1. XML-RPC a lightweight data communication protocol
Jing Deng
Computer Science Department
University of Colorado at Boulder
26 September 2001
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2. Overview Introduction XML-RPC protocol
How it works
Data format
How to use XML-RPC (Java example)
References
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3. Introduction What is XML-RPC What can it do
Remote process calling protocol with XML format
What can it do
allow software running on disparate operating systems, running in different environments to make procedure calls over the Internet.
History
Created by UserLand Software in April 1998, for its Frontier software communication
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4. Fundamentals XML RPC HTTP
A very powerful meta-language for description data. XML-RPC just uses a little bit of XML
RPC
A mechanism which allows a program running on one computer to execute a function that is actually running on another computer
HTTP
Most data on Internet are transferred under HTTP protocol
Not very efficient, but easy to use
Make XML-RPC more convenient to be used in web applications
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5. Definition
XML-RPC is a remote procedure calling protocol that works over the Internet.
XML-RPC is composed by an HTTP-POST request and a HTTP reply.
The body of the request and the value returned from server is formatted by XML.
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6. XML-RPC Overview XML-RPC call is conducted between two parties:
A client to send RPC request
A server to process RPC request and send back the return value to the client
Server’s address is in a standard URL
The data is composed by a HTTP header and a XML body
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7. XML-RPC Overview (Cont.)
A XML-RPC request and a XML-RPC response
Both of them are composed by a HTTP header and a XML body
Request should indicate a method name and its parameters
Response should contain a function return value and indicates if it is a successful return or a error message
There is a data type set for parameters and return value
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8. How does XML-RPC work client Web server HTTP POST (XML)
call
HTTP REPLY (XML)
return
XML
XML
Client program
procedure
call
return
XML-RPC listener
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9. Request Example <value><i4>41</i4></value>
POST /RPC2 HTTP/1.0
User-Agent: Frontier/5.1.2
Host: xml.colorado.edu
Content-Type: text/xml
Content-length: 181
<?xml version=“1.0”?>
<methodCall>
<methodName>examples.getStateName</methodName>
<params> <param>
<value><i4>41</i4></value>
</param></params>
</methodCall>
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10. Request Format A single <methodCall> structure, which contains
A single <methodName>. It contains the calling method’s name
A single <params>, which can contain any number of
<param>s. Each <param> has a
<value>
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11. Data Type – Scalar <value>s
<i4> or <int> four-byte signed integer -12
<boolean> (false) or 1 (true)
<string> ASCII string Hi!
<double> double-precision
<dateTime.iso8601> date/time T14:08:55
<base64> base64-encoded binary eW91IGNhbid
(default type is string)
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12. Data Type (Cont.) - <struct>
<struct> contains <member>s, each <member> contains a <name> and a <value>
<struct>
<member>
<name>lowerBound</name> <value><i4>18</i4></value>
</member>
<name>upperBound</name> <value><i4>122</i4></value>
</struct>
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13. Data Type (Cont.) - <array>
An <array> contains a single <data> element, which can contain any number of <value>s
<array>
<data>
<value><i4>12</i4></value>
<value><string>Egypt</<string></value>
<value><boolean>0</boolean></value>
<value><i4>-31</i4></value>
</data>
</array>
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14. Response Example HTTP/1.1 200 OK Connection: close Content-Length: 158
Content-Type: text/xml
Date: Wed, 26 Sep :10:28 GMT
Server: UserLand Frontier/5.1.2-WinNT
<?xml version=“1.0”?>
<methodResponse>
<params> <param>
<value><string>South Dakota</string></value>
</param></params>
</methodResponse>
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15. Response Format One <methodResponse>, it may contains either
A single <params> -- a successful procedure return
It contains a single <param> which contains a single <value>
A <fault> -- a failure procedure return
It contains a <value> which is a <struct> that contains two members: <faultCode> and <int>, <faultString> and <string>
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16. Example - XML-RPC in Java
Many XML-RPC applications encapsulate the details of XML-RPC protocol
They provides an interface for users to send remote procedure call, and retrieve return value
A XML-RPC Java library: helma.xmlrpc
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17. Helma.xmlprc A free XML-RPC library http://xmlrpc.helma.org/
Contains source code, documentations, and examples
Has a jar file as a library: xmlrpc.jar, which contains a OpenXML parser as well
Easy to install
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18. XML-RPC Client Send XML-RPC to server, and get the return value
Interface (encapsulate most protocol details: HTTP, XML)
XmlRpcClient class
XmlRpcClient(String URL);
public Object execute(String procedure_name,
Vector params);
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19. XML-RPC Server
Process XML-RPC request, call the procedure that request wants to call, and send back the return value
Two kinds of server
A mini web server, only process XML-RPC
WebServer class
(See its interface later…)
XML-RPC listener which cooperates with a web server
XmlRpcServer class
Input is a XML stream, and output is a XML stream also
execute() method to process RPC
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20. XML-RPC Handler Contains the procedures client wants to call
We need to register handler to server
Automatic registration
Explicit registration
Implement XmlRpcHanlder interface
Use Xml.RpcHandler.execute() to process input parameter
Interface
WebServer.addHandler(String handler_name, Object handler);
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21. Example - Handler public class AreaHandler {
public Double rectArea(double length, double width) {
return new Double(length * width); }
public Double circleArea(double radious) {
double value = (radious * radious * Math.PI);
return new Double (value);
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22. Example - Server import java.io.IOException;
import helma.xmlrpc.WebServer;
import helma.xmlrpc.XmlRpc;
public class AreaServer {
public static void main(String[] args) {
try {
WebServer server = new WebServer(Integer.parseInt(args[0]));
server.addHandler("area", new AreaHandler());
} catch (IOException e) {
System.out.println("Could not start server: " + e.getMessage()); } }}
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23. Example - Client import java.io.IOException; import java.util.Vector;
import helma.xmlrpc.XmlRpc;
import helma.xmlrpc.XmlRpcClient;
import helma.xmlrpc.XmlRpcException;
public class AreaClient {
public static void main(String args[]) {
try {
XmlRpcClient client =
new XmlRpcClient("
// continue….
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24. Example – Client (Cont.)
// continue from last slide…..
Vector params = new Vector();
params.addElement(new Double(args[0]));
Object result = client.execute("area.circleArea", params);
System.out.println(result.toString());
} catch (IOException e) {
System.out.println("IO Exception: " + e.getMessage());
} catch (XmlRpcException e) {
System.out.println("Exception within XML-RPC: " + e.getMessage()); }
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25. Discussions Characters of XML-RPC
Platform independent because it is a protocol
Very simple, very easy to implement, very ease to use
Too simple for some applications
Implemented with many languages: Java, C/C++, Perl, Python, etc…
Other important issues I didn’t mention…
Security
Apply XML-RPC in web applications
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26. Discussions (Cont.) Comparisons Beyond XML-RPC
Differences between XML-RPC and web page
Differences between XML-RPC and RMI, Corba
Differences between XML-RPC and SOAP
Beyond XML-RPC
SOAP, UDDI, WSDL, BXXP
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27. References XML-RPC documents http://www.xmlrpc.com
XML-RPC in Java
XML-RPC in C and C++
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28. References (Cont.) Book
Simon St.Laurent, Joe Johnston, Edd Dumbill, programming web services with XML-RPC, O’Reilly, 2001
Others
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29. Thanks!
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