMessage =
        '<h4>You are receiving this because you (or someone else) have requested the reset of the password for your account.</h4>' +
        '<p>Please click on the following link, or paste this into your browser to complete the process:</p>' +
        "<p><a href='http://" + host + '/reset/' + token + "'> Link to password reset </a></p>" +
        '<p>If you did not request this, please ignore this email and your password will remain unchanged.</p>';
    var emailInfo = {
        to: userEmail,
        from: "[e-mail]",
        subject: "Small Change Project Password Reset",
        message: htmlMessage,
        fromName: "Small Change Project"
    };
    .... some code for sending the email ...
     return cb(null, 'email has been sent');
}

最后，用户应该收到一封像这样的电子邮件:

您收到此消息是因为您(或其他人)已请求重置您的帐户密码。

请点击以下链接，或将其粘贴到您的浏览器中完成流程:

密码重置链接

令人惊讶的是，这段代码确实可以工作，但是它吐出了一堆丑陋的错误——告诉我我不知道异步回调是如何工作的;)

error: Sending 500 ("Server Error") response: 
 Error: Can't set headers after they are sent.
    at ServerResponse.OutgoingMessage.setHeader (http.js:690:11)
    at ServerResponse.res.setHeader (/usr/lib/node_modules/sails/node_modules/express/node_modules/connect/lib/patch.js:133:22)
    at ServerResponse.res.set.res.header (/home/zacharyhustles/smallChangeAPI/node_modules/sails/node_modules/express/lib/response.js:577:10)
    at ServerResponse.res.send (/home/zacharyhustles/smallChangeAPI/node_modules/sails/node_modules/express/lib/response.js:142:12)
    at ServerResponse.res.json (/home/zacharyhustles/smallChangeAPI/node_modules/sails/node_modules/express/lib/response.js:223:15)
    at /home/zacharyhustles/smallChangeAPI/api/controllers/UserController.js:123:15
    at /home/zacharyhustles/smallChangeAPI/api/services/AuthService.js:50:4
    at Object.module.exports.simpleSendEmail (/home/zacharyhustles/smallChangeAPI/api/services/EmailService.js:48:12)
    at Object.bound [as simpleSendEmail] (/home/zacharyhustles/smallChangeAPI/node_modules/lodash/dist/lodash.js:729:21)
    at Object.module.exports.sendForgotPasswordEmail (/home/zacharyhustles/smallChangeAPI/api/services/AuthService.js:46:16)
    at Object.bound [as sendForgotPasswordEmail] (/home/zacharyhustles/smallChangeAPI/node_modules/lodash/dist/lodash.js:729:21)
    at Object.module.exports.forgot (/home/zacharyhustles/smallChangeAPI/api/controllers/UserController.js:121:15)
    at bound (/home/zacharyhustles/smallChangeAPI/node_modules/lodash/dist/lodash.js:729:21)
    at routeTargetFnWrapper (/home/zacharyhustles/smallChangeAPI/node_modules/sails/lib/router/bind.js:179:5)
    at callbacks (/home/zacharyhustles/smallChangeAPI/node_modules/sails/node_modules/express/lib/router/index.js:164:37)
    at param (/home/zacharyhustles/smallChangeAPI/node_modules/sails/node_modules/express/lib/router/index.js:138:11) [Error: Can't set headers after they are sent.]

正确的方法是什么?

Answer 1

就像错误信息已经建议的那样，在你已经发送了一个响应之后，你不允许再向浏览器发送另一个响应，因为在一个网页请求的经典请求-响应周期中，浏览器每个请求只接受一个响应。

你必须将第二个服务函数的调用放到第一个服务函数的回调中，并将服务帮助器的结果发送到一个组合对象中，例如:

    forgot: function (req, res) {
        var token = "febfoebfoui38383303cnc";
        var userEmail = req.body.email;
        var host = req.headers.host;
        AuthService.saveResetPasswordValues(token, userEmail, function (err, savedRecord) {
            if (err) { return res.send(404, 'nnerror occurrednn'); }
            AuthService.sendForgotPasswordEmail(token, userEmail, host, function (err, message) {
                if (err) { return res.send(404, 'nnerror occurrednn'); }
                // make sure to adapt your client logic for this response
                return res.json({savedRecord: savedRecord, message: message);
            });
        });
    },

异步回调的一般结论是，如果你有一个函数调用依赖于前一个调用的结果，你必须将第二个调用嵌套到前一个调用的回调中，因此它们以正确的顺序被调用，并且第二个调用可以访问第一个调用的结果。

如果你想在一个响应中发送几个异步函数的结果，只需嵌套函数调用，这样你就可以在最后的最深回调中访问所有结果。