[HttpPost]
public async Task<IActionResult> Test([FromBody]string postStr)
{

    using (var reader = new StreamReader(Request.Body, System.Text.Encoding.UTF8))
    {
        reader.BaseStream.Seek(0, SeekOrigin.Begin);  //大概是== Request.Body.Position = 0;的意思
        var readerStr = await reader.ReadToEndAsync();
        reader.BaseStream.Seek(0, SeekOrigin.Begin);  //读完后也复原

        return Ok(readerStr);
    }
}

curl --location --request POST 'http://localhost:5001/api/TestPostReader/test' 
--header 'Content-Type: application/json' 
--data-raw '{"name":"hei"}'

System.NotSupportedException: Specified method is not supported.
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpRequestStream.Seek(Int64 offset, SeekOrigin origin)
   at Push.WebApi.Controllers.TestPostReaderController.Test() in D:工作39solution-pushPush.WebApiControllersTestPostReaderController.cs:line 21
   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Logged|12_1(ControllerActionInvoker invoker)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

app.Use((context, next) =>
{
    context.Request.EnableBuffering();
    return next();
});
//这个在后边
app.UseRouting();