Reading WCF Configuration from a Custom Location
Came across an issue today where we want to be able to read WCF service and client configuration from a custom location. That’s actually more difficult than you’d think.
By default, WCF configuration is stored in your app.config (or web.config) file in the <system.serviceModel> section. When you create a client (like with ChannelFactory<T>) or a service host, the application configuration file gets read, the contents get parsed into the appropriate strong types, and “magic happens” - the appropriate object is created.
In our situation, we wanted to do exactly that, but in a Powershell script… and that’s a problem, because the only way we could get WCF to see the configuration was to actually create a Powershell.exe.config file in the Powershell installation directory, run the script, and then remove the configuration. Not so great. We needed the ability to say, “Hey, WCF, use the configuration file that we explicitly specify.”
That, as I said, is a little more difficult than you’d think.
A lot of searching led me to two articles:
- For service hosting, “Custom Config File for a WCF Service Hosted in IIS.”
- For clients, a forum thread called “Config Hosting Multiple WCF Services in One NT Service.”
I agree, the titles don’t necessarily sound like they’d help much, but they do. They even include source for how to do this so you can see what I’m talking about. That said, I’ll summarize the steps here.
For service hosting, what it boils down to is:
- Create a custom service host class that derives from System.ServiceModel.ServiceHost.
- Override the protected ApplyConfiguration method. In the override, load your custom configuration file, find the System.ServiceModel.Configuration.ServiceElement corresponding to the service you want to host, and call LoadConfigurationSection on it.
For clients, it’s slightly more work:
- Create a custom class deriving from ChannelFactory<T>.
- Override the protected CreateDescription
the override, you need to…
- Call base.CreateDescription().
- Read in your custom configuration.
- Create a custom ServiceEndpoint based on your configuration. Don’t forget the bindings, behaviors, etc. (That’s what makes this hard.)
- Return that custom ServiceEndpoint.
Once you do that, you’re set - you can create a standalone XML configuration file with the <system.serviceModel> section and point WCF at that rather than having to store the configuration in the default app.config/web.config. You are limited to using your custom service host and client classes, but then, if you’re getting into things this deep you’re probably not afraid of getting your hands dirty.
Again, both of those articles contain full source to the solutions so you can see how it works. Check ‘em out.