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RESTful Web Services

Cover of RESTful Web Services by Leonard Richardson... Published by O'Reilly Media, Inc.
  1. RESTful Web Services
    1. SPECIAL OFFER: Upgrade this ebook with O’Reilly
    2. A Note Regarding Supplemental Files
    3. Foreword
    4. Preface
      1. The Web Is Simple
      2. Big Web Services Are Not Simple
      3. The Story of the REST
      4. Reuniting the Webs
      5. What’s in This Book?
      6. Administrative Notes
      7. Conventions Used in This Book
      8. Using Code Examples
      9. Safari® Enabled
      10. How to Contact Us
      11. Acknowledgments
    5. 1. The Programmable Web and Its Inhabitants
      1. Kinds of Things on the Programmable Web
      2. HTTP: Documents in Envelopes
      3. Method Information
      4. Scoping Information
      5. The Competing Architectures
      6. Technologies on the Programmable Web
      7. Leftover Terminology
    6. 2. Writing Web Service Clients
      1. Web Services Are Web Sites
      2. The Sample Application
      3. Making the Request: HTTP Libraries
      4. Processing the Response: XML Parsers
      5. JSON Parsers: Handling Serialized Data
      6. Clients Made Easy with WADL
    7. 3. What Makes RESTful Services Different?
      1. Introducing the Simple Storage Service
      2. Object-Oriented Design of S3
      3. Resources
      4. HTTP Response Codes
      5. An S3 Client
      6. Request Signing and Access Control
      7. Using the S3 Client Library
      8. Clients Made Transparent with ActiveResource
      9. Parting Words
    8. 4. The Resource-Oriented Architecture
      1. Resource-Oriented What Now?
      2. What’s a Resource?
      3. URIs
      4. Addressability
      5. Statelessness
      6. Representations
      7. Links and Connectedness
      8. The Uniform Interface
      9. That’s It!
    9. 5. Designing Read-Only Resource-Oriented Services
      1. Resource Design
      2. Turning Requirements Into Read-Only Resources
      3. Figure Out the Data Set
      4. Split the Data Set into Resources
      5. Name the Resources
      6. Design Your Representations
      7. Link the Resources to Each Other
      8. The HTTP Response
      9. Conclusion
    10. 6. Designing Read/Write Resource-Oriented Services
      1. User Accounts as Resources
      2. Custom Places
      3. A Look Back at the Map Service
    11. 7. A Service Implementation
      1. A Social Bookmarking Web Service
      2. Figuring Out the Data Set
      3. Resource Design
      4. Design the Representation(s) Accepted from the Client
      5. Design the Representation(s) Served to the Client
      6. Connect Resources to Each Other
      7. What’s Supposed to Happen?
      8. What Might Go Wrong?
      9. Controller Code
      10. Model Code
      11. What Does the Client Need to Know?
    12. 8. REST and ROA Best Practices
      1. Resource-Oriented Basics
      2. The Generic ROA Procedure
      3. Addressability
      4. State and Statelessness
      5. Connectedness
      6. The Uniform Interface
      7. This Stuff Matters
      8. Resource Design
      9. URI Design
      10. Outgoing Representations
      11. Incoming Representations
      12. Service Versioning
      13. Permanent URIs Versus Readable URIs
      14. Standard Features of HTTP
      15. Faking PUT and DELETE
      16. The Trouble with Cookies
      17. Why Should a User Trust the HTTP Client?
    13. 9. The Building Blocks of Services
      1. Representation Formats
      2. Prepackaged Control Flows
      3. Hypermedia Technologies
    14. 10. The Resource-Oriented Architecture Versus Big Web Services
      1. What Problems Are Big Web Services Trying to Solve?
      2. SOAP
      3. WSDL
      4. UDDI
      5. Security
      6. Reliable Messaging
      7. Transactions
      8. BPEL, ESB, and SOA
      9. Conclusion
    15. 11. Ajax Applications as REST Clients
      1. From AJAX to Ajax
      2. The Ajax Architecture
      3. A Example
      4. The Advantages of Ajax
      5. The Disadvantages of Ajax
      6. REST Goes Better
      7. Making the Request
      8. Handling the Response
      9. JSON
      10. Don’t Bogart the Benefits of REST
      11. Cross-Browser Issues and Ajax Libraries
      12. Subverting the Browser Security Model
    16. 12. Frameworks for RESTful Services
      1. Ruby on Rails
      2. Restlet
      3. Django
    17. A. Some Resources for REST and Some RESTful Resources
      1. Standards and Guides
      2. Services You Can Use
    18. B. The HTTP Response Code Top 42
      1. Three to Seven Status Codes: The Bare Minimum
      2. 1xx: Meta
      3. 2xx: Success
      4. 3xx: Redirection
      5. 4xx: Client-Side Error
      6. 5xx: Server-Side Error
    19. C. The HTTP Header Top Infinity
      1. Standard Headers
      2. Nonstandard Headers
    20. Index
    21. About the Authors
    22. Colophon
    23. SPECIAL OFFER: Upgrade this ebook with O’Reilly
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Chapter 4. The Resource-Oriented Architecture

I’ve shown you the power of REST, but I haven’t shown you in any systematic way how that power is structured or how to expose it. In this chapter I outline a concrete RESTful architecture: the Resource-Oriented Architecture (ROA). The ROA is a way of turning a problem into a RESTful web service: an arrangement of URIs, HTTP, and XML that works like the rest of the Web, and that programmers will enjoy using.

In Chapter 1 I classified RESTful web services by their answers to two questions. These answers correspond to two of the four defining features of REST:

  • The scoping information (“why should the server send this data instead of that data?”) is kept in the URI. This is the principle of addressability.

  • The method information (“why should the server send this data instead of deleting it?”) is kept in the HTTP method. There are only a few HTTP methods, and everyone knows ahead of time what they do. This is the principle of the uniform interface.

In this chapter I introduce the moving parts of the Resource-Oriented Architecture: resources (of course), their names, their representations, and the links between them. I explain and promote the properties of the ROA: addressability, statelessness, connectedness, and the uniform interface. I show how the web technologies (HTTP, URIs, and XML) implement the moving parts to make the properties possible.

In the previous chapters I illustrated concepts by pointing to existing web services, like S3. I continue that tradition in this chapter, but I’ll also illustrate concepts by pointing to existing web sites. Hopefully I’ve convinced you by now that web sites are web services, and that many web applications (such as search engines) are RESTful web services. When I talk about abstract concepts like addressability, it’s useful to show you real URIs, which you can type into your web browser to see the concepts in action.

Resource-Oriented What Now?

Why come up with a new term, Resource-Oriented Architecture? Why not just say REST? Well, I do say REST, on the cover of this book, and I hold that everything in the Resource-Oriented Architecture is also RESTful. But REST is not an architecture: it’s a set of design criteria. You can say that one architecture meets those criteria better than another, but there is no one “REST architecture.”

Up to now, people have tended to mint one-off architectures as they design their services, according to their own understandings of REST. The most obvious outcome of this is the wide variety of REST-RPC hybrid web services that their creators claim are RESTful. I’m trying to put a stop to that by presenting a set of concrete rules for building web services that really will be RESTful. In the next two chapters I’ll even show simple procedures you can follow to turn requirements into resources. If you don’t like my rules, you’ll at least have an idea of what you can change and stay RESTful.

As a set of design criteria, REST is very general. In particular, it’s not tied to the Web. Nothing about REST depends on the mechanics of HTTP or the structure of URIs. But I’m talking about web services, so I explicitly tie the Resource-Oriented Architecture to the technologies of the Web. I want to talk about how to do REST with HTTP and URIs, in specific programming languages. If the future produces RESTful architectures that don’t run on top of the Web, their best practices will probably look similar to the ROA, but the details will be different. We’ll cross that bridge when we come to it.

The traditional definition of REST leaves a lot of open space, which practitioners have seeded with folklore. I deliberately go further than Roy Fielding in his dissertation, or the W3C in their standards: I want to clear some of that open space so that the folklore has room to grow into a well-defined set of best practices. Even if REST were an architecture, it wouldn’t be fair to call my architecture by the same name. I’d be tying my empirical observations and suggestions to the more general thoughts of those who built the Web.

My final reason for coming up with a new term is that “REST” is a term used in religious nerd wars. When it’s used, the implication is usually that there is one true RESTful architecture and it’s the one the speaker prefers. People who prefer another RESTful architecture disagree. The REST community fragments, despite a general agreement on basic things like the value of URIs and HTTP.

Ideally there would be no religious wars, but I’ve seen enough to know that wishing won’t end them. So I’m giving a distinctive name to my philosophy of how RESTful applications should be designed. When these ideas are, inevitably, used as fodder in wars, people who disagree with me can address aspects of the Resource-Oriented Architecture separate from other RESTful architectures, and from REST in general. Clarity is the first step toward understanding.

The phrases “resource-oriented” and “resource-oriented architecture” have been used to describe RESTful architectures in general.[10]I don’t claim that “Resource-Oriented Architecture” is a completely original term, but I think that my usage meshes well with preexisting uses, and that it’s better to use this term than claim to speak for REST as a whole.

[10] The earliest instance of “resource-oriented” I’ve found is a 2004 IBM developerWorks article by James Snell: Resource-oriented vs. activity-oriented Web services. Alex Bunardzic used “Resource-Oriented Architecture” in August 2006, before this book was announced: I don’t agree with everything in those articles, but I do acknowledge their priority in terminology.

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