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, logfmt stringifier, a logging facility, and both streaming and non-streaming body parsers for express and restify.
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
node.js
The logfmt module is a singleton that works directly from require.
var logfmt = require('logfmt');
logfmt.stringify({foo: 'bar'});
// 'foo=bar'
logfmt.parse('foo=bar');
// {foo: 'bar'}It is also a constructor function, so you can use new logfmt to create
a new logfmt that you can configure differently.
var logfmt2 = new logfmt;
// replace our stringify with JSON's
logfmt2.stringify = JSON.stringify
// now we log JSON!
logfmt2.log({foo: 'bar'})
// {"foo":"bar"}
// and the original logfmt is untouched
logfmt.log({foo: 'bar'})
// foo=barcommand 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
round trips for free!
> 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 }
API
stringifying
Serialize an object to logfmt format
logfmt.stringify(object)
Serializes a single object.
logfmt.stringify({foo: "bar", a: 14, baz: 'hello kitty'})
//> 'foo=bar a=14 baz="hello kitty"'parsing
Parse a line in logfmt format
logfmt.parse(string)
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" }The only conversions are from the strings true and false to their proper boolean counterparts.
We cannot arbitrarily convert numbers because that will drop precision for numbers that require more than 32 bits to represent them.
Streaming
Put this in your pipe and smoke it.
logfmt.streamParser()
Creates a streaming parser that will automatically split and parse incoming lines and emit javascript objects.
Stream in from STDIN
process.stdin.pipe(logfmt.streamParser())Or pipe from an HTTP request
req.pipe(logfmt.streamParser())logfmt.streamStringify([options])
Pipe objects into the stream and it will write logfmt.
You can customize the delimiter via the options object, which
defaults to \n (newlines).
var parseJSON = function(line) {
if(!line) return;
this.queue(JSON.parse(line.trim()))
}
process.stdin
.pipe(split())
.pipe(through(parseJSON))
.pipe(logfmt.streamStringify())
.pipe(process.stdout)Example
Example command line of parsing logfmt and echoing objects to STDOUT:
var logfmt = require('logfmt');
var through = require('through');
process.stdin
.pipe(logfmt.streamParser())
.pipe(through(function(object){
console.log(object);
}))Example HTTP request parsing logfmt and echoing objects to STDOUT:
var http = require('http');
var logfmt = require('logfmt');
var through = require('through');
http.createServer(function (req, res) {
req.pipe(logfmt.streamParser())
.pipe(through(function(object){
console.log(object);
}))
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('OK');
}).listen(3000);express/restify parsing middleware
// streaming
app.use(logfmt.bodyParserStream());
// buffering
app.use(logfmt.bodyParser());logfmt.bodyParserStream([opts])
Valid Options:
contentType: defaults toapplication/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 toapplication/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/logslogging
Log an object to logfmt.stream (defaults to STDOUT)
Uses the logfmt.stringify function to write the result to logfmt.stream
logfmt.log({foo: "bar", a: 14, baz: 'hello kitty'})
//=> foo=bar a=14 baz="hello kitty"
//> undefinedlogfmt.log(object, [stream])
Defaults to logging to process.stdout
logfmt.log({ "foo": "bar", "a": 14, baz: 'hello kitty'})
//=> foo=bar a=14 baz="hello kitty"customizing logging location
logfmt.log() Accepts as 2nd argument 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 global location by setting logfmt.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"You can have multiple, isolated logfmts by using new.
var logfmt = require('logfmt');
var errorLogger = new logfmt;
errorLogger.stream = process.stderr
logfmt.log({hello: 'stdout'});
//=> hello=stdout
errorLogger.log({hello: 'stderr'});
//=> hello=stderrlogfmt.namespace(object)
Returns a new logfmt with object's data included in every log call.
var logfmt = require('logfmt').namespace({app: 'logfmt'});
logfmt.log({ "foo": "bar", "a": 14, baz: 'hello kitty'})
//=> app=logfmt foo=bar a=14 baz="hello kitty"
logfmt.log({})
//=> app=logfmt
logfmt.log({hello: 'world'})
//=> app=logfmt hello=worldlogfmt.time([label])
Log how long something takes.
Returns a new logfmt with elapsed milliseconds included in every log call.
label: optional name for the milliseconds key. defaults to:elapsed=<milliseconds>ms
var timer = logfmt.time();
timer.log();
//=> elapsed=1msString label changes the key to <string>=<milliseconds>ms
var timer = logfmt.time('time');
timer.log();
//=> time=1ms
timer.log();
//=> time=2msIf you'd like to include data, just chain a call to namespace.
var timer = logfmt.time('time').namespace({foo: 'bar'});
timer.log();
//=> time=1ms foo=bar
timer.log();
//=> time=2ms foo=barlogfmt.error(error)
Accepts a Javascript Error object and converts it to logfmt format.
It will print up to logfmt.maxErrorLines lines.
var logfmt = require('logfmt');
logfmt.error(new Error('test error'));
//=> at=error id=12345 message="test error"
//=> at=error id=12345 line=0 trace="Error: test error"
//=> ...express/restify logging middleware
app.use(logfmt.requestLogger());
//=> ip=127.0.0.1 time=2013-08-05T20:50:19.216Z method=POST path=/logs status=200 content_length=337 content_type=application/logplex-1 elapsed=4mslogfmt.requestLogger([options], [formatter(req, res)])
If no formatter is supplied it will default to logfmt.requestLogger.commonFormatter which is based
on having similar fields to the Apache Common Log format.
Valid Options:
immediate: log before call tonext()(ie: before the request finishes)elapsed: renames theelapsedkey to a key of your choice when in non-immediate mode
Defaults to immediate: true and elapsed: 'elapsed'
app.use(logfmt.requestLogger({immediate: true}, function(req, res){
return {
method: req.method
}
}));
//=> method=POSTapp.use(logfmt.requestLogger({elapsed: 'request.time'}, function(req, res){
return {
"request.method": req.method
}
}));
//=> request.method=POST request.time=12msformatter(req, res)
A formatter takes the request and response and returns a JSON object for logfmt.log
app.use(logfmt.requestLogger(function(req, res){
return {
method: req.method
}
}));
//=> method=POST elapsed=4msIt's always possible to piggyback on top of the commonFormatter
app.use(logfmt.requestLogger(function(req, res){
var data = logfmt.requestLogger.commonFormatter(req, res)
return {
ip: data.ip,
time: data.time,
foo: 'bar'
};
}));
//=> ip=127.0.0.1 time=2013-08-05T20:50:19.216Z foo=bar elapsed=4msDevelopment
Pull Requests welcome.
Tests
> npm test
License
MIT