HttpWebRequst中https的验证处理问题

最近在公司项目中使用了HttpWebRequst相关API，运行环境为.Net/Mono 2.0，是一款针对Unity平台的工具。开发过程中碰到了大家可能都碰到过的问题，Http还是Https？ 为什么Http可以正常响应，Https就会失败，返回结果为authorize or decrypt failed.

by th way, .Net 4.0及以上版本好像已经没有这个问题了，巨硬默默把坑填了。

使用Http的写法：

public void Get(string Url)
{

HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create (Url);
webRequest.Method="GET";
webRequest.UserAgent = "Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/36.0.1985.125 Safari/537.36";
webRequest.BeginGetResponse(GetResponseCallback,webRequest);
}


private void GetResponseCallback(IAsyncResult ar)
{
//RequestState myRequestState = (RequestState)ar.AsyncState;
HttpWebRequest webRequest = (HttpWebRequest)ar.AsyncState;
try{
WebResponse response = webRequest.EndGetResponse(ar);
streamReader = new StreamReader(response.GetResponseStream ());
}
catch(Exception es)
{
Debug.Log (es.Message);
}
if (GetDataCompleted != null) {
GetDataCompleted(this,new GetDataCompletedArgs(streamReader.ReadToEnd ()));
}
}

这里使用了异步，同步的写法效果相同。

但是如果此时使用了Https的Url，结果会一直返回失败。这是为什么呢？原因是Https基于SSL/TLS协议，需要在请求之前进行证书验证，而我们上面的写法并没有进行相关的验证，所以导致通信失败。怎么解决此问题呢？很简单，我们在请求发出前进行验证，在.Net 2.0或更高版本，我们加入回调函数即可。

解决办法：

public void Get(string Url)
        {
            //SSL/TLS certificate method
            ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(CheckValidationResult);
            HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create (Url);
            webRequest.Method="GET";
            webRequest.UserAgent = "Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/36.0.1985.125 Safari/537.36";
            webRequest.BeginGetResponse(GetResponseCallback,webRequest);
        }

/// <summary>
        /// SSL/TLS certificate callback method
        /// Must return true
        /// </summary>
        /// <returns><c>true</c>, if validation result was checked, <c>false</c> otherwise.</returns>
        /// <param name="sender">Sender.</param>
        /// <param name="certificate">Certificate.</param>
        /// <param name="chain">Chain.</param>
        /// <param name="sslPolicyErrors">Ssl policy errors.</param>
        public bool CheckValidationResult (object sender, System.Security.Cryptography.X509Certificates.X509Certificate certificate, System.Security.Cryptography.X509Certificates.X509Chain chain, SslPolicyErrors sslPolicyErrors)
        {
            //Debug.LogWarning (certificate.GetSerialNumberString ());
            return true;
        }

        /// <summary>
        /// Gets the response callback.
        /// </summary>
        /// <param name="ar">Ar.</param>
        private void GetResponseCallback(IAsyncResult ar)
        {
            //RequestState myRequestState = (RequestState)ar.AsyncState;
            HttpWebRequest webRequest = (HttpWebRequest)ar.AsyncState;
            try{
                WebResponse response = webRequest.EndGetResponse(ar);
                streamReader = new StreamReader(response.GetResponseStream ());
            }
            catch(Exception es)
            {
                Debug.Log (es.Message);
            }
            if (GetDataCompleted != null) {
                GetDataCompleted(this,new GetDataCompletedArgs(streamReader.ReadToEnd ()));
            }
        }

至此就可以，解决此问题，这类问题说大不大，说小不小，属于我们开发中遇到的小坑之一，.Net4.0以上版本不需注意此问题。

关于更低的.Net 1.1的写法，大家可以去看一下博客，本篇博文也是参照他的解决方案：

http://blog.sina.com.cn/s/blog_4ae95c270101qnn1.html