Poor man display errors–part 2 – API
The idea of previous post was that I want to display the errors from a WebApplication – composed by a backend ( WebAPI .NET Core )and frontend( Blazor )
In this post I will show what modifications I must do in the API – code in .NET Core . There are 3 steps
Step1 : Intercept Errors
First I should intercept ( via a middleware ) all errors that can occur in an WebAPI.
using NLog.Web;
namespace XP.API;
public class LogErrorsMiddleware : IMiddleware
{
static LogErrorsMiddleware()
{
logger = NLog.LogManager.GetCurrentClassLogger();
}
private static NLog.Logger logger;
public LogErrorsMiddleware()
{
}
public Task InvokeAsync(HttpContext context, RequestDelegate next)
{
try
{
logger.Debug("Starting "+ context.Request.Path);
return next(context);
}
catch(Exception ex)
{
// Log the exception
logger.Error(ex, "An error occurred while processing the request.");
throw;
}
finally
{
logger.Debug("Ending " + context.Request.Path);
}
}
}
And I register in program.cs
builder.Services.AddTransient<LogErrorsMiddleware>(); //other statemtents app.UseMiddleware<XP.API.LogErrorsMiddleware>();
Step2 : Add errors to memory
Now we should register the errors from the logging framework into the memory . NLog has a target for registering in memory
( https://github.com/NLog/NLog/wiki/Memory-target ) . ( Serilog has https://github.com/serilog-contrib/SerilogSinksInMemory)
So this is the nlog xml
<?xml version="1.0" encoding="utf-8" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" autoReload="true" throwConfigExceptions="true" internalLogLevel="Info" internalLogFile="c:\temp\internal-nlog-AspNetCore.txt">
<!-- enable asp.net core layout renderers -->
<extensions>
<add assembly="NLog.Web.AspNetCore"/>
</extensions>
<!-- the targets to write to -->
<targets>
<target xsi:type="Memory" name="stringData" MaxLogsCount="200" layout="${longdate}|${aspnet-user-isauthenticated}|${aspnet-user-identity}|${level:uppercase=true}|${logger}|${message:withexception=true}" />
<!-- File Target for all log messages with basic details -->
<target xsi:type="File" name="allfile" fileName="c:\temp\nlog-AspNetCore-all-${shortdate}.log" layout="${longdate}|${event-properties:item=EventId:whenEmpty=0}|${level:uppercase=true}|${logger}|${message} ${exception:format=tostring}" />
<!-- File Target for own log messages with extra web details using some ASP.NET core renderers -->
<target xsi:type="File" name="ownFile-web" fileName="c:\temp\nlog-AspNetCore-own-${shortdate}.log" layout="${longdate}|${event-properties:item=EventId:whenEmpty=0}|${level:uppercase=true}|${logger}|${message} ${exception:format=tostring}|url: ${aspnet-request-url}|action: ${aspnet-mvc-action}" />
<!--Console Target for hosting lifetime messages to improve Docker / Visual Studio startup detection -->
<target xsi:type="Console" name="lifetimeConsole" layout="${MicrosoftConsoleLayout}" />
</targets>
<!-- rules to map from logger name to target -->
<rules>
<!-- All logs, including from Microsoft -->
<!--<logger name="*" minlevel="Trace" writeTo="allfile" />-->
<!-- Suppress output from Microsoft framework when non-critical -->
<logger name="System.*" finalMinLevel="Warn" />
<logger name="Microsoft.*" finalMinLevel="Warn" />
<!-- Keep output from Microsoft.Hosting.Lifetime to console for fast startup detection -->
<logger name="Microsoft.Hosting.Lifetime*" finalMinLevel="Info" writeTo="lifetimeConsole" />
<logger name="*" minLevel="Trace" writeTo="lifetimeConsole" />
<logger name="*" minLevel="Error" writeTo="stringData" />
<!--<logger name="*" minLevel="Trace" writeTo="ownFile-web" />-->
</rules>
</nlog>
Step3 : Expose Errors
Now we should expose the API to the outside world. I have considered 2 API, one for retrieving and the other for clearing
app.MapGet("/nlog/memory/{name:alpha}/list", (string name) =>
{
var target = LogManager.Configuration.FindTargetByName<MemoryTarget>(name);
var logEvents = target.Logs;
return logEvents.Select((line, nr) => new
{
nr = (nr+1),
line,
}).ToArray();
});
app.MapGet("/nlog/memory/{name}/clear", (string name) =>
{
var target = LogManager.Configuration.FindTargetByName<MemoryTarget>(name);
var logEvents = target.Logs;
var nr = logEvents.Count;
logEvents.Clear();
return (nr.ToString());
})
//.ShortCircuit()
.WithTags("andrei");
In part three, we’ll explore how to call these endpoints from your Blazor frontend and display errors in a user-friendly way.