CS603 Communication Mechanisms: SOAP

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CS603Communication MechanismsSOAP

• 25 January 2002

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SOAPSimple 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

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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

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SOAPComponents

• Client side Ability to generate http calls and
  listen for response
• Sounds like a browser!
• Server
• Listen for HTTP
• Bind to procedure
• Respond with HTTP
• First and last are Web Server!

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SOAP call

• ltsoapEnvelopegt
• ltsoapBodygt
• ltxmlnsm"http//www.stock.org/stock" /gt
• ltmGetStockPricegt
• ltmStockNamegtIBMlt/mStockNamegt
• lt/mGetStockPricegt
• lt/soapBodygt
• lt/soapEnvelopegt

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SOAP response

• ltsoapEnvelopegt
• ltsoapBodygt
• ltxmlnsm"http//www.stock.org/stock" /gt
• ltmGetStockPriceResponsegt
• ltmPricegt34.5lt/mPricegt
• lt/mGetStockPriceResponsegt
• lt/soapBodygt
• lt/soapEnvelopegt

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SOAP Template

• ltsoapEnvelope
• xmlnssoap"http//schemas.xmlsoap.org/soap/envel
  ope/"
• soapencodingStyle"http//schemas.xmlsoap.org/so
  ap/encoding/"gt
• ltsoapHeadergt
• User-created definitions, e.g. language of
  message
• lt/soapHeadergt
• ltsoapBodygt
• Call and arguments, or results for a response
• lt/soapBodygt
• ltsoapFaultgt
• Errors (response only)
• lt/soapFaultgt
• lt/soapEnvelopegt

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Key SOAP Attributes

• Header
• Actor URI of intended recipient
• encodingStyle URI of definition of types used
• mustUnderstand True if receiver MUST process
  element
• Fault
• ltfaultcodegt VersionMismatch, MustUnderstand,
  Client, Server
• ltfaultstringgt Error as a string
• ltfaultactorgt Who caused it
• ltdetailgt Additional information

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Building a clientApache 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

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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//localhost8080/apache-s
  oap/servlet/rpcrouter")
• Call call new Call()
• call.setTargetObjectURI("urnHello")
• call.setMethodName(HelloWorld")
• call.setEncodingStyleURI(Constants.NS_URI_SOAP_EN
  C)
• Vector params new Vector()
• params.addElement(new Parameter("name",
  String.class, Argument, null))
• call.setParams(params)

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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())

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SOAPServer code

• public class HelloServer
• public String HelloWorld(String name)
• System.out.println(name)
• return "Hello World!

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Activating the server

• org.apache.soap.server.ServiceManagerClienthttp/
  /localhost8080/apache-soap/servlet/rpcrouter
  deploy DeploymentDescriptor.xml
• DeploymentDescripter.xml
• ltisdservice xmlnsisd"http//xml.apache.org/xml-
  soap/deployment" id"urnHello"gt
• ltisdprovider type"java" scope"Application
  methodsHelloWorld"gt
• ltisdjava class"HelloServer" static"false"/gt
• lt/isdprovidergt
• lt/isdservicegt

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Client-generated call

• ltsoapEnvelope
• xmlnssoap"http//schemas.xmlsoap.org/soap/enve
  lope/"
• xmlnsxsi"http//www.w3.org/1999/XMLSchema-inst
  ance"
• xmlnsxsd"http//www.w3.org/1999/XMLSchema"gt
• ltsoapHeadergt
• lt/soapHeadergt
• ltsoapBodygt
• ltns1HelloWorld
• xmlnsns1"Hello"
• soapencodingStyle "http//schemas.xmlsoap.org
  /soap/encoding/"gt
• ltname xsitype"xsdstring"gtArgumentslt/namegt
• lt/ns1HelloWorldgt
• lt/soapBodygt
• lt/soapEnvelopegt

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Server-generated response

• ltsoapEnvelope
• xmlnssoap "http//schemas.xmlsoap.org/soap/env
  elope/"
• xmlnsxsi"http//www.w3.org/1999/XMLSchema-inst
  ance"
• xmlnsxsd"http//www.w3.org/1999/XMLSchema"gt
• ltsoapBodygt
• ltns1HelloWorld
• xmlnsns1"Hello"
• soapencodingStyle "http//schemas.xmlsoap.org
  /soap/encoding/"gt
• ltreturn xsitype"xsdstring"gtHello
  World!lt/returngt
• lt/ns1HelloWorldgt
• lt/soapBodygt
• lt/soapEnvelopegt

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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

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Which do I use?

• All-JAVA world? RMI
• Need security / fault tolerance? RPC
• Need to get through firewalls? SOAP
• Performance?
• Objects as arguments?