Home arrow ASP arrow Page 2 - An Introduction To XML SOAP Using ASP and VB6
ASP

An Introduction To XML SOAP Using ASP and VB6


Using ASP and VB6 but still haven't come to grips with SOAP? In this article the ComponentSource team show us how to create a request/respose system in next to no time using simple VBScript and MSXML.

Author Info:
By: ComponentSource Team
Rating: 5 stars5 stars5 stars5 stars5 stars / 85
August 12, 2002
TABLE OF CONTENTS:
  1. · An Introduction To XML SOAP Using ASP and VB6
  2. · Step By Step
  3. · The Server
  4. · VB Client Code
  5. · Conclusion

print this article
SEARCH DEVARTICLES

An Introduction To XML SOAP Using ASP and VB6 - Step By Step
(Page 2 of 5 )

As we know, SOAP is a call-response mechanism, which operates in a client-server paradigm. The client (your application) makes a call to the server (a web server, somewhere on the internet), passing in parameters; and the server provides a response. Both call and response are transported in the form of XML documents. Therefore, to build our own example SOAP system, we need both a client and a server a caller and a responder.

The example we will follow is a very simple one: we will build a service that will calculate the tax due on a sales transaction. In traditional VB terms well will create a function with the following definition:

Public Function GetSalesTax(ByVal pSalesTotal As Double) as Double
GetSalesTax = pSalesTotal * 0.04
End Function


Crude, but effective (if you live in a state where the sales tax rate is 4%!)

This function defines a method name (GetSalesTax), a parameter (pSalesTotal representing the total value of the sale) and a return value (the result of the function). In more traditional object-oriented terms, we might think of pSalesTotal as an "IN" parameter, and the GetSalesTax result as an "OUT" parameter. Quite straightforwardly: sales-total in; sales-tax out. A SOAP service can be thought of in terms of "IN" and "OUT" parameters the client passes "IN" parameters to the server, and then receives the "OUT" parameters in return. So, in order to create our SOAP service, we need a server that will listen for requests to GetSalesTax, accompanied by "IN" parameters, and which will respond with "OUT" parameters, indicating the correct tax amount. Let's start with the client the caller. How do we call the SOAP service to make our request.

The Client
In traditional VB terms, our request to the GetSalesTax function described above, would be something such as:

dblSalesTax = GetSalesTax(100)

Returning a value of $4.

If the GetSalesTax function was contained within an external object, such as an MTS server, then the call would need to reference the server DLL:

Dim objTax As New CTaxCalc

dblSalesTax = objTax.GetSalesTax(100


In a SOAP system the call is little different, only the request is formatted as an XML document, which is passed up to the server. The appropriate document contains the same details as the MTS call a method to call, and the parameter name and value.

<GetSalesTax>
<SalesTotal>100</SalesTotal>
<GetSalesTax>


In order to ensure that the server can correctly identify and decrypt this method call, it is wrapped up in a larger document, called a SOAP envelope, which references the universal name-space of the SOAP envelope standard.

<SOAP:Envelope xmlns:SOAP="urn:schemas-xmlsoap-org:soap.v1">
<SOAP:Header></SOAP:Header>
<SOAP:Body>
<GetSalesTax>
<SalesTotal>100</SalesTotal>
<GetSalesTax>
</SOAP:Body>
</SOAP:Envelope>


Finally, to complete our SOAP request document, we will add a name-space reference to our method call, which points to the object which contains the method the equivalent of the object declaration (Dim objTax As New CTaxCalc) in our MTS method call.

<SOAP:Envelope xmlns:SOAP="urn:schemas-xmlsoap-org:soap.v1">
<SOAP:Header></SOAP:Header>
<SOAP:Body>
<m:GetSalesTax xmlns:m="urn:myserver/soap:TaxCalc">
<SalesTotal>100</SalesTotal>
</m:GetSalesTax>
</SOAP:Body>
</SOAP:Envelope>


Now that we have built our SOAP request document, we are ready to send it to the server. The request is a simple HTTP post - just like posting a web form in your internet browser. Of course, your internet browser masks all the complexity of sending a form to a server; and in the longer-term .NET will mask this process from your VB code too. But for now, we need to do the job ourselves; and I have been using Microsoft's XML HTTP Request object to give me a helping hand. (The XMLHTTPRequest is an object within the MSXML class library (MSXML.DLL), and it comes with IE5.) Assuming that strEnvelope contains the XML document described above, the request is formatted thus:

Dim objHTTP As New MSXML.XMLHTTPRequest
Dim strEnvelope As String

'Set up to post to our localhost server
objHTTP.open "post", "http://localhost/soap/soap.asp"

'Set a standard SOAP/ XML header for the content-type
objHTTP.setRequestHeader "Content-Type", "text/xml"

'Set a header for the method to be called
objHTTP.setRequestHeader "SOAPMethodName", _
"urn:myserver/soap:TaxCalc#GetSalesTax"

'Make the SOAP call
objHTTP.send strEnvelope

'Get the return value
strReturn = objHTTP.responseBody


Now that we have sent our request, we move to the server, to see how we set up a SOAP service to listen and respond to our calls.
blog comments powered by Disqus
ASP ARTICLES

- Central Scoreboard with Flash and ASP
- Calorie Counter Using WAP and ASP
- Creating PGP-Encrypted E-Mails Using ASP
- Be My Guest in ASP
- Session Replacement in ASP
- Securing ASP Data Access Credentials Using t...
- The Not So Ordinary Address Book
- Adding and Displaying Data Easily via ASP an...
- Sending Email From a Form in ASP
- Adding Member Services in ASP
- Removing Unconfirmed Members
- Trapping HTTP 500.100 - Internal Server Error
- So Many Rows, So Little Time! - Case Study
- XDO: An XML Engine Class for Classic ASP
- Credit Card Fraud Prevention Using ASP and C...

Watch our Tech Videos 
Dev Articles Forums 
 RSS  Articles
 RSS  Forums
 RSS  All Feeds
Write For Us 
Weekly Newsletter
 
Developer Updates  
Free Website Content 
Contact Us 
Site Map 
Privacy Policy 
Support 

Developer Shed Affiliates

 




© 2003-2017 by Developer Shed. All rights reserved. DS Cluster - Follow our Sitemap
Popular Web Development Topics
All Web Development Tutorials