class MLogger

Description

The Logger class provides a simple but sophisticated logging utility that you can use to output messages.

The messages have associated levels, such as INFO or ERROR that indicate their importance. You can then give the Logger a level, and only messages at that level of higher will be printed.

The levels are:

FATAL

an unhandleable error that results in a program crash

ERROR

a handleable error condition

WARN

a warning

INFO

generic (useful) information about system operation

DEBUG

low-level information for developers

For instance, in a production system, you may have your Logger set to INFO or even WARN When you are developing the system, however, you probably want to know about the program's internal state, and would set the Logger to DEBUG.

Note: Logger does not escape or sanitize any messages passed to it. Developers should be aware of when potentially malicious data (user-input) is passed to Logger, and manually escape the untrusted data:

logger.info("User-input: #{input.dump}")
logger.info("User-input: %p" % input)

You can use formatter= for escaping all data.

original_formatter = MLogger::Formatter.new
logger.formatter = proc { |severity, datetime, progname, msg|
  original_formatter.call(severity, datetime, progname, msg.dump)
}
logger.info(input)

Example

This creates a logger to the standard output stream, with a level of WARN

log = MLogger.new(STDOUT)
log.level = MLogger::WARN
# as run: log.level = :warn

log.debug("Created logger")
log.info("Program started")
log.warn("Nothing to do!")

begin
  File.each_line(path) do |line|
    unless line =~ /^(\w+) = (.*)$/
      log.error("Line in wrong format: #{line}")
    end
  end
rescue => err
  log.fatal("Caught exception; exiting")
  log.fatal(err)
end

Because the Logger's level is set to WARN, only the warning, error, and fatal messages are recorded. The debug and info messages are silently discarded.

Features

There are several interesting features that Logger provides, like auto-rolling of log files, setting the format of log messages, and specifying a program name in conjunction with the message. The next section shows you how to achieve these things.

HOWTOs

How to create a logger

The options below give you various choices, in more or less increasing complexity.

  1. Create a logger which logs messages to STDERR/STDOUT.

    logger = MLogger.new(STDERR)
    logger = MLogger.new(STDOUT)
    
  2. Create a logger for the file which has the specified name.

    logger = MLogger.new('logfile.log')
    
  3. Create a logger for the specified file.

    file = File.open('foo.log', File::WRONLY | File::APPEND)
    # To create new (and to remove old) logfile, add File::CREAT like;
    #   file = open('foo.log', File::WRONLY | File::APPEND | File::CREAT)
    logger = MLogger.new(file)
    
  4. Create a logger which ages logfile once it reaches a certain size. Leave 10 “old log files” and each file is about 1,024,000 bytes.

    logger = MLogger.new(['foo.log', {age: 10, size: 1024000}])
    
  5. Create a logger which ages logfile daily/weekly/monthly.

    logger = MLogger.new(['foo.log', {age: 'daily'}])
    logger = MLogger.new(['foo.log', {age: 'weekly'}])
    logger = MLogger.new(['foo.log', {age: 'monthly'}])
    
  6. Create a logger with multiIO

    logger = MLogger.new STDOUT, STDERR
    logger = MLogger.new ['foo.log', {age: 'daily'}], ['foo2.log', {age: 'weekly'}]
    logger = MLogger.new STDOUT, 'foo.log'
    logger = MLogger.new STDOUT, ['foo.log', {age: 'daily'}]
    
  7. Create a logger with different log levels with different IO.

    logger = MLogger.new STDOUT # default io
    logger.change_level_logdev MLogger::WARN, STDERR
    logger.change_level_logdev [:warn, :error], STDERR
    

How to log a message

Notice the different methods (fatal, error, info) being used to log messages of various levels? Other methods in this family are warn and debug. add is used below to log a message of an arbitrary (perhaps dynamic) level.

  1. Message in block.

    logger.fatal { "Argument 'foo' not given." }
    
  2. Message as a string.

    logger.error "Argument #{ @foo } mismatch."
    
  3. With progname.

    logger.info('initialize') { "Initializing..." }
    

The block form allows you to create potentially complex log messages, but to delay their evaluation until and unless the message is logged. For example, if we have the following:

logger.debug { "This is a " + potentially + " expensive operation" }

If the logger's level is INFO or higher, no debug messages will be logged, and the entire block will not even be evaluated. Compare to this:

logger.debug("This is a " + potentially + " expensive operation")

Here, the string concatenation is done every time, even if the log level is not set to show the debug message.

How to close a logger

logger.close

Setting severity threshold

  1. Original interface.

    logger.sev_threshold = MLogger::WARN
    
  2. Log4r (somewhat) compatible interface.

    logger.level = MLogger::INFO
    
    DEBUG < INFO < WARN < ERROR < FATAL
    

Format

Log messages are rendered in the output stream in a certain format by default. The default format and a sample are shown below:

Log format:

SeverityID, [Date Time mSec #pid] SeverityLabel -- ProgName: message

Log sample:

I, [Wed Mar 03 02:34:24 JST 1999 895701 #19074]  INFO -- Main: info.

You may change the date and time format via datetime_format=

logger.datetime_format = "%Y-%m-%d %H:%M:%S"
      # e.g. "2004-01-03 00:54:26"

Or, you may change the overall format with formatter= method.

logger.formatter = proc do |severity, datetime, progname, msg|
  "#{datetime}: #{msg}\n"
end
# e.g. "Thu Sep 22 08:51:08 GMT+9:00 2005: hello world"

Constants

LOGGER_LEVEL

When you set +$LOGGER_LEVEL+ before require mlogger, you can define yourself log level like default value [:DEBUG, :INFO, :WARN, :ERROR, :FATAL] DEBUG < INFO < WARN < ERROR < FATAL

VERSION

Attributes

formatter[RW]

Logging formatter, as a Proc that will take four arguments and return the formatted message. The arguments are:

severity

The Severity of the log message

time

A Time instance representing when the message was logged

progname

The progname configured, or passed to the logger method

msg

The Object the user passed to the log message; not necessarily a String.

The block should return an Object that can be written to the logging device via write. The default formatter is used when no formatter is set.

level[R]

Logging severity threshold (e.g. Logger::INFO).

progname[RW]

program name to include in log messages.

sev_threshold[R]

Logging severity threshold (e.g. Logger::INFO).

sev_threshold=[R]

Logging severity threshold (e.g. Logger::INFO).

Public Class Methods

new(*logdev) click to toggle source

Synopsis

MLogger.new(+logdev+)
MLogger.new([name, {age: 7, size: 1048576}])
MLogger.new([name, {age: 'weekly'}])
MLogger.new([+logdev+, {age: +shift_age+, size: +shift_size+}])

Args

Every Arg is a logdev information:

logdev

The log device. Array This is a filename (String) or IO object (typically STDOUT, STDERR, or an open file).

shift_age

Number of old log files to keep, or frequency of rotation (daily, weekly or monthly).

shift_size

Maximum logfile size (only applies when shift_age is a number).

Description

Create an instance.

# File lib/mlogger.rb, line 301
def initialize(*logdev)
  @progname = nil
  @level = 0
  @default_formatter = Formatter.new
  @formatter = nil
  logdev << STDOUT if logdev.empty?
  @logdev = LogDeveices.new(*logdev)
  @level_logdev = {}
end

Public Instance Methods

<<(msg) click to toggle source

Dump given message to the log device without any formatting. If no log device exists, return nil.

# File lib/mlogger.rb, line 352
def <<(msg)
  unless @logdev.nil?
    @logdev.write(msg)
  end
end
change_level_logdev(levels, *logdev) click to toggle source

Synopsis

Logger#change_level_logdev(levels, *logdev)

Use

logger.change_level_logdev :warn, STDERR
logger.change_level_logdev [:warn, :error], STDERR
logger.change_level_logdev MLogger::WARN..MLogger::FATAL, STDERR

Args

levels

Severity. Constants are defined in Logger namespace: DEBUG, INFO, WARN, ERROR, FATAL. Also can use a Severity Array.

logdev

The log device. This is a filename (String) or IO object (typically STDOUT, STDERR, or an open file).

shift_age

Number of old log files to keep, or frequency of rotation (daily, weekly or monthly).

shift_size

Maximum logfile size (only applies when shift_age is a number).

Description

Change LEVEL LogDev

# File lib/mlogger.rb, line 340
def change_level_logdev(levels, *logdev)
  levels = [levels] unless levels.is_a? Enumerable
  log_deveices = LogDeveices.new(*logdev)
  levels.each do |level|
    @level_logdev[trans_level level] = log_deveices
  end
end
close() click to toggle source

Close the logging device.

# File lib/mlogger.rb, line 361
def close
  @logdev.close if @logdev
  @level_logdev.values.each {|logdev| logdev.close if logdev}
end
datetime_format() click to toggle source

Returns the date format being used. See datetime_format=

# File lib/mlogger.rb, line 257
def datetime_format
  @default_formatter.datetime_format
end
datetime_format=(datetime_format) click to toggle source

Set date-time format.

datetime_format

A string suitable for passing to strftime.

# File lib/mlogger.rb, line 252
def datetime_format=(datetime_format)
  @default_formatter.datetime_format = datetime_format
end

Private Instance Methods

add(severity, message = nil, progname = nil) { || ... } click to toggle source

Synopsis

MLogger#add(severity, message = nil, progname = nil) { ... }

Args

severity

Severity. Constants are defined in Logger namespace: DEBUG, INFO, WARN, ERROR, FATAL.

message

The log message. A String or Exception.

progname

Program name string. Can be omitted. Treated as a message if no message and block are given.

block

Can be omitted. Called to get a message string if message is nil.

Return

true if successful, false otherwise.

When the given severity is not high enough (for this particular logger), log no message, and return true.

Description

Log a message if the given severity is high enough. This is the generic logging method. Users will be more inclined to use debug, info, warn, error, and fatal.

Message format: message can be any object, but it has to be converted to a String in order to log it. Generally, inspect is used if the given object is not a String. A special case is an Exception object, which will be printed in detail, including message, class, and backtrace. See msg2str for the implementation if required.

Bugs

  • Logfile is not locked.

  • Append open does not need to lock file.

  • If the OS which supports multi I/O, records possibly be mixed.

# File lib/mlogger.rb, line 425
def add(severity, message = nil, progname = nil, &block)
  if @logdev.nil? or severity < @level
    return true
  end
  progname ||= @progname
  if message.nil?
    if block_given?
      message = yield
    else
      message = progname
      progname = @progname
    end
  end
  (@level_logdev[severity] || @logdev).write(
      format_message(format_severity(severity), Time.now, progname, message))
  true
end
Also aliased as: log
format_message(severity, datetime, progname, msg) click to toggle source
# File lib/mlogger.rb, line 377
def format_message(severity, datetime, progname, msg)
  (@formatter || @default_formatter).call(severity, datetime, progname, msg)
end
format_severity(severity) click to toggle source
# File lib/mlogger.rb, line 373
def format_severity(severity)
  LOGGER_LEVEL[severity] || 'ANY'
end
log(severity, message = nil, progname = nil, &block)
Alias for: add
trans_level(level) click to toggle source
# File lib/mlogger.rb, line 368
def trans_level(level)
  (level.is_a? String or level.is_a? Symbol) ?
      MLogger.const_get(level.upcase) : level
end