Chapter 1 introduces the concepts related to the programmable Web, shows how HTTP and web services are related to each other, introduces the principles behind REST, explains how HTTP verbs are used in REST applications, explains the need for RESTFul web services while building PHP web applications, and introduces some frameworks and tools that can be used to work with REST in PHP.

Chapter 2 takes a first look at REST with PHP. While providing and consuming REST-style web services, the primary pre-requisites are an HTTP server or an HTTP client library and an XML parser library. In this chapter, we will see how to use the PHP CURL API to consume web services using various HTTP verbs such as HTTP GET, POST, PUT, and DELETE. The DOM API and SimpleXML API for building XML object structures and parsing XML streams are also discussed. We will discuss in detail how to build XML request payloads and also how to parse XML response payloads. The final section of this chapter demonstrates how to use the HTTP client features and XML parser features to invoke the Flickr REST API.

Chapter 3 looks into some real-world applications and discusses how to combine multiple service interfaces to build value-added custom applications. In this chapter, we will see how to use RSS or ATOM feeds, Yahoo search API, and Yahoo maps API. With the know-how you gain in this chapter and the previous chapters, you could build very powerful value-added applications like mashups using publicly available REST-style services.

Chapter 4 covers the steps that you would have to follow in designing and implementing a resource-oriented service in detail. Identifying resources and business operations for a given problem statement, designing the URI patterns, selecting the correct HTTP verbs, mapping URI and HTTP verbs to business operations are covered using the library example. Implementing the services and business operations using PHP is explained in detail, step by step.

Chapter 5 covers the steps that you would have to follow in designing and implementing resource-oriented clients in detail. The design of the clients is governed by the design of the service. And the client programmer needs to understand the semantics of the service, which is usually communicated through service API documentation. In the examples of this chapter, we will use the library service API designed in Chapter 4 to explain how we could use an existing API while designing PHP applications.

Chapter 6 uses the REST classes provided with the Zend Framework to implement the sample library system. The design of the service and client are covered, along with the MVC concepts supported by the Zend Framework. We will discuss how resources map to the model in MVC, and how HTTP verbs when combined with resource URIs map to the controller in MVC. We will explore how to combine Zend_Rest_Server with Zend_Controller to implement the business operations of the service and how to use Zend_Rest_Client class to consume the services.

Chapter 7 looks into the use of tools to trace and look into the messages to figure out possible problems with request and response pairs passed between clients and services. That helps with debugging and troubleshooting of services and clients. We will also look into how we could look at the XML documents to figure out possible problems in building XML in this chapter, and discuss how we can locate problems in parsing incoming XML messages.

Appendix A introduces the WSO2 Web Services Framework for PHP (WSO2 WSF/PHP) and discusses how to use the WSF/PHP service API to implement the sample Library system as a REST service and implement a REST client to consume it. We will also look into using the SOAP features provided in the frameworks to implement a SOAP client to consume the same service using SOAP-style messages. This chapter also discusses the differences between REST and SOAP message styles, in brief.

Appendix B introduces a PHP class named RESTClient that can be used to consume REST-style services. This class supports all key HTTP verbs, GET, POST, PUT, and DELETE. The advantage of using such a class is that it minimizes the complexity of your client code. At the same time, you can re-use this class for all your REST-style client implementations. This PHP class is sufficient for most simple REST-style client programs, and requires no third-party libraries. However, if you want to implement services and also want advanced clients, it is advised to use a more established framework such as Zend Framework or WSO2 WSF/PHP introduced in Chapter 6 and Appendix A of this book.

You need PHP5 installed with Apache httpd server to try out the samples of this book. You would require a MySQL installation to try out the library sample discussed in the book.

You also need to install Zend Framework and WSO2 WSF/PHP to try out the samples based on those frameworks.

This book is for PHP programmers who are interested in using Web Services in their applications. Sometimes, you would be interested in using the publicly available REST-style services in your own applications, in which case, the REST client concepts discussed in this book would be very useful. You might also be involved with the implementation of PHP applications where you want to expose some aspects of the application as services to the outside world, in which case, you can benefit from the REST service concepts covered in this book. In addition, if you are a software developer looking for a hands-on text that will help you understand REST principles, from the ground up, this book would be a very good guide for you.

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