.NET 6最小API调用返回200但响应内容为空，Postman正常

服务端代码（.NET 6 Minimal API） #

app.MapGet("/", () =>
{
    return $"{{\"error\":\"0\", \"message\":\"\", \"rows\":\"0\", \"data\":\"It is working !\"}}";
});

客户端代码 #

using System.Net.Http;
using System.Net.Http.Headers;
using System.Threading.Tasks;

HttpClient httpClient = new HttpClient();
httpClient.BaseAddress = new Uri($"{(Properties.Settings.Default.use_https ? "https://" : "http://")}{Properties.Settings.Default.server_address}:Properties.Settings.Default.server_port}/");
HttpResponseMessage response = await httpClient.GetAsync("");

问题现象 #

调用后response.Content的内部信息如下：

{System.Net.Http.StreamContent}
    Headers: {Content-Type: text/plain; charset=utf-8
}
    IsBuffered: true
    bufferSize: 4096
    bufferedContent: {System.Net.Http.HttpContent.LimitMemoryStream}
    canCalculateLength: false
    content: {System.Net.Http.HttpClientHandler.WebExceptionWrapperStream}
    contentConsumed: true
    contentReadStream: null
    disposed: false
    headers: {Content-Type: text/plain; charset=utf-8
}
    start: 0

使用 Postman 调用http://localhost:5400/的 GET 接口可正常返回 JSON 结果：{"error":"0", "message":"", "rows":"0", "data":"It is working !"}，怀疑问题与System.Net.Http.HttpClientHandler.WebExceptionWrapperStream相关。

解决方案 #

1. 修复客户端 BaseAddress 拼接错误 #

客户端代码中 BaseAddress 的字符串拼接存在语法错误，Properties.Settings.Default.server_port未被正确解析为变量，导致 URI 格式无效，这是引发 WebExceptionWrapperStream 的核心原因：

// 错误代码
httpClient.BaseAddress = new Uri($"{(Properties.Settings.Default.use_https ? "https://" : "http://")}{Properties.Settings.Default.server_address}:Properties.Settings.Default.server_port}/");

// 修正后代码
httpClient.BaseAddress = new Uri($"{(Properties.Settings.Default.use_https ? "https://" : "http://")}{Properties.Settings.Default.server_address}:{Properties.Settings.Default.server_port}/");

需在server_port前添加{，确保变量被正确插入到 URI 字符串中。

2. 正确读取响应内容 #

即使 BaseAddress 正确，也需显式调用读取方法获取响应内容，而非直接查看response.Content的内部属性：

HttpResponseMessage response = await httpClient.GetAsync("");
// 确保请求未返回错误状态码
response.EnsureSuccessStatusCode();
// 将响应内容读取为字符串
string content = await response.Content.ReadAsStringAsync();
// 如需反序列化为对象，可使用 System.Text.Json
var result = System.Text.Json.JsonSerializer.Deserialize<YourResultModel>(content);

3. 服务端响应格式优化（可选） #

当前服务端直接返回字符串，框架默认将其识别为text/plain类型，建议直接返回匿名对象，让框架自动处理 JSON 序列化，响应头会自动设置为application/json：

app.MapGet("/", () =>
{
    return new 
    {
        error = "0",
        message = "",
        rows = "0",
        data = "It is working !"
    };
});

内容的提问来源于stack exchange，提问作者Srikanth S