|By Jason Bloomberg||
|December 17, 2012 08:45 AM EST||
REST quiz of the day: which is more important when following REST: updating the resource state or updating state on the client? Most developers are likely to say that REST focuses on updating resource state on the server. After all, POST, PUT, and DELETE all do so. GET is the only HTTP verb that fetches resource state without changing it.
If you've been reading ZapThink's discussion on REST, you probably realize that those developers are incorrect. Updating resource state is clearly an important part of REST, but updating state on the client is even more important. Why? Because client state is the foundation for distributed hypermedia applications. And after all, such applications are the point of REST.
In fact, the RESTful world distinguishes between resource state and application state, which is the state information the client maintains. And since hypermedia are the engine of application state, it makes sense that application state is more important to REST than resource state. After all, REST is representational state transfer. The representations are what the resources send to the clients, including application state information that belongs on the client.
HATEOAS and the Cloud
The topic of application state came up in an interesting discussion during our recent Cloud Computing for Architects course in San Diego. I was explaining how it's important to maintain a stateless application tier in the Cloud, because we want to put the components on that tier (Web servers, application servers, ESBs, etc.) onto virtual machine (VM) instances. In order to achieve the elasticity and resilience of the Cloud, then, we can't afford to maintain state information on such instances. We always have the option of persisting such state information, making it a part of the resource state, but relying too heavily on our resource state limits our scalability. The clear alternative is to transfer state information to the client, and let hypermedia be the engine of application state (otherwise known as the dreaded HATEOAS REST constraint).
One of the attendees in the class was confused by this discussion. He pointed out that if we use the client (say, a browser) to maintain state in a stateful application like an eCommerce shopping cart, then such state information must either go into hidden form fields or into the URL, so that the server can pass it along to the browser from one request to the next. But if the user is clicking a link rather than submitting a form, then they are executing a GET, and with a GET, the only place to put state information from the client to the server is in the URL. And we all know that URLs have a maximum length. What do we do, he asked, if we have too much state information for the URL? For example, we might have dozens of items in our cart. Was I suggesting passing the entire contents of each cart - product descriptions, prices, etc. - in the URL?
With REST, however, we're working with an abstracted client. It need not be a browser, and in fact, it need not have a user interface at all. A RESTful client may serve as an intermediary, for example. Even when the client has a UI, it could be any type of application. For example, most mobile apps are written natively to the mobile environment (iPhone or Android, for the most part), and will continue to be at least until HTML5 is fully baked.
Even when the client is a browser, however, we have numerous ways of maintaining application state. Each approach, as you might expect, has its strengths and weaknesses:
- Cookies - long a part of the HTTP protocol, cookies are universally supported and almost as universally reviled. We love them for enabling the "remember me" feature on Web sites with logins we visit frequently, and we hate them for enabling advertisers to track our browsing habits. Few app developers would rely on them for much else.
- Hidden form fields - every Web developer's secret sauce. You can put whatever you want into such fields, and as long as the user submits the corresponding form, the contents of hidden fields go along for the ride. The problem is that hidden form fields only work with POST. In REST, POST is only for initializing a subsidiary resource, so if that's not what you're doing, then you don't want to POST. The other downside to hidden form fields is that application state information must always make a round trip to the server and back again, whether the server needs to do anything with it or not.
- Signed scripts - What about simply writing arbitrary content to the user's hard drive? Browser publishers have been monkeying with this capability since signed scripts debuted in the 1990s. The problem with giving the browser write privileges, of course, is security. One flaw and hackers can easily take over your computer. Needless to say, this capability never took off, although plugins like Adobe Flash can allow the ability to write to the users' hard drive.
- DOM storage - Today we have DOM storage. Think cookies on steroids. Every modern browser can essentially store a JSON object that persists as the browser loads different pages. You have the option of maintaining such information for a browser session (you lose it when you quit the browser) or persisting it across browser sessions (where the browser writes the data to a file). This capability also enables developers to write browser apps that can function properly when the user is offline. The downside to DOM storage is that it only works in newer browsers - although Firefox, Internet Explorer, Chrome, and Safari all support it.
- URL query string - finally, let's discuss storing state information in the URL. Yes, there's a character limit - the HTTP spec recommends sticking to 255 characters or less, although most browsers and Web servers support much longer URLs. So, how much can you cram into 255 characters? More than you might expect, if you use a tool like RISON for compacting JSON to squeeze more of it into each URL. Don't like RISON? There are alternatives available or you can create your own approach. Even with such techniques, however, there is still a size limit, and all such information must make the round trip to server and back.
The ZapThink Take
Based on the discussion above, you should have no more concerns about storing application state on the client. There are always tradeoffs, but one of the scenarios above should handle virtually every application state issue you're likely to come up with. Feel free to transfer application state to the client and rest assured you're following REST.
That is, of course, if you really are following REST, which means that you're building a hypermedia application. And while POST, PUT, and DELETE update resource state for hypermedia applications, every representation from resource back to client updates client state. Even a GET, which never changes resource state, still changes the application state. In other words, clicking a link or submitting a form loads a new page. Of course REST behaves that way.
While this article focused more on maintaining state on the client, therefore, REST is more concerned with updating state on the client. The real point here is that we have the luxury of choosing to maintain the state information we require while running an application whose state is supposed to change. Either way, hypermedia are the engine of application state.
Image source: bloggyboulga
SYS-CON Events announced today that Micron Technology, Inc., a global leader in advanced semiconductor systems, will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Micron’s broad portfolio of high-performance memory technologies – including DRAM, NAND and NOR Flash – is the basis for solid state drives, modules, multichip packages and other system solutions. Backed by more than 35 years of technology leadership, Micron's memory solutions enable the world's most innovative computing, consumer,...
Sep. 2, 2015 05:30 PM EDT Reads: 257
SYS-CON Events announced today the Containers & Microservices Bootcamp, being held November 3-4, 2015, in conjunction with 17th Cloud Expo, @ThingsExpo, and @DevOpsSummit at the Santa Clara Convention Center in Santa Clara, CA. This is your chance to get started with the latest technology in the industry. Combined with real-world scenarios and use cases, the Containers and Microservices Bootcamp, led by Janakiram MSV, a Microsoft Regional Director, will include presentations as well as hands-on demos and comprehensive walkthroughs.
Sep. 2, 2015 04:45 PM EDT Reads: 387
In his session at @ThingsExpo, Lee Williams, a producer of the first smartphones and tablets, will talk about how he is now applying his experience in mobile technology to the design and development of the next generation of Environmental and Sustainability Services at ETwater. He will explain how M2M controllers work through wirelessly connected remote controls; and specifically delve into a retrofit option that reverse-engineers control codes of existing conventional controller systems so they don't have to be replaced and are instantly converted to become smart, connected devices.
Sep. 2, 2015 04:15 PM EDT Reads: 207
SYS-CON Events announced today that Pythian, a global IT services company specializing in helping companies leverage disruptive technologies to optimize revenue-generating systems, has been named “Bronze Sponsor” of SYS-CON's 17th Cloud Expo, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Founded in 1997, Pythian is a global IT services company that helps companies compete by adopting disruptive technologies such as cloud, Big Data, advanced analytics, and DevOps to advance innovation and increase agility. Specializing in designing, imple...
Sep. 2, 2015 04:15 PM EDT Reads: 347
With the Apple Watch making its way onto wrists all over the world, it’s only a matter of time before it becomes a staple in the workplace. In fact, Forrester reported that 68 percent of technology and business decision-makers characterize wearables as a top priority for 2015. Recognizing their business value early on, FinancialForce.com was the first to bring ERP to wearables, helping streamline communication across front and back office functions. In his session at @ThingsExpo, Kevin Roberts, GM of Platform at FinancialForce.com, will discuss the value of business applications on wearable ...
Sep. 2, 2015 04:00 PM EDT
Akana has announced the availability of the new Akana Healthcare Solution. The API-driven solution helps healthcare organizations accelerate their transition to being secure, digitally interoperable businesses. It leverages the Health Level Seven International Fast Healthcare Interoperability Resources (HL7 FHIR) standard to enable broader business use of medical data. Akana developed the Healthcare Solution in response to healthcare businesses that want to increase electronic, multi-device access to health records while reducing operating costs and complying with government regulations.
Sep. 2, 2015 04:00 PM EDT Reads: 276
17th Cloud Expo, taking place Nov 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Meanwhile, 94% of enterprises are using some form of XaaS – software, platform, and infrastructure as a service.
Sep. 2, 2015 04:00 PM EDT Reads: 1,577
The 3rd International WebRTC Summit, to be held Nov. 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA, announces that its Call for Papers is now open. Topics include all aspects of improving IT delivery by eliminating waste through automated business models leveraging cloud technologies. WebRTC Summit is co-located with 15th International Cloud Expo, 6th International Big Data Expo, 3rd International DevOps Summit and 2nd Internet of @ThingsExpo. WebRTC (Web-based Real-Time Communication) is an open source project supported by Google, Mozilla and Opera that aims to enable bro...
Sep. 2, 2015 03:45 PM EDT Reads: 1,559
The 17th International Cloud Expo has announced that its Call for Papers is open. 17th International Cloud Expo, to be held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, APM, APIs, Microservices, Security, Big Data, Internet of Things, DevOps and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding business opportunity. Submit your speaking proposal today!
Sep. 2, 2015 03:30 PM EDT Reads: 1,640
SYS-CON Events announced today that the "Second Containers & Microservices Expo" will take place November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Containers and microservices have become topics of intense interest throughout the cloud developer and enterprise IT communities.
Sep. 2, 2015 03:15 PM EDT Reads: 623
WebRTC services have already permeated corporate communications in the form of videoconferencing solutions. However, WebRTC has the potential of going beyond and catalyzing a new class of services providing more than calls with capabilities such as mass-scale real-time media broadcasting, enriched and augmented video, person-to-machine and machine-to-machine communications. In his session at @ThingsExpo, Luis Lopez, CEO of Kurento, will introduce the technologies required for implementing these ideas and some early experiments performed in the Kurento open source software community in areas ...
Sep. 2, 2015 02:15 PM EDT
Consumer IoT applications provide data about the user that just doesn’t exist in traditional PC or mobile web applications. This rich data, or “context,” enables the highly personalized consumer experiences that characterize many consumer IoT apps. This same data is also providing brands with unprecedented insight into how their connected products are being used, while, at the same time, powering highly targeted engagement and marketing opportunities. In his session at @ThingsExpo, Nathan Treloar, President and COO of Bebaio, will explore examples of brands transforming their businesses by t...
Sep. 2, 2015 02:00 PM EDT Reads: 264
SYS-CON Events announced today that HPM Networks will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. For 20 years, HPM Networks has been integrating technology solutions that solve complex business challenges. HPM Networks has designed solutions for both SMB and enterprise customers throughout the San Francisco Bay Area.
Sep. 2, 2015 01:30 PM EDT Reads: 939
While many app developers are comfortable building apps for the smartphone, there is a whole new world out there. In his session at @ThingsExpo, Narayan Sainaney, Co-founder and CTO of Mojio, will discuss how the business case for connected car apps is growing and, with open platform companies having already done the heavy lifting, there really is no barrier to entry.
Sep. 2, 2015 12:45 PM EDT Reads: 194
Too often with compelling new technologies market participants become overly enamored with that attractiveness of the technology and neglect underlying business drivers. This tendency, what some call the “newest shiny object syndrome,” is understandable given that virtually all of us are heavily engaged in technology. But it is also mistaken. Without concrete business cases driving its deployment, IoT, like many other technologies before it, will fade into obscurity.
Sep. 2, 2015 12:15 PM EDT Reads: 414
With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo in Silicon Valley. Learn what is going on, contribute to the discussions, and ensure that your enterprise is as "IoT-Ready" as it can be! Internet of @ThingsExpo, taking place Nov 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 17th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal an...
Sep. 2, 2015 11:30 AM EDT Reads: 1,997
With the proliferation of connected devices underpinning new Internet of Things systems, Brandon Schulz, Director of Luxoft IoT – Retail, will be looking at the transformation of the retail customer experience in brick and mortar stores in his session at @ThingsExpo. Questions he will address include: Will beacons drop to the wayside like QR codes, or be a proximity-based profit driver? How will the customer experience change in stores of all types when everything can be instrumented and analyzed? As an area of investment, how might a retail company move towards an innovation methodolo...
Sep. 2, 2015 11:15 AM EDT Reads: 494
As more intelligent IoT applications shift into gear, they’re merging into the ever-increasing traffic flow of the Internet. It won’t be long before we experience bottlenecks, as IoT traffic peaks during rush hours. Organizations that are unprepared will find themselves by the side of the road unable to cross back into the fast lane. As billions of new devices begin to communicate and exchange data – will your infrastructure be scalable enough to handle this new interconnected world?
Sep. 2, 2015 11:15 AM EDT Reads: 185
The Internet of Things is in the early stages of mainstream deployment but it promises to unlock value and rapidly transform how organizations manage, operationalize, and monetize their assets. IoT is a complex structure of hardware, sensors, applications, analytics and devices that need to be able to communicate geographically and across all functions. Once the data is collected from numerous endpoints, the challenge then becomes converting it into actionable insight.
Sep. 2, 2015 09:00 AM EDT
Contrary to mainstream media attention, the multiple possibilities of how consumer IoT will transform our everyday lives aren’t the only angle of this headline-gaining trend. There’s a huge opportunity for “industrial IoT” and “Smart Cities” to impact the world in the same capacity – especially during critical situations. For example, a community water dam that needs to release water can leverage embedded critical communications logic to alert the appropriate individuals, on the right device, as soon as they are needed to take action.
Sep. 2, 2015 08:45 AM EDT