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2.0.0 • Public • Published


Output stream for Bunyan which prints human readable logs.


What is it?

BunyanDebugStream is a stream for Bunyan which takes in Bunyan logs and outputs human readable log lines (which look sort of vaguely like syslog output.)

There are plenty of other npm packages out there that do something similar, but this is the best one. ;)


  • Colored output based on log level.
  • Concise and pretty stack traces using exception-formatter.
  • A morgan inspired custom formatter for request/response objects. Will automatically fetch response time out of res.responseTime or duration (from bunyan-middleware) or response-time (from express-bunyan-logger.)
  • Easy to customize output of different fields.


npm install --save-dev bunyan-debug-stream


The most basic usage involves just creating a Bunyan logger which writes raw objects to the stream:

var bunyanDebugStream = require('bunyan-debug-stream');

var log = bunyan.createLogger({
    name: "myLog",
    streams: [{
        level:  'info',
        type:   'raw',
        stream: bunyanDebugStream({
            basepath: __dirname, // this should be the root folder of your project.
            forceColor: true
    serializers: bunyanDebugStream.serializers

This will get you up and running with 90% of the functionality you probably want, but there are lots of ways you can customize the behavior of bunyan-debug-stream. Note you can also use the Bunyan stdSerializers - the bunyanDebugStream.serializers are the same as stdSerializers, but add a few custom fields.


basepath and basepathReplacement

basepath should be the root folder of your project. This is used in two ways; if you turn on src: true in your Bunyan logger, then instead of printing filenames like '/users/me/myprojects/project/src/file.js', your logger will strip the basepath and instead print './s/file.js'. (Note that we also shorten folder names to keep log lines short.) This same value also gets passed on to exception-formatter. If you don't specify a value, this will default to process.cwd().

basepathReplacement defaults to './' - this is what we replace the basepath with.


If you don't like the default color scheme, you can easily change it. Bunyan-debug-stream uses the colors module to color lines. Pass in something like:

    colors: {
        'info': 'blue',
        'error': ['red', 'bold']


By default, colors are disabled when outputting to a non-tty. If you're having problems getting colors to work in grunt or gulp, set this to true. Note that under the hood, this sets colors.enabled to true (see colors.js#102) so this may affect other modules that use colors.

stringifiers and prefixers

Bunyan logs can contain extra data beyond just the log message. If you call:{foo: {bar: "baz"}}, "Hello World");

Then bunyan-debug-stream might print something like:

Nov 27 09:50:04 MyLogger[649] INFO:  main (./s/app:195): Hello World
  foo: {"bar": "baz"}

Sometimes you might want to have more specific control over how certain objects are printed. This is where stringifiers and prefixers come in.

options.stringifiers is a hash where keys are object names and values are functions which return a string. So, for example, you might do:

    stringifiers: {
        'foo': function(foo) {return "The value of bar is " +;}

This would change the output to be:

Nov 27 09:50:04 MyLogger[649] INFO:  main (./s/app:195): Hello World
  foo: The value of bar is baz

Specifying a stringifier of null will prevent a value from being displayed at all.

Usually you can do what you want with a simple stringifier which takes a single parameter and returns a string, but for those extra special complicated cases, you can do something like:

    stringifiers: {
        'req': function(req, options) {
            return {
                value: req.url + " - " + options.entry.res.statusCode,
                consumed: ["req", "res"]

options here will be a {entry, useColor, debugStream} object, where entry is the full Bunyan log entry, useColor is true if output is in color and false otherwise, and debugStream is the BunyanDebugStream object. This will let you combine multiple properties into a single line. This will also prevent the "res" property from being shown. (Note if you don't like the way we write out requests, you can do exactly this.)

For short objects that you include in many logs, such as user names or host names, you might not want to print them on a line by themselves. prefixers work just like stringifiers, except the value will be prefixed at the beginning of the message:

    prefixers: {
        'foo': function(foo) {return;}

would result in the output:

Nov 27 09:50:04 MyLogger[649] INFO:  main (./s/app:195): [baz] Hello World

showProcess and processName

By default bunyan-debug-stream will show the logger name and the PID of the current process. If options.showProcess is true, bunyan-debug-stream will also show the process name. This defaults to the second argument in process.argv (minus the path and the extension) on the assumption that you're running with node myApp.js, but you can override this by passing an explicit options.processName.


Turned on by default. If options.showDate is false, bunyan-debug-stream doesn't print timestamps in the output, e.g.:

    MyLogger[649] INFO:  main (./s/app:195): [baz] Hello World

You may also specify a function(time, entry) here to generate a custom date string:

    showDate: (time) => return time.toISOString()


Turned on by default. If options.showPid is false, bunyan-debug-stream doesn't print the process ID in the output, e.g.:

    Nov 27 09:50:04 MyLogger INFO:  main (./s/app:195): [baz] Hello World


Turned on by default. If options.showLoggerName is false, bunyan-debug-stream doesn't print name property of the logger in the output, e.g.:

    Nov 27 09:50:04 [649] INFO:  main (./s/app:195): [baz] Hello World


Turned on by default. If options.showLevel is false, bunyan-debug-stream doesn't print the log level (e.g. INFO, DEBUG) in the output, e.g.:

    Nov 27 09:50:04 MyLogger[649]  main (./s/app:195): [baz] Hello World


Turned on by default. If options.showMetadata is false, bunyan-debug-stream doesn't print arbitrary properties of passed metadata objects (also known as extra fields) to the log. However, this option does not apply to properties that have specific prefixer or stringifier handlers. For example, if you have foo stringifier and arbitrary field extraField: 1, like below:

    const log = bunyanDebugStream({
        stringifiers: {
            'foo': function(foo) {return "The value of bar is " +;}
    });{extraField: 1, foo: {bar: "baz"}}, "Hello World");

Then you can expect that extraField will get omitted, and only foo will be printed:

    Nov 27 09:50:04 MyLogger[649] INFO:  main (./s/app:195): Hello World
      foo: The value of bar is baz


If present, options.maxExceptionLines is passed along to exception-formatter as options.maxLines. This controls the maximum number of lines to print in a stack trace. 0 for unlimited (the default.)


options.out is the stream to write data to. Must have a .write() method.

Special Handling for Requests

If the object you pass has a req field, then bunyan-debug-stream will automatically turn this into a log line (somewhat inspired by the morgan logger's 'dev' mode.) To get the most out of this, you should pass req and res and use the default bunyan serializers (or use our custom serializers.) If you don't pass a message to the logger, then the request line will replace the message.

bunyan-debug-stream tries to play nice with bunyan-middleware and express-bunyan-logger.

bunyan-debug-stream will read the following values from the following locations. entry is the log entry passed in to bunyan-debug-stream. Where multiple locations are listed, bunyan-debug-stream will try to fetch the value in the order specified.

  • statusCode - From res.statusCode or from entry['status-code'] (express-bunyan-logger.)
  • user - bunyan-debug-stream will look for a req.user or a entry.user object. In either case it will user user.username,, or user.toString().
  • responseTime - res.responseTime, entry.duration (bunyan-middleware), or entry['response-time'] (express-bunyan-logger.)
  • contentLength - res.headers['content-length'] or entry['res-headers']['content-length'] (express-bunyan-logger.)
  • host -
  • url - req.url
  • method - req.method

Note that user, contentLength, and responseTime will not show up if you are using the standard Bunyan serializers.

Special Handling for Errors

By default, errors are processed using exception-formatter. If you don't like the way exception-formatter works, you can specify your own serializer for err to print them however you like. :)


npm i bunyan-debug-stream

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