minlog

minlog is a minimalistic logger (Swedish pun intended; it translates to "my log"), inspired by bunyan which was meant to be "a simple and fast JSON logging module", but in time got one too many built-in (aka forced) features. This minimalism translates to high performance as well, as seen in benchmarks.

minlog works with 4 concepts:

logging levels which create the platform of logging verbosity
a log entry which is an object that carries the logging information (level, timestamp, etc)
serializer functions which are called in order to transform the log call's arguments into a log entry
listener functions which are called in parallel (async) to handle the log entry (i.e. print/save/proxy it)

Example

import {
  MinLog,
  logToConsole,
  serializeErr,
  serializeTime
} from 'minlog';

let log = new MinLog({
  serializers: [
    serializeTime(),
    serializeErr()
  ],
  listeners: [
    logToConsole({
      level: 'error' // ignore log entries below the "error" level threshold
    })
  ]
});

log.warn('This is a warning!'); // logToConsole will ignore this
log.error('This is an error!');

// if you want to make sure that a log entry has been processed by all serializers/listeners
await log.error('This is an error!').promise;

// if you want to make sure that all previous log entries have been processed by all serializers/listeners
await log.flush();

Docs

All signatures take one argument, which is an object, with the properties acting as named arguments.

The MinLog constructor takes an object (or a Promise/function that returns an object) with:

serializers: a list of serializer functions
listeners: a list of listener functions
levels: a list of extra mapping from semantical level to numerical one
requireRawEntry: a flag to enable rawEntry in serializers/listeners. Defaults to false for performance reasons.
requireSrc: a flag to enable _src (caller info) in entry. Defaults to false for performance reasons.

The serializer and the listener functions take:

entry: the logging information in its current form
logger: a reference to the MinLog instance
rawEntry: the pre-serializers state of the logging information

The serializer function must return a Promise with an amended entry.

In its raw form, the entry knows only of:

_time: a Date object
_level: the logging level
_src: the logging source (file, line and function)
_argN: the positional argument passed to the logging call, where N is the numerical index
_args: the positional arguments passed to the logging call
err: the first Error object passed to the logging call
msg: the first String object passed to the logging call
properties of the plain objects passed to the logging call

The logging call arguments are handled as below for convenience:

first String argument becomes entry.msg, if entry.msg is undefined at that point
first Error argument becomes entry.err, if entry.err is undefined at that point
all plain object arguments gets merged into entry
all other arguments are wrapped in a plain object {_argN: <value>} and merged into entry

Clarifications

There is no builtin functionality for filtering log entries based on a logging level. This is by design, as it is up to the listener to worry about checking the entry's level and decide to ignore it or not.

Datadog Grok Parser

If you intend to use minlog in a AWS Lambda and want Datadog to properly parse minlog messages, use

this definition:

minlog_rule %{minlog_timestamp}\s+%{minlog_lambda_request_id}\s+%{minlog_level}\s+(%{minlog_src}\s+)?%{minlog_msg}\s+%{minlog_extra}
minlog_raw_rule %{minlog_timestamp}\s+%{minlog_lambda_request_id}\s+%{minlog_level}\s+[^\{]*\s+%{minlog_extra}

### NO CHANGES BELOW THIS LINE

# Common
report_rule REPORT %{request_id}\s+Duration: %{number:duration:scale(1000000)} ms\s+Billed Duration: %{number:lambda.billed_duration} ms\s+Memory Size: %{number:lambda. memorysize} MB\s+Max Memory Used: %{number:lambda.max_memory_used} MB%{data:xray:keyvalue(": ")}

default_request_rule %{word:lambda.step}\s+%{request_id}(\s+Version: %{notSpace:lambda.version})?

timeout_rule (%{date("yyyy-MM-dd'T'HH:mm:ss.SSSZ"):timestamp}|%{date("yyyy-MM-dd'T'HH:mm:ss.SSZ"):timestamp})\s+%{notSpace:lambda.request_id}\s+%{regex("Task timed out"):error.message} after (%{number:duration:scale(1000000000)} seconds|%{number:duration:scale(1000000)} milliseconds)

process_error_rule %{request_id} (%{regex("Process exited before completing request"):error.message}|%{regex("Error"):level}:%{data:error.message})

# Node
node_json_rule %{node_prelude}(\s*Invoke Error\s*)?%{data::json}

# Python
python_rule %{python_prelude}.*
python_error %{regex("[^:]*"):error.message}: %{notSpace:error.kind}(\n|\s|\t)*Traceback \(most recent call last\):(?s)\s*%{data:error.stack}

# Ruby
ruby_basic %{regex("[\\w]")},\s\[%{date("yyyy-MM-dd'T'HH:mm:ss.SSSSSS"):timestamp} #%{number}\]\s+%{word:level} --\s*: %{data::keyvalue}

fallback_json (%{date("yyyy-MM-dd'T'HH:mm:ss.SSSZ"):timestamp}|%{date("yyyy-MM-dd'T'HH:mm:ss.SSZ"):timestamp})\s+%{notSpace:lambda.request_id}\s+(%{word:level}:)?(%{data::json})
# Sample
# START RequestId: c9a3b892-c2ca-4391-82fe-a47570039262 Version: $LATEST
# REPORT RequestId: ab5d39f5-1270-4226-9878-27f51b1bed57	Duration: 8384.24 ms	Billed Duration: 8400 ms 	Memory Size: 128 MB	Max Memory Used: 128 MB
# 2019-07-18T18:58:55.265Z	189a9433-fb77-4659-90d4-bc06edb890e0	ERROR	Invoke Error	{"errorType":"Error","errorMessage":"A test error"}
# 2019-07-18T18:58:22.286Z b5264ab7-2056-4f5b-bb0f-a06a70f6205d Task timed out after 30.03 seconds
# [ERROR]	2019-07-18T21:30:46.599Z	ffbce4c2-d80e-4ffa-a0bc-505361e28b8a	This is a regular python error
# 2019-07-18T19:47:18.146Z	95ce2ab7-cf99-4030-bede-2055a69cedec	ERROR	This is a regular node error

Advanced settings:

Extract from message:

minlog_timestamp %{date("yyyy-MM-dd'T'HH:mm:ss.SSSZ"):timestamp}
minlog_lambda_request_id (\-|%{notSpace:lambda.request_id})
minlog_level %{word:level}
minlog_src %{regex("[^:]+"):minlog._src.filename}:%{regex("[0-9]+"):minlog._src.line}:%{regex("[0-9]+"):minlog._src.column}( in %{notSpace:minlog._src.function})?
minlog_msg %{data:minlog.msg}([\u00A0]{0,255}\.)?
minlog_extra %{regex("\\{.*\\}"):minlog:json}

### NO CHANGES BELOW THIS LINE

request_id RequestId: %{notSpace:lambda.request_id}
node_prelude (%{date("yyyy-MM-dd'T'HH:mm:ss.SSSZ"):timestamp}|%{date("yyyy-MM-dd'T'HH:mm:ss.SSZ"):timestamp})\s+%{notSpace:lambda.request_id}\s+(\[)?+%{word:level}+(\])?
python_prelude \[%{word:level}\]?\s+(%{date("yyyy-MM-dd'T'HH:mm:ss.SSSZ"):timestamp}|%{date("yyyy-MM-dd'T'HH:mm:ss.SSZ"):timestamp})\s+%{notSpace:lambda.request_id}

License