Using XML technology to construct remote services in PHP (Part 1)_PHP Tutorial

The future Web will be a service-centered Web, and the XML_RPC standard makes it very simple to write and apply services. This article introduces the XML_RPC standard and its PHP implementation, and demonstrates how to develop XML_RPC services and client programs in PHP through examples.

1. Serviced Web
From the simple methods adopted by content providers to the future vision of UDDI (Universal Description, Discovery and Integration), the industry has already had a lot of explanations and explanations about the "Serviced Web" Comment. In the early stages of the Web, it was just a collection and distribution center for documents, providing only browsable information. With the development of the Web, running services on the Web is becoming more and more attractive. In the future, the Web will become a carrier for enterprises to provide convenient services to customers and other enterprises. The collaboration between B2B and B2C models can be regarded as a service-oriented Web.

A very important question is, what services can be provided on the Web? The Web can provide many services, some of which are already in use now, and some of which will appear in the near future. To illustrate the problem, here is a small list of services that can be provided through the Web:

Topic-oriented vertical search engine.
A knowledge base for users to find information.
Expert system where users can ask questions.
Banking services.
News and information publishing services.
Digital payment related services.
Graphics processing services.
Health and wellness services.

So, what is the correct way for enterprises and organizations to provide services through the Web? This is a very important question. Today, some services provide HTML interfaces, and they provide services in the form of documents, but what is hidden behind the service interface? Web browsers are not alone in the race to take over the Web. Mobile phones, handheld devices, and devices like microwave ovens all want to access the Web, query databases, transform data, extract information, and more. To achieve a truly serviced Web, there should be another layer below the presentation layer (HTML).

2. XML_RPC standard
XML may be the most important standard in the past 10 years, and the XML vocabulary (Vocabulary) provides the cornerstone for enterprises to construct service environments. To build a serviced Web, it is necessary to learn the XML_RPC standard, not only because XML_RPC is useful for putting services on the Web, but also because XML_RPC is an already established standard that is easy to adopt. For B2B services, the standards for providing services are extremely important. Companies that follow the standards can achieve rapid growth by utilizing the services provided by other companies. It is impossible to imagine that a truly serviced Web can be built on various private service standards. Services must have a standard that can be followed.

XML_RPC is a standard for Internet distributed processing. RPC is the abbreviation of Remote Procedure Call. It is a remote calling mechanism used to call procedures that may reside on other machines and may be written in other languages. Remote procedure calls are an important pillar of distributed computing. For example, in a distributed computing environment, we can find and exploit processes that perform addition and subtraction operations running on other machines. The process that performs the addition operation may be written in APL and runs on the RS6000 machine. The process that performs the subtraction operation Probably written in C and running on Unix. Other developers who want to use such distributed calculators can also use them, or they can choose another better calculator.

In RPC, procedure is the most important component, and the server provides the process for the client to call. Procedures can receive parameters and return results. XML_RPC uses HTTP as the protocol carrier and implements the RPC mechanism through an XML vocabulary for sending and receiving data. The XML_RPC server receives the XML_RPC request and returns the XML_RPC response, and the XML_RPC client sends the XML_RPC request and receives the XML_RPC response. Servers and clients must handle responses and requests in accordance with the requirements of the XML_RPC standard.

3. XML_RPC protocol
The complete XML_RPC specification can be found at http://www.xmlrpc.com/spec. The following is an explanation of its key points.

3.1 XML_RPC request

XML_RPC request should be an HTTP POST request, and its body is in XML format. The format of the XML part of the request is as follows:

＜?xml version="1.0" ?＞
＜methodCall＞
＜methodName＞examples.getStateName＜/methodName＞
＜params＞
＜param＞
＜value＞＜i4＞41＜/i4＞＜/value＞
＜/param＞
＜/params＞
＜/methodCall＞


The URL specifying where the data is sent is not specified here. If the server is dedicated to RPC processing, it may be "/".The payload in the above XML document is a "methodCall" structure. methodCall must contain a "methodName" sub-element, which contains a string describing the method to be called. How to interpret the content of "methodName" is entirely up to the server, for example it can be the name of an executable file, the name of a record in the database, or anything else. If the procedure accepts parameters, "methodCall" can contain a "params" element and several "param" child elements. Each "param" element contains a value with a type descriptor. The type descriptor is as shown in the following table:


Tag Description
＜i4＞ or ＜int＞ Four-byte band Signed integer, such as 12
0 (false), or 1 (true)
String, such as "Hello World"
Double-precision signed floating point number, such as - 12.214
Date/time, such as 19980717T14:08:55
base64-encoded binary data, such as eW91IGbid0IHJlQgdGhpcyE


3.1.1 Structure

The value can be a structure, and the structure is described with elements. Each contains multiple , and each contains a and a . The following is a structure composed of two elements:

＜struct＞
＜member＞
＜name＞name＜/name＞
＜value＞＜string＞member1＜/string ＞＜/value＞
＜/member＞
＜member＞
＜name＞member2＜/name＞
＜value＞＜i4＞19＜/i4＞＜/value＞
＜/member＞
＜/struct＞


can be nested, and any can contain or any other type, including .

3.1.2 Array

The value can be an array type, and the array is described with elements. Each element contains a element, and the element can contain any number of elements. The following is an example of array elements:

＜array＞
＜data＞
＜value＞＜boolean＞0＜/boolean＞＜/value＞
＜value＞＜i4＞ 9＜/i4＞＜/value＞
＜value＞＜string＞Hello＜/string＞＜/value＞
＜/data＞
＜/array＞


The element has no name. As shown in the previous example, the value of the element can be of various types. elements can be nested, and any can contain or other types, such as the introduced above.

3.2 XML_RPC response

XML_RPC response is an HTTP response, and the content type is text/xml. The format of the response body is as follows:

＜?xml version="1.0"?＞
＜methodResponse＞
＜params＞
＜param＞
＜value＞＜string＞ABCDEFG ＜/string＞＜/value＞
＜/param＞
＜/params＞
＜/methodResponse＞


may contain a structure , or may contain a structure, depending on whether the procedure call was successful. The structure is the same as in the XML request. The syntax of the element is as follows:

＜fault＞
＜value＞
＜struct＞
＜member＞
＜name＞faultCode＜/name＞
＜value＞＜int＞4＜/int＞＜/value＞
＜/member＞
＜member＞
＜name＞faultString＜/name ＞
＜value＞＜string＞Error!＜/string＞＜/value＞
＜/member＞
＜/struct＞
＜/value＞
＜/fault＞