HttpWebRequest、RestSharp等请求重定向站点无响应超时如何解决？

根本原因 #

• 目标站点配置了CDN/反向代理防护规则，会直接拦截没有携带标准User-Agent请求头的请求，挂起连接直到超时
• 低版本.NET Framework（低于4.8）默认启用的TLS最高版本为TLS 1.1，当前绝大多数站点已要求使用TLS 1.2及以上版本，TLS握手失败也会导致请求无响应超时
• 部分站点跳转时会校验请求来源等header，默认自动跳转配置未携带对应参数也会被拦截

修复方案 #

HttpClient 修复（微软官方推荐优先使用此实现） #

// 全局只初始化一次HttpClient即可，不要每次请求都新建
private static readonly HttpClient _client = new HttpClient(new HttpClientHandler()
{
    AllowAutoRedirect = true,
    // 显式指定支持的TLS版本
    SslProtocols = SslProtocols.Tls12 | SslProtocols.Tls13
})
{
    Timeout = TimeSpan.FromSeconds(30)
};

static async Task Main(string[] args)
{
    // 低版本.NET需要加这行全局配置默认TLS版本
    ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls13;
    // 给请求添加User-Agent头，模拟浏览器请求
    using var requestMessage = new HttpRequestMessage(HttpMethod.Get, "https://www.eventim.pl");
    requestMessage.Headers.UserAgent.ParseAdd("Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36");
    try
    {
        HttpResponseMessage response = await _client.SendAsync(requestMessage);
        response.EnsureSuccessStatusCode();
        var res = response.StatusCode;
        Console.WriteLine((int)res);
    }
    catch (HttpRequestException e)
    {
        Console.WriteLine("Exception Caught!");
        Console.WriteLine("Message :{0} ", e.Message);
    }
}

HttpWebRequest 修复 #

// 全局配置TLS版本
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls13;
HttpWebRequest init = (HttpWebRequest)WebRequest.Create(url);
init.AllowAutoRedirect = true;
// 添加User-Agent头
init.UserAgent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36";
init.Timeout = 30000;
HttpWebResponse resp = (HttpWebResponse)init.GetResponse();
Console.WriteLine(resp.StatusCode);

RestSharp 修复 #

// 全局配置TLS版本
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls13;
var client = new RestClient(url);
client.Timeout = 30000;
client.FollowRedirects = true;
var request = new RestRequest(Method.GET);
// 添加User-Agent头
request.AddHeader("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36");
IRestResponse response = client.Execute(request);
Console.WriteLine(response.StatusCode);

注意事项 #

• 若使用.NET Core/.NET 5+版本，默认已支持TLS 1.2/1.3，可省略TLS版本配置步骤，仅添加User-Agent头即可正常请求
• 不要频繁新建HttpClient实例，会导致端口占用过多，建议全局单例复用

内容的提问来源于stack exchange，提问作者Adam Wróbel