.NET MAUI Android连接API遇400错误，Xamarin版本正常运行

关键差异对比 #

从你提供的请求/响应信息中，能看到两个核心差异点：

• HTTP协议版本：Xamarin请求使用HTTP/1.1，而.NET MAUI请求默认使用HTTP/2.0
• 请求内容长度：成功请求的Content-Length为79，失败请求为78，说明两次发送的表单内容存在字节级差异

针对性排查方案 #

1. 强制HttpClient使用HTTP/1.1
   部分老版本IIS（如你使用的IIS 10.0）对HTTP/2兼容性可能存在问题，可在MAUI中通过配置HttpClientHandler指定协议版本：

   var handler = new HttpClientHandler();
   handler.DefaultRequestVersion = HttpVersion.Version11;
   handler.MaxRequestVersion = HttpVersion.Version11;
   var client = new HttpClient(handler);
   

2. 核对请求表单的具体内容
   虽同为FormUrlEncodedContent，但可能存在编码或参数细节差异：

   • 检查参数完整性（如用户名、密码、grant_type等是否与Xamarin完全一致）
   • 排查特殊字符的URL编码差异（Xamarin与MAUI的编码规则可能略有不同）
   • 直接输出表单字符串对比内容：

     var content = new FormUrlEncodedContent(yourParameters);
     string contentString = await content.ReadAsStringAsync();
     Debug.WriteLine(contentString);
     

3. 解析400响应的具体错误信息
   失败响应的Content-Length为82，其中的JSON内容包含API返回的具体拒绝原因，务必解析查看：

   var response = await client.PostAsync(...);
   if (!response.IsSuccessStatusCode)
   {
       string errorContent = await response.Content.ReadAsStringAsync();
       Debug.WriteLine(errorContent);
   }
   

4. 核对NuGet包版本
   重点对比System.Net.Http、Microsoft.Extensions.Http等HTTP相关包的版本，确保MAUI项目的包版本与Xamarin项目兼容，或尝试回退到Xamarin使用的包版本测试。

附请求/响应原始信息 #

成功请求（Xamarin）

{Method: POST, RequestUri: 'http://api.xxx.net/token', Version: 1.1, Content: System.Net.Http.FormUrlEncodedContent, Headers:
{
  Content-Type: application/x-www-form-urlencoded
  Content-Length: 79
}}

{StatusCode: 200, ReasonPhrase: 'OK', Version: 1.1, Content: System.Net.Http.StreamContent, Headers:
{
  Access-Control-Allow-Credentials: true
  Access-Control-Allow-Headers: Content-Type, Authorization
  Access-Control-Allow-Methods: *
  Access-Control-Allow-Origin: *
  Cache-Control: no-cache
  Date: Sun, 17 Mar 2024 18:37:42 GMT
  Pragma: no-cache
  Server: Microsoft-IIS/10.0
  X-Android-Received-Millis: 1710700662659
  X-Android-Response-Source: NETWORK 200
  X-Android-Selected-Protocol: http/1.1
  X-Android-Sent-Millis: 1710700662393
  X-Powered-By: ASP.NET
  X-Powered-By-Plesk: PleskWin
  Content-Length: 541
  Content-Type: application/json; charset=UTF-8
  Expires: -1
}}

失败请求（.NET MAUI）

{Method: POST, RequestUri: 'http://api.xxx.net/token', Version: 2.0, Content: System.Net.Http.FormUrlEncodedContent, Headers:
{
  Content-Type: application/x-www-form-urlencoded
  Content-Length: 78
}}

{StatusCode: 400, ReasonPhrase: 'Bad Request', Version: 1.1, Content: System.Net.Http.StreamContent, Headers:
{
  Access-Control-Allow-Credentials: true
  Access-Control-Allow-Headers: Content-Type, Authorization
  Access-Control-Allow-Methods: *
  Access-Control-Allow-Origin: *
  Cache-Control: no-cache
  Date: Sun, 17 Mar 2024 18:27:50 GMT
  Pragma: no-cache
  Server: Microsoft-IIS/10.0
  X-Android-Received-Millis: 1710700070765
  X-Android-Response-Source: NETWORK 400
  X-Android-Selected-Protocol: http/1.1
  X-Android-Sent-Millis: 1710700069943
  X-Powered-By: ASP.NET
  X-Powered-By-Plesk: PleskWin
  Content-Length: 82
  Content-Type: application/json; charset=UTF-8
  Expires: -1
}}

内容的提问来源于stack exchange，提问作者Joey007