Question

我查看了此问题的先前答案，但我不明白为什么如果多个路径中有res.send()，则会出现此错误。

我的代码是这样的（表达4.13）：

var user ={
    username: "some",
    password: "a"
}

router.post('/login', authenticate, function (req, res) {
    //if it passes the middleware, send back the user

    var token = jwt.sign({
        username: user.username
    }, jwtSecret);
    res.send({
         token: token,
        user: user
    });
});

function authenticate(req, res, next) {
    var body = req.body;
    var username = body.username, password = body.password;

    //if nothing is sent
    if(!username || !password){
        res.status(400).end('Must send a user and pass');
    }

    //if incorrect credentials are sent
    if(username !== user.username || password !== user.password){
        res.status(401).end("Incorrect credentials");
    }

    //if it reaches here, it means credentials are correct
    next();
}

当我从前端发送任何内容时，我收到400错误消息，但我的服务器显示：

POST /apis/auth/login 401 0.841 ms - -
Error: Can't set headers after they are sent.
at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:346:11)
at ServerResponse.header     (/home/vivek/dev/qwiksplit/jsback/node_modules/express/lib/response.js:718:10)
at ServerResponse.json (/home/vivek/dev/qwiksplit/jsback/node_modules/express/lib/response.js:246:10)
at ServerResponse.send (/home/vivek/dev/qwiksplit/jsback/node_modules/express/lib/response.js:151:21)
at /home/vivek/dev/qwiksplit/jsback/app.js:81:9
at Layer.handle_error (/home/vivek/dev/qwiksplit/jsback/node_modules/express/lib/router/layer.js:71:5)
at trim_prefix (/home/vivek/dev/qwiksplit/jsback/node_modules/express/lib/router/index.js:310:13)
at /home/vivek/dev/qwiksplit/jsback/node_modules/express/lib/router/index.js:280:7
at Function.process_params (/home/vivek/dev/qwiksplit/jsback/node_modules/express/lib/router/index.js:330:12)
at next (/home/vivek/dev/qwiksplit/jsback/node_modules/express/lib/router/index.js:271:10)

我不确定在发送响应后如何设置标头。

Answer 1

一定要回来！

return res.status(400).end('Must send a user and pass');

Answer 2

在您的中间件功能中，您需要确保在您已发送回复后调用next() <（例如，通过调用res.send()，{ {1}}或类似的。）

最简单的解决方案是在您发送回复后立即从中间件返回：

res.end()

Answer 3

您缺少一些退货声明。如果您不从函数status返回，send会在response对象上多次调用，最后甚至会调用next，所以即将推出的中间件也会对响应进行操作。

function authenticate(req, res, next) {
    var body = req.body;
    var username = body.username, password = body.password;

    //if nothing is sent
    if(!username || !password){
        res.status(400).end('Must send a user and pass');
        return;
    }

    //if incorrect credentials are sent
    if(username !== user.username || password !== user.password){
        res.status(401).end("Incorrect credentials");
        return;
    }

    //if it reaches here, it means credentials are correct
    next();
}

Answer 4

请确保在此代码后添加return语句

    res.status(400).end('Must send a user and pass');

可以是

    return; or return res.status(400).end('Must send a user and pass');

只需在该行之后返回任何内容，基本上在此之后停止执行代码。

在快递js中发送标题后无法设置标题

4 个答案: