Category excluding filter.

This filtering appender allows you to choose some category
names that won't be logged to the delegated appender. This
is useful if you have e.g. a category that you use to log
web requests to one file, but want to keep those entries
out of the main log file without having to explicitly list
all the other categories that you _do_ want to include.

Has one option, "exclude", which is a category name or
array of category names. The child appender is set in
"appender", modelled on the logLevelFilter.

lib/appenders/categoryFilter.js

@@ -0,0 +1,24 @@
+var levels = require('../levels');
+var log4js = require('../log4js');
+
+function contains(list, value) {
+    return list.indexOf(value) !== -1;
+}
+
+function categoryFilter (excludes, appender) {
+    if (typeof(excludes) === 'string') excludes = [excludes];
+    return function(logEvent) {
+        if (excludes.indexOf(logEvent.categoryName) === -1) {
+            appender(logEvent);
+        }
+    }
+}
+
+function configure(config) {
+    log4js.loadAppender(config.appender.type);
+    var appender = log4js.appenderMakers[config.appender.type](config.appender);
+    return categoryFilter(config.exclude, appender);
+}
+
+exports.appender = categoryFilter;
+exports.configure = configure;

test/categoryFilter-test.js

@@ -0,0 +1,79 @@
+'use strict';
+
+var vows = require('vows')
+, fs = require('fs')
+, assert = require('assert');
+
+function remove(filename) {
+    try {
+        fs.unlinkSync(filename);
+    } catch (e) {
+        //doesn't really matter if it failed
+    }
+}
+
+vows.describe('log4js categoryFilter').addBatch({
+    'appender': {
+        topic: function() {
+
+            var log4js = require('../lib/log4js'), logEvents = [], webLogger, appLogger;
+            log4js.clearAppenders();
+            var appender = require('../lib/appenders/categoryFilter').appender(['app'], function(evt) { logEvents.push(evt); });
+            log4js.addAppender(appender, ["app","web"]);
+
+            webLogger = log4js.getLogger("web");
+            appLogger = log4js.getLogger("app");
+
+            webLogger.debug('This should get logged');
+            appLogger.debug('This should not');
+            webLogger.debug('Hello again');
+            log4js.getLogger('db').debug('This shouldn\'t be included by the appender anyway');
+
+            return logEvents;
+        },
+        'should only pass matching category' : function(logEvents) {
+            assert.equal(logEvents.length, 2);
+            assert.equal(logEvents[0].data[0], 'This should get logged');
+            assert.equal(logEvents[1].data[0], 'Hello again');
+        }
+    },
+
+    'configure': {
+        topic: function() {
+            var log4js = require('../lib/log4js')
+          , logger, weblogger;
+
+            remove(__dirname + '/categoryFilter-web.log');
+            remove(__dirname + '/categoryFilter-noweb.log');
+
+            log4js.configure('test/with-categoryFilter.json');
+            logger = log4js.getLogger("app");
+            weblogger = log4js.getLogger("web");
+
+            logger.info('Loading app');
+            logger.debug('Initialising indexes');
+            weblogger.info('00:00:00 GET / 200');
+            weblogger.warn('00:00:00 GET / 500');
+            //wait for the file system to catch up
+            setTimeout(this.callback, 100);
+        },
+        'tmp-tests.log': {
+            topic: function() {
+                fs.readFile(__dirname + '/categoryFilter-noweb.log', 'utf8', this.callback);
+            },
+            'should contain all log messages': function(contents) {
+                var messages = contents.trim().split('\n');
+                assert.deepEqual(messages, ['Loading app','Initialising indexes']);
+            }
+        },
+        'tmp-tests-web.log': {
+            topic: function() {
+                fs.readFile(__dirname + '/categoryFilter-web.log','utf8',this.callback);
+            },
+            'should contain only error and warning log messages': function(contents) {
+                var messages = contents.trim().split('\n');
+                assert.deepEqual(messages, ['00:00:00 GET / 200','00:00:00 GET / 500']);
+            }
+        }
+    }
+}).export(module);

test/with-categoryFilter.json

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+{
+  "appenders": [
+    { 
+      "type": "categoryFilter",
+      "exclude": "web",
+      "appender": {
+        "type": "file",
+        "filename": "test/categoryFilter-noweb.log", 
+        "layout": { 
+          "type": "messagePassThrough" 
+        } 
+      }
+    },
+    { 
+      "category": "web", 
+      "type": "file",
+      "filename": "test/categoryFilter-web.log", 
+      "layout": { 
+        "type": "messagePassThrough" 
+      } 
+    }
+  ]
+}