${aspnet-request-posted-body} could throw 'Synchronous operations are disallowed' for ASP.NET Core 3

[304NotModified]

NLog 4.7.0
Nlog.Target.Http 1.0.1
Nlog.web.AspNet.Core 4.9.1
Aspnet.Core 3.1.201

internal logging first was indicating :

Warn Exception in 'NLog.Web.LayoutRenderers.AspNetRequestPostedBody.Append()' 
Exception: System.InvalidOperationException: 
Synchronous operations are disallowed. 
Call ReadAsync or set AllowSynchronousIO to true instead.

After googling I found that I must add

 services.Configure<IISServerOptions>(options =>
 {
     options.AllowSynchronousIO = true;
  });

Originally posted by @husseinshaib1 in NLog/NLog#3906 (comment)

[304NotModified]

related graphql-dotnet/graphql-dotnet#1325

See also: https://docs.microsoft.com/en-us/dotnet/core/compatibility/aspnetcore#http-synchronous-io-disabled-in-all-servers

[vlmironoff]

For Kestrel use:
services.Configure<KestrelServerOptions>(options => { options.AllowSynchronousIO = true; });

[vlmironoff]

@304NotModified ${aspnet-request-posted-body} is always empty in logs. I'm using asp.net core 3.1
NLog.Web.AspNetCore assembly is added to nlog.config

[304NotModified]

@vlmironoff I think it depends when you're doing the logger call and if it's async. Please open a new issue for ths

[diegosps]

@vlmironoff
This might help you or someone.
Like 304 said, if you are doing the logging after the request, you hava to enable the rewind of the stream:

public async Task Invoke(HttpContext httpContext, ILogger<RequestLogMiddleware> logger)
        {
            var sw = Stopwatch.StartNew();
            httpContext.Request.EnableBuffering(); //this line is the key (asp.net core 3.1)
            await _next(httpContext);

            sw.Stop();
            var code = httpContext.Response?.StatusCode;
            string usuario = string.Empty;
            if (!string.IsNullOrEmpty(httpContext.User.Identity.Name))
                usuario = httpContext.User.Identity.Name;
            if (httpContext.Request?.Method != "OPTIONS")
                logger.LogInformation("Testando o middleware: {usuario}, {codigo}, {tempo}", usuario, code, (int)Math.Truncate(sw.Elapsed.TotalMilliseconds));
        }

I also had to add the options.AllowSynchronousIO = true for kestrel and IIS

[snakefoot]

Thanks to @bakgerman now NLog.Web.AspNetCore v5.1 re-introduces ${aspnet-request-posted-body} with help from middleware:

app.UseMiddleware<NLog.Web.NLogRequestPostedBodyMiddleware>();

It is no longer necessary to explicit call context.Request.EnableBuffering(); as it is handled by the middleware.