Provide a way of limiting the mail storage size

MailDev may sometimes be used as a part of a development/staging
environment where the process may be running for a very long time
without interruption. In those cases, it is undesirable to let that
process grow freely. This limit makes sure that the memory usage is
bounded.

index.js

@@ -41,6 +41,7 @@ module.exports = function (config) {
         'Comma separated list of SMTP extensions to NOT advertise (STARTTLS, SMTPUTF8, PIPELINING, 8BITMIME)',
         function (val) { return val.split(',') }
       )
+      .option('--store-limit <limit>', 'Limit the number of stored messages')
       .option('-o, --open', 'Open the Web GUI after startup')
       .option('-v, --verbose')
       .option('--silent')
@@ -54,7 +55,14 @@ module.exports = function (config) {
   }
 
   // Start the Mailserver & Web GUI
-  mailserver.create(config.smtp, config.ip, config.incomingUser, config.incomingPass, config.hideExtensions)
+  mailserver.create(
+    config.smtp,
+    config.ip,
+    config.incomingUser,
+    config.incomingPass,
+    config.hideExtensions,
+    config.storeLimit
+  )
 
   if (config.outgoingHost ||
       config.outgoingPort ||

lib/mailserver.js

@@ -57,6 +57,11 @@ function saveEmail (id, envelope, mailObject) {
 
   store.push(object)
 
+  if (mailServer.storeLimit && store.length > mailServer.storeLimit) {
+    const removedMail = store.shift()
+    eventEmitter.emit('delete', {id: removedMail.id, index: 0})
+  }
+
   logger.log('Saving email: ', mailObject.subject)
 
   if (outgoing.isAutoRelayEnabled()) {
@@ -161,7 +166,7 @@ function createTempFolder () {
  * Create and configure the mailserver
  */
 
-mailServer.create = function (port, host, user, password, hideExtensions) {
+mailServer.create = function (port, host, user, password, hideExtensions, storeLimit) {
   const hideExtensionOptions = getHideExtensionOptions(hideExtensions)
   const smtpServerConfig = Object.assign({
     onAuth: smtpHelpers.createOnAuthCallback(user, password),
@@ -179,6 +184,7 @@ mailServer.create = function (port, host, user, password, hideExtensions) {
 
   mailServer.port = port || defaultPort
   mailServer.host = host || defaultHost
+  mailServer.storeLimit = storeLimit
 
   // testability requires this to be exposed.
   // otherwise we cannot test whether error handling works

test/api.test.js

@@ -6,6 +6,7 @@
  */
 
 const assert = require('assert')
+const expect = require('expect')
 const nodemailer = require('nodemailer')
 
 const MailDev = require('../index.js')
@@ -133,5 +134,47 @@ describe('API', function () {
         transporter.sendMail(emailOpts)
       })
     })
+
+    it('should respect store size limit', function (done) {
+      const maildev = new MailDev({
+        silent: true,
+        disableWeb: true,
+        storeLimit: 2
+      })
+
+      const transporter = nodemailer.createTransport({
+        port: 1025,
+        ignoreTLS: true
+      })
+
+      const emailOpts = {
+        from: 'Angelo Pappas <angelo.pappas@fbi.gov>',
+        to: 'Johnny Utah <johnny.utah@fbi.gov>',
+        subject: 'You were right.',
+        text: 'They are surfers.\n'
+      }
+
+      let emailCount = 3
+
+      maildev.on('new', function (email) {
+        expect(maildev.store.length).toBeLessThan(3)
+
+        if (!--emailCount) {
+          maildev.close(function () {
+            maildev.removeAllListeners()
+            transporter.close()
+            done()
+          })
+        }
+      })
+
+      maildev.listen(function (err) {
+        if (err) return done(err)
+
+        transporter.sendMail(emailOpts)
+        transporter.sendMail(emailOpts)
+        transporter.sendMail(emailOpts)
+      })
+    })
   })
 })