Node.js Express 中间件错误链

Question

我必须从网页上抓取一个密钥，以便以后用作 cookie。那部分有效。但是因为请求是异步的，所以不会处理错误。我想确保错误通过中间件链传递。但我无法理解这个问题。感谢您的帮助。

app.use('/', makeLoginCookie, function (req, res, next){
    console.log('My app.use() starts here.');
    //console.log('makeLoginCookie: %s', err);
    next(); 
});

这是函数

function makeLoginCookie(req, res, next) {
    httpOptions = {
        url: site.url,
        headers: {
            Cookie: null
        }
    }

// Get HIDDEN key, build login cookie
request(httpOptions, function(error, response, body) {
    if (!error && response.statusCode == 200) {
        //console.log(body)
        var match = body.match( /\<INPUT TYPE=HIDDEN id=\"key\", value=\"([0-9a-f]+)\"\>/i );
        var key = match[1]
        var encrypted = sha1(key + site.username + site.password);
        loginCookie = "username=" + key + ";password=" + encrypted;
        next();
    } else {
        console.log("Connect failed %s" , error);
        //err = new Error("Can't connect");
        next();
    }
  });
};

Answer 1

参考Express Error handling，可以使用next(err);传递Express中的错误。 Here 是一个很好的链接。

Answer 2

我会使用promises (Q library) 来解决这个问题，以及其他事情，特别是用于网络抓取。您的“makeLoginCookie”函数可能会返回一个 deferred.promise，并且当请求失败时，会以错误拒绝它。

编辑 1：我推荐这个很棒的视频，它解释了如何使用异步代码 https://www.youtube.com/watch?v=obaSQBBWZLk 正常工作。它可以帮助您解决这个问题和其他问题。

编辑2：使用promise会是这样，看看是否对你有帮助：

var Q = require("q");

app.use('/', function (req, res, next) {

    // This part, we will call your function "makeLoginCookie"
    makeLoginCookie().then(function(){
        // This is called when your function RESOLVES the promise

        // Here you could log or do some stuff...

        // Then, go next...
        next();
    }, function(error){
        // This is called when your function REJECTS the promise
        console.log("Connect failed %s" , error);

        // And then, handle the error, like stopping the request and sending an error:
        res.status(400).json({errorMessage: error});
    })
}, function (req, res, next){
    console.log('My app.use() starts here.');
    next(); 
});

// Removed parameters from function
function makeLoginCookie() {
    // This is the object that will return a promise
    var deferred = Q.defer();

    httpOptions = {
        url: site.url,
        headers: {
            Cookie: null
        }
    }

    // Get HIDDEN key, build login cookie
    request(httpOptions, function(error, response, body) {
        if (!error && response.statusCode == 200) {
            //console.log(body)
            var match = body.match( /\<INPUT TYPE=HIDDEN id=\"key\", value=\"([0-9a-f]+)\"\>/i );
            var key = match[1]
            var encrypted = sha1(key + site.username + site.password);
            loginCookie = "username=" + key + ";password=" + encrypted;

            // Instead of using next(), RESOLVE your promise
            // next();
            deferred.resolve(); // You can pass some data into it..
        } else {

            // Instead of using next(), REJECT your promise
            // next();
            deferred.reject(error); // You can pass some data into it, like an error object or string...
        }
    });

    // Promise that something will be fulfilled or reject later
    return deferred.promise;
};

Answer 3

我的代码中的其他地方一定有一些错误，因为它现在按预期工作。

} else {
    console.log("Connect failed %s" , error);
    err = new Error("Can't connect");
    next(err);
}