CS603Communication Mechanisms:

SOAP

25 January 2002

SOAP:Simple Object Access Protocol

• Overview– Goal: RPC protocol that works over wide area networks

• Interoperable• Language independent

– Problem: Firewalls• Solution: HTTP/XML

• History– Work started in 1998 – produced XML-RPC

• Vendor-led, big Microsoft influence– 1999: SOAP 1 – type system from XML Schemas

• More vendors– 2001: Picked up by W3C – XML Protocol working group

• Now called XP (XML Protocol)• Microsoft using it for their .NET replacement for DCOM

SOAP

• Advantages– Goes anywhere

• http is universal protocol

– Open standard• Based on XML, defined by W3C working group

• Disadvantages– Type semantics must be defined

• Extra work for users

– Pure text protocol• High cost to translate at endpoints• Eats bandwidth

SOAPComponents

• Client side: Ability to generate http calls and listen for responseSounds like a browser!

• Server:– Listen for HTTP– Bind to procedure– Respond with HTTP

First and last are Web Server!

SOAP call

<soap:Envelope>

<soap:Body>

<xmlns:m="http://www.stock.org/stock" />

<m:GetStockPrice>

<m:StockName>IBM</m:StockName>

</m:GetStockPrice>

</soap:Body>

</soap:Envelope>

SOAP response

<soap:Envelope>

<soap:Body>

<xmlns:m="http://www.stock.org/stock" />

<m:GetStockPriceResponse>

<m:Price>34.5</m:Price>

</m:GetStockPriceResponse>

</soap:Body>

</soap:Envelope>

SOAP Template<soap:Envelope

xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"soap:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"><soap:Header>

User-created definitions, e.g. language of message</soap:Header><soap:Body>

Call and arguments, or results for a response</soap:Body><soap:Fault>

Errors (response only)</soap:Fault>

</soap:Envelope>

Key SOAP Attributes

• Header– Actor: URI of intended recipient– encodingStyle: URI of definition of types used– mustUnderstand: True if receiver MUST process

element

• Fault– <faultcode>: VersionMismatch, MustUnderstand,

Client, Server– <faultstring>: Error as a string– <faultactor>: Who caused it– <detail>: Additional information

Building a client:Apache SOAP

• Open source web server driven by IBM

• SOAP available as integral part

• Java packages to interface between java programs and SOAP

• Also supports javascript SOAP clients/servers

SOAPSample Client

import java.net.URL; import java.util.Vector; import org.apache.soap.SOAPException; import org.apache.soap.Constants;import org.apache.soap.Fault; import org.apache.soap.rpc.Call; import org.apache.soap.rpc.Parameter; import org.apache.soap.rpc.Response;public class Client {public static void main(String[] args) throws Exception {

URL url = new URL("http://localhost:8080/apache-soap/servlet/rpcrouter"); Call call = new Call();call.setTargetObjectURI("urn:Hello");call.setMethodName(“HelloWorld");call.setEncodingStyleURI(Constants.NS_URI_SOAP_ENC); Vector params = new Vector();params.addElement(new Parameter("name", String.class, “Argument”, null)); call.setParams(params);

SOAPSample Client

Response resp = null; try { resp = call.invoke(url, ""); }catch( SOAPException e ) {

System.err.println("Caught SOAPException (" + e.getFaultCode() + "): " +e.getMessage());

System.exit(-1);} // Check the response.if( !resp.generatedFault() ) {

Parameter ret = resp.getReturnValue();Object value = ret.getValue(); System.out.println(value);

} else {Fault fault = resp.getFault(); System.err.println("Generated fault: ");System.out.println (" Fault Code = " + fault.getFaultCode()); System.out.println (" Fault String = " + fault.getFaultString());

}}

SOAPServer code

public class HelloServer{ public String HelloWorld(String name) {

System.out.println(name);return "Hello World!”;

} }

Activating the server

• org.apache.soap.server.ServiceManagerClienthttp://localhost:8080/apache-soap/servlet/rpcrouter deploy DeploymentDescriptor.xml

• DeploymentDescripter.xml:<isd:service

xmlns:isd="http://xml.apache.org/xml-soap/deployment" id="urn:Hello"><isd:provider type="java" scope="Application“ methods=“HelloWorld">

<isd:java class="HelloServer" static="false"/></isd:provider>

</isd:service>

Client-generated call<soap:Envelope

xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance"xmlns:xsd="http://www.w3.org/1999/XMLSchema">

<soap:Header></soap:Header><soap:Body>

<ns1:HelloWorldxmlns:ns1="Hello"soap:encodingStyle=

"http://schemas.xmlsoap.org/soap/encoding/"><name xsi:type="xsd:string">Arguments</name>

</ns1:HelloWorld></soap:Body>

</soap:Envelope>

Server-generated response<soap:Envelope

xmlns:soap= "http://schemas.xmlsoap.org/soap/envelope/"xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance"xmlns:xsd="http://www.w3.org/1999/XMLSchema">

<soap:Body><ns1:HelloWorld

xmlns:ns1="Hello"soap:encodingStyle=

"http://schemas.xmlsoap.org/soap/encoding/"><return xsi:type="xsd:string">Hello World!</return>

</ns1:HelloWorld></soap:Body>

</soap:Envelope>

DCE vs. Java RMI vs. SOAP

• Philosophy– DCE RPC: generic interface

• Define “clean sheet” system• Port to variety of protocols/systems/languages

– Java RMI: “proprietary” interface• Coupled to single language/run time system• Port entire system to multiple platforms

– SOAP: single standard interface• Define interface on single protocol• Pick protocol that is universal

Which do I use?

• All-JAVA world? RMI

• Need security / fault tolerance? RPC

• Need to get through firewalls? SOAP

• Performance?

• Objects as arguments?