Test email components in your software
Tutorial Details:
Test email components in your software
Test email components in your software
By: By Jason Kitchen
Write a simple email server that can integrate into your testing environment
he basis of a maintainable and stable software system is the ability to easily unit test the system in an automated way using testing frameworks such as JUnit. Unfortunately, verifying correct delivery of a system's email messages and validating content in an automated fashion is not a trivial task due to the complexity of typical email servers. Such testing is possible but tricky and may involve complex administration tasks or integration with proprietary message stores?tasks not conducive to successful automated testing.
I had been thinking about this problem for some time when I came up with the idea of writing my own SMTP (Simple Mail Transfer Protocol) server designed from the ground up to be used solely as an aid to automated testing. The idea was to create a server that could respond appropriately to SMTP commands, but, rather than attempting to deliver email messages to the receiver or forward to another server as appropriate, it would simply cache the received headers and message body for later extraction and verification by a test client.
One of the main attractions of using Java for network-based applications is access to a range of quality networking libraries provided as standard in the Java development environment. Complex yet robust networking software can be written in a few lines of code. In Java, the javax.mail package may be used to communicate with both email servers for the delivery of SMTP-based email messages, and message stores using POP (Post Office Protocol) or IMAP (Internet Message Access Protocol). This article will concentrate on the former?SMTP to send email messages?rather than message-store protocols that a user agent would use to extract messages from the store.
The basic requirements for such a "dummy" server are:
The ability to manage (i.e., start and stop) the server from a Java program?specifically a JUnit test case
No server administration tasks, configuration, authentication
The server would not (and should not) try to deliver messages since we are simply using the server to unit test
The ability to extract delivered messages from the server itself, rather than connecting to multiple and potentially remote message stores to verify delivery and content
This article explains how to write this simple email server; see Resources to download its code.
Email standards
Before we start writing an SMTP server, an overview of the standards documents that we will use in building the dummy SMTP server is in order.
Most commercial email servers in the world today support the SMTP protocol, originally defined in RFC (Request for Comments) 821 in August 1982. As an historic side note, the word simple in Simple Mail Transfer Protocol is derived from the fact that SMTP itself was based on an earlier more complex protocol definition named, unsurprisingly, the Mail Transfer Protocol (MTP). RFC 821 itself is currently being superceded by the draft standard RFC 2821, published in April 2001. This new draft standard adds no new functionality or updates to existing functionality, so, for the remainder of this article, when referring to SMTP, I mean the protocol as defined in RFC 2821. Since we will not be implementing anything more complex than the basic set of SMTP commands, for all intents and purposes, use of this later draft standard should not affect our solution.
In the interest of completeness, I should mention some of the other standards documents that relate to the SMTP protocol:
RFC 2822, Internet Message Format: Defines the syntax of email messages themselves, including the headers (supercedes RFC 822).
RFC 2920, SMTP Service Extension for Command Pipelining: Defines an SMTP protocol extension that allows multiple commands to be sent within one TCP send operation. In the interests of simplicity, our dummy SMTP server will not support this extension.
RFC 3030, SMTP Service Extensions for Transmission of Large and Binary MIME (Multipurpose Internet Mail Extensions) Messages: Defines an SMTP extension for attaching large binary objects to email messages.
Many other standards documents relate to SMTP, adequate coverage of which reaches beyond this article's scope. For further information, see the IETF (Internet Engineering Task Force) Website .
The SMTP protocol by example
SMTP is a relatively straightforward protocol to understand. All communication between the client and the server is plain text and, hence, more or less human readable. Here is an example of a simple exchange between a Java mail client and the dummy SMTP server. Once the client has connected to the server on the default SMTP port (25), the following conversation ensues:
1 S: 220 localhost Dumbster SMTP service ready
2 C: EHLO WKS-JKITCHEN
3 S: 250 OK
4 C: MAIL FROM:
5 S: 250 OK
6 C: RCPT TO:
7 S: 250 OK
8 C: DATA
9 S: 354 Start mail input; end with .
10 C:
11 C: .
12 S: 250 OK
13 C: QUIT
Whenever client-server conversations are shown in this article, the prefix S: will be used to indicate the server part of the conversation and C: to indicate the client part.
In the above client-server exchange, the client connects to the email server using a socket connection. In fact, the standards don't dictate how this communication should occur, but invariably, socket connections are used. At Line 1, the server responds using a 220 code indicating that it is ready to talk. Some information related to the email server itself is also returned?in this case, the host name and email server name (Dumbster, the project name I used during code development).
At Line 2, the client issues an EHLO command, which initiates the conversation, and at Line 3, the server responds with a 250 code indicating that the client may proceed.
At Line 4, the client issues a MAIL command indicating the sender's email address, and, at Line 5, the server replies with a 250 code indicating that the sender address was validated and may proceed.
At Line 6, the client issues a RCPT command to identify the message's recipient. Multiple recipients may be indicated using multiple consecutive RCPT commands. In this case, we have just one recipient. At Line 7, the server again responds with a 250 code indicating that the address is valid and the client may proceed.
At Line 8, the client issues a DATA command indicating that it is ready to start sending the message's headers and body.
At Line 9, the server responds with a 354 code indicating to the client that it may proceed. Since the client will most likely send multiple lines of text, the server also indicates how the client data should terminate: with a single point character on its own line of input. In this case, there is no message body?not likely to happen in the real world, but I wanted to keep this example short to concentrate on essentials. So at Lines 10 and 11, the DATA command terminates.
At Line 12, the server responds with a 250 code indicating that the message was correctly received.
At Line 13, the client sends a QUIT command, at which point the client-server exchange terminates.
Required toolset
To develop an SMTP server, the tools listed below are required. I have given specific versions, but you will most likely be able to swap these out for previous or later versions if required, as nothing depends on specific versions of the JDK or JavaMail implementation.
Java 2 Platform, Standard Edition (J2SE) 1.4.1_02
JavaMail 1.3
JavaBeans Activation Framework (JAF) 1.0.2
JUnit 3.8.1
Apache Ant 1.5.3
Overview of implementation
To create a functioning dummy email server, we must implement a server that will interact in a standards-based fashion with clients that connect to it. The implementation needs to be able to send the correct response to SMTP commands received from the client and track the state of the interaction with the client to send the correct response or error. This involves implementing the set of SMTP commands to which the server must respond. These are:
EHLO / HELO : identifies the client to SMTP server
MAIL : used to initiate a mail transaction and identify the sender?actually a return path
RCPT : identifies a single recipient's email address
DATA : used to send headers and body text
RSET : resets the mail transaction without dropping the connection
VRFY : requests the server to verify the given email address's correctness, which our dummy server doesn't support
EXPN : requests the server to verify that the given address is a mailing list and, if so, replies with a list of addresses that make up the list?not supported by our dummy server
HELP : requests useful information from the server?our implementation returns a simple nondescript message
NOOP : no operation command, often used by clients to determine if the connection is still open without affecting the current transaction's state
QUIT : instructs the server that it may close the connection after sending a reply to the client
A great degree of depth is not required for the implementation of these commands. For example, for the RCPT command, the email address is always assumed correct.
The client-server conversation's state is preserved in the SMTP server. This helps generate the correct responses to commands received from the client. The following is a state table that summarizes the server's main internal states and how client input affects a change of state and the responses generated by the server. For simplicity, only the principle SMTP commands are shown, with no error conditions.
Server internal state machine
State
Request
Response
Next State
Connect
Socket connection
220
Greet
Greet
EHLO / HELO
250
Mail
Mail
MAIL
250
Mail
Receipt
RCPT
250
Receipt
Receipt
DATA
354
Data headers
Data headers
Blank line
Data body
Data hea
Read
Tutorial at: Click here to view the tutorial
Rate Tutorial: Test email components in your software
View Tutorial: Test email components in your software
Related
Tutorials:
 Test infect your
Enterprise JavaBeans - JavaWorld May 2000
Test infect your
Enterprise JavaBeans - JavaWorld May 2000
|
Frameworks save the
day - JavaWorld September 2000
Frameworks save the
day - JavaWorld September 2000
|
JavaMail quick start
JavaMail quick start
|
Create email-based apps with JAMES
Create email-based apps with JAMES
|
Listen to heartbeats using
JMS
Listen to heartbeats using
JMS
|
Take command of your
software
Take command of your
software
|
Jini's relevance emerges, Part
1
Jini's relevance emerges, Part
1
|
Test email components in your software
Test email components in your software
|
Bug patrol
Bug patrol
|
Control your test-environment with DbUnit and Anthill
The inception of the Extreme Programming methodology has brought test-driven development and continuous integration into mainstream Java development practices. Applying these techniques to Java server-side development can quickly become a nightmare if you
|
Developing Swing Components Using Simulators
Developing Swing Components Using Simulators
In this article, you'll learn about a technique for developing encapsulated components. You'll also learn about how to test graphical parts of your application that JUnit can't, such as layouts and other visua
|
g4j - GMail API for Java
GMailer API for Java (g4j) is set of API that allows Java programmer to communicate to GMail. With G4J programmers can made Java based application that based on huge storage of GMail.
|
Reporting Application Errors by Email
Reporting Application Errors by Email
It is common practice for server-side applications to log messages to files on the server's file system. These logs are a vital source of information for system administrators and the application development team. If
|
developing a Session Bean and a Servlet and deploy the web application on
JBoss 3.0
developing a Session Bean and a Servlet and deploy the web application on JBoss 3.0
Writing Stateless Session Bean and Calling through Servlet
Previous Tutorial Index Next
In this lesson I will show you how to develop a Stateless Session Bean and
|
Buy Fedora Core 3 Test 1 Linux CD's in India.
Buy Fedora Core 3 Test 1 Linux CD's in India.
Fedora Core 3 Test 1 Linux
Fedora Core 3 Is Available
Now Available Fedora Core 3 Test 1CD's
We are providing the free downloadable version of Fedora Core 3 Test 1 Linux CDs, which is distributed
|
Submit project to get developed
Submit project to get developed
T his page contains answers to common questions handled by our support staff, along with some tips and tricks that we have found useful and presented here as questions.
How do I Submit my Project ?
Who can submit a
|
Your suggestions
Your suggestions
Use the form on this page to tell us your ideas for enhancing our products, or improving our customer service, or anything else that comes to mind.
Subject:
Suggestion:
Your name:
Your Email:
|
What is WAP? Detailed discussion of WAP API with examples.
What is WAP? Detailed discussion of WAP API with examples.
Learn WAP in 60 minutes
W ireless Application Protocol or WAP for short, allows the developers to develop next generation web application for cellular devices. Through WAP enabled mobile
|
Updated Hardware Certification Test Suite Available for Download
Version 2.4 of the HCTS is now available. Use it to certify your hardware on the Solaris 9 Operating System (and updates) and the Solaris 10 OS, 32-bit and 64-bit environments.
|
Solaris 10 OS Released
The Solaris 10 Operating System is now officially a production release. Download it today at no cost and see how Solaris software can make a difference for you.
|
|
|
|
