CODEWITHSUNDEEP
c#asp.net-coreloggingserilog
Nazarii
Nazarii

Reputation: 500

ASP.Net Core Serilog How to read from log file during runtime

I'm working on a ASP.NET Core 3.1 application. I want to log events to file and be able to read them during application runtime. To do that I'm trying to use Serilog.Extensions.Logging.File NuGet package and then specifying log file path as following:

Startup.cs

 public void Configure(IApplicationBuilder app, ILoggerFactory logFactory)
 {
     logFactory.AddFile("Log");
 }

Any attempt to read or write to file like this way

string ReadLog(string logPath)
{
    return System.IO.File.ReadAllText(logPath);
}

ends in System.IO.IOException: 'The process cannot access the file {log-path} because it is being used by another process.' exception.

EDIT: I have installed Serilog.AspNetCore and made changes shown below while also removing logFactory from Configure function. But exception continues to occur.


Program.cs 

public static int Main(string[] args)
{
    Log.Logger = new LoggerConfiguration()
        .MinimumLevel.Debug()
        .MinimumLevel.Override("Microsoft", LogEventLevel.Information)
        .Enrich.FromLogContext()
        .WriteTo.Console()
        .WriteTo.File(
            "Logs/log-.txt", 
            shared: true,
            flushToDiskInterval: TimeSpan.FromSeconds(5),
            rollingInterval: RollingInterval.Day)
        .CreateLogger();

    try
    {
        Log.Information("Starting web host");
        CreateHostBuilder(args).Build().Run();
        return 0;
    }
    catch (Exception ex)
    {
        Log.Fatal(ex, "Host terminated unexpectedly");
        return 1;
    }
    finally
    {
        Log.CloseAndFlush();
    }
}

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.UseStartup<Startup>();
        }).UseSerilog();

EDIT 2: As requested by julealgon I'm sharing my exact read logic. I'm trying to read using a controller, which I declared following way:

[Controller]
[Route("[controller]")]
public class LogController : Controller
{
    [Route("Read")]
    public IActionResult ReadLog(string logPath)
    {
        if (System.IO.File.Exists(logPath))
        {
            string logContent = System.IO.File.ReadAllText(logPath);//exception appears here.
            return Content(logContent);
        }
        else return NotFound();
    }
}

Then using example query below to read log recorded by Friday, March 13, 2020.

https://localhost:44323/Log/Read?logPath=Logs\log-20200313.txt

Upvotes: 11

Views: 11765

Answers (4)

Shervin Ivari
Shervin Ivari

Reputation: 2611

After setting the shared option to true you can read and write in the log file.

For writing

  using var stream = new FileStream(logFilePath, FileMode.Create, FileAccess.Write, FileShare.ReadWrite);
  using var writer = new StreamWriter(stream);
  writer.Write(string.Empty);

For Reading

   using var stream = new FileStream(logFilePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
   using var reader = new StreamReader(stream);
   vat txt = await reader.ReadToEndAsync();

Upvotes: 0

DomenPigeon
DomenPigeon

Reputation: 1127

Another way, where you don't need to read the file all the time is to create a simple sink which collects the logs:

using Serilog.Core;
using Serilog.Events;

public class RuntimeLogsSink : ILogEventSink
{
    private const int MaxLogs = 1000;
    private readonly List<LogEvent> _logEvents = new(MaxLogs);

    public void Emit(LogEvent logEvent)
    {
        lock (_logEvents)
        {
            if (_logEvents.Count == MaxLogs)
            {
                _logEvents.RemoveAt(0);
            }

            _logEvents.Add(logEvent);
        }
    }

    public ImmutableArray<LogEvent> GetLogs()
    {
        lock (_logEvents)
        {
            return [.._logEvents];
        }
    }
}

Then you can simply use it:

var sink = new RuntimeLogsSink();
Log.Logger = new LoggerConfiguration()
        // your configuration ...
        .WriteTo.Sink(sink)
        .CreateLogger();

// Inject sink into some service and use it

Upvotes: 0

Mike Goatly
Mike Goatly

Reputation: 7578

When reading the file, I think use something like this will work:

using (var stream = File.Open(file, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
using (var reader = new StreamReader(stream))
{
    return reader.ReadToEnd();
}

The trick appears to be the specification of FileShare.ReadWrite as this is the policy used to write to when the sink opens the log file to write to. There's a similar bug reported over in the serilog-sinks-file repo.

Upvotes: 11

julealgon
julealgon

Reputation: 8221

When configuring the File sink, there is an overload that provides a shared Boolean argument. If you set that to true (it's false by default) you should then be able to read the contents of the file somewhere else in your application.

Upvotes: 10

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