如何使用casperjs从XHR响应中捕获和处理数据？

Question

网页上的数据是动态显示的,似乎检查html中的每个更改并提取数据是一项非常艰巨的任务,还需要我使用非常不可靠的XPath.所以我希望能够从XHR数据包中提取数据.

我希望能够从XHR数据包中提取信息,并生成要发送到服务器的"XHR"数据包.提取信息部分对我来说更重要,因为可以通过使用casperjs自动触发html元素来轻松处理信息的发送.

我附上了我的意思截图.

响应选项卡中的文本是我之后需要处理的数据.(已从服务器收到此XHR响应.)

Answer 1

这不容易实现,因为resource.received事件处理程序仅提供元数据url,headers或者status不提供实际数据.底层的phantomjs事件处理程序的行为方式相同.

无状态AJAX请求

如果ajax调用是无状态的,您可以重复该请求

casper.on("resource.received", function(resource){
    // somehow identify this request, here: if it contains ".json"
    // it also also only does something when the stage is "end" otherwise this would be executed two times
    if (resource.url.indexOf(".json") != -1 && resource.stage == "end") {
        var data = casper.evaluate(function(url){
            // synchronous GET request
            return __utils__.sendAJAX(url, "GET");
        }, resource.url);
        // do something with data, you might need to JSON.parse(data)
    }
});
casper.start(url); // your script

您可能想要添加事件侦听器resource.requested.这样你就不需要通过电话来完成.

您也可以在控制流内部执行此操作(源:A:CasperJS waitForResource:如何获取我等待的资源):

casper.start(url);

var res, resData;
casper.waitForResource(function check(resource){
    res = resource;
    return resource.url.indexOf(".json") != -1;
}, function then(){
    resData = casper.evaluate(function(url){
        // synchronous GET request
        return __utils__.sendAJAX(url, "GET");
    }, res.url);
    // do something with the data here or in a later step
});

casper.run();

有状态的AJAX请求

如果它不是无状态的,则需要替换XMLHttpRequest的实现.您需要注入自己的onreadystatechange处理程序实现,收集页面window对象中的信息,然后在另一个evaluate调用中收集它.

您可能希望查看sinon.js中的XHR faker或使用以下完整代理XMLHttpRequest(我在如何创建XMLHttpRequest包装器/代理的方法3之后对其进行建模？):

function replaceXHR(){
    (function(window, debug){
        function args(a){
            var s = "";
            for(var i = 0; i < a.length; i++) {
                s += "\t\n[" + i + "] => " + a[i];
            }
            return s;
        }
        var _XMLHttpRequest = window.XMLHttpRequest;

        window.XMLHttpRequest = function() {
            this.xhr = new _XMLHttpRequest();
        }

        // proxy ALL methods/properties
        var methods = [ 
            "open", 
            "abort", 
            "setRequestHeader", 
            "send", 
            "addEventListener", 
            "removeEventListener", 
            "getResponseHeader", 
            "getAllResponseHeaders", 
            "dispatchEvent", 
            "overrideMimeType"
        ];
        methods.forEach(function(method){
            window.XMLHttpRequest.prototype[method] = function() {
                if (debug) console.log("ARGUMENTS", method, args(arguments));
                if (method == "open") {
                    this._url = arguments[1];
                }
                return this.xhr[method].apply(this.xhr, arguments);
            }
        });

        // proxy change event handler
        Object.defineProperty(window.XMLHttpRequest.prototype, "onreadystatechange", {
            get: function(){
                // this will probably never called
                return this.xhr.onreadystatechange;
            },
            set: function(onreadystatechange){
                var that = this.xhr;
                var realThis = this;
                that.onreadystatechange = function(){
                    // request is fully loaded
                    if (that.readyState == 4) {
                        if (debug) console.log("RESPONSE RECEIVED:", typeof that.responseText == "string" ? that.responseText.length : "none");
                        // there is a response and filter execution based on url
                        if (that.responseText && realThis._url.indexOf("whatever") != -1) {
                            window.myAwesomeResponse = that.responseText;
                        }
                    }
                    onreadystatechange.call(that);
                };
            }
        });

        var otherscalars = [
            "onabort",
            "onerror",
            "onload",
            "onloadstart",
            "onloadend",
            "onprogress",
            "readyState",
            "responseText",
            "responseType",
            "responseXML",
            "status",
            "statusText",
            "upload",
            "withCredentials",
            "DONE",
            "UNSENT",
            "HEADERS_RECEIVED",
            "LOADING",
            "OPENED"
        ];
        otherscalars.forEach(function(scalar){
            Object.defineProperty(window.XMLHttpRequest.prototype, scalar, {
                get: function(){
                    return this.xhr[scalar];
                },
                set: function(obj){
                    this.xhr[scalar] = obj;
                }
            });
        });
    })(window, false);
}

如果要从一开始就捕获AJAX调用,则需要将其添加到第一个事件处理程序之一

casper.on("page.initialized", function(resource){
    this.evaluate(replaceXHR);
});

或者evaluate(replaceXHR)当你需要它时.

控制流程如下所示:

function replaceXHR(){ /* from above*/ }

casper.start(yourUrl, function(){
    this.evaluate(replaceXHR);
});

function getAwesomeResponse(){
    return this.evaluate(function(){
        return window.myAwesomeResponse;
    });
}

// stops waiting if window.myAwesomeResponse is something that evaluates to true
casper.waitFor(getAwesomeResponse, function then(){
    var data = JSON.parse(getAwesomeResponse());
    // Do something with data
});

casper.run();

如上所述,我为XMLHttpRequest创建了一个代理,这样每次在页面上使用它时,我都可以用它做一些事情.您抓取的页面使用xhr.onreadystatechange回调来接收数据.通过定义特定的setter函数来完成代理,该函数将接收的数据写入window.myAwesomeResponse页面上下文中.您唯一需要做的就是检索此文本.

JSONP请求

如果你知道前缀(用加载的JSON调用的函数,例如insert({"data":["Some", "JSON", "here"],"id":"asdasda")),为JSONP编写代理就更容易了.您可以insert在页面上下文中覆盖

1. 页面加载后

   casper.start(url).then(function(){
       this.evaluate(function(){
           var oldInsert = insert;
           insert = function(json){
               window.myAwesomeResponse = json;
               oldInsert.apply(window, arguments);
           };
       });
   }).waitFor(getAwesomeResponse, function then(){
       var data = JSON.parse(getAwesomeResponse());
       // Do something with data
   }).run();
   

2. 或者在收到请求之前(如果函数是在调用请求之前注册的)

   casper.on("resource.requested", function(resource){
       // filter on the correct call
       if (resource.url.indexOf(".jsonp") != -1) {
           this.evaluate(function(){
               var oldInsert = insert;
               insert = function(json){
                   window.myAwesomeResponse = json;
                   oldInsert.apply(window, arguments);
               };
           });
       }
   }).run();
   
   casper.start(url).waitFor(getAwesomeResponse, function then(){
       var data = JSON.parse(getAwesomeResponse());
       // Do something with data
   }).run();
   

Answer 2

我可能会迟到这个聚会,但答案可能会帮助像我这样的人,以后会遇到这个问题.

我不得不从PhantomJS开始,然后转移到CasperJS但最终与SlimerJS达成和解.Slimer基于Phantom,与Casper兼容,并且可以使用相同的onResponseReceived方法将响应主体发送回"response.body"部分.

参考:https://docs.slimerjs.org/current/api/webpage.html#webpage-onresourcereceived