Awesome

dlogg

Library that consilidates logging utilites according following goals:

Scalability
Nothrow and stable work under high loads and concurrency
Working with daemons
Log rotating
Lazy logging including buffered loggers
Customizeable messages and logging levels
Support for colorful output via d-colorize [Optional]

Installing

Add following in your dub package file:

"dependencies": {
  "dlogg": ">=0.4.0"
}

Examples:

Each logger in the package implements dlogg.ILogger interface and forced to be shared between threads. There are 5 different styles of logg messages:

enum LoggingLevel
{
    Notice,
    Warning,
    Debug,
    Fatal,
    Muted // Used only to mute all writing to console
}

So, to put message in log you can use:

  void ILogger.log(lazy string message, LoggingLevel level) shared;

Or one of handy wrappers:

  final nothrow shared
  {
    void logDebug(E...)(E args) shared @trusted; // not lazy
    void ILogger.logInfo(lazy string message);
    void ILogger.logWarning(lazy string message);
    void ILogger.logError(lazy string message);
  }

Note that major logging funcs are lazy and we don't have overhead while logg call isn't needed but in strict version D performs string concatinations.

And finally full example:

   shared ILogger logger = new shared StrictLogger("my_awesome_log.log");
   logger.minOutputLevel = LoggingLevel.Warning; // info msgs won't be printed in console 
   logger.logInfo("Info message!");
   logger.logError("Error message!");
   logger.logDebug("Debug message!");

Output file:

[2014-04-06T19:50:22.8193333]:Notice: Notice msg!
[2014-04-06T19:50:22.819406]:Warning: Warning msg!
[2014-04-06T19:50:22.8194323]:Debug: Debug msg!
[2014-04-06T19:50:22.8194548]:Error: Fatal msg!

minOutputLevel property controls which message types should be printed in console. LoggingLevel.Muted is used to create daemon loggers that don't try to write into stdout.

Buffered logger

In many cases (for instance, unittesting) we don't want log output just in time. Buffered logger adds control when messages would be written into wrapped log. Example:

   auto delayed = new shared BufferedLogger(logger); // wrapping a logger
   scope(exit) delayed.finalize(); // write down information in wrapped logger
   scope(failure) delayed.minOutputLevel = LoggingLevel.Notice; // if failed, spam in console
   delayed.logNotice("Hello!");

   // do something that can fail

Log rotating

StrictLogger.reload function checks if the log file is exists at specified location and if can't find it, recreates the file and continues write into it. Useful for logrotate utility. GNU/Linux system checks file identity by inode, that doesn't change while renaming. Thus after renaming the file at location log continues write into the renamed file. The call to the reload method force splitting log into two parts.

Custom styles

Since v0.2.0 custom styled logs are available. Consider how standart logger is implemented:

alias StrictLogger = StyledStrictLogger!(LoggingLevel
                , LoggingLevel.Debug,   "Debug: %1$s",   "[%2$s]: Debug: %1$s"
                , LoggingLevel.Notice,  "Notice: %1$s",  "[%2$s]: Notice: %1$s"
                , LoggingLevel.Warning, "Warning: %1$s", "[%2$s]: Warning: %1$s"
                , LoggingLevel.Fatal,   "Fatal: %1$s",   "[%2$s]: Fatal: %1$s"
                , LoggingLevel.Muted,   "",              ""
                );

StyledStrictLogger(StyleEnum, US...) is template class that implements IStyledLogger!StyleEnum interface. First template parameter is used to define your logging level enum (also StyleEnum values ordering is important for muting features).

Last template parameters have format of list of triples (StyleEnum value, string, string). Style value defines for which logging level following format strings are. First format string is used for console output, the second one is for file output.

Format strings could use two arguments: '%1$s' is message that is passed to a logger and '%2$s' is current time string. Formatting is handled by std.format module.

Now example of custom logger:

enum MyLevel
{
    Error,
    Debug
}

mixin generateStyle!(MyLevel
            , MyLevel.Debug,   "Debug: %1$s",   "[%2$s] Debug: %1$s"
            , MyLevel.Error,   "Fatal: %1$s",   "[%2$s] Fatal: %1$s"
            );

Colored output

You can use d-colorize package to color your styled logger:

        alias StrictLogger = StyledStrictLogger!(LoggingLevel
                        , LoggingLevel.Debug,   "Debug:".color(fg.light_magenta) ~ " %1$s",   "[%2$s]: Debug: %1$s"
                        , LoggingLevel.Notice,  "Notice:".color(fg.light_green) ~ " %1$s",  "[%2$s]: Notice: %1$s"
                        , LoggingLevel.Warning, "Warning:".color(fg.light_yellow) ~ " %1$s", "[%2$s]: Warning: %1$s"
                        , LoggingLevel.Fatal,   "Fatal:".color(fg.light_red) ~ " %1$s",   "[%2$s]: Fatal: %1$s"
                        , LoggingLevel.Muted,   "",              ""
                        );

And to use colorized version of default loggers add following to your dub.json:

{
	...
	"dependencies": {
		"dlogg": ">=0.3.3"
	},
	"subConfigurations": {
		"dlogg": "colorized"
	}
}

Custom time formatting

You can pass function or delegate to logger style to control how time is formatted. The function should have string return type and parameters of (DistType t, SysTime time) where t refers to distination (file or console) where message is printed to and time is a time value that should be converted to string by your function.

Example of usage:

    import dlogg.strict;
    import dlogg.style;
    import std.datetime;
    
    string myTimeFormatting(DistType t, SysTime time)
    {
        final switch(t)
        {
            case(DistType.Console): return time.toSimpleString();
            case(DistType.File): return time.toISOExtString();
        }
    }
    
    alias MyLogger = StyledStrictLogger!(LoggingLevel, myTimeFormatting
                    , LoggingLevel.Debug,   "Debug: %1$s",   "[%2$s]: Debug: %1$s"
                    , LoggingLevel.Notice,  "Notice: %1$s",  "[%2$s]: Notice: %1$s"
                    , LoggingLevel.Warning, "Warning: %1$s", "[%2$s]: Warning: %1$s"
                    , LoggingLevel.Fatal,   "Fatal: %1$s",   "[%2$s]: Fatal: %1$s"
                    , LoggingLevel.Muted,   "",              ""
                    );
    
    auto logger = new shared MyLogger("TimeFormatTestLog");
    scope(exit) logger.close();
    
    logger.logInfo("Msg1");
    logger.logWarning("Msg2");
    logger.logError("Msg2");