WCF service with 4 input parms and 3 out parms gets reordered by Add Service Reference in Proxy Class Project

Question

I've looked in SO and elsewhere and seen questions posed about this along with some answers that still make no sense to me in my case.

I'm refactoring my working VStudio 2010 solution which has:

• one project with an ASMX webservice
• another separate project for the proxy class (no code here except what is generated by Add Web Reference
• another separate project for the client (contains a reference to the ProxyClass.dll

The new VStudio 2010 solution has:

• one project of type WCF service library for the contract by itself (IFileService.cs) one project of type WCF service library for the implementation of the contract (FileService.cs)
• another separate project for the proxy class (no code here except what is generated by Add Service Reference
• another separate project for the client (contains a reference to the WCFProxyClass.dll)

Here is the contract which ends with 3 out parameters (and the implementation of same is the same order):

[ServiceContract(Name = "IFileService", Namespace =  "http://www.cbmiweb.com/TrimWCF/2011/11")]
public interface IFileService
{
    [OperationContract]
        public string DownloadFile(string trimURL
         , string TrimRecordNumber
         , string CallerPC
         , string RequestorID
         , out byte[] docContents
         , out string returnFiletype
         , out string returnFilename)
    {

Here is what Add Service Reference generated in my proxy class project:

public string DownloadFile(
  out byte[] docContents
, out string returnFiletype
, out string returnFilename
, string trimURL
, string TrimRecordNumber
, string CallerPC
, string RequestorID) 
{
    return base.Channel.DownloadFile(out docContents, out returnFiletype, out returnFilename, trimURL, TrimRecordNumber, CallerPC, RequestorID);
}

I have read answers ranging from "you cannot use out parms in WCF" to "you should not use Add Service Reference but instead use svcutil.exe" to "the order of the parameters do not matter...it will still work".

I am confused about what to do here (and what I've done wrong that led to this re-arranged order and WHY that happened).

Answer 1

First of all, you haven't done anything wrong :). Even though the signatures in the methods in the client and the server are different, they're equivalent wrt the messages which will be produced / consumed by them. You can use that proxy class without any problems, and it should work just as well.

Why this happens is another story - in the service description (WSDL), there are two "messages" for each (non-one-way) operation: one with the input parameters, one with the output parameters. The messages contains respectively the input(s) and output(s) of the operation, but there's nothing in the WSDL which shows the order of them. So when a tool such as Add Service Reference or svcutil is generating the client proxy, it will simply "choose" one order (out parameters first), but the request which the proxy will send to the service will be compatible with what the server expects (and also, the response from the server will be correctly understood by the proxy).

If you want to maintain the order of the parameters, you can create the proxy class yourself. For this you can either use the ChannelFactory<T> class, or create your own client class derived from ChannelBase<T>. But you don't really need to do that, as I mentioned before.