SOAP Simple Object Access Protocol An Introduction

1
SOAPSimple Object Access ProtocolAn Introduction

• by Juan J Vargas
• University of Central Florida
• CDA 5937 Fall 2002

2
Agenda

• What is SOAP?
• SOAP History
• The SOAP Structure
• The SOAP Message Exchange Model
• Examples of HTTP / XML / SOAP
• SOAP Security
• Conclusions and References

3
What is SOAP?

• SOAP Simple Object Access Protocol is a
  lightweight communication protocol for exchange
  of information in a decentralized, distributed
  environment.
• SOAP combines HTTP (medium of communication) with
  XML (language of communication)
• SOAP XML parser server/client code HTTP
  server
• SOAP invokes methods on servers, services,
  components, and objects via Internet.

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What is SOAP? (cont.)

• SOAP has no explicit programming model, unlike
  DCOM and CORBA no special components or tools
  needed to make an implementation.
• Can be implemented in any language (Java, Perl,
  C, VB, Windows and UNIX)
• SOAP promotes distributed computing thru
  communication

5
SOAP goals

• Developed to be a platform and language
  independent
• Simplicity and extensibility
• SOAP meets these goals by omitting features often
  found in messaging systems and distributed object
  systems
• garbage collection, batching of messages,
  objects-by-reference

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SOAP goals (cont)

• Simple standardized mechanism for moving
  structured information
• Format for sending messages
• Enables different programs, written in different
  languages and running on different platforms, to
  communicate with each other

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SOAP History

• SOAP 0 Developed by UserLand, Microsoft, and
  DevelopMentor in 1998
• SOAP 1.0 in 2000
• W3C (World Wide Web Consortium)
• v1.1 final May 2000
• W3C v1.2 draft July 2001
• Specification can be found at
• http//www.w3.org/TR/soap12/

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The SOAP Message Exchange Model (Client/Server)

• SOAP defines two types of messages
• Requests
• Responses
• Clients send a request to a server to invoke a
  service, and the server sends back the results

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The SOAP 1.1 Structure

• A SOAP message contains 3 parts
• Envelope defines the content of the message
• Must be associated with a namespace, e.g.
  http//www.w3.org/2001/06/soap-envelope
• Header (optional) contains header information
• Body contains call and response information

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SOAP Header

• Is an optional component
• The Header has information about how the message
  is to be processed
• Can contain extensions to the message like
  transaction ids
• Can also contain security information

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Sample ltsoapHeadergt

• ltsoapEnvelopegt
• ltsoapHeadergt
• lttTransaction xmlnstsome-URI
• soap mustUnderstand1gt
• 12345  lt/tTransactiongtlt/soapHeadergt
• ltsoapBodygt lt/soapBodygt
• lt/soapEnvelopegt

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SOAP Body

• Contains the message referred to as payload
• Must be a child of the Envelope element
• Can contain the encodingStyle
• Can also contain a ltFaultgt element

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Sample ltsoapBodygt

• ltsoapEnvelopegt
• ltsoapHeadergt lt/soapHeadergt
• ltsoapBodygt
• ltwarticle xmlnswwww.w3.org gt
• ltwnamegt SOAP v1.1 lt/wnamegt
• ltwurlgt http//www.w3.org/TR/SOAP lt/wurlgt
• lt/warticlegt
• lt/soapBodygt
• lt/soapEnvelopegt

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Sample ltsoapFaultgt

• ltsoapEnvelopegt ltsoapBodygt
•   ltsoapFaultgt  ltfaultcodegtsoapServerlt/faultcode
  gt  ltfaultstringgtServer Errorlt/faultstringgt 
  ltdetailgt     ltemyfaultdetails
  xmlnse"Hello"gt      ltmessagegt Ooops
  lt/messagegt      lterrorcodegt 1001
  lt/errorcodegt     lt/emyfaultdetailsgt 
  lt/detailgtlt/soapFaultgt  
• lt/soapBodygt lt/soapEnvelopegt

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SOAP request
POST /Temperature HTTP/1.1 Host
www.weather.com Content-Type text/xml Content-Len
gth ltwhatevergt SOAPMethodName
ltsome-URIgtCurrentTemp ltSOAPEnvelope
xmlnsSOAP"urnschemas-xmlsoap-orgsoap.v1"gt ltSO
APBodygt ltmCurrentTemp xmlnsm"some-URI"gt lt
zip_codegt37919lt/zip_codegt ltmCurrentTempgt lt/SOA
PBODYgt ltSOAPEnvelopegt URI- Uniform Resource
Identifier some-URI -gt www.netsolve.com or
www.globus.com
Http Header
Soap Extensions
Xml Payload
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SOAP response
HTTP/1.1 200 OK Content-Type text/xml Content-Len
gth ltwhatevergt ltSOAPEnvelope
xmlnsSOAP"urnschemas-xmlsoap-orgsoap.v1"gt ltSO
APHeadergt lttTransaction xmlnst"some-URI"gt
5 lt/tTransactiongt lt/SOAPHeadergt ltSOAPBodygt
ltmCurrentTempResponse xmlnsm"some-URI"gt lt
returngt42lt/returngt lt/mCurrentTempResponsegt lt/S
OAPBodygt lt/SOAPEnvelopegt
Http Header
Xml Payload
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The SOAP 1.2 Structure

• A SOAP message contains 4 parts
• Envelope defines a framework describing what is
  in the message
• Set of encoding rules expresses instances of
  application-defined data types
• Convention for representing remote procedure
  calls (RPCs) and responses
• A transport binding convention for exchanging
  messages

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HTTP Example

• The following is a legal HTTP request message
• HTTP headers are just plain text.

POST /foobar HTTP/1.1 Host 209.110.197.12 Content
-Type text/plain Content-Length 12 Hello, World
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HTTP Example

• First line of an HTTP request contains three
  components
• The HTTP method POST
• The Internet Engineering Task Force (IETF) has
  standardized a fixed number of HTTP methods
• GET is the HTTP method used to surf the Web.
• POST is the most commonly used HTTP method for
  building applications.
• The Request-URI /foobar
• URI (Uniform Resource Identifier) to identify
  target of request
• The protocol version HTTP/1.1
• The protocol version in this example is
  HTTP/1.1, which indicates that the rules of RFC
  2616 are to be observed.

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HTTP Example

• The third and fourth lines of the request specify
  the type and size of the request payload
• Content-Type text/plain
• syntax of the payload information as a MIME type
• Most DCE (Distributed Computing Environment)
  applications use NDR (Network Data
  Representation).
• Most Web applications use text/html or other
  text-based syntaxes. SOAP uses text/xml
• Content-Length 12
• number of bytes of payload information

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HTTP Example

• The blank line between the Content-Length header
  and the request payload is a delimiter.
• Individual HTTP headers are delimited by a
  carriage-return / line-feed sequence.
• The headers are delimited from the payload using
  an extra carriage-return / line-feed sequence.

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HTTP Example

• The following is an HTTP response message

• If server unable to decode the request

400 Bad Request Content-Length 0
200 OK Content-Type text/plain Content-Length
12 dlroW ,olleH
307 Temporarily Moved Location
http//209.110.197.44/foobar Content-Length 0
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XML NameSpaces

• To support extensibility, every element and
  attribute in XML has a namespace URI associated
  with it.
• This URI is specified using the xmlns attribute.

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XML NameSpaces Example

• ltreverse_string
• xmlns"urnschemas-develop-comStringProcs"gt
• ltstring1gtHello, Worldlt/string1gt
• ltcomment xmlns'http//foo.com/documentation'gt
  
• This is a comment!!
• lt/commentgt
• lt/reverse_stringgt

URIs
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XML NameSpaces Example

• XML allows namespace URIs to be mapped to locally
  unique prefixes as a convenience.

ltspreverse_string xmlnssp"urnschemas-dev
elop-comStringProcs" xmlnsdoc'http//foo.
com/documentation'gt ltspstring1gtHello,
Worldlt/spstring1gt ltdoccommentgt This is
a comment!! lt/doccommentgt lt/spreverse_stringgt
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Sample SOAP Namespaces

• SOAP envelope
• http//www.w3.org/2001/06/soap-envelope
• SOAP serialization
• http//www.w3.org/2001/06/soap-encoding
• SOAP mustUnderstand fault http//www.w3.org/2001/
  06/soap-faults
• SOAP upgrade
• http//www.w3.org/2001/06/soap-upgrade

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Example SOAP Method Request

• POST /string_server/Object17 HTTP/1.1
• Host 209.110.197.2
• Content-Type text/xml
• Content-Length 152
• SOAPMethodName urnstrings-comIStringreverse
• ltEnvelopegt
• ltBodygt
• ltmreverse xmlnsm'urnstrings-comIString'gt
• lttheStringgtHello, Worldlt/theStringgt
• lt/mreversegt
• lt/Bodygt
• lt/Envelopegt

URI delim method name
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Example SOAP Response

• 200 OK
• Content-Type text/xml
• Content-Length 162
• ltEnvelopegt
• ltBodygt
• ltmreverseResponse xmlnsm'urnstrings-comIStr
  ing'gt
• ltresultgtdlroW ,olleHlt/resultgt
• lt/mreverseResponsegt
• lt/Bodygt
• lt/Envelopegt

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SOAP Request Structure
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Another SOAP Example
Lets build a service that calculates the tax due
on a sales transaction. In traditional VB (Visual
Basic) terms we will create a function with the
following definition
Public Function GetSalesTax(ByVal pSalesTotal As
Double) As Double    GetSalesTax pSalesTotal
0.04End Function
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SOAP Example (cont)
If the amount is 100 and GetSalesTax is within
the objTax object the VB call looks like
Dim objTax As New CTaxCalcdblSalesTax
objTax.GetSalesTax(100)
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SOAP Example (cont)CLIENT side
The request is formatted as an XML document,
which is passed up to the server.
ltSOAPEnvelope xmlnsSOAP"urnschemas-xmlsoap-org
soap.v1"gt    ltSOAPHeadergtlt/SOAPHeadergt   
ltSOAPBodygt        ltGetSalesTaxgt           
ltSalesTotalgt100lt/SalesTotalgt       
ltGetSalesTaxgt    lt/SOAPBodygtlt/SOAPEnvelopegt
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How to send the XML document to the server?

• The request is a simple HTTP post.
• The internet browser masks all the complexity of
  sending a form to a server.
• But if we are going to do the job ourselves,
  Microsoft's XML HTTP Request object can be used
  to give us a helping hand.
• The LHTTPRequest is an object within the MSXML
  class library (MSXML.DLL), and it comes with IE5.

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SOAP Client (cont)
Assuming that strEnvelope contains the XML
document described above, the request is
formatted thus
Dim objHTTP As New MSXML.XMLHTTPRequestDim
strEnvelope As String 'Set up to post to our
localhost serverobjHTTP.open "post",
"http//localhost/soap/soap.asp"'Set a standard
SOAP/ XML header for the content-typeobjHTTP.setR
equestHeader "Content-Type", "text/xml"'Set a
header for the method to be calledobjHTTP.setRequ
estHeader "SOAPMethodName", _"urnmyserver/soapT
axCalcGetSalesTax"'Make the SOAP
callobjHTTP.send strEnvelope'Get the return
valuestrReturn objHTTP.responseBody
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SOAP Server Side
The first job is to create the soap.asp page, to
listen for, and process SOAP calls to our
server. For the basic listener service, we need
to parse the body of the request (the SOAP
envelope) and pull out the value of the
SalesTotal parameter. Because the request is XML,
we can load it into an instance of Microsoft's
XMLDOM.
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SOAP Server Side (cont)
Soap.asp begins like this
Set objReq Server.CreateObject("Microsoft.XMLDOM
")objReq.Load Request
objReq contains the SOAP envelope from the
client.
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SOAP Server Side (cont)
The value of SalesTotal can be extracted by
running an XSL pattern query, using the
SelectSingleNode method of the XML DOM object,
and tax is calculated
strQuery "SOAPEnvelope/SOAPBody/mGetSalesTax/
SalesTotalvarSalesTotal objReq.SelectSingleNod
e(strQuery).Text varSalesTax varSalesTotal
0.04
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SOAP Server Side (cont)
The response is ready to be passed back to the
client. The SOAP response envelope conforms to a
format-type almost identical to the request.
ltSOAPEnvelope xmlnsSOAP"urnschemas-xmlsoap-org
soap.v1"gt ltSOAPHeadergtlt/SOAPHeadergt
ltSOAPBodygt ltmGetSalesTaxResponse
xmlnsm"urnmyserver/soapTaxCalc"gt
ltSalesTaxgt4lt/SalesTaxgt lt/mGetSalesTaxResp
onsegt lt/SOAPBodygt lt/SOAPEnvelopegt
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SOAP Client Side (cont)
The response document can be built either by
string-concatenation, or by creating a new
instance of a DOM (Document Object Model), and
appending the appropriate nodes. Back on the
client, the response is received, and can be
decoded by extracting the appropriate node from
the Envelope document
Dim objReturn As New MSXML.DomDocumentobjReturn.L
oadXML strReturn strQuery _"SOAPEnvelope/SOAP
Body/mGetSalesTaxResponse/SalesTax"dblTax
objReturn.SelectSingleNode(strQuery).Text
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Problems with example

• OK, I got it workingby Ned Robinson(nrobinson_at_bas
  eline.com)Tuesday, August 28, 2001
• Here is the trick. You must have Application
  Protection on your web server set to Low so that
  the service and the application can run in the
  same address space. Go to IIS Manager, right
  click on your Web Site and go to Properties. Go
  to the Home Directory tab and make the change to
  Application Protection at the bottom.

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SOAP Security

• SOAP specification does not define any
  protocol-specific security features. Potential
  security threat due to plain text nature of data.
  
• Security features may be added to the SOAP header
  (e.g. digital signatures).
• Transport protocols such as SSL (using HTTPS),
  TLS, and IP SECurity (IPSec) can provide the
  integrity and confidentiality of the message
  during transmission.

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Conclusions

• SOAP new and simple protocol. SOAP well suited
  for internet. Excellent foundation upon which
  other protocols may be built
• Primary goal of SOAP is interoperability
• SOAP XML (data representation) HTTP
  (transport) RPC (call/response mechanism)
• Today SOAP does not address some critical
  distributed services (e.g. security). But SOAP
  is evolving rapidly.

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References

• http//www.vbip.com/xml/soap_syd.asp
• http//msdn.microsoft.com/msdnmag/issues/0300/soap
  /default.aspx
• http//www.w3.org/TR/SOAP/
• http//www.xml.org/xml/resources_focus_soap.shtml
• http//www.javaworld.com/javaworld/jw-03-2001/jw-0
  330-soap.html
• http//msdn.microsoft.com/library/default.asp?url
  /library/en-us/dnexxml/html/xml10152001.asp
• http//msdn.microsoft.com/library/default.asp?url
  /library/en-us/dnwebsrv/html/Xmloverchap2.asp
• http//www.microsoft.com/mind/0100/soap/soap.asp