Omega logger

A simple and powerful logger inspired by Python's logging module. While designed for use in omega, it is general enough that it can be used just about anywhere.

Basic use

var logger = require('omega-logger').loggerFor(module);

logger.warn("This is a warning. You have to the count of %s to surrender.", 3);
logger.info("Also, you might want to know this information. It's useful.");
logger.critical("OMG, we have an object: %s", logger.dump({foo: "bar"}));

Dumping objects

If you need to dump an object, you can use the convienence function, logger.dump(object). (also available as require('omega-logger').dump) This is just a wrapper for Node's util.inspect that will automatically produce color output when logged to the console, but not in other log handlers.

logger.info("Here's your object:", logger.dump({some: 'object'}));

Configuration

Configuring Loggers

You can configure individual loggers:

var logger = require('omega-logger').loggerFor(module);

// Only display messages from this logger if they're at the 'INFO' level or above.
logger.level = 'INFO';

To change the configuration for all loggers, simply modify the root logger:

var logging = require('omega-logger');

logging.root.level = 'DEBUG';

Note that this does not change the logging level of any of the handlers; instead, you would have to configure the handler directly. (for instance, if you want to change what levels of messages are printed to the console, you would need to set the level of the Console handler; see below)

See the Logger documentation below for more information about the properties and methods available.

Configuring Handlers

Handlers are the objects that actually do something with log messages, like print them to the console or write them to a file. They can be configured similarly to loggers:

var logging = require('omega-logger');

logging.root.handlers = [
    new logging.handlers.Console()
];

Each handler has its own level setting, similar to loggers, which tells the handler to ignore certain messages:

logging.root.handlers = [
    new logging.handlers.Console({
        // Only display messages on this handler if they're at the 'WARN' level or above.
        level: 'WARN'
    })
];

Note: The console handler defaults to only displaying messages at the INFO level or above; other handlers default to logging messages at any level. If you wish to change the level of messages printed to the console, you can simply change the default console handler's level directly:

logging.root.handlers[0].level = 'DEBUG';

Each logger can have its own collection of handlers, though typically only the root logger has any configured. The propagate property on Logger instances controls whether or not messages get propagated to ancestor loggers' handlers. (see the Logger documentation below)

Environment Variables

omega-logger recognizes several environment variables automatically, to simplify changing its behavior on the fly:

• LOG_LEVEL: If present, sets the logging level of the root handler. (see above)
• LOG_MSG_DATA: If present, this is parsed as a JSON object, and its properties are added to all emitted log messages. This is especially useful in conjunction with LOG_AS_JSON (see below), since any properties set here will appear in each line of the JSON output.

There are also some variables that are only processed by certain handlers:

• LOG_AS_JSON (console handler only): If enabled, output log messages as JSON, one line per message, similar to bunyan. (this is useful when using a log-shipping system like Logstash, since pretty much everything can parse JSON)
• LOG_PREFIX (console handler only): If present, and LOG_AS_JSON is not enabled, all logged messages will be prefixed with the given string.
• DEBUG (console handler only): If enabled, and LOG_AS_JSON is not enabled, also display the filename, line number, and column of the call that generated each message.

Boolean variables listed above recognize the (case-insensitive) values off, no, false, 0, disabled, and an empty string as falsy (disabled) values; any other value will cause the variable to be enabled.

The omega-logger Module

Properties

• levels - the list of logging levels, in order from lowest to highest severity (default: ['TRACE', 'DEBUG', 'INFO', 'WARN', 'ERROR', 'CRITICAL'])
• root - the root logger; generally speaking, you should NOT log to this

Functions

loggerFor(object)

Get a logger for the object passed in. Typically, this should be the module object.

getLogger(name)

Retrieve (or create, if needed) the logger with the given name.

log(level, message)

A convenience logging method, for when you don't want to have to call getLogger() first. Instead of using this, you should probably use logging.loggerFor(module) or logging.getLogger('logger.name'), and log using the returned Logger instance.

dump(object[, depth])

Render a dump of the given object. You may specify a maximum depth to render. (defaults to 2) When logged to the console handler, the dump will be colored using ANSI escape codes; when logged to other handlers, it will be rendered as plain text.

Logger

Loggers may be configured by setting properties on each logger instance. Logger properties are inherited from parent loggers if not specified on a given logger; if no logger in the hierarchy sets a given property, it is retrieved from the root logger.

Properties

• name - the name of the logger; read-only
• level - the minimum log level at which messages from this logger or its descendants will be logged (default: log all messages)
• handlers - the list of log handlers which should be notified when a messages is logged to this logger or one of its descendants
• propagate - if set to false, this will prevent this logger from passing log messages on to any of its ancestors' handlers (default: true)

Methods

logger.info(message, ...), logger.warn(message, ...), logger.error(message, ...), etc.

The log methods. These are automatically created for all built-in log levels, and are shorthand for:

logger.log(level, message, ...);

...where level is the level corresponding to the log method's name.

logger.log(level, message, ...)

The main implementation method of logging. If any arguments are passed after the message, they are passed to util.format(message) as additional arguments. Then, the given message and level are passed on to any configured handlers on the given logger, and finally to the parent logger, if propagate is true.

logger.dump(object[, depth])

Render a dump of the given object. An alias of require('omega-logger').dump.

Handlers

Handlers are responsible for displaying or recording log messages to a given place, such as the console or a file.

Properties

Log handler properties may either be set when instantiating a handler (by passing them into the constructor in an object), or after the handler's been created (by setting the property on the handler object directly). See the individual handler objects below for a list of the available properties of each.

Methods

handler.onMessage(context)

The main implementation method for log handlers; the message is already rolled into a Context instance, allowing for easy string formatting using logging.strFormat(formatString, context /*, positional args... */).

Available Handlers

logging.handlers.Console

The default console logger; provides ANSI-colored log output to the console.

Properties:

• format - the format string used when writing messages to the console (default: '\033[90m{datetime}\033[m \033[1;30m[\033[{levelColor}m{level}\033[1;30m]\033[0;1m {logger}:\033[m {message}')
• level - the minimum log level at which messages will be logged to this handler (default: 'DEBUG')
• levelColors - an object associating logging levels with ANSI terminal colors. (default: {TRACE: '1;30', DEBUG: '37', INFO: '32', WARN: '33', ERROR: '31', CRITICAL: '1;31'})

logging.handlers.File

A handler that can write to a file. You can set the following properties to change its behavior:

Properties:

• format - the format string used when writing messages to the file (default: '{datetime} [{level}] {logger}: {message}')
• level - the minimum log level at which messages will be logged to this handler (default: 'DEBUG')
• newline - the newline character(s) to write after each line (default: '\n')
• fileName - the name of the file to log to (default: './logging.log')
• fileFlags - the flags to use when opening the log file; use 'w' to truncate the log each time it's opened, or 'a' to append to the log if it exists (default: 'a')
• fileEncoding - the encoding to use when opening the file (default: null)
• fileMode - the octal UNIX file mode to use if creating a new log file (default: 0660)

Troubleshooting

Installation on MS Windows

If your installation fails with a message like this:

C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\Microsoft.Cpp.InvalidPlatform.Targets(23,7): error MSB8007: The Platform for project 'weakref.vcxproj' is invalid. Platform='x64'. You may be seeing this message because you are trying to build a project without a solution file, and have specified a non-default Platform that doesn't exist for this project. [C:\MyProject\node_modules\omega-logger\node_modules\weak\build\weakref.vcxproj]

...chances are, the version of Microsoft Visual C++ that node-gyp has found isn't capable of building things that will work with your version of Node.js. See the node-gyp installation instructions at https://github.com/nodejs/node-gyp#installation for more information.

TODO

See the issue list on GitHub.