Calling a web service from behind a proxy

Once again I need to call out to an external web service from behind a proxy. Last time it was installing WATIR. This time it is just straight up .NET code, but somehow this configuration feels like something I have to learn over each time I see it, so I am going to burn it into my blog.

I am working through some hands on labs configuring the Unity Inversion Of Control Container. The labs come with a sample Stocks Ticker application which calls out to an external web service to get its updates. So when running behind a proxy that requires authentication, by default, what you will see when running this application is:

stockTickerNoProxy

So I open up the MoneyCentralStockQuoteService.vb file, which defines the class that is calling the service, and find this constructor:

Public Sub New(ByVal implementation As MoneyCentralRemote) 
     Me.implementation = implementation 
     Me.Logger = New NullLogger 
End Sub

My first attempt to resolve the issue is this, setting up a manual proxy reference (an instance of WebProxy), which requires that I not only tell the proxy to use the default credentials but also provide the ISA server’s address.

Public Sub New(ByVal implementation As MoneyCentralRemote)
        Me.implementation = implementation

        'wire up proxy information here 
        Dim proxy As New Net.WebProxy("http://servername:8080")
        proxy.UseDefaultCredentials = True
        Me.implementation.Proxy = proxy

        Me.Logger = New NullLogger
End Sub

This works and I can start working with the sample application:

stockTickerProxy

However, hard-coding the server name seems less than terrific. I then remember that I can also configure the proxy settings in the app.config file like below, which also works.

<system.net> 
    <defaultProxy useDefaultCredentials="true" /> 
</system.net>

What this approach reminds me of is that I shouldn’t have to hard-code my proxy server address. If the application can load up the correct default proxy information based on a config file setting it should be able to do so in code as well. There must be a way to wire into this default functionality in code. So, back to the syntax drawing board ... and I end up with this, somewhat cleaner option, that gets a reference to the default WebProxy by way of the WebRequest class:

Public Sub New(ByVal implementation As MoneyCentralRemote) 
     Me.implementation = implementation 
     'set up proxy information here 
     implementation.Proxy = System.Net.WebRequest.DefaultWebProxy 
     implementation.Proxy.Credentials = Net.CredentialCache.DefaultCredentials 
     Me.Logger = New NullLogger 
End Sub

Of the three approaches, I strongly favor setting up the proxy settings in the configuration file, as it is specific to the environment. Are there any options that I missed?

 
 
© Copyright 2009 - Andreas Zenker

 
 
 
 

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