logfmtr

An implementation of the logr minimal logging API that writes in logfmt style.

Getting Started

This is a no frills logging package that follows the logr minimal logging API and by default writes logs in logfmt format, a line of space delimited key/value pairs.

level=0 logger=MyName ts=2020-09-20T14:31:10.905267839Z msg=hello user=you val1=1 val2=map[k:1]
level=1 logger=MyName ts=2020-09-20T14:31:10.905279546Z msg="you should see this" user=you
level=0 logger=MyName ts=2020-09-20T14:31:10.905288008Z msg="uh oh" error=<nil> user=you trouble=true reasons="[0.1 0.11 3.14]"
level=0 logger=MyName ts=2020-09-20T14:31:10.905291479Z msg=goodbye error="an error occurred" user=you code=-1

A more human friendly output format is also provided which can be configured using the humanize option:

0 info  | 14:31:10.905297 | hello                          logger=MyName user=you val1=1 val2=map[k:1]
1 info  | 14:31:10.905302 | you should see this            logger=MyName user=you
0 error | 14:31:10.905307 | uh oh                          logger=MyName error=<nil> user=you trouble=true reasons="[0.1 0.11 3.14]"
0 error | 14:31:10.905311 | goodbye                        logger=MyName error="an error occurred" user=you code=-1

Loggers defer applying their configuration until they are used. The logger is instantiated when either Info, Error or Enabled is called. At that point the logger will read and use any options set from a prior call to UseOptions.

package main

import (
    "github.com/iand/logfmtr"
)

func main() {
    // Set options that all loggers will be based on
    opts := logfmtr.DefaultOptions()
    opts.Humanize = true
    opts.AddCaller = true
    logfmtr.UseOptions(opts)
}

Any new loggers will use the options set in main when they first start logging.

package worker

import (
    "github.com/iand/logfmtr"
)

// Create the logger
var logger = logfmtr.New().WithName("worker")


func doWork() }
    // Logger is instantiated with the options set earlier
    logger.Info("the sun is shining")
}

Loggers can be created with specific configuration by using NewWithOptions:

func otherWork() }
    opts := logfmtr.DefaultOptions()
    opts.Writer = os.Stderr

    logger := logfmtr.NewWithOptions(opts)
    logger.Info("important system information")
}

Several predefined keys are used when writing logs in logfmt style:

• msg - the log message
• error - error message passed to the Error method
• logger - the name of the logger writing the log entry
• level - the verbosity level of the logger writing the log entry
• caller - filename and line number of the origin of the log entry

Author

• Ian Davis - http://iandavis.com/

License

This is free and unencumbered software released into the public domain. Anyone is free to copy, modify, publish, use, compile, sell, or distribute this software, either in source code form or as a compiled binary, for any purpose, commercial or non-commercial, and by any means. For more information, see http://unlicense.org/ or the accompanying UNLICENSE file.