In there a replacement for OnBeforeResourceLoad in IRequestHandler?

Question

I'm trying to change the user agent dynamically using CefSharp. I have looked at the IRequestHandler class and I no longer see a method called OnBeforeResourceLoad.

I did, however, find a method called OnBeforeBrowse. However, all of the request headers are empty and when I try and add one, it simply does not add. I have tried to take a reference, change the value and re-assign, but no dice.

• CefSharp: 75.1.142
• .NET: 4.7.2
• OffScreen

I found a method called OnBeforeBrowse in IRequestHandler. However, all of the request headers are empty and when I try and add one via the IRequest param, it simply does not add. I have tried to take a reference, change the value and re-assign, but no dice. Always comes back empty with no keys.

protected override bool OnBeforeBrowse(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, IRequest request, bool userGesture, bool isRedirect)
{
    var headers = request.Headers;
    headers["User-Agent"] = "New user agent";
    request.Headers = headers;
    return false;
}

I expect the user agent to change to the value I give it.

Answer 1

I have spent a lot of time on this and I couldn't find any examples in light of these new changes to the CefSharp library, so I have put together something that works. I used bits and pieces I found online and put it all together. It may not be perfect, but I couldnt find a straight forward answer anywhere!

Define the class which implements ResourceRequestHandler. The base class has the required OnBeforeResourceLoad function. I added a userAgent string to the constructor see it can be passed from calling fucntions.

    public class ResourceRequestHandlerExt : ResourceRequestHandler
    {
        private string userAgent;

        public ResourceRequestHandlerExt(string userAgent)
        {
            this.userAgent = userAgent;
        }

        protected override CefReturnValue OnBeforeResourceLoad(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, IRequest request, IRequestCallback callback)
        {
            var headers = request.Headers;
            headers["User-Agent"] = userAgent;
            request.Headers = headers;

            return base.OnBeforeResourceLoad(chromiumWebBrowser, browser, frame, request, callback);
        }
    }

Define the class which implements RequestHandler. The base class has a required GetResourceRequestHandler function which allows use to pass our user agent to the ResourceRequestHandlerExt class.

    public class RequestHandlerExt : RequestHandler
    {
        private string userAgent;

        public RequestHandlerExt(string userAgent)
        {
            this.userAgent = userAgent;
        }

        protected override IResourceRequestHandler GetResourceRequestHandler(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, IRequest request, bool isNavigation, bool isDownload, string requestInitiator, ref bool disableDefaultHandling)
        {
            if (!string.IsNullOrEmpty(userAgent)) return new ResourceRequestHandlerExt(userAgent);
            else return base.GetResourceRequestHandler(chromiumWebBrowser, browser, frame, request, isNavigation, isDownload, requestInitiator, ref disableDefaultHandling);
        }
    }

When instantiating the ChromiumWebBrowser object, you set the RequestHandler to the RequestHandlerExt class above using:

ChromiumWebBrowser browser = new ChromiumWebBrowser();
browser.RequestHandler = new RequestHandlerExt(userAgent);

• Specifying a user agent in CefSettings will get overwritten, so its not needed in this case.
• If you do not specify a user agent, then no headers will be added/modified
• The user agent can be changed for each browser.Load(url) call.

Answer 2

Starting with version 75 CEF now supports the Chromium Network Service which brings a huge number of breaking API changes.

As per https://github.com/cefsharp/CefSharp/issues/2743

Resource-related callbacks have been moved from IRequestHandler to a new IResourceRequestHandler interface which is returned via the IRequestHandler.GetResourceRequestHandler method

• New RequestHandler is available to override only the methods you require
• New ResourceRequestHandler is available to override only the methods you require