CS 580 Client-Server Programming Fall Semester, 2002 XML-RPC
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Doc 2, XML-RPC Slide # 2

RPC

• Cross platform

Primitive data types may be different on client & server

• Marshalling/unmarshalling of parameters and results

Procedure parameters must be sent from client to server

How can one handle pointers as parameters?

Result of procedure call must be sent back to client

• Different contexts of client and server

• Registering and finding servers

Doc 2, XML-RPC Slide # 3

XML-RPC

• HTTP as transport layer and
• XML to encode request/response
• Language and platform independent

• Java, Perl, Python, Tcl, C, C++, Smalltalk
• ASP, PHP, AppleScript, COM
• Zope, WebCrossing

Doc 2, XML-RPC Slide # 4

| client sum |
client :=XmlRpcClient url: 'http://xmlrpc.usefulinc.com/demo/server.php'.
sum := client 
         perform: 'examples.addtwo' 
         with: 5
         with: 3.
^sum

Doc 2, XML-RPC Slide # 5

import java.util.*;
import org.apache.xmlrpc.*;
public class XmlRpcExample 
    {
   public static void main (String args[]) 
        {
        try
            {
            XmlRpcClient xmlrpc =  new XmlRpcClientLite 
                  ("http://xmlrpc.usefulinc.com/demo/server.php");
         Vector parameters = new Vector ();
            parameters.addElement (new Integer(5) );
            parameters.addElement (new Integer(3) );
            Integer sum = 
               (Integer) xmlrpc.execute ("examples.addtwo", parameters);
            System.out.println( sum.intValue() );
            }
        catch (java.net.MalformedURLException badAddress)
            {
            badAddress.printStackTrace( System.out);
            }
        catch (java.io.IOException connectionProblem)
            {
            connectionProblem.printStackTrace( System.out);
            }
        catch (Exception serverProblem)
            {
            serverProblem.printStackTrace( System.out);
            }
        }
    }
Doc 2, XML-RPC Slide # 6

Converts the requests in to a format that can be sent on the network

• Sends the marshaled version to the server
• Waits for server response

• Unmarshals the request,
• Runs the requested method
• Marshals the result
• Send the marshaled result back to the client

Doc 2, XML-RPC Slide # 7

POST /demo/server.php HTTP/1.1
Host: xmlrpc.usefulinc.com
Content-length: 190
Content-type: text/xml;charset=iso-8859-1
User-Agent: Smalltalk XMLRPC version 0.5 (VisualWorksÆ NonCommercial, Release 7 of June 14, 2002)
Connection: keep-alive
<?xml version="1.0"?>
<methodCall>
   <methodName>examples.addtwo</methodName>
   <params>
      <param>
         <value><int>5</int></value>
      </param>
      <param>
         <value><int>3</int></value>
      </param>
   </params>
</methodCall>

Doc 2, XML-RPC Slide # 8

Issues

• Server machine name or IP ( xmlrpc.usefulinc.com)
• Path to server program (/demo/server.php)
• Name of remote method (examples.addtwo)
• Number, Type and Order of arguments

Doc 2, XML-RPC Slide # 9

Java Client

• Uses java.net.URLConnection
• Supports proxies, redirects, cookies

• Contains its own http client implementation
• Does not support proxies, redirects, cookies
• Faster than XmlRpcClient
• Supports same methods as XmlRpcClient

Doc 2, XML-RPC Slide # 10

Returns a client which interacts with the indicated server

Executes the method with the parameters on the server

Server must be written to support the method

Returns the result

IOException if can not connect to server from some reason

XmlRpcException if server has problem executing method

Doc 2, XML-RPC Slide # 11

Smalltalk Client

Returns a client which interacts with the indicated server

XmlRpcClient>>perform: aMethodName
XmlRpcClient>>perform: aMethodName with: oneArgument
XmlRpcClient>>
   perform: aMethodName 
   with: firstArgument
   with: secondArgument
XmlRpcClient>>
   perform: aMethodName withArguments: collectionOfArguments

Executes the method with the parameters on the server

Server must be written to support the method

Returns the result

XmlRpcParseError

Error

Doc 2, XML-RPC Slide # 12

XmlRpc Servers

Java Example

import org.apache.xmlrpc.*;
public class JavaServer 
    {
   public Integer addtwo(int x, int y) 
        {
        return new Integer( x + y);
        }
    
    public static void main( String[] args) 
        {
        try
            {
            System.out.println("Starting server on port 8080");
            WebServer addTwoServer = new WebServer(8080);
            addTwoServer.addHandler("examples", new JavaServer());
            System.out.println("server running");
          }
        catch (Exception webServerStartError)
            {
            System.err.println( "JavaServer " + webServerStartError.toString());
            }
        }
    }
Doc 2, XML-RPC Slide # 13

Smalltalk Server Example

Smalltalk defineClass: #WaveXmlRpcAddtwo
   superclass: #{Smalltalk.WaveXmlRpcServer}
   indexedType: #none
   private: false
   instanceVariableNames: ''
   classInstanceVariableNames: ''
   imports: ''
   category: 'Network-XMLRPC-Server'
   
WaveXmlRpcAddtwo class methodsFor: 'utility'

allowedServerMethods
   "Answer a dictionary
   Key is the string the client will use to request the method
   Value is the symbol for the method to actually call"
   
   ^(Dictionary new)
      at: 'examples.addtwo' put: #add:to:;
      yourself
      
      
WaveXmlRpcAddtwo methodsFor: 'accessing'

add: anInteger to: aSecondInteger
   ^anInteger + aSecondInteger

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