logfmt

node-logfmt

"logfmt" is the name for a key value logging convention we've adopted at Heroku.

This library is for both converting lines in logfmt format to objects and for logging objects to a stream in logfmt format. It provides a logfmt parser, a logging facility, and both streaming and non-streaming body parsers for express.

You should use this library if you're trying to write structured logs or if you're consuming them (especially if you're writing a logplex drain).

install

npm install logfmt

use

var logfmt = require('logfmt');

parser

logfmt.parse(string)

var logfmt = require('logfmt');

logfmt.parse("foo=bar a=14 baz=\"hello kitty\" cool%story=bro f %^asdf code=H12")
//=>{ "foo": "bar", "a": 14, "baz": "hello kitty", "cool%story": "bro", "f": true, "%^asdf": true, "code" : "H12" }

logging

logfmt.log(object, [stream])

Defaults to logging to process.stdout

var logfmt = require('logfmt');
logfmt.log({ "foo": "bar", "a": 14, baz: 'hello kitty'})
//=> foo=bar a=14 baz="hello kitty"

customizing logging location

log() Accepts as 2nd arg anything that responds to write(string)

var logfmt = require('logfmt');
logfmt.log({ "foo": "bar", "a": 14, baz: 'hello kitty'}, process.stderr)
//=> foo=bar a=14 baz="hello kitty"

Overwrite the default location by setting .stream

var logfmt = require('logfmt');
logfmt.stream = process.stderr

logfmt.log({ "foo": "bar", "a": 14, baz: 'hello kitty'})
//=> foo=bar a=14 baz="hello kitty"

express middleware

Streaming

logfmt.bodyParserStream([opts])

Valid Options:

• contentType: defaults to application/logplex-1

If you use the logfmt.bodyParserStream() for a body parser, you will have a req.body that is a readable stream.

Pipes FTW:

var app    = require('express')();
var http   = require('http');
var through = require('through');
var logfmt  = require('logfmt');

app.use(logfmt.bodyParserStream());

app.post('/logs', function(req, res){
  if(!req.body) return res.send('OK');

  req.body.pipe(through(function(line){
    console.dir(line);
  }))

  res.send('OK');
})

http.createServer(app).listen(3000);

Or you can just use the readable event:

var app    = require('express')();
var http   = require('http');
var logfmt  = require('logfmt');

app.use(logfmt.bodyParserStream());

// req.body is now a Readable Stream
app.post('/logs', function(req, res){
  req.body.on('readable', function(){
    var parsedLine = req.body.read();
    if(parsedLine) console.log(parsedLine);
    else res.send('OK');
  })
})

http.createServer(app).listen(3000);

Non-Streaming

logfmt.bodyParser([opts])

Valid Options:

• contentType: defaults to application/logplex-1

If you use the logfmt.bodyParser() for a body parser, you will have a req.body that is an array of objects.

var logfmt   = require('logfmt');

app.use(logfmt.bodyParser());

// req.body is now an array of objects
app.post('/logs', function(req, res){

  console.log('BODY: ' + JSON.stringify(req.body));

  req.body.forEach(function(data){
    console.log(data);
  });

  res.send('OK');
})

http.createServer(app).listen(3000);

test it:

curl -X POST --header 'Content-Type: application/logplex-1' -d "foo=bar a=14 baz=\"hello kitty\" cool%story=bro f %^asdf" http://localhost:3000/logs

command line

logfmt

accepts lines on STDIN and converts them to json

> echo "foo=bar a=14 baz=\"hello kitty\" cool%story=bro f %^asdf" | logfmt
{ "foo": "bar", "a": 14, "baz": "hello kitty", "cool%story": "bro", "f": true, "%^asdf": true }

logfmt -r (reverse)

accepts JSON on STDIN and converts them to logfmt

> echo '{ "foo": "bar", "a": 14, "baz": "hello kitty", "cool%story": "bro", "f": true, "%^asdf": true }' | logfmt -r
foo=bar a=14 baz="hello kitty" cool%story=bro f=true %^asdf=true

> echo "foo=bar a=14 baz=\"hello kitty\" cool%story=bro f %^asdf" | logfmt | logfmt -r | logfmt
{ "foo": "bar", "a": 14, "baz": "hello kitty", "cool%story": "bro", "f": true, "%^asdf": true }