Bringing SOAP to Flash 5

The problem

Flash 5 has support for XML communications over HTTP. Sadly enough however, there is no support for setting HTTP headers.
The 'SOAPAction' HTTP header is however essential if you want to communicate with SOAP-compliant webservices.

And what is very popular these days ? Yes, SOAP-based webservices...

And why are they popular ? Because they allow you to access business logic functionalities (for example doing a query to retrieve flight availability or the wheather in your city or live stock quotes or ...) over the Internet in a structured form (in other words without having to do screen- or HTML-scraping).

Do you, as a Flash developer, want to have access to these functionalities (check out http://uddi.microsoft.com for an overview of some of the webservices available to you today) ?

I do ! In order to make it possible for our Carels.VirtualClient Studio tool (which allows you to build rich, web-enabled, user interfaces for business applications) to communicate with SOAP-compliant webservices I had to come up with a solution.

A possible solution

The solution is based on an ASP script but could be implemented using a Java servlet as well.
The idea is to send the XML request to this script. The script then adds, using information passed through the URL, the necessary SOAP elements in order to make the request SOAP-compliant. The ASP script can be downloaded.

An example of what a SOAP request and response looks like can be found at:
http://www22.brinkster.com/prasads/LiveQuoteService.asmx

SOAPAction HTTP-header issue

The major issue is the SOAPAction HTTP-header. It is just not possible to set such headers through Flash 5. Specificying the URL and the SOAPAction as variables in the URL used to call the ASP script makes it possible for the ASP script to use this information in order to build the required SOAP-compliant request.

Use the following URL construction (this solution only works with the POST method, NOT with the GET method !) :

SOAP envelop and body issue

Another, but minor, issue is the SOAP envelope and body. Support has been foreseen in the script for automatically adding the SOAP envelope and body can be done by adding the variable 'Envelope' to the URL. This variables has 3 possible values :

1 : Add the envelope and body to the outgoing XML
2 : Add the envelope and body to the outgoing XML and remove the envelope and body from the incoming XML
3 : Remove the envelope and body from the incoming XML

When automatically adding the SOAP envelope and body (by specifying 1 or 2 for the Envelope variable) you can optionally set the encoding attribute of the XML processing instruction. This can be achieved by specifying the 'Encoding' variable on the URL :

The application domain issue

If you have been playing around with the XML over HTTP communication support in Flash then you are probably aware that it doesn't allow you to communicate outside your application domain. In other words hostnames different from the hostname used to access your Flash movie don't work.
The presented solution allows you to route your Web service calls via the ASP script. You circumvent the application domain limitation by installing the script in the same application domain as the rest of your application.

Conclusion

This script solves the SOAP-specific issues as well as the application domain issue. Please feel free to send me your questions, comments and improvements.

About the author

Tom Van den Eynde is Product Marketing Director at Carels Corporation. Tom promotes the usage of XML and web services, not only for use in B2B and B2C scenarios but also as a means to build better user interfaces for business applications, portals, ... In the past he has developed thin client solutions that are being used by major companies worldwide. He can be reached at tom.vandeneynde@carels.com.