.NET中使用GET发送JSON触发Cannot send a content-body错误

我用以下代码调用外部REST API时，SendAsync()抛出了**"Cannot send a content-body with this verb-type."**错误：

var request = new HttpRequestMessage( HttpMethod.Get, url );
request.Content = new StringContent( json, Encoding.UTF8, "application/json" );
client.SendAsync(request);

这个外部API要求用GET方法接收JSON数据，虽然不符合REST规范，但在Postman中可以正常运行。API文档细节如下：

Method: GET
URL: http://server/api/organization/status/39bd8abc-6022-44e9-8a70-ed4830b8afc1
Authentication: Bearer
Header:
Key: X-Request-Partner
Value: 7e884abc-2cd9-4990-a559-18f7def375e9
Body (raw JSON):

{
"Fields": [
{
  "Name": "IdPerson",
  "ObjectType": "Person"
},
{
  "Name": "IdCard",
  "ObjectType": "PersonBadgeNumber"
},
{
  "Name": "BookingDateTime",
  "ObjectType": "DataExchangePersonalStatusLastBookingTime"
},
{
  "Name": "TerminalApiKey",
  "ObjectType": "DataExchangePersonalStatusLastTerminal",
  "Representation": "Naming"
},
{
  "Name": "Status",
  "ObjectType": "DataExchangePersonalStatusActual",
  "Replacements": {
    "DefaultValue": "Abwesend",
    "ReplaceBy": [
      {
        "SearchValue": "Present",
        "ReplaceBy": "Anwesend"
      }
    ]
  }
}
]
}

.NET的HttpClient默认会阻止GET请求携带请求体，这是遵循HTTP规范的行为，但针对这类非常规API，可通过以下方式实现需求：

方法一：反射绕过HttpClient检查 #

通过反射修改HttpClientHandler的私有配置，允许GET请求带Body：

var handler = new HttpClientHandler();
// 调用私有方法开启GET请求允许带Body的配置
var allowGetBodyMethod = typeof(HttpClientHandler).GetMethod(
    "AllowGetRequestBody", 
    System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance
);
allowGetBodyMethod.Invoke(handler, new object[] { true });

var client = new HttpClient(handler);

var request = new HttpRequestMessage(HttpMethod.Get, url);
request.Content = new StringContent(json, Encoding.UTF8, "application/json");
// 添加API要求的请求头
request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", "你的Bearer令牌");
request.Headers.Add("X-Request-Partner", "7e884abc-2cd9-4990-a559-18f7def375e9");

var response = await client.SendAsync(request);
response.EnsureSuccessStatusCode();
var responseContent = await response.Content.ReadAsStringAsync();

方法二：使用HttpWebRequest（兼容全.NET版本） #

HttpWebRequest不会限制GET请求的请求体，直接使用即可：

var request = (HttpWebRequest)WebRequest.Create(url);
request.Method = "GET";
request.ContentType = "application/json";
// 添加请求头
request.Headers["Authorization"] = "Bearer 你的Bearer令牌";
request.Headers["X-Request-Partner"] = "7e884abc-2cd9-4990-a559-18f7def375e9";

// 写入JSON请求体
using (var streamWriter = new StreamWriter(request.GetRequestStream()))
{
    streamWriter.Write(json);
    streamWriter.Flush();
}

// 获取响应
using (var response = (HttpWebResponse)request.GetResponse())
using (var streamReader = new StreamReader(response.GetResponseStream()))
{
    var responseContent = streamReader.ReadToEnd();
}

方法三：手动设置ContentLength（.NET Core 3.0+） #

在.NET Core 3.0及以上版本，可通过手动设置ContentLength绕过检查：

var request = new HttpRequestMessage(HttpMethod.Get, url);
var content = new StringContent(json, Encoding.UTF8, "application/json");
request.Content = content;
// 手动赋值ContentLength，绕过默认检查逻辑
request.Content.Headers.ContentLength = content.Headers.ContentLength;

// 添加请求头
request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", "你的Bearer令牌");
request.Headers.Add("X-Request-Partner", "7e884abc-2cd9-4990-a559-18f7def375e9");

var client = new HttpClient();
var response = await client.SendAsync(request);

内容的提问来源于stack exchange，提问作者Powerslave