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How to Fix Default Namespace Issues When Calling ASP.NET Web Services Using SOAP Client from ASP

When working with ASP.NET web services, you may find that calling these services from classic ASP might lead to some unexpected behaviors, especially concerning XML namespaces. This can be particularly frustrating if you are in the midst of a project, trying to integrate legacy ASP applications with modern ASP.NET services.

In this blog post, we’ll address a specific problem: how to handle the default namespace issue when using SOAP clients to communicate with ASP.NET web services. Let’s dive into the details.

Understanding the Problem

Imagine you have a web service defined in ASP.NET that processes XML messages. When you call this service from your classic ASP code using a SOAP client, you might notice something strange. The XML that reaches your ProcessMessage method has an unexpected default namespace attached, which can lead to processing errors because it alters the expected XML structure.

To put it simply, here’s what happens:

  • Expected XML Structure: The web service expects an XML message without an added default namespace.
  • Actual XML Sent: The SOAPClient wraps the XML message in a default namespace, causing issues when processing the message in the server-side method.

Here’s a snippet that illustrates both versions of the XML message:

  • From SOAPClient:

    <request xmlns="http://internalservice.net/messageprocessing">
  <task>....various xml</task>
</request>

  • Expected XML:

    <request>
  <task>....various xml</task>
</request>

This discrepancy can lead to confusion and likely errors during execution.

The Solution

Fortunately, there is a simpler fix than creating a whole new COM callable .NET proxy. All it requires is a small tweak in the way you construct the XML message in your ASP code before sending it to the web service.

Step 1: Modify the XML Message

The trick lies in explicitly defining the XML without a namespace or using an empty default namespace. Here’s how you can do it:

  1. Create the XML Message: Ensure that when you build the XML message, you set the default namespace to an empty string. This method essentially overrides the SOAPClient’s behavior.

    Here’s the updated line of code that constructs the XML message:

    xmlMessage = "<request xmlns=''><task>....various xml</task></request>"

Step 2: Send the Updated XML

Continue with your original code to call the web service using the modified xmlMessage. Here’s how your complete call might look afterward:

provWSDL = "http://servername:12011/MessageProcessor.asmx?wsdl"
Set service = CreateObject("MSSOAP.SoapClient30")
service.ClientProperty("ServerHTTPRequest") = True
Call service.MSSoapInit(provWSDL)

xmlMessage = "<request xmlns=''><task>....various xml</task></request>"
result = service.ProcessMessage(xmlMessage)

Why This Works

By specifying xmlns='', you effectively tell the SOAP client not to apply any default namespace to the <request> element. This ensures that your XML is sent in the format that your ASP.NET web service can process without adding unnecessary complexity.

Conclusion

Navigating the integration of classic ASP with ASP.NET web services can be challenging, especially when dealing with XML namespaces and SOAP messaging. By simply adjusting how you construct your XML messages, you can maintain a smoother interaction with web services and avoid potential pitfalls.

If you encounter similar issues in the future, remember to check how namespaces are being handled and feel free to modify your XML accordingly. Happy coding!