Class: Logging::Layouts::Pattern

Inherits:
Logging::Layout show all
Defined in:
lib/logging/layouts/pattern.rb

Overview

A flexible layout configurable via a conversion pattern string.

The goal of this class is to format a LogEvent and return the results as a String. The results depend on the conversion pattern.

The conversion pattern is closely related to the conversion pattern of the sprintf function. A conversion pattern is composed of literal text and format control expressions called conversion specifiers.

You are free to insert any literal text within the conversion pattern.

Each conversion specifier starts with a percent sign (%) and is followed by optional format modifiers and a conversion character. The conversion character specifies the type of data, e.g. logger, level, date, thread ID. The format modifiers control such things as field width, padding, left and right justification. The following is a simple example.

Let the conversion pattern be “%-5l [%c]: %mn” and assume that the logging environment was set to use a Pattern layout. Then the statements

root = Logging.logger[:root]
root.debug("Message 1")
root.warn("Message 2")

would yield the output

DEBUG [root]: Message 1
WARN  [root]: Message 2

Note that there is no explicit separator between text and conversion specifiers. The pattern parser knows when it has reached the end of a conversion specifier when it reads a conversion character. In the example above the conversion specifier %-5l means the level of the logging event should be left justified to a width of five characters. The recognized conversion characters are

[c]  Used to output the name of the logger that generated the log
     event. Supports an optional "precision" described further below.
[d]  Used to output the date of the log event. The format of the
     date is specified using the :date_pattern option when the Layout
     is created. ISO8601 format is assumed if not date pattern is given.
[F]  Used to output the file name where the logging request was issued.
[l]  Used to output the level of the log event.
[L]  Used to output the line number where the logging request was
     issued.
[m]  Used to output the application supplied message associated with
     the log event.
[M]  Used to output the method name where the logging request was
     issued.
[h]  Used to output the hostname
[p]  Used to output the process ID of the currently running program.
[r]  Used to output the number of milliseconds elapsed from the
     construction of the Layout until creation of the log event.
[t]  Used to output the object ID of the thread that generated the
     log event.
[T]  Used to output the name of the thread that generated the log event.
     Name can be specified using Thread.current[:name] notation. Output
     empty string if name not specified. This option helps to create
     more human readable output for multi-threaded application logs.
[X]  Used to output values from the Mapped Diagnostic Context. Requires
     a key name to lookup the value from the context. More details are
     listed below.
[x]  Used to output values from the Nested Diagnostic Context. Supports
     an optional context separator string. More details are listed below.
[%]  The sequence '%%' outputs a single percent sign.

The logger name directive 'c' accepts an optional precision that will only print the rightmost number of name space identifiers for the logger. By default the logger name is printed in full. For example, for the logger name “Foo::Bar::Baz” the pattern %c2 will output “Bar::Baz”.

The directives F, L, and M will only work if the Logger generating the events is configured to generate tracing information. If this is not the case these fields will always be empty.

The directives for including diagnostic context information in the log messages are X and x. For the Mapped Diagnostic Context the directive must be accompanied by the key identifying the value to insert into the log message. The X directive can appear multiple times to include multiple values from the mapped context.

%X{Cookie}      Insert the current session cookie
%X{X-Session}   Insert a session identifier

For the Nested Diagnostic Context you need only include the directive once. All contexts currently in the stack will be added to the log message separated by spaces. If spaces are not your style, a separator string can be given, too.

%x      Insert all contexts separated by spaces
%x{, }  Insert all contexts separate by a comma and a space

By default the relevant information is output as is. However, with the aid of format modifiers it is possible to change the minimum field width, the maximum field width and justification.

The optional format modifier is placed between the percent sign and the conversion character.

The first optional format modifier is the left justification flag which is just the minus (-) character. Then comes the optional minimum field width modifier. This is a decimal constant that represents the minimum number of characters to output. If the data item requires fewer characters, it is padded on either the left or the right until the minimum width is reached. The default is to pad on the left (right justify) but you can specify right padding with the left justification flag. The padding character is space. If the data item is larger than the minimum field width, the field is expanded to accommodate the data. The value is never truncated.

This behavior can be changed using the maximum field width modifier which is designated by a period followed by a decimal constant. If the data item is longer than the maximum field, then the extra characters are removed from the end of the data item.

Below are various format modifier examples for the category conversion specifier.

%20c       Left pad with spaces if the logger name is less than 20
           characters long
%-20c      Right pad with spaces if the logger name is less than 20
           characters long
%.30c      Truncates the logger name if it is longer than 30 characters
%20.30c    Left pad with spaces if the logger name is shorter than
           20 characters. However, if the logger name is longer than
           30 characters, then truncate the name.
%-20.30c   Right pad with spaces if the logger name is shorter than
           20 characters. However, if the logger name is longer than
           30 characters, then truncate the name.

Below are examples of some conversion patterns.

%.1l, [%d] %5l -- %c: %m\n

This is how the Logger class in the Ruby standard library formats messages. The main difference will be in the date format (the Pattern Layout uses the ISO8601 date format). Set the :date_method on the Pattern Layout to be 'to_s' and then the date formats will agree.

Defined Under Namespace

Classes: FormatMethodBuilder

Constant Summary collapse

ISO8601 =

default date format

"%Y-%m-%dT%H:%M:%S".freeze

Instance Attribute Summary collapse

Attributes inherited from Logging::Layout

#backtrace, #cause_depth, #utc_offset

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from Logging::Layout

#apply_utc_offset, #footer, #format, #format_cause, #format_cause_backtrace, #format_obj, #header, #try_json, #try_yaml

Constructor Details

#initialize(opts = {}) ⇒ Pattern

call-seq:

Pattern.new( opts )

Creates a new Pattern layout using the following options.

:pattern       =>  "[%d] %-5l -- %c : %m\n"
:date_pattern  =>  "%Y-%m-%d %H:%M:%S"
:date_method   =>  "usec" or "to_s"
:utc_offset    =>  "-06:00" or -21600 or "UTC"
:color_scheme  =>  :default

If used, :date_method will supersede :date_pattern.

The :color_scheme is used to apply color formatting to the log messages. Individual tokens can be colorized witch the level token [%l] receiving distinct colors based on the level of the log event. The entire generated log message can also be colorized based on the level of the log event. See the ColorScheme documentation for more details.


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# File 'lib/logging/layouts/pattern.rb', line 219

def initialize( opts = {} )
  super
  @created_at = Time.now.freeze

  @date_pattern = opts.fetch(:date_pattern, nil)
  @date_method = opts.fetch(:date_method, nil)
  @date_pattern = ISO8601 if @date_pattern.nil? && @date_method.nil?

  @pattern = opts.fetch(:pattern,
      "[%d] %-#{::Logging::MAX_LEVEL_LENGTH}l -- %c : %m\n")

  cs_name = opts.fetch(:color_scheme, nil)
  @color_scheme =
      case cs_name
      when false, nil; nil
      when true; ::Logging::ColorScheme[:default]
      else ::Logging::ColorScheme[cs_name] end

  self.class.create_date_format_methods(self)
  self.class.create_format_method(self)
end

Instance Attribute Details

#color_schemeObject (readonly)

Returns the value of attribute color_scheme.


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# File 'lib/logging/layouts/pattern.rb', line 241

def color_scheme
  @color_scheme
end

#date_methodObject

Returns the value of attribute date_method.


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# File 'lib/logging/layouts/pattern.rb', line 241

def date_method
  @date_method
end

#date_patternObject

Returns the value of attribute date_pattern.


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# File 'lib/logging/layouts/pattern.rb', line 241

def date_pattern
  @date_pattern
end

#patternObject

Returns the value of attribute pattern.


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# File 'lib/logging/layouts/pattern.rb', line 241

def pattern
  @pattern
end

Class Method Details

.create_date_format_methods(pl) ⇒ Object

call-seq:

Pattern.create_date_format_methods( pl )

This method will create the date_format method in the given Pattern Layout pl based on the configured date pattern and/or date method specified by the user.


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# File 'lib/logging/layouts/pattern.rb', line 164

def self.create_date_format_methods( pl )
  code = "undef :format_date if method_defined? :format_date\n"
  code << "def format_date( time )\n"
  code << "time = apply_utc_offset(time)\n"
  if pl.date_method.nil?
    if pl.date_pattern =~ %r/%s/
      code << "time.strftime('#{pl.date_pattern.gsub('%s','%6N')}')\n"
    else
      code << "time.strftime('#{pl.date_pattern}')\n"
    end
  else
    code << "time.#{pl.date_method}\n"
  end
  code << "end\n"
  ::Logging.log_internal(0) {code}

  pl._meta_eval(code, __FILE__, __LINE__)
end

.create_format_method(pl) ⇒ Object

call-seq:

Pattern.create_format_method( pl )

This method will create the `format` method in the given Pattern Layout `pl` based on the configured format pattern specified by the user.


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# File 'lib/logging/layouts/pattern.rb', line 190

def self.create_format_method( pl )
  builder = FormatMethodBuilder.new(pl)
  code = builder.build_code

  ::Logging.log_internal(0) { code }

  pl._meta_eval(code, __FILE__, __LINE__)
end

Instance Method Details

#_meta_eval(code, file = nil, line = nil) ⇒ Object

Evaluates the given string of `code` if the singleton class of this Pattern Layout object.

Returns this Pattern Layout instance.


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# File 'lib/logging/layouts/pattern.rb', line 283

def _meta_eval( code, file = nil, line = nil )
  meta = class << self; self end
  meta.class_eval code, file, line
  self
end