Welcome!

You will be redirected in 30 seconds or close now.

ColdFusion Authors: Yakov Fain, Jeremy Geelan, Maureen O'Gara, Nancy Y. Nee, Tad Anderson

Related Topics: ColdFusion

ColdFusion: Article

Expect The Unexpected

Expect The Unexpected

No one wants to write buggy code, at least no one I choose to know. Bugs are annoying, bugs are embarrassing. And bugs can cost you (and your clients) lots of time and money.

Bugfree code is the ideal all developers strive for - at least should strive for - but it's a lofty goal not easily attained.

To write bugfree code it's important to understand how bugs are introduced. I'd like to explore what I believe to be one of the primary causes for the introduction of bugs into your code: failure to expect the unexpected. While many of these ideas apply to application development in general, the positioning of this column relates specifically to ColdFusion.

Flow? What Flow?
Applications are designed with a particular program flow in mind. Users start at point A, go to point B, then to point C. Program flow is an important part of any application, and when developers write they anticipate a particular program flow.

Here are some examples.

  • A search dialog is displayed, the user enters search criteria, a search is performed and the results are displayed.

  • The user browses a product catalog, makes multiple selections with possible confirmations and provides payment information, after which the order is saved and processed.

  • A login screen is displayed and the user provides authentication information, which is validated against a database. If authenticated, access is granted; otherwise the login screen is redisplayed.

    In each of these examples there's a logical starting point, then a series of steps. The search dialog must be displayed before the search can be performed, users must select items from the product catalog before the order can be processed, and login information must be provided before access can be authenticated.

    In traditional application development, programmers had total control over program flow. Users had no way to access screens out of order, nor could they start from a screen other than the one they were supposed to start at. But Web applications, for better or worse, behave differently. As every Web page has a unique address (its URL), it's indeed possible for users to execute pages out of order, just as it's possible for them to start from the wrong page.

    How could this occur? There are several ways. Users could bookmark pages directly, search engines might index pages below your root, and newer browsers feature an auto-fill option that completes URLs for users but frequently uses the most recently visited page in the site (often the wrong page).

    To understand this better, look at the following code:

    <!--- Perform search --->
    <CFQUERY DATASOURCE="ds" NAME="search">
    SELECT title FROM books
    WHERE title LIKE %#FORM.title#%'
    </CFQUERY>
    <!--- Create page --->
    <HTML>
    <BODY>
    <H1>Search Results</H1>
    <UL>
    <!--- Display search results --->
    <CFOUTPUT QUERY="search">
    <LI>#title#
    </CFOUTPUT>
    </UL>
    </BODY>
    </HTML>

    What's wrong with the above code?

    Actually, this is fairly typical ColdFusion code (it's even commented). It performs a simple database search and displays the results. The search itself is driven by a form that contains a field named "title"

    And that's what's wrong. The code makes two dangerous assumptions - that the page will be called from a form and that the form contains a field named "title". If either assumption turns out to be incorrect, ColdFusion throws an error because #FORM.title# would refer to a variable that didn't exist.

    What's the solution? There are a couple of things you can and should do. The first is always check for the existence of variables before using them, initializing them with default values if needed. The ColdFusion <CFPARAM> tag is very useful for this, and good programming practices demand that every variable be initialized this way so they always exist (either as submitted FORM or URL values, or as locally created variables). If the following code were inserted above the code example, the page would always execute correctly, regardless of how it was invoked and what fields were passed:

    <CFPARAM NAME="FORM.title" DEFAULT="">

    Sometimes you may not want to use default values. For example, in the preceding code you may not want to display the entire contents of the table if the page is executed directly. If a user ends up on this page without having filled in the form to perform the search, you'd want to send them to the search page instead. Here's one way you could do this (assuming the search page was named search.cfm):

    <!--- Is form field present? --->
    <CFIF NOT IsDefined("FORM.title")>
    <!--- Not present, redirect to search screen --->
    <CFLOCATION URL="search.cfm">
    </CFIF>

    With this snippet at the top of the page your code is now safe. If users try to execute the page directly, you'll programmatically redirect them to where they really should be.

    The truth is, every page on your site should be written so that it's safe to execute directly. That way you'll never make assumptions about program flow, and your code won't break when the unexpected occurs.

    Are you up for a challenge? How about writing code that uses <CFDIRECTORY> to traverse your code tree to find all CFM pages, then looping through each one, executing it via <CFHTTP> to see which ones throw errors and which work. You could call this code daily (or weekly or monthly) and e-mail yourself the results so you'll know as soon as possible if things might break.

    Changes in Site Usage
    Another phenomenon that's part of Web site use is the frequency with which that use changes. Programmers anticipate that their site will be used in one way, but, inevitably, users find another way to use it. That's not a bad thing in and of itself, but it does present an interesting problem.

    All applications, not just Web-based applications, are designed so that particular parts perform better than others. This is usually because certain parts of the application are more critical and get more use, so the time and effort needed to improve and enhance the site tends to be best spent on these parts.

    The application hums along nicely, handling the load thrown at it, and everything works well until those pesky users start using your site in ways you didn't expect. Suddenly the efficient and highly optimized parts are being executed less and less, and the less fine-tuned (I'm being generous) parts start to buckle under the growing load.

    This is actually a very common problem. Some of the largest and most impressive sites on the Internet have fallen victim to it.

    The good news is that ColdFusion provides you with an invaluable (and frequently overlooked) tool you can use to identify these potential trouble spots. The ColdFusion Administrator (starting in version 4) features a checkbox that, when checked, allows you to log page requests that take longer than a specified amount of time.

    Again, the key here is to expect the unexpected and be ready when it occurs. Individual log entries aren't necessarily indicative of a problem, but repeated entries most definitely are. I'd strongly advise all site administrators to enable this option, even on production sites. Determine what the "normal" response time should be (and then pad that number a little) and have ColdFusion log all page requests that take longer. If specific pages start appearing in the log repeatedly, you'll know where to spend your fine-tuning and performance-enhancing efforts.

    Up for another challenge? Write a scheduled event that checks this log file daily for new entries. If it finds any, it should e-mail them to you so you'll know about them immediately.

    When Bad Things Happen
    You've cleaned up your site. You no longer expect specific program flow, nor do you expect specific usage patterns. That's great, but it's not enough.

    The other big trouble spot is reliance on other systems and technologies. Whether it's database integration, execution of third-party objects and components, or interaction with other Internet protocols (like HTTP, FTP and NNTP), the more you rely on other systems and technologies, the more room there is for something to go wrong.

    Whether it's database failure, the inability to connect to a specific host, or errors and problems in calls resources, they're all your problem because to the end user your site is broken. It's not an ideal world out there; bad things do happen and you'll be blamed. And you're not going to escape this one anytime soon.

    So what do you do? Again, ColdFusion (version 4 or later) provides a tool to respond to these situations - try catch error handling. While full coverage of try catch is beyond the scope of this column (I'll devote an entire column to error handling in the future), here's the basic idea.

    Try catch error handling allows you to trap errors in your code, then pick up the processing elsewhere when an error occurs. The basic page layout looks like this:

    <CFTRY>
    ... page goes here ...
    <CFCATCH>
    ... error processing goes here ...
    </CFCATCH>
    </CFTRY>

    By wrapping an entire page between <CFTRY> and </CFTRY> tags, any error that occurs within that page will be trapped. As soon as an error is caught, processing will be taken over by the catch block (the code between <CFCATCH> and </CFCATCH>). There's no limit to what you can place in the catch block-you can change variables, redirect requests, generate e-mail, write logs and even try to fix error conditions.

    Experienced developers take this one step further by nesting try catch error handling. Generic error handling is implemented at the page level, and additional error handling is implemented around specific features or functions. This type of implementation provides the greatest level of control and allows developers to not just expect the unexpected, but also to handle the unexpected.

    Conclusion
    The Internet is a highly dynamic and configurable environment. With all that flexibility and power comes the need for greater caution and planning to ensure that applications don't suddenly break. Bugfree code is a wonderful ideal, but for most of us, writing good code that doesn't break in unexpected scenarios is as close as we'll get to attaining it.

    The bottom line is that as developers writing code for this new environment, we must all expect the unexpected- because it's going to happen and usually at the least opportune time.

  • More Stories By Ben Forta

    Ben Forta is Adobe's Senior Technical Evangelist. In that capacity he spends a considerable amount of time talking and writing about Adobe products (with an emphasis on ColdFusion and Flex), and providing feedback to help shape the future direction of the products. By the way, if you are not yet a ColdFusion user, you should be. It is an incredible product, and is truly deserving of all the praise it has been receiving. In a prior life he was a ColdFusion customer (he wrote one of the first large high visibility web sites using the product) and was so impressed he ended up working for the company that created it (Allaire). Ben is also the author of books on ColdFusion, SQL, Windows 2000, JSP, WAP, Regular Expressions, and more. Before joining Adobe (well, Allaire actually, and then Macromedia and Allaire merged, and then Adobe bought Macromedia) he helped found a company called Car.com which provides automotive services (buy a car, sell a car, etc) over the Web. Car.com (including Stoneage) is one of the largest automotive web sites out there, was written entirely in ColdFusion, and is now owned by Auto-By-Tel.

    Comments (0)

    Share your thoughts on this story.

    Add your comment
    You must be signed in to add a comment. Sign-in | Register

    In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


    @ThingsExpo Stories
    Nordstrom is transforming the way that they do business and the cloud is the key to enabling speed and hyper personalized customer experiences. In his session at 21st Cloud Expo, Ken Schow, VP of Engineering at Nordstrom, will discuss some of the key learnings and common pitfalls of large enterprises moving to the cloud. This includes strategies around choosing a cloud provider(s), architecture, and lessons learned. In addition, he’ll go over some of the best practices for structured team migrat...
    SYS-CON Events announced today that Taica will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Taica manufacturers Alpha-GEL brand silicone components and materials, which maintain outstanding performance over a wide temperature range -40C to +200C. For more information, visit http://www.taica.co.jp/english/.
    SYS-CON Events announced today that MIRAI Inc. will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. MIRAI Inc. are IT consultants from the public sector whose mission is to solve social issues by technology and innovation and to create a meaningful future for people.
    Recently, REAN Cloud built a digital concierge for a North Carolina hospital that had observed that most patient call button questions were repetitive. In addition, the paper-based process used to measure patient health metrics was laborious, not in real-time and sometimes error-prone. In their session at 21st Cloud Expo, Sean Finnerty, Executive Director, Practice Lead, Health Care & Life Science at REAN Cloud, and Dr. S.P.T. Krishnan, Principal Architect at REAN Cloud, will discuss how they bu...
    Coca-Cola’s Google powered digital signage system lays the groundwork for a more valuable connection between Coke and its customers. Digital signs pair software with high-resolution displays so that a message can be changed instantly based on what the operator wants to communicate or sell. In their Day 3 Keynote at 21st Cloud Expo, Greg Chambers, Global Group Director, Digital Innovation, Coca-Cola, and Vidya Nagarajan, a Senior Product Manager at Google, will discuss how from store operations...
    As hybrid cloud becomes the de-facto standard mode of operation for most enterprises, new challenges arise on how to efficiently and economically share data across environments. In his session at 21st Cloud Expo, Dr. Allon Cohen, VP of Product at Elastifile, will explore new techniques and best practices that help enterprise IT benefit from the advantages of hybrid cloud environments by enabling data availability for both legacy enterprise and cloud-native mission critical applications. By rev...
    Join IBM November 1 at 21st Cloud Expo at the Santa Clara Convention Center in Santa Clara, CA, and learn how IBM Watson can bring cognitive services and AI to intelligent, unmanned systems. Cognitive analysis impacts today’s systems with unparalleled ability that were previously available only to manned, back-end operations. Thanks to cloud processing, IBM Watson can bring cognitive services and AI to intelligent, unmanned systems. Imagine a robot vacuum that becomes your personal assistant tha...
    SYS-CON Events announced today that Datera will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Datera offers a radically new approach to data management, where innovative software makes data infrastructure invisible, elastic and able to perform at the highest level. It eliminates hardware lock-in and gives IT organizations the choice to source x86 server nodes, with business model option...
    With major technology companies and startups seriously embracing Cloud strategies, now is the perfect time to attend 21st Cloud Expo October 31 - November 2, 2017, at the Santa Clara Convention Center, CA, and June 12-14, 2018, at the Javits Center in New York City, NY, and learn what is going on, contribute to the discussions, and ensure that your enterprise is on the right path to Digital Transformation.
    Infoblox delivers Actionable Network Intelligence to enterprise, government, and service provider customers around the world. They are the industry leader in DNS, DHCP, and IP address management, the category known as DDI. We empower thousands of organizations to control and secure their networks from the core-enabling them to increase efficiency and visibility, improve customer service, and meet compliance requirements.
    Digital transformation is changing the face of business. The IDC predicts that enterprises will commit to a massive new scale of digital transformation, to stake out leadership positions in the "digital transformation economy." Accordingly, attendees at the upcoming Cloud Expo | @ThingsExpo at the Santa Clara Convention Center in Santa Clara, CA, Oct 31-Nov 2, will find fresh new content in a new track called Enterprise Cloud & Digital Transformation.
    SYS-CON Events announced today that N3N will exhibit at SYS-CON's @ThingsExpo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. N3N’s solutions increase the effectiveness of operations and control centers, increase the value of IoT investments, and facilitate real-time operational decision making. N3N enables operations teams with a four dimensional digital “big board” that consolidates real-time live video feeds alongside IoT sensor data a...
    SYS-CON Events announced today that NetApp has been named “Bronze Sponsor” of SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. NetApp is the data authority for hybrid cloud. NetApp provides a full range of hybrid cloud data services that simplify management of applications and data across cloud and on-premises environments to accelerate digital transformation. Together with their partners, NetApp emp...
    Smart cities have the potential to change our lives at so many levels for citizens: less pollution, reduced parking obstacles, better health, education and more energy savings. Real-time data streaming and the Internet of Things (IoT) possess the power to turn this vision into a reality. However, most organizations today are building their data infrastructure to focus solely on addressing immediate business needs vs. a platform capable of quickly adapting emerging technologies to address future ...
    SYS-CON Events announced today that Avere Systems, a leading provider of hybrid cloud enablement solutions, will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Avere Systems was created by file systems experts determined to reinvent storage by changing the way enterprises thought about and bought storage resources. With decades of experience behind the company’s founders, Avere got its ...
    SYS-CON Events announced today that Avere Systems, a leading provider of enterprise storage for the hybrid cloud, will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Avere delivers a more modern architectural approach to storage that doesn't require the overprovisioning of storage capacity to achieve performance, overspending on expensive storage media for inactive data or the overbui...
    SYS-CON Events announced today that IBM has been named “Diamond Sponsor” of SYS-CON's 21st Cloud Expo, which will take place on October 31 through November 2nd 2017 at the Santa Clara Convention Center in Santa Clara, California.
    SYS-CON Events announced today that Ryobi Systems will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Ryobi Systems Co., Ltd., as an information service company, specialized in business support for local governments and medical industry. We are challenging to achive the precision farming with AI. For more information, visit http:...
    High-velocity engineering teams are applying not only continuous delivery processes, but also lessons in experimentation from established leaders like Amazon, Netflix, and Facebook. These companies have made experimentation a foundation for their release processes, allowing them to try out major feature releases and redesigns within smaller groups before making them broadly available. In his session at 21st Cloud Expo, Brian Lucas, Senior Staff Engineer at Optimizely, will discuss how by using...
    In this strange new world where more and more power is drawn from business technology, companies are effectively straddling two paths on the road to innovation and transformation into digital enterprises. The first path is the heritage trail – with “legacy” technology forming the background. Here, extant technologies are transformed by core IT teams to provide more API-driven approaches. Legacy systems can restrict companies that are transitioning into digital enterprises. To truly become a lead...