Introduction
LuaLogging provides a simple API to use logging features in Lua. Its design was based on log4j. LuaLogging currently supports console, file, email, socket and sql outputs through the use of appenders.
The logging
module holds a new
function to create
new logger
objects.
This logger constructor receives a function (known as the appender function) that will be called on each call to log a message.
An appender function receives three arguments:
- self: the logger object
- level: the logging level
- message: the message to be logged
The logger constructor also receives a optional second argument which should be a table with parameters
Installation
LuaLogging is installed as a regular Lua module called logging
.
installation is easiest using LuaRocks; "luarocks install lualogging
",
or alternatively using the Makefile
.
Logging module
The logging module has a number of global functions:
- logging.new( function[, logLevel] )
- Creates a new logger object from a custom 'appender' function. See examples below.
The appender function signature is
function(self, level, message)
. The optional logLevel argument specifies the initial log-level to set (the value must be a valid log-level constant). If omitted defaults tologging.defaultLevel
. - patts = logging.buildLogPatterns([table], [string])
- Creates a log-patterns table. The returned table will for each level have
the logPattern set to 1. the value in the table, or alternatively 2. the
string value, or 3. the pattern from the global defaults.
Returns a logPatterns table.
Example logging source info only on debug-level, and coloring error and fatal
messages:
local patterns = logging.buildLogPatterns( { [logging.DEBUG] = "%date %level %message (%source)\n" [logging.ERROR] = "%date "..ansi_red.."%level %message"..ansi_reset.."\n" [logging.FATAL] = "%date "..ansi_red.."%level %message"..ansi_reset.."\n" }, "%date %level %message\n" )
- patts = logging.defaultLogPatterns([string | table])
- Sets the default logPatterns (global!) if a parameter is given.
If the parameter is a string then that string will be used as the pattern for
all log-levels. If a table is given, then it must have all log-levels defined
with a pattern string. See also
logging.buildLogPatterns
. The default is"%date %level %message\n"
for all log-levels. Available placeholders in the pattern string are;"%date"
,"%level"
,"%message"
,"%file"
,"%line"
,"%function"
and"%source"
. The"%source"
placeholder evaluates to"%file:%line in function'%function'"
. Returns the current defaultLogPatterns value. NOTE: since this is a global setting, libraries should never set it, only applications should. - patt = logging.defaultTimestampPattern([string])
- Sets the default timestampPattern (global!) if given.
The default is
nil
, which results in a system specific date/time format. The pattern should be accepted by the Lua functionos.date
for formatting. Returns the current defaultTimestampPattern value. NOTE: since this is a global setting, libraries should never set it, only applications should. - level = logging.defaultLevel([level constant])
- Sets the default log-level (global!) if given. Each new logger object created
will start with the log-level as specified by this value.
The level parameter must be one of the log-level constants. The default is
logging.DEBUG
. Returns the current defaultLevel value. NOTE: since this is a global setting, libraries should never set it, only applications should. - logger = logging.defaultLogger([logger object])
- Sets the default logger object (global!) if given.
The logger parameter must be a LuaLogging logger object. The default is to
generate a new
console
logger (with "destination" set to "stderr") on the first call to get the default logger. Returns the current defaultLogger value. NOTE: since this is a global setting, libraries should never set it, only applications should. Libraries should get this logger and use it, assuming the application has set it.-- Example: application setting the default logger local color = require("ansicolors") -- https://github.com/kikito/ansicolors.lua local ll = require("logging") require "logging.console" ll.defaultLogger(ll.console { destination = "stderr", timestampPattern = "!%y-%m-%dT%H:%M:%SZ", -- ISO 8601 in UTC logPatterns = { [ll.DEBUG] = color("%{white}%date%{cyan} %level %message (%source)\n"), [ll.INFO] = color("%{white}%date%{white} %level %message\n"), [ll.WARN] = color("%{white}%date%{yellow} %level %message\n"), [ll.ERROR] = color("%{white}%date%{red bright} %level %message %{cyan}(%source)\n"), [ll.FATAL] = color("%{white}%date%{magenta bright} %level %message %{cyan}(%source)\n"), } }) -- Example: library using default if available (fallback to nop) local log do local ll = package.loaded.logging if ll and type(ll) == "table" and ll.defaultLogger and tostring(ll._VERSION):find("LuaLogging") then -- default LuaLogging logger is available log = ll.defaultLogger() else -- just use a stub logger with only no-op functions local nop = function() end log = setmetatable({}, { __index = function(self, key) self[key] = nop return nop end }) end end log:debug("starting my library")
Logger objects
Logger objects are created by loading the 'appender' module, and calling on it. For example:
local logger = require("logging.console") { -- options go here (see appenders for options) }
A logger object offers the following methods that write log messages.
For each of the methods below, the parameter message
may be any lua value,
not only strings. When necessary message
is converted to a string.
The parameter level
can be one of the variables enumerated below.
The values are presented in descending criticality, so if the minimum level is
defined as logger.WARN
then logger.INFO
and
logger.DEBUG
level messages are not logged.
The default set level at startup is logger.DEBUG
.
Constants
- logger.DEBUG
- The DEBUG level designates fine-grained informational events that are most useful to debug an application.
- logger.INFO
- The INFO level designates informational messages that highlight the progress of the application at coarse-grained level.
- logger.WARN
- The WARN level designates potentially harmful situations.
- logger.ERROR
- The ERROR level designates error events that might still allow the application to continue running.
- logger.FATAL
- The FATAL level designates very severe error events that would presumably lead the application to abort.
- logger.OFF
- The OFF level will stop all log messages.
Methods
- logger:log (level, [message]|[table]|[format, ...]|[function, ...])
- Logs a message with the specified level.
- logger:setLevel (level)
- This method sets a minimum level for messages to be logged.
- logger:getPrint (level)
- This method returns a print-like function that redirects all output to
the logger instead of the console. The
level
parameter specifies the log-level of the output.
The following set of methods is dynamically generated from the log-levels.
- logger:debug ([message]|[table]|[format, ...]|[function, ...])
- Logs a message with DEBUG level.
- logger:info ([message]|[table]|[format, ...]|[function, ...])
- Logs a message with INFO level.
- logger:warn ([message]|[table]|[format, ...]|[function, ...])
- Logs a message with WARN level.
- logger:error ([message]|[table]|[format, ...]|[function, ...])
- Logs a message with ERROR level.
- logger:fatal ([message]|[table]|[format, ...]|[function, ...])
- Logs a message with FATAL level.
Examples
The example below creates a logger that prints the level and message to the standard output (or whatever the print function does).
local Logging = require "logging" local appender = function(self, level, message) print(level, message) return true end local logger = Logging.new(appender) logger:setLevel(logger.WARN) logger:log(logger.INFO, "sending email") logger:info("trying to contact server") logger:warn("server did not respond yet") logger:error("server unreachable") -- dump a table in a log message local tab = { a = 1, b = 2 } logger:debug(tab) -- use string.format() style formatting logger:info("val1='%s', val2=%d", "string value", 1234) -- complex log formatting. local function log_callback(val1, val2) -- Do some complex pre-processing of parameters, maybe dump a table to a string. return string.format("val1='%s', val2=%d", val1, val2) end -- function 'log_callback' will only be called if the current log level is "DEBUG" logger:debug(log_callback, "string value", 1234) -- create a print that redirects to the logger at level "INFO" logger:setLevel (logger.INFO) local print = logger:getPrint(logger.INFO) print "hello\nthere!"
Upon execution of the above example the following lines will show in the standard output. Notice that some of the INFO log requests are not handled because the minimum level is set to WARN.
WARN server did not responded yet ERROR server unreachable INFO hello INFO there!
Appenders
The following appenders are included in the standard distribution.Upgrading from 1.0.0
Upgrading from LuaLogging 1.0.0 is very easy. The
logger
object is fully compatible. You just need to
change the code that creates the object.
The logger
constructor from 1.0.0 received a single
argument which was a filename. To upgrade to 1.1.0 you should
create a logging.file
object instead, passing the
filename as argument. As simple as this.