Singleton Logging Module

singlog is a singleton logging module written in the D programming language, designed to provide thread-safe, cross-platform logging with flexible output targets. It supports multiple log levels, configurable output destinations (syslog, console, file), and optional colored console output, making it a versatile tool for application logging.

Features

• Thread-Safety: Utilizes a Mutex to ensure safe logging in multi-threaded applications.
• Cross-Platform: Works on both Windows (Event Log, console) and POSIX (syslog, console) systems.
• Flexible Output Targets: Supports logging to:
  • System logs (syslog on POSIX, Event Log on Windows).
  • Standard output (stdout for NOTICE and above, stderr for ERROR and below).
  • Files (with configurable file paths).
• Log Levels: Seven configurable levels:
  • DEBUGGING (highest priority)
  • ALERT
  • CRITICAL
  • ERROR
  • WARNING
  • NOTICE
  • INFORMATION (lowest priority)
• Fluent Interface: Provides a chaining API for easy configuration of output targets, log levels, and settings.
• Colored Output: Optional ANSI color support for console messages (on POSIX) or Windows console colors.
• Singleton Design: Ensures a single logger instance throughout the application, accessible via Log.msg or the log alias.
• Aliases: Short aliases (e.g., d for debugging, e for error) for concise logging.

Installation

To use singlog, include it in your D project:

1. Via Source: Copy the singlog.d file into your project’s source directory.

2. Via DUB (if packaged):

   Add it to your dub.json:

   "dependencies": {
       "singlog": "~>1.0.0"
   }
   

Usage

Basic Configuration and Logging

The singlog module provides a singleton logger instance accessible via Log.msg or the global log alias. Here’s a basic example:

import singlog;

void main() {
    // Configure the logger
    log.program("MyApp")                   // Set program name for syslog/Event Log
       .color(true)                        // Enable colored console output
       .level(log.level.debugging)         // Set minimum log level to DEBUGGING
       .output(log.output.std.file.syslog) // Output to console, file, and syslog
       .file("./myapp.log");               // Set log file path

    // Log messages
    log.debugging("Starting application in debug mode");
    log.information("Initialization complete");
    log.error("Failed to load resource");
}

This configures the logger to:

• Identify as "MyApp" in system logs.
• Use colored output on the console.
• Log all messages (from DEBUGGING up).
• Write to the console, a file (myapp.log), and the system log.

Log Levels and Aliases

The logger supports seven log levels with corresponding methods and aliases:

Level	Method	Alias	Description
DEBUGGING	debugging()	d()	Debugging information
ALERT	alert()	a()	High-priority alerts
CRITICAL	critical()	c()	Critical errors
ERROR	error()	e()	General errors
WARNING	warning()	w()	Warnings
NOTICE	notice()	n()	Notices
INFORMATION	information()	i()	Informational messages

Example using aliases:

log.d("Debug message");
log.i("Info message");
log.e("Error message");

Output Targets

Output targets can be configured using the output() method and its fluent interface:

• syslog(): Logs to the system log (Event Log on Windows, syslog on POSIX).
• std(): Logs to the console (stdout or stderr based on log level).
• file(): Logs to a file (requires file() to set the path).

Example:

log.output(log.output.std.file); // Console and file output
log.i("This goes to console and file");

Temporary Output Override

Use now() to temporarily override output targets for the next log call:

log.now(log.output.std).n("This goes only to console");
log.i("This uses default outputs again");

Colored Output

Enable colored output with color(true):

log.color(true);
log.w("This warning will be yellow on POSIX or Windows");
log.c("This critical message will be magenta");

Colors differ by platform:

• POSIX: Uses ANSI escape codes (e.g., green for DEBUGGING, red for ERROR).
• Windows: Uses console color attributes (e.g., yellow for WARNING, white for INFORMATION).

File Logging

Set a log file with file():

log.file("app.log");
log.e("This error goes to app.log");

The file is opened in append mode ("a+") and includes timestamps.