Implemented shutdown function for SMTP appender

lib/appenders/smtp.js

@@ -1,7 +1,8 @@
 "use strict";
 var layouts = require("../layouts")
 , mailer = require("nodemailer")
-, os = require('os');
+, os = require('os')
+, unsentCount = 0;
 
 /**
 * SMTP Appender. Sends logging events using SMTP protocol. 
@@ -27,6 +28,7 @@ function smtpAppender(config, layout) {
       var transport = mailer.createTransport(config.transport, config[config.transport]);
       var firstEvent = logEventBuffer[0];
       var body = "";
+      var count = logEventBuffer.length;
       while (logEventBuffer.length > 0) {
         body += layout(logEventBuffer.shift()) + "\n";
       }
@@ -51,6 +53,7 @@ function smtpAppender(config, layout) {
           console.error("log4js.smtpAppender - Error happened", error);
         }
         transport.close();
+        unsentCount -= count;
       });
     }
 	}
@@ -65,6 +68,7 @@ function smtpAppender(config, layout) {
 	}
 	
 	return function(loggingEvent) {
+		unsentCount++;
 		logEventBuffer.push(loggingEvent);
 		if (sendInterval > 0) {
 			scheduleSend();
@@ -82,7 +86,16 @@ function configure(config) {
 	return smtpAppender(config, layout);
 }
 
+function shutdown(cb) {
+	async.until(function() {
+		return unsentCount === 0;
+	}, function(done) {
+		setTimeout(done, 100);
+	}, cb);
+}
+
 exports.name = "smtp";
 exports.appender = smtpAppender;
 exports.configure = configure;
+exports.shutdown = shutdown;