detecting resubmitted SOAP messages

I've got an ASP.NET website that calls an ASP.NET web service.

How can I detect a resubmitted SOAP message? Is that something I need to worry about if the app and the service are both .NET a开发者_StackOverflow社区nd on the same server?

Since .NET creates the proxy and takes care of the SOAP details, how can you detect resubmitted SOAP messages?

---

I can't speak to the specifics of ASP.NET, it might have some "magic" to help in this area, but generally your Web Services need to be designed to be resilient to duplicate requests unless there is cleverness in the infrastructure.

There are several scenarios:

The Web App makes a service call. Does the infrastructure make any any attempts to retry if an answer does not come in a certain time? I don't know what ASP.NET does here, my guess is "no", but that is very much a guess. Equally your Web App itself might choose to retry. In either case we might get exactly the same request sent twice. Any responsibility for detecting the duplicate request would lie with the server. This is very much easier if the request contains some unique label.

A second scenario is the "impatient user" scenario. The user hits submit too often. A well designed Web App will prevent this or detect this and not resubmit the web service. In this case the Service should not see any duplicate.

A more difficult scenario is the "did you really mean to buy two Rolls Royces?" The customer submits a request, let's pretend it's a high value request. Then their computer crashes, or they lose connectivity. Later, maybe even from a different computer, the user attempts the same purchase, not realising that the first one actually worked. Now that's a hard one to spot, and many vendors don't even try, but in some scenarios you need to make a really clever service with the duplicate detection being quite sophisticated pattern matching - for really high value customers this extra effort may be essential.