Develop Reference

How to log with a tree like structure

I want to log with log4net (and I am doing this right now) to a file, but with log4net, there are just simple log outputs with a message each line.
Now I want to log to the same log file, but in a tree like structure. For example I've got the following method calls and each method logs its method name (there should be an indentation):
firstMethod().secondMethod().thirdMethod();
Should print this log for example:
2016-07-26 15:44:56,042 > firstMethod
2016-07-26 15:44:56,043 > secondMethod
2016-07-26 15:44:56,044 > thirdMethod
2016-07-26 15:44:56,045 < thirdMethod
2016-07-26 15:44:56,046 < secondMethod
2016-07-26 15:44:56,047 < firstMethod
The < and > signs are printed within the method at the start and at the end of the method.

It is not very efficient but you can look at using the call stack to get the hierarchy of methods and then pad/indent each log entry based on the depth of the call in the call stack.
StackTrace stackTrace = new StackTrace();
StackFrame[] stackFrames = stackTrace.GetFrames();
Alternatives could include using PostSharp or (possibly) writing a custom appender for log4net. Another thought is to forget about indenting and use the full namespace and method name to track where your log entry is coming from. This way you will still get a tree like view.
var methodInfo = System.Reflection.MethodBase.GetCurrentMethod();
var fullName = methodInfo.DeclaringType.FullName + "." + methodInfo.Name;
All that said, it seems like a very a-typical requirement. Do you really need to do this?

How about adding another method for logging with parameter for enter/exit, and do the padding there :
int curLevel = 0;
public void MyLogInfo( bool enter, [System.Runtime.CompilerServices.CallerMemberName] string callingMethod = "", )
{
string prefix;
if (enter)
{
prefix = "> ";
curLevel++;
}
else
{
prefix = "< ";
curLevel--;
}
logger.info(prefix.PadLeft(curLevel+prefix.Length) + callingMethod);
}
You just call MyLogInfo(true) or MyLogInfo(false) - .NET will set the callingMethod name if you do not specify it yourself.
You would have to ensure that you do always call the method on entry/exit of each method you log - maybe check you don't decrement curLevel below zero.

You can use NDC to achieve similar behavior. But it is deprecated. Now, you can use Contexts and Contexts Stacks. Check out this documentation: https://logging.apache.org/log4net/release/manual/contexts.html
You can define multiple stacks (instead of indentation). One stack for a set of behaviors you want to debug. Let's say you want to log creating a Sales Order and its Items. In this example, this stack is defined in ThreadContext. However you can define it in a GlobalContext , LogicalThreadContext or LoggingEvent.
using(log4net.ThreadContext.Stacks["SalesOrderLogic"].Push("SalesOrder"))
{
log.Info("Created the sales order");
using(log4net.ThreadContext.Stacks["SalesOrderLogic"].Push("Items"))
{
log.Info("Created the sales order items");
}
}
And then you should add it to your configuration:
<appender name="ConsoleAppender" type="log4net.Appender.ConsoleAppender">
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%logger - %property{SalesOrderStatus} - [%level]- %message%newline" />
</layout>
</appender>
DISCLAIMER: I did not test this code.
Note 1: The old NDC will appear in one thread. So if you pushed a message in one thread, it won't appear in another. And it has only one stack unlike the new Context Stack method.
Note 2: Don't forget to checkout Contexts. It is very useful.
Note 3: Also you might find it useful if you research Ninject and log4net working together

How to access existing NLog MemoryTarget

I'm reworking an existing logging system to use NLog Instead. I've manually added a reference to NLog in my configuration file:
<targets>
<target xsi:type="File" name="fileLogger" fileName="${basedir}\TRACE\${date:format=yyyy-MM-dd}.log" layout="TimeStamp:[${date}]|${message}" />
<target xsi:type="Memory" name="MemLogger" layout="TimeStamp:[${date}]|${message}|${Type}" />
</targets>
<rules>
<logger name="ApplicationLogger" levels="Info,Warn,Error" writeTo="fileLogger" />
<logger name="ApplicationLogger" levels="Info,Warn,Error" writeTo="fileLogger" />
</rules>
What I want to do is in code pull out the MemLogger Logs and access the different parts (Type, Message, Timestamp). How would I accomplish this? I've seen how to create a new log from scratch, but I don't want to create a new memorytarget, I want to access the existing one in my config, pull the log data out of it, and then clear the memory (so that I don't have a memory leak).
How to I access the MemLogger MemoryTarget in C#?

Unfortunately you cannot access different parts of log. Logs stored as rendered strings, with all layout renderers already replaced with their values. All you can do is manually parse each log string. E.g.
var target =(MemoryTarget)LogManager.Configuration.FindTargetByName("MemLogger");
foreach (string log in target.Logs)
{
var parts = log.Split('|');
var date = parts[0].Replace("TimeStamp:[", "").TrimEnd(']');
var message = parts[1];
var type = parts[2];
//...
}

Something like this:
var target = LogManager.Configuration.FindTargetByName("MemLogger");
Optionally, you can cast received target to MemoryTarget type.

I've just had to do this myself:
Natively:
IList<string> logs = LogManager.Configuration.FindTargetByName<MemoryTarget>("MyTarget").Logs;
or using a Cast:
IList<string> logs = ((MemoryTarget)LogManager.Configuration.FindTargetByName("MyTarget")).Logs;

Log4net output to My Documents

In our C# app, we write files to Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments). Our log4net logfile should go there too, so we've defined application.conf as follows:
<appender name="LogFile" type="log4net.Appender.RollingFileAppender">
<appendToFile value="true"/>
<file value="%USERPROFILE%\My Documents\MyApp\log.txt"/>
...snip...
</appender>
This works, until we run in on a PC which has a non-English Windows. Because then, SpecialFolder.MyDocuments points to the folder Mijn Documenten, while the log still goes to My Documents. Confusion ensues, because now our files are in two places.
I want to write my log to the "real" My Documents folder. How do I do this?
I tried to find an environment variable like %USERPROFILE%, but there doesn't seem to exist one for My Documents.
There's a registry key that defines the true location of My Documents but it's not accessible from application.conf.
I tried to override the File parameter of my appender programmatically, like this:
public static void ConfigureLogger()
{
XmlConfigurator.Configure();
Hierarchy hierarchy = (Hierarchy)log4net.LogManager.GetRepository();
foreach (var appender in hierarchy.Root.Appenders)
{
if (appender is FileAppender)
{
var fileAppender = appender as FileAppender;
var logDirectory = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments), "MyApp");
var pathElements = fileAppender.File.Split(Path.DirectorySeparatorChar);
var logFileName = pathElements.Last();
var fullLogFilePath = Path.Combine(logDirectory, logFileName);
fileAppender.File = fullLogFilePath;
}
}
}
This doesn't work either: when I inspect the internals of my logger, the File property happily reports Mijn Documenten, but in the mean time the logs still go to My Documents.
I'm running out of ideas!

Change the line
<file value="%USERPROFILE%\My Documents\MyApp\log.txt"/>
to
<file type="log4net.Util.PatternString" value="%envFolderPath{MyDocuments}\MyApp\log.txt" />

The accepted answer is out of date.
You should now use:
<file value="${UserProfile}\Documents\log-messages.log" />
(This should work even on Windows 7, where "Documents" is referred to by the alias "My Documents".)
${UserProfile} will map to C:\Users[UserName], even if you don't see this variable explicitly defined in your environment variable list.

There seem to be at least 2 approaches. The simplest is kind of a hack:
Specify a custom environment variable to indicate the root path in you log4net config:
<file value="%MYAPP_USER_ROOTFOLDER%\MyApp\log.txt"/>
At startup, before initializing logging, set this environment variable value:
Environment.SetEnvironmentVariable("MYAPP_USER_ROOTFOLDER", Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments));
The more complicated but recommended approach is explained here: http://marc.info/?l=log4net-user&m=110142086820117&w=2 and here http://ziqbalbh.com/articles/log4net-another-way-to-change-log-file-location-on-runtime/

SLF Releasing File Lock

I have a program which uses SLF for logging. This program runs 24/7 and I would like to upload the log files to a remote server every night for later review.
My question is, how do I release the file lock for the log without closing the program?
I was hoping to suspend logging, upload the logs, either delete the log file or erase the contents, and then resume logging.
ILogger logger = LoggerService.GetLogger(typeof(TaskScheduler).FullName);
// Other initialization here
foreach (var task in managedTasks.OrderBy(t => t.Priority))
{
if (task.NextRunTime <= DateTime.Now)
{
dataManager.CurrentStatus = AppStatus.Running;
if (task.Name == "Log Sender")
{
logger = null;
}
// Run the task
if (task.Name == "Log Sender")
{
logger = LoggerService.GetLogger(typeof(TaskScheduler).FullName);
}
dataManager.CurrentStatus = AppStatus.Idle;
}
}
Currently, when I do this, I'm still getting an IOException because the file is still locked by the Task Scheduler.
EDIT: I'm using SLF over log4net if that helps.

I would consider this as a design issue rather than technical. Log events for each day in an individual file and upon next day you can do anything you want with yesterday's log file. You can narrow log period according to your need (i.g. every 12 hours).

After posting this question and getting the recommendations to reconsider my design. I started to look into creating a rolling log file for each date. I happened across this, which solved my problem completely:
<appender name="InfoRollingLogFileAppender" type="log4net.Appender.RollingFileAppender,log4net">
<param name="File" value="log.txt" />
<param name="StaticLogFileName" value="true"/>
<maximumFileSize value="1024KB" />
<appendToFile value="true" />
<lockingModel type="log4net.Appender.FileAppender+MinimalLock" />
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%logger: %date{dd MMM yyyy HH:mm:ss} [%thread] %-5level - %message %newline" />
</layout>
</appender>
I configured the log4net appender in my app.config to follow the lockingModel to include a "MinimalLock" this enabled me to pull the contents of the logs, upload them to the server and then erase the local logs without having to create separate log files for a specified time/date span.
Again, thanks to everyone for your help, I wouldn't have stumbled across this handy change without your suggestions.

c# log4net store entries in memory and Email under certain conditions

I currently use log4net with a RollingFileAppender.
As each Log call is made I'd like to store this in memory. At the end of my console application run I'd like to (if an app.config setting is true) take only the Warns and Fatals and send all these messages in an Email. I notice MemoryAppender but not quite sure how to use it. Also see SMTPAppender but not sure it is the right tool, else I'll use MemoryAppender and somehow filter out only events of Levels Warn/Fatal and then email using the SmtpClient class.
How to achieve this?
Thanks
Update
My last part of log4net config now looks like.
<appender name="MemoryAppender" type="log4net.Appender.MemoryAppender" >
<onlyFixPartialEventData value="true" />
<threshold value="WARN" />
</appender>
<root>
<level value="DEBUG" />
<appender-ref ref="Console" />
<appender-ref ref="RollingFile" />
<appender-ref ref="MemoryAppender" />
</root>
In code I do:
private static MemoryAppender MemoryAppender
{
get
{
if (memoryAppender == null)
{
Hierarchy h = LogManager.GetRepository() as Hierarchy;
memoryAppender = h.Root.GetAppender("MemoryAppender") as MemoryAppender;
}
return memoryAppender;
}
}
Then when I want the events I call:
MemoryAppender.GetEvents();
I've tried MemoryAppender.GetEvents()[0].RenderedMessage but that is not the correct output, how do I get the message string as it was written to the File/Console logs with the correct pattern and time etc and build myself a StringBuilder? I'll then put this in the body of my Email and send it using the SmtpClient. RenderMessage is just giving me the string that was provided to the Log.Warn() call not what was written to the log. Is this due to not setting a layout pattern on the MemoryAppender?
Thanks

MemoryAppender will only "append" to memory and is thus mostly useful only for development and testing purposes. And there is currently no appender that will only append on application shutdown.
The SMTPAppender is something in between, since it inherits the BufferingAppenderSkeleton. These appenders have a BufferSize property which controls how many messages are kept in memory before they are flushed.
Which messages to pass to the appenders are controlled with the level settings either on the root element or on individual logger elements. In your case use a level of WARN which will let through WARN, ERROR and FATAL. If you don't want the ERROR messages you will have to put a level filter on your appender.
Update: MemoryAppender is not using any layout to "render" message objects. What you get from MemoryAppender is just the raw message objects as they are produced by log4net. You will have to convert those to meaningfull text yourself.
Alternatively, if you require both layout functionality and in-memory appending you could look into subclassing AppenderSkeleton. That way you get the basic Layout support. When implementing the Append method you can do what MemoryAppender does, that is just appending to an internal list of messages.
Update 2: to implement the MemoryAppender alternative I suggest taking the MemoryAppender as a starting point. MemoryAppender is a subclass of AppenderSkeleton and have thus access to the RenderLoggingEvent method. So, we subclass MemoryAppender and add a method that renders the current batch of logging events:
public class RenderingMemoryAppender : MemoryAppender
{
public IEnumerable<string> GetRenderedEvents()
{
foreach(var loggingEvent in GetEvents())
{
yield return RenderLoggingEvent(loggingEvent);
}
}
}

You can use SMTPAppender and look at how the flush functionality works. Log4net keeps all messages in memory until flush is called (if it's setup this way), so the email will be sent when you flush it.
Another thing you can do is create a separate appender (Rolling or FileAppender) with filters WARN and FATAL, then attach this appender to the same logger, and at the end of your run email this file if it's non-empty (and you can choose to send it as an attachment or right in the body of the email). Let me know if you want more details, this is almost the same I'm doing know.
Good luck!
Ricardo.