PHP Web Services Lorna Jane Mitchell Beijing • Cambridge • Farnham • Köln • Sebastopol • Tokyo Special Upgrade Offer If you purchased this ebook directly from oreilly.com, you have the following benefits: DRM-free ebooks—use your ebooks across devices without restrictions or limitations Multiple formats—use on your laptop, tablet, or phone Lifetime access, with free updates Dropbox syncing—your files, anywhere If you purchased this ebook from another retailer, you can upgrade your ebook to take advantage of all these benefits for just $4.99. Click here to access your ebook upgrade. Please note that upgrade offers are not available from sample content. Preface In this age, when it can sometimes seem like every system is connected to every other system, dealing with data has become a major ingredient in building the Web. Whether you will be delivering services or consuming them, web service is a key part of all modern, public-facing applications, and this book is here to help you navigate your way along the road ahead. We will cover the different styles of service—from RPC, to SOAP, to REST—and you will see how to devise great solutions using these existing approaches, as well as examples of APIs in the wild. Whether you’re sharing data between two internal systems, using a service backend for a mobile application, or just plain building an API so that users can access their data, this book has you covered, from the technical sections on HTTP, JSON, and XML to the “big picture” areas such as creating a robust service. Why did we pick PHP for this book? Well, PHP has always taken on the mission to “solve the web problem.” Web services are very much part of that “problem” and PHP is ideally equipped to make your life easy, both when consuming external services and when creating your own. As a language, it runs on many platforms and is the technology behind more than half of the Web, so you can be sure that it will be widely available, wherever you are. This book does not adopt any particular frameworks; instead, it aims to give you the tools you will need to understand the topic as a whole and apply that knowledge to whichever frameworks, libraries, or other wrappers you choose to use. The book walks you through everything you need to know in three broad sections. We begin by covering HTTP and the theory that goes with it, including detailed chapters on the request/response cycle, HTTP verbs and headers, and cookies. There are also chapters on JSON and XML: when to choose each data format, and how to handle them from within PHP. The second section aims to give very practical advice on working with RPC and SOAP services, with RESTful services, and on how to debug almost anything that works over HTTP, using a variety of tools and techniques. In the final section, we look at some of the wider issues surrounding the design of top-quality services, choosing what kind of service will work for your application, and determining how to make it robust. Another chapter is dedicated to handling errors and giving advice on why and how to document your API. Whether you dip into the book as a reference for a specific project, or read it in order to find out more about this area of technology, there’s something here to help you and your project to be successful. Enjoy! Conventions Used in This Book The following typographical conventions are used in this book: Italic Indicates new terms, URLs, email addresses, filenames, and file extensions. Constant width Used for program listings, as well as within paragraphs to refer to program elements such as variable or function names, databases, data types, environment variables, statements, and keywords. Constant width bold Shows commands or other text that should be typed literally by the user. Constant width italic Shows text that should be replaced with user-supplied values or by values determined by context. TIP This icon signifies a tip, suggestion, or general note. WARNING This icon indicates a warning or caution. Using Code Examples This book is here to help you get your job done. In general, if this book includes code examples, you may use the code in this book in your programs and documentation. You do not need to contact us for permission unless you’re reproducing a significant portion of the code. For example, writing a program that uses several chunks of code from this book does not require permission. Selling or distributing a CD-ROM of examples from O’Reilly books does require permission. Answering a question by citing this book and quoting example code does not require permission. Incorporating a significant amount of example code from this book into your product’s documentation does require permission. We appreciate, but do not require, attribution. An attribution usually includes the title, author, publisher, and ISBN. For example: “PHP Web Services by Lorna Jane Mitchell (O’Reilly). Copyright 2013 Lorna Jane Mitchell, 978-1-449- 35656-9.” If you feel your use of code examples falls outside fair use or the permission given above, feel free to contact us at [email protected]. Safari® Books Online Safari Books Online is an on-demand digital library that delivers expert content in both book and video form from the world’s leading authors in technology and business. Technology professionals, software developers, web designers, and business and creative professionals use Safari Books Online as their primary resource for research, problem solving, learning, and certification training. 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How to Contact Us Please address comments and questions concerning this book to the publisher: O’Reilly Media, Inc. 1005 Gravenstein Highway North Sebastopol, CA 95472 800-998-9938 (in the United States or Canada) 707-829-0515 (international or local) 707-829-0104 (fax) We have a web page for this book, where we list errata, examples, and any additional information. You can access this page at http://oreil.ly/php-web- services. To comment or ask technical questions about this book, send email to [email protected]. For more information about our books, courses, conferences, and news, see our website at http://www.oreilly.com. Find us on Facebook: http://facebook.com/oreilly Follow us on Twitter: http://twitter.com/oreillymedia Watch us on YouTube: http://www.youtube.com/oreillymedia Acknowledgments While this is quite a small book on the scale of things, a great many people gave their input to make it happen and they deserve to be acknowledged for the contributions they made. Several people reviewed early drafts of the book from a technical standpoint and asked many difficult questions at a stage when there was scope for answering them. Thanks to Sean Coates, Jon Phillips, Michele Davis, and Chris Willcock for all their input. My editors Maria Gulick and Rachel Roumeliotis have been patient and supportive throughout, something I’m sure gets tiring with such a large number of titles coming past at high speed. Their advice and support were invaluable, and I thank them for their gracious help. The rest of the O’Reilly staff have been rockstars also, in particular Josette Garcia, who always makes me believe, and the team that supports the tools I broke so regularly. My wider “geek support network” has been at once encouraging and providers of practical help. Many people rescued me from my own code samples, gave advice where my own experience fell short, and pointed me to further reading on a variety of topics that made it into this book (and many others that did not). This was very much a hive effort and I consider myself lucky to be part of a community from which help can be requested and given so readily. Finally, thanks are due to my mystified, but fantastically supportive, family and friends. Chief among these, of course, is my husband, Kevin, who served as cheerleader, proofreader, and head technical support consultant throughout this project and so many others. Chapter 1. HTTP HTTP stands for HyperText Transfer Protocol, and is the basis upon which the Web is built. Each HTTP transaction consists of a request and a response. The HTTP protocol itself is made up of many pieces: the URL at which the request was directed, the verb that was used, other headers and status codes, and of course, the body of the responses, which is what we usually see when we browse the Web in a browser. When surfing the Web, ideally we experience a smooth journey between all the various places that we’d like to visit. However, this is in stark contrast to what is happening behind the scenes as we make that journey. As we go along, clicking on links or causing the browser to make requests for us, a series of little “steps” is taking place behind the scenes. Each step is made up of a request/response pair; the client (usually your browser or phone if you’re surfing the Web) makes a request to the server, and the server processes the request and sends the response back. At every step along the way, the client makes a request and the server sends the response. As an example, point a browser to http://oreilly.com/ and you’ll see a page that looks something like Figure 1-1; either the information desired can be found on the page, or the hyperlinks on that page direct us to journey onward for it. Figure 1-1. O’Reilly home page The web page arrives in the body of the HTTP response, but it tells only half of the story. The rest is elsewhere in the HTTP traffic. Consider the following examples. Request header: GET / HTTP/1.1 User-Agent: Mozilla/5.0 (X11; Linux i686) AppleWebKit/537.8 (KHTML, like Gecko) Chrome/23.0.1246.0 Safari/537.8 Host: oreilly.com Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Encoding: gzip,deflate,sdch Accept-Language: en-GB,en-US;q=0.8,en;q=0.6 Response header: HTTP/1.1 200 OK Date: Thu, 15 Nov 2012 09:36:05 GMT Server: Apache