布局以外的类型的 nlog 渲染器（用于目标属性）答案

【问题标题】：nlog renderer for types other than the Layout (for target attributes)布局以外的类型的 nlog 渲染器（用于目标属性）
【发布时间】：2023-04-09 03:16:01
【问题描述】：

我正在尝试使用自定义渲染器通过 app.config 中的参数配置邮件目标。我的 NLog 邮件目标：

<target name="AlertMail" xsi:type="Mail"
  to="${mailTo}"
  from="${mailFrom}"
  html="true"
  encoding="${enc}"
  subject="[APPNAME][${mailEnv}][${instanceName}][${logger:uppercase=true}]"
  smtpServer="${smtpHost}"
  smtpAuthentication="${smtpAuth}"
  smtpUserName="${smtpUserName}"
  smtpPassword="${smtpPassword}"
  header="${mailHtmlHeader}${mailBodyHeader}"
  layout="${mailMessage}"
  footer="${mailBodyFooter}${mailHtmlFooter}"/>

NLog 变量：

<variable name="${enc}" value="${app-settings:default.encoding}" />
<variable name="${smtpAuth}" value="${app-settings:alerting.smtp.authentication}" />

NLog 布局渲染器：

[LayoutRenderer("app-settings")]
public class AppSettingsRenderer : LayoutRenderer
{
    [RequiredParameter]
    [DefaultParameter]
    public string Key { get; set; }
    protected override void Append(StringBuilder builder, NLog.LogEventInfo logEvent)
    {
        var param = ConfigurationManager.AppSettings[this.Key];
        builder.Append(param);
    }
}

我遇到了错误

Error when setting property 'Encoding' on Mail Target[AlertMail]
at NLog.Internal.PropertyHelper.SetPropertyFromString(Object o, String name, String value, ConfigurationItemFactory configurationItemFactory)
at NLog.Config.XmlLoggingConfiguration.ConfigureObjectFromAttributes(Object targetObject, NLogXmlElement element, Boolean ignoreType)
at NLog.Config.XmlLoggingConfiguration.ParseTargetElement(Target target, NLogXmlElement targetElement)
at NLog.Config.XmlLoggingConfiguration.ParseTargetsElement(NLogXmlElement targetsElement)
at NLog.Config.XmlLoggingConfiguration.ParseNLogElement(NLogXmlElement nlogElement, String baseDirectory)
at NLog.Config.XmlLoggingConfiguration.ParseTopLevel(NLogXmlElement content, String baseDirectory)
at NLog.Config.XmlLoggingConfiguration.Initialize(XmlReader reader, String fileName, Boolean ignoreErrors)
at NLog.Config.XmlLoggingConfiguration..ctor(String fileName)
at Common.Logging.NLog.NLogLoggerFactoryAdapter..ctor(NameValueCollection properties) in D:\Project\GSJSJZB\GSJ_SJZB\Common.Logging.NLog\Logging\NLog\NLogLoggerFactoryAdapter.cs:line 109

这显然是因为 LayoutRenderer 处理的属性只有 Layout 类型。属性 smtpAuthentication 有同样的问题。如何解决此限制以将 appconfig 中的参数用于 Layout 以外的类型？

【问题讨论】：

标签： layout config nlog renderer

【解决方案1】：

我使用派生自 MailTarget 的自定义 Target 解决了这个问题：

[Target("MyMail")]
class MyMailTarget : MailTarget
{
    /// <summary>
    /// Wrapper for enum to use placeholders
    /// </summary>
    [DefaultValue("None")]
    public Layout SmtpAuth { get; set; }

    protected override void Write(NLog.Common.AsyncLogEventInfo logEvent)
    {
        Write(new[] {logEvent});
    }

    protected override void Write(NLog.Common.AsyncLogEventInfo[] logEvents)
    {
        var renderedAuthType = SmtpAuth.Render(logEvents.Last().LogEvent);
        SmtpAuthenticationMode mode;
        if (Enum.TryParse(renderedAuthType, true, out mode))
            SmtpAuthentication = mode;
        else
        {
            InternalLogger.Warn("Could not convert '{0}' to SmtpAuthenticationMode, valid values are None, Basic and Ntlm.");
            throw new NLogRuntimeException(String.Format("Cannot render SmtpAuthentication. SmtpAuth = {0}", renderedAuthType));
        }
        base.Write(logEvents);
    }
}

使用：

<extensions>
  <add assembly="AssemplyNameWithMyMailTarget" />
</extensions>

<variable name="smtpAuth" value="${app-settings:alerting.SMTP.Authentication}"/>

<!-- smtpAuth - my custom attribute -->

<target name="AlertMail" xsi:type="MyMail"
  to="${mailTo}"
  from="${mailFrom}"
  subject="[APPNAME][ALERT][${mailEnv}][${instanceName}]"
  smtpServer="${smtpHost}"
  smtpAuth="${smtpAuth}" 
  smtpUserName="${smtpUserName}"
  smtpPassword="${smtpPassword}"
  layout="${longdate}${newline}${message}${newline}"
  />

【讨论】：