NLog LogEventInfo.Message 在自定義 LayoutRenderer 上為 {0} 而不是 null 或空

Question

我有一個自定義的LayoutRenderer 。

如果我調用以下語句，那么我總是得到LogEventInfo.Message = {0}而不是null或"" 。 我是不是誤會了什么？

try
{
    int a = 1;
    int b = 0;
    var c = a / b;
}
catch (Exception e)
{
    var logger = LogManager.GetCurrentClassLogger();

    logger.Error(e);
}

public class HtLayoutRenderer : LayoutRenderer
{
    protected override void Append(StringBuilder builder, LogEventInfo logEvent)
    {
        // logEvent.Message is {0} instead of being null or empty ""
    }
}

更新 1 - 添加了完整的示例代碼

我只發布了一個很小的例子。

我有兩個自定義Exceptions ： HtReturnStatus和HtExceptions 。 它們都是Exception類型。 HtReturnStatus可以包含HtExceptions 。 HtLayoutRenderer正在解包對象並制作方便的日志布局。 提供什么類型的類/對象並不重要。

我的問題是{0} 。 如果這是正常行為，那么我會檢查logEvent.Message是否為{0}並忽略它。

try
{
    int a = 1;
    int b = 0;
    var c = a / b;
}
catch (Exception e)
{
    LayoutRenderer.Register<HtLayoutRenderer>("htmessage");

    TraceTarget target = new TraceTarget();
    target.Name = "console";
    target.Layout = Layout.FromString("${longdate} | ${level:uppercase=true} | ${logger} | ${htmessage}");
    LogManager.Configuration = new LoggingConfiguration();
    LogManager.Configuration.AddTarget(target);
    LogManager.Configuration.LoggingRules.Insert(0, new LoggingRule("*", LogLevel.FromString("Trace"), target));
    LogManager.ReconfigExistingLoggers();

    var logger = LogManager.GetCurrentClassLogger();

    logger.Error("1");
    logger.Error(e);
    logger.Error("2");
    logger.Error(e, "Hello World");
    logger.Error("");
    logger.Error("3");
    logger.Error(HtReturnStatus.Failed(e), "Lorem Ipsum");
    logger.Error("");
    logger.Error("4");
    logger.Error(HtReturnStatus.Failed(e, "Error on division"));
    logger.Error("");
    logger.Error("5");
    logger.Error(HtReturnStatus.Failed(HtErrorCode.OPC_BAD_CERTIFICATE_INVALID));
    logger.Error("");
    logger.Error("6");
    logger.Error(HtReturnStatus.Failed(HtErrorCode.OPC_BAD_UNEXPECTED_ERROR, "Error on division #2"));

    logger.Error("");
    logger.Error("7");
    logger.Error(new HtException(HtErrorCode.CODE_READER_DMC_MultipleMatches));
    logger.Error("");
    logger.Error("8");
    logger.Error(new HtException(HtErrorCode.CODE_READER_DMC_MultipleMatches, "hello world"));
    logger.Error("");
    logger.Error("9");
    logger.Error(new HtException(HtErrorCode.CODE_READER_DMC_MultipleMatches, "lorem ipsum", e));
}

testhost Error: 0 : 2020-01-21 10:14:01.1168 | ERROR | Haprotec.Error.NLogOutputTest | 1
testhost Error: 0 : 2020-01-21 10:14:01.1383 | ERROR | Haprotec.Error.NLogOutputTest | {0} - Attempted to divide by zero. - System.DivideByZeroException: Attempted to divide by zero.
StackTrace:    at Haprotec.Error.NLogOutputTest.HtReturnStatusOutputTest() in D:\Repositories\gitlab.haprotec\dotNet\HtCore\src\HtCore.Tests\Error\NLogOutputTest.cs:line 26
testhost Error: 0 : 2020-01-21 10:14:01.1572 | ERROR | Haprotec.Error.NLogOutputTest | 2
testhost Error: 0 : 2020-01-21 10:14:01.1572 | ERROR | Haprotec.Error.NLogOutputTest | Hello World - Attempted to divide by zero. - System.DivideByZeroException: Attempted to divide by zero.
StackTrace:    at Haprotec.Error.NLogOutputTest.HtReturnStatusOutputTest() in D:\Repositories\gitlab.haprotec\dotNet\HtCore\src\HtCore.Tests\Error\NLogOutputTest.cs:line 26
testhost Error: 0 : 2020-01-21 10:14:01.1572 | ERROR | Haprotec.Error.NLogOutputTest | 
testhost Error: 0 : 2020-01-21 10:14:01.1572 | ERROR | Haprotec.Error.NLogOutputTest | 3
testhost Error: 0 : 2020-01-21 10:14:01.1742 | ERROR | Haprotec.Error.NLogOutputTest | Lorem Ipsum - System.DivideByZeroException: Attempted to divide by zero.
StackTrace:    at Haprotec.Error.NLogOutputTest.HtReturnStatusOutputTest() in D:\Repositories\gitlab.haprotec\dotNet\HtCore\src\HtCore.Tests\Error\NLogOutputTest.cs:line 26
testhost Error: 0 : 2020-01-21 10:14:01.1742 | ERROR | Haprotec.Error.NLogOutputTest | 
testhost Error: 0 : 2020-01-21 10:14:01.1742 | ERROR | Haprotec.Error.NLogOutputTest | 4
testhost Error: 0 : 2020-01-21 10:14:01.1742 | ERROR | Haprotec.Error.NLogOutputTest | {0} - Error on division - System.DivideByZeroException: Attempted to divide by zero.
StackTrace:    at Haprotec.Error.NLogOutputTest.HtReturnStatusOutputTest() in D:\Repositories\gitlab.haprotec\dotNet\HtCore\src\HtCore.Tests\Error\NLogOutputTest.cs:line 26
testhost Error: 0 : 2020-01-21 10:14:01.1905 | ERROR | Haprotec.Error.NLogOutputTest | 
testhost Error: 0 : 2020-01-21 10:14:01.1905 | ERROR | Haprotec.Error.NLogOutputTest | 5
testhost Error: 0 : 2020-01-21 10:14:01.2166 | ERROR | Haprotec.Error.NLogOutputTest | {0} - Haprotec.Error.HtException: 563021 (OPC_BAD_CERTIFICATE_INVALID)
StackTrace:    at Haprotec.Error.NLogOutputTest.HtReturnStatusOutputTest() in D:\Repositories\gitlab.haprotec\dotNet\HtCore\src\HtCore.Tests\Error\NLogOutputTest.cs:line 26
testhost Error: 0 : 2020-01-21 10:14:01.2204 | ERROR | Haprotec.Error.NLogOutputTest | 
testhost Error: 0 : 2020-01-21 10:14:01.2204 | ERROR | Haprotec.Error.NLogOutputTest | 6
testhost Error: 0 : 2020-01-21 10:14:01.2204 | ERROR | Haprotec.Error.NLogOutputTest | {0} - Error on division #2 - Haprotec.Error.HtException: 563001 (OPC_BAD_UNEXPECTED_ERROR)
StackTrace:    at Haprotec.Error.NLogOutputTest.HtReturnStatusOutputTest() in D:\Repositories\gitlab.haprotec\dotNet\HtCore\src\HtCore.Tests\Error\NLogOutputTest.cs:line 26
testhost Error: 0 : 2020-01-21 10:14:01.2204 | ERROR | Haprotec.Error.NLogOutputTest | 
testhost Error: 0 : 2020-01-21 10:14:01.2204 | ERROR | Haprotec.Error.NLogOutputTest | 7
testhost Error: 0 : 2020-01-21 10:14:01.2374 | ERROR | Haprotec.Error.NLogOutputTest | {0} - Haprotec.Error.HtException: 500251 (CODE_READER_DMC_MultipleMatches)
StackTrace:    at Haprotec.Error.NLogOutputTest.HtReturnStatusOutputTest() in D:\Repositories\gitlab.haprotec\dotNet\HtCore\src\HtCore.Tests\Error\NLogOutputTest.cs:line 26
testhost Error: 0 : 2020-01-21 10:14:01.2374 | ERROR | Haprotec.Error.NLogOutputTest | 
testhost Error: 0 : 2020-01-21 10:14:01.2374 | ERROR | Haprotec.Error.NLogOutputTest | 8
testhost Error: 0 : 2020-01-21 10:14:01.2374 | ERROR | Haprotec.Error.NLogOutputTest | {0} - hello world - Haprotec.Error.HtException: 500251 (CODE_READER_DMC_MultipleMatches)
StackTrace:    at Haprotec.Error.NLogOutputTest.HtReturnStatusOutputTest() in D:\Repositories\gitlab.haprotec\dotNet\HtCore\src\HtCore.Tests\Error\NLogOutputTest.cs:line 26
testhost Error: 0 : 2020-01-21 10:14:01.2374 | ERROR | Haprotec.Error.NLogOutputTest | 
testhost Error: 0 : 2020-01-21 10:14:01.2506 | ERROR | Haprotec.Error.NLogOutputTest | 9
testhost Error: 0 : 2020-01-21 10:14:01.2506 | ERROR | Haprotec.Error.NLogOutputTest | {0} - lorem ipsum - System.DivideByZeroException: Attempted to divide by zero.
StackTrace:    at Haprotec.Error.NLogOutputTest.HtReturnStatusOutputTest() in D:\Repositories\gitlab.haprotec\dotNet\HtCore\src\HtCore.Tests\Error\NLogOutputTest.cs:line 26

Answer 1

這完全是故意的。 您正在調用此記錄器方法，其中一個記錄隨機對象：

Logger.Error<T>(T value);

這是對此的簡寫，以確保string.Format可以工作：

Logger.Error("{0}", value);

但是您可能已經注意到，已經為Exception實現了特殊處理。 NLog 執行額外檢查以捕獲${exception}的異常參數，但不會更改格式字符串。

在您的HtLayoutRenderer您可以像這樣識別它：

public class HtLayoutRenderer : LayoutRenderer
{
    protected override void Append(StringBuilder builder, LogEventInfo logEvent)
    {
       if ( logevent.Exception != null
         && logevent.Message == "{0}"
         && logevent.Parameters?.Length == 1
         && ReferenceEquals(logevent.Exception, logevent.Parameters[0])
       {
          // Exception given as single parameter without any message
       }
    }
}

請注意， LogEventInfo.Message和LogEventInfo.FormattedMessage之間存在差異