From 79767c70cd70c28344d90ca518c2f52d6083b244 Mon Sep 17 00:00:00 2001
From: indexzero <charlie.robbins@gmail.com>
Date: Thu, 29 Oct 2015 02:50:46 -0700
Subject: [PATCH] [refactor] Make some performance optimizations for
 `Logger.prototype.log`.

---
 lib/winston/logger.js | 99 ++++++++++++++++++++++++++-----------------
 1 file changed, 61 insertions(+), 38 deletions(-)

diff --git a/lib/winston/logger.js b/lib/winston/logger.js
index 8fc71bed1..1bf03240a 100755
--- a/lib/winston/logger.js
+++ b/lib/winston/logger.js
@@ -104,22 +104,27 @@ Logger.prototype.configure = function (options) {
 // Core logging method exposed to Winston. Metadata is optional.
 //
 Logger.prototype.log = function (level) {
-  var self = this,
-      args = Array.prototype.slice.call(arguments, 1);
+  var args = Array.prototype.slice.call(arguments, 1),
+      self = this,
+      transports;
 
-  while(args[args.length - 1] === null) {
+  while (args[args.length - 1] === null) {
     args.pop();
   }
 
+  //
+  // Determining what is `meta` and what are arguments for string interpolation
+  // turns out to be VERY tricky. e.g. in the cases like this:
+  //
+  //    logger.info('No interpolation symbols', 'ok', 'why', { meta: 'is-this' });
+  //
   var callback = typeof args[args.length - 1] === 'function' ? args.pop() : null,
       meta     = typeof args[args.length - 1] === 'object' && Object.prototype.toString.call(args[args.length - 1]) !== '[object RegExp]' ? args.pop() : {},
       msg      = util.format.apply(null, args);
 
-  // If we should pad for levels, do so
-  if (this.padLevels) {
-    msg = new Array(this.levelLength - level.length + 1).join(' ') + msg;
-  }
-
+  //
+  // Handle errors appropriately.
+  //
   function onError(err) {
     if (callback) {
       callback(err);
@@ -129,13 +134,49 @@ Logger.prototype.log = function (level) {
     }
   }
 
-  if (Object.keys(this.transports).length === 0) {
+  if (this._names.length === 0) {
     return onError(new Error('Cannot log with no transports.'));
   }
   else if (typeof self.levels[level] === 'undefined') {
     return onError(new Error('Unknown log level: ' + level));
   }
 
+  //
+  // If there are no transports that match the level
+  // then be eager and return. This could potentially be calculated
+  // during `setLevels` for more performance gains.
+  //
+  var targets = this._names.filter(function (name) {
+    var transport = self.transports[name];
+    return (transport.level && self.levels[transport.level] >= self.levels[level])
+      || (!transport.level && self.levels[self.level] >= self.levels[level]);
+  });
+
+  if (!targets.length) {
+    if (callback) { callback(); }
+    return;
+  }
+
+  //
+  // Respond to the callback.
+  //
+  function finish(err) {
+    if (callback) {
+      if (err) return callback(err);
+      callback(null, level, msg, meta);
+    }
+
+    callback = null;
+    if (!err) {
+      self.emit('logged', level, msg, meta);
+    }
+  }
+
+  // If we should pad for levels, do so
+  if (this.padLevels) {
+    msg = new Array(this.levelLength - level.length + 1).join(' ') + msg;
+  }
+
   this.rewriters.forEach(function (rewriter) {
     meta = rewriter(level, msg, meta, self);
   });
@@ -165,39 +206,21 @@ Logger.prototype.log = function (level) {
   //
   // Log for each transport and emit 'logging' event
   //
-  function emit(name, next) {
+  function transportLog(name, next) {
     var transport = self.transports[name];
-    if ((transport.level && self.levels[transport.level] >= self.levels[level])
-      || (!transport.level && self.levels[self.level] >= self.levels[level])) {
-      transport.log(level, msg, meta, function (err) {
-        if (err) {
-          err.transport = transport;
-          cb(err);
-          return next();
-        }
-        self.emit('logging', transport, level, msg, meta);
-        next();
-      });
-    } else {
-      next();
-    }
-  }
+    transport.log(level, msg, meta, function (err) {
+      if (err) {
+        err.transport = transport;
+        finish(err);
+        return next();
+      }
 
-  //
-  // Respond to the callback
-  //
-  function cb(err) {
-    if (callback) {
-      if (err) return callback(err);
-      callback(null, level, msg, meta);
-    }
-    callback = null;
-    if (!err) {
-      self.emit('logged', level, msg, meta);
-    }
+      self.emit('logging', transport, level, msg, meta);
+      next();
+    });
   }
 
-  async.forEach(this._names, emit, cb);
+  async.forEach(targets, transportLog, finish);
   return this;
 };