C# 如何忽略http响应头错误？

Question

使用过各种AI工具，给出的方案均无法解决

项目1

string framework = RuntimeInformation.FrameworkDescription;
// 获取.NET版本=.NET Framework 4.8.9310.0
Version version = Environment.Version;
//4.0.30319.42000

另一个项目2

string framework = RuntimeInformation.FrameworkDescription;
// 获取.NET版本=.NET 8.0.18
Version version = Environment.Version;
// 获取CLR版本 8.0.18
执行同一段代码

使用同一段代码，参数也一样，地址也一样

AppContext.SetSwitch("System.Net.Http.UseStrictHttpHeaders", false);
string retString = "";
try
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://localhost:7999/api/app_print");

request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";
request.ContentLength = Encoding.UTF8.GetByteCount("VER_ID=00&TASK_ID=0&CMD_ID=00&TYPE=04");
request.ServicePoint.Expect100Continue = false;
request.KeepAlive = false;
request.Timeout = 6000;

Stream myRequestStream = request.GetRequestStream();
StreamWriter myStreamWriter = new StreamWriter(myRequestStream);

myStreamWriter.Write("VER_ID=00&TASK_ID=0&CMD_ID=00&TYPE=04");
myStreamWriter.Close();

HttpWebResponse response = (HttpWebResponse)request.GetResponse();
string encoding = response.CharacterSet.Trim();
Stream myResponseStream = response.GetResponseStream();
StreamReader myStreamReader = new StreamReader(myResponseStream, Encoding.GetEncoding(encoding));

retString = myStreamReader.ReadToEnd();

myStreamReader.Close();
myResponseStream.Close();
}
catch (Exception e)
{
retString = e.Message;
retString = "";
}

项目1获取结果正常，能够正常获取响应数据 如下

项目2报错

System.Net.WebException:“Received an invalid header line: 'Access-Control-Allow-Methods??"POST, GET, OPTIONS, DELETE"
'.”

HttpRequestException: Received an invalid header line: 'Access-Control-Allow-Methods??"POST, GET, OPTIONS, DELETE"
'.

已经使用过deepseek chatGTp等AI ，给出方案均无法解决

Answer 1

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解决方案

你可以使用 HttpClient 的 DefaultRequestHeaders 属性来忽略 HTTP 响应头错误。具体代码如下：

using System.Net.Http;
using System.Net.Http.Headers;

// ...

var client = new HttpClient();
client.DefaultRequestHeaders.IfModifiedSince = DateTime.MinValue;
client.DefaultRequestHeaders.IfModifiedSince = DateTime.MinValue;

var response = await client.GetAsync("你的URL");

或者使用 ServicePointManager 来设置忽略 HTTP 响应头错误：

using System.Net;

// ...

ServicePointManager.ServerCertificateCustomValidationCallback = (sender, cert, chain, sslPolicyErrors) => true;

注意

上述代码可能会导致安全问题，请根据实际情况选择合适的解决方案。