javascript - 使用 CefSharp.Offscreen 检索需要 Javascript 呈现的网页

Question

我的任务很简单，但需要精通 CefSharp 的人才能解决。

我有一个 url，我想从中检索 HTML。问题是这个特定的 url 实际上并没有在 GET 上分发页面。相反，它将一堆 Javascript 推送到浏览器，然后浏览器执行并生成实际呈现的页面。这意味着涉及 HttpWebRequest 和 HttpWebResponse 的常用方法不会起作用。

我看过许多不同的“ headless ”选项，出于多种原因，我认为最能满足我的需求的是 CefSharp.Offscreen。但是我不知道这东西是如何工作的。我看到有几个可以订阅的事件和一些配置选项，但我不需要嵌入式浏览器之类的东西。

我真正需要的是一种方法来做这样的事情(伪代码):

string html = CefSharp.Get(url);

我订阅事件没有问题，如果这是等待 Javascript 执行和生成渲染页面所需要的。

Answer 1

我知道我正在做一些考古学来恢复 2yo 的帖子，但详细的回答可能对其他人有用。

是的，Cefsharp.Offscreen 适合这项任务。

下面是一个将处理所有浏览器事件的类。

using System;
using System.IO;
using System.Threading;
using CefSharp;
using CefSharp.OffScreen;

namespace [whatever]
{
    public class Browser
    {

        /// <summary>
        /// The browser page
        /// </summary>
        public ChromiumWebBrowser Page { get; private set; }
        /// <summary>
        /// The request context
        /// </summary>
        public RequestContext RequestContext { get; private set; }

        // chromium does not manage timeouts, so we'll implement one
        private ManualResetEvent manualResetEvent = new ManualResetEvent(false);

        public Browser()
        {
            var settings = new CefSettings()
            {
                //By default CefSharp will use an in-memory cache, you need to     specify a Cache Folder to persist data
                CachePath =     Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "CefSharp\\Cache"),
            };

            //Autoshutdown when closing
            CefSharpSettings.ShutdownOnExit = true;

            //Perform dependency check to make sure all relevant resources are in our     output directory.
            Cef.Initialize(settings, performDependencyCheck: true, browserProcessHandler: null);

            RequestContext = new RequestContext();
            Page = new ChromiumWebBrowser("", null, RequestContext);
            PageInitialize();
        }

        /// <summary>
        /// Open the given url
        /// </summary>
        /// <param name="url">the url</param>
        /// <returns></returns>
        public void OpenUrl(string url)
        {
            try
            {
                Page.LoadingStateChanged += PageLoadingStateChanged;
                if (Page.IsBrowserInitialized)
                {
                    Page.Load(url);

                    //create a 60 sec timeout 
                    bool isSignalled = manualResetEvent.WaitOne(TimeSpan.FromSeconds(60));
                    manualResetEvent.Reset();

                    //As the request may actually get an answer, we'll force stop when the timeout is passed
                    if (!isSignalled)
                    {
                        Page.Stop();
                    }
                }
            }
            catch (ObjectDisposedException)
            {
                //happens on the manualResetEvent.Reset(); when a cancelation token has disposed the context
            }
            Page.LoadingStateChanged -= PageLoadingStateChanged;
        }

        /// <summary>
        /// Manage the IsLoading parameter
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void PageLoadingStateChanged(object sender, LoadingStateChangedEventArgs e)
        {
            // Check to see if loading is complete - this event is called twice, one when loading starts
            // second time when it's finished
            if (!e.IsLoading)
            {
                manualResetEvent.Set();
            }
        }

        /// <summary>
        /// Wait until page initialization
        /// </summary>
        private void PageInitialize()
        {
            SpinWait.SpinUntil(() => Page.IsBrowserInitialized);
        }
    }
}

现在在我的应用程序中，我只需要执行以下操作:

public MainWindow()
{
    InitializeComponent();
    _browser = new Browser();
}

private async void GetGoogleSource()
{
    _browser.OpenUrl("http://icanhazip.com/");
    string source = await _browser.Page.GetSourceAsync();
}

这是我得到的字符串

"<html><head></head><body><pre style=\"word-wrap: break-word; white-space: pre-wrap;\">NotGonnaGiveYouMyIP:)\n</pre></body></html>"