Hi!
The new NLog snapshot has been released. It adds some new features which
exploit the recently added Wrapper targets.
1. The first one is ASPNetBufferingWrapper which is a specialized buffering
wrapper which works on ASP.NET requests. All log events generated during the
execution of the HTTP Request in ASP.NET are gathered in a buffer. As soon
as the request finishes, the log events are sent down to the wrapped
targets. It means, you can, for example, send the trace of a HTTP request in
a single email and different sessions won't interfere.
To use this feature you need to add the <httpModules> entry in your
Web.config:
<configuration>
<system.web>
<httpModules>
<add name="NLog" type="NLog.Web.NLogHttpModule, NLog"/>
</httpModules>
</system.web>
</configuration>
If you don't do this - ASPNetBufferingWrapper will not work.
2. Another wrapper is PostFilteringWrapper which operates on buffers (you
should always wrap it around the buffering wrapper like BufferingTarget,
AsyncTarget or ASPNetBuffering target) and lets you filter the buffers with
the filtering condition evaluated based on the entire buffer. The typical
use case is this:
* we want all HTTP Requests to only include messages at the Info level
* should there be any Warn, Error or Fatal during the request
processing, we want to dump DETAILED log (Debug level and above)
* should there be any Fatal errors, we want to dump VERY DETAILED log
(Trace level and above)
This is very easy using the new wrapper:
===========================================================
<?xml version="1.0" encoding="windows-1250" ?>
<nlog autoReload="true" internalLogLevel="Trace">
<targets>
<target name="userlog" type="ASPNetBufferingWrapper">
<target type="PostFilteringWrapper" defaultFilter="(level >=
LogLevel.Info)">
<when exists="level >= LogLevel.Fatal" filter="level >=
LogLevel.Trace" />
<when exists="level >= LogLevel.Warn" filter="level >=
LogLevel.Debug" />
<target name="file" type="File"
fileName="${basedir}/../logs/${shortdate}.log" />
</target>
</target>
</targets>
<rules>
<logger name="*" minlevel="Trace" appendTo="userlog" />
</rules>
</nlog>
===========================================================
3.The filter expressions in the above example are written in a special
mini-language which has also been recently introduced in NLog. Some
documentation is available in the help file. Below are some most important
features:
The language consists of:
* relational operators (==, !=, <=, <=, >= and >)
* and, or, not boolean operators
* string literals which are always evaluated as layouts - '${somerenderer}'
* boolean literals - true and false
* numeric literals - 12345 (integer literal) and 12345.678 (floating point
literal)
* log level literals - LogLevel.Trace, LogLevel.Debug, ... LogLevel.Fatal
* predefined keywords to access the most common log event properties -
level, message and logger
* braces - to override default priorities and group expressions together
Examples
Here are some examples of conditions:
level > LogLevel.Debug - matches the messages whose level is greater than
Debug
(level > LogLevel.Debug) or contains(message,'xxx') - matches the messages
whose level is greater than Debug or which include the xxx substring in the
log message
starts-with(logger,'Kopytko.') - matches the loggers whose names start with
Kopytko.
ends-with(logger,'.SQL') or ends-with(logger,'.XML') - matches the loggers
whose names end with either .SQL or .XML
true - matches everything
false - matches nothing
length(message) > 100 - matches the log events where the length of the log
message is greater than 100
'${shortdate}' == '2005-11-10' - matches on the specified date
Available functions
The following functions are available:
contains(s1,s2)
Determines whether the second string is a substring of the first one.
Returns: true when the second string is a substring of the first string,
false otherwise.
ends-with(s1,s2)
Determines whether the second string is a suffix of the first one. Returns:
true when the second string is a prefix of the first string, false
otherwise.
equals(o1,o2)
Compares two objects for equality.
Returns: true when two objects are equal, false otherwise.
length(s)
Returns the length of a string.
Returns: The length of a string.
starts-with(s1,s2)
Determines whether the second string is a prefix of the first one. Returns:
true when the second string is a prefix of the first string, false
otherwise.
New functions are ultra-easy to add, just create an ordinary function and
mark it with [ConditionMethod] attribute. See this example:
http://trac.sav.net/nlog/file/trunk/NLog/src/NLog/Conditions/ConditionMethods.cs4. There's a new <when condition="..." action="..." /> filter which lets you
specify filters using the condition language:
<rules>
<logger name="*" writeTo="file">
<filters>
<when condition="(level >= LogLevel.Debug and
contains(message,'Kopytko')) or level==LogLevel.Warn" action="Ignore" />
</filters>
</logger>
</rules>
Comments are - as always - welcome.
BTW. The server which hosts TRAC and SVN has been moved to the new
colocation facility after a crash. Things should be more stable than before,
but in case of any problems - report them here. Can you send me your ping
times to trac.sav.net?
--
Jaroslaw Kowalski
http://blog.jkowalski.net/
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