No slowdown when logging through child loggers.

.gitignore

@@ -31,3 +31,7 @@ node_modules
 
 # Optional REPL history
 .node_repl_history
+
+# 0x
+.__browserify_string_empty.js
+profile-*

README.md

@@ -114,6 +114,7 @@ Into this:
 ## API
 
   * <a href="#constructor"><code><b>pino()</b></code></a>
+  * <a href="#child"><code>logger.<b>child()</b></code></a>
   * <a href="#level"><code>logger.<b>level</b></code></a>
   * <a href="#fatal"><code>logger.<b>fatal()</b></code></a>
   * <a href="#error"><code>logger.<b>error()</b></code></a>
@@ -153,6 +154,25 @@ var instance = pino({
 }
 ```
 
+<a name="child"></a>
+### logger.child(bindings)
+
+Creates a child logger, setting all key-value pairs in `bindings` as
+properties in the log lines. All serializers will be applied to the
+given pair.
+
+Example:
+
+```js
+logger.child({ a: 'property' }).info('hello child!')
+// generates
+// {"pid":46497,"hostname":"MacBook-Pro-di-Matteo.local","level":30,"msg":"hello child!","time":1458124707120,"v":0,"a":"property"}
+```
+
+It leverage the output stream of the parent and
+its log level. These settings are immutable and pulled out during the
+instantiation of the child logger.
+
 <a name="level"></a>
 ### logger.level
 

benchmarks/basic.js

@@ -0,0 +1,55 @@
+'use strict'
+
+var bench = require('fastbench')
+var pino = require('../')
+var bunyan = require('bunyan')
+var bole = require('bole')('bench')
+var winston = require('winston')
+var fs = require('fs')
+var dest = fs.createWriteStream('/dev/null')
+var plog = pino(dest)
+var max = 10
+var blog = bunyan.createLogger({
+  name: 'myapp',
+  streams: [{
+    level: 'trace',
+    stream: dest
+  }]
+})
+
+require('bole').output({
+  level: 'info',
+  stream: dest
+})
+
+winston.add(winston.transports.File, { filename: '/dev/null' })
+winston.remove(winston.transports.Console)
+
+var run = bench([
+  function benchBunyan (cb) {
+    for (var i = 0; i < max; i++) {
+      blog.info('hello world')
+    }
+    setImmediate(cb)
+  },
+  function benchWinston (cb) {
+    for (var i = 0; i < max; i++) {
+      winston.info('hello world')
+    }
+    setImmediate(cb)
+  },
+  function benchBole (cb) {
+    for (var i = 0; i < max; i++) {
+      bole.info('hello world')
+    }
+    setImmediate(cb)
+  },
+  function benchPino (cb) {
+    for (var i = 0; i < max; i++) {
+      plog.info('hello world')
+    }
+    setImmediate(cb)
+  }
+], 10000)
+
+run(run)

benchmarks/child.js

@@ -0,0 +1,45 @@
+'use strict'
+
+var bench = require('fastbench')
+var pino = require('../')
+var bunyan = require('bunyan')
+var bole = require('bole')('bench')('child')
+var fs = require('fs')
+var dest = fs.createWriteStream('/dev/null')
+var plog = pino(dest).child({ a: 'property' })
+var max = 10
+var blog = bunyan.createLogger({
+  name: 'myapp',
+  streams: [{
+    level: 'trace',
+    stream: dest
+  }]
+}).child({ a: 'property' })
+
+require('bole').output({
+  level: 'info',
+  stream: dest
+})
+
+var run = bench([
+  function benchBunyanObj (cb) {
+    for (var i = 0; i < max; i++) {
+      blog.info({ hello: 'world' })
+    }
+    setImmediate(cb)
+  },
+  function benchPinoChild (cb) {
+    for (var i = 0; i < max; i++) {
+      plog.info({ hello: 'world' })
+    }
+    setImmediate(cb)
+  },
+  function benchBoleChild (cb) {
+    for (var i = 0; i < max; i++) {
+      bole.info({ hello: 'world' })
+    }
+    setImmediate(cb)
+  }
+], 10000)
+
+run(run)

benchmarks/childCreation.js

@@ -0,0 +1,48 @@
+'use strict'
+
+var bench = require('fastbench')
+var pino = require('../')
+var bunyan = require('bunyan')
+var bole = require('bole')('bench')
+var fs = require('fs')
+var dest = fs.createWriteStream('/dev/null')
+var plog = pino(dest)
+var max = 10
+var blog = bunyan.createLogger({
+  name: 'myapp',
+  streams: [{
+    level: 'trace',
+    stream: dest
+  }]
+})
+
+require('bole').output({
+  level: 'info',
+  stream: dest
+})
+
+var run = bench([
+  function benchPinoCreation (cb) {
+    var child = plog.child({ a: 'property' })
+    for (var i = 0; i < max; i++) {
+      child.info({ hello: 'world' })
+    }
+    setImmediate(cb)
+  },
+  function benchBunyanCreation (cb) {
+    var child = blog.child({ a: 'property' })
+    for (var i = 0; i < max; i++) {
+      child.info({ hello: 'world' })
+    }
+    setImmediate(cb)
+  },
+  function benchBoleCreation (cb) {
+    var child = bole('child')
+    for (var i = 0; i < max; i++) {
+      child.info({ hello: 'world' })
+    }
+    setImmediate(cb)
+  }
+], 10000)
+
+run(run)

benchmark.js → benchmarks/object.js

@@ -1,7 +1,7 @@
 'use strict'
 
 var bench = require('fastbench')
-var pino = require('./')
+var pino = require('../')
 var bunyan = require('bunyan')
 var bole = require('bole')('bench')
 var winston = require('winston')
@@ -26,30 +26,6 @@ winston.add(winston.transports.File, { filename: '/dev/null' })
 winston.remove(winston.transports.Console)
 
 var run = bench([
-  function benchBunyan (cb) {
-    for (var i = 0; i < max; i++) {
-      blog.info('hello world')
-    }
-    setImmediate(cb)
-  },
-  function benchWinston (cb) {
-    for (var i = 0; i < max; i++) {
-      winston.info('hello world')
-    }
-    setImmediate(cb)
-  },
-  function benchBole (cb) {
-    for (var i = 0; i < max; i++) {
-      bole.info('hello world')
-    }
-    setImmediate(cb)
-  },
-  function benchPino (cb) {
-    for (var i = 0; i < max; i++) {
-      plog.info('hello world')
-    }
-    setImmediate(cb)
-  },
   function benchBunyanObj (cb) {
     for (var i = 0; i < max; i++) {
       blog.info({ hello: 'world' })

example.js

@@ -12,3 +12,5 @@ info({ obj: 42, b: 2 }, 'hello world')
 info({ obj: { aa: 'bbb' } }, 'another')
 setImmediate(info, 'after setImmediate')
 error(new Error('an error'))
+
+pino.child({ a: 'property' }).info('hello child!')

pino.js

@@ -25,7 +25,7 @@ function pino (opts, stream) {
   var slowtime = opts.slowtime
   var stringify = opts.safe !== false ? stringifySafe : JSON.stringify
   var name = opts.name
-  var level
+  var level = opts.level
   var funcs = {}
   var result = {
     fatal: null,
@@ -36,33 +36,24 @@ function pino (opts, stream) {
     trace: null
   }
   var serializers = opts.serializers || {}
+  var end = '}\n'
 
   for (var key in levels) {
     funcs[key] = genLogFunction(key)
   }
 
-  Object.defineProperty(result, 'level', {
-    enumerable: false,
-    get: function () {
-      return level
-    },
-    set: function (l) {
-      level = levels[l]
-      if (!level) {
-        throw new Error('unknown level ' + l)
+  if (opts.meta) {
+    end = ',' + opts.meta + end
+    Object.keys(levels).forEach(function (key) {
+      if (level <= levels[key]) {
+        result[key] = funcs[key]
+      } else {
+        result[key] = noop
       }
-
-      Object.keys(levels).forEach(function (key) {
-        if (level <= levels[key]) {
-          result[key] = funcs[key]
-        } else {
-          result[key] = noop
-        }
-      })
-    }
-  })
-
-  result.level = opts.level || 'info'
+    })
+  } else {
+    setup(result, funcs, level, stream, opts, serializers, stringify)
+  }
 
   return result
 
@@ -113,7 +104,7 @@ function pino (opts, stream) {
         }
       }
     }
-    return data + '}\n'
+    return data + end
   }
 
   // returns string json with final brace omitted
@@ -129,6 +120,59 @@ function pino (opts, stream) {
   }
 }
 
+function setup (result, funcs, level, stream, opts, serializers, stringify) {
+  var safe = opts.safe
+
+  Object.defineProperty(result, 'level', {
+    enumerable: false,
+    get: function () {
+      return level
+    },
+    set: function (l) {
+      level = levels[l]
+      if (!level) {
+        throw new Error('unknown level ' + l)
+      }
+
+      Object.keys(levels).forEach(function (key) {
+        if (level <= levels[key]) {
+          result[key] = funcs[key]
+        } else {
+          result[key] = noop
+        }
+      })
+    }
+  })
+
+  result.level = opts.level || 'info'
+  result.child = child
+
+  function child (bindings) {
+    if (!opts) {
+      throw new Error('missing bindings for child logger')
+    }
+
+    var data = ''
+    var value
+    for (var key in bindings) {
+      value = bindings[key]
+      if (bindings.hasOwnProperty(key) && value !== undefined) {
+        value = serializers[key] ? serializers[key](value) : value
+        data += '"' + key + '":' + stringify(value)
+      }
+    }
+
+    var toPino = {
+      safe: safe,
+      meta: data,
+      level: level,
+      serializers: serializers
+    }
+
+    return pino(toPino, stream)
+  }
+}
+
 function noop () {}
 
 function mapHttpRequest (req) {