Exercise - Add a filter service to the kernel

8 minutes

In this exercise, you add a filter function that will request the user's approval before allowing the agent to book a flight on their behalf. Let's get started!

Open the Program.cs in the M04-Project folder.
Create a new file named PermissionFilter.cs.
Enter the following code in the new file:
```
#pragma warning disable SKEXP0001 
using Microsoft.SemanticKernel;

public class PermissionFilter : IFunctionInvocationFilter
{
    public async Task OnFunctionInvocationAsync(FunctionInvocationContext context, Func<FunctionInvocationContext, Task> next)
    {

    }
}
```
Note

In version 1.30.0 of the Semantic Kernel SDK, function filters are subject to change and require a warning suppression.

In this code, you implement the IFunctionInvocationFilter interface. The OnFunctionInvocationAsync method is always called whenever a function is invoked from an AI agent.
Add the following code to detect when the book_flight function is invoked:
```
if (context.Function.PluginName == "FlightBooking" && context.Function.Name == "book_flight")
{

}

await next(context);
```
This code uses the FunctionInvocationContext to determine which plugin and function were invoked.

Add the following logic to request the user's permission to book the flight:

if (context.Function.PluginName == "FlightBooking" && context.Function.Name == "book_flight")
{
    Console.WriteLine("System Message: The agent requires an approval to complete this operation. Do you approve (Y/N)");
    Console.Write("User: ");
    string shouldProceed = Console.ReadLine()!;

    if (shouldProceed != "Y")
    {
        context.Result = new FunctionResult(context.Result, "The operation was not approved by the user");
        return;
    }
}

await next(context);

Navigate to the Program.cs file.

Add the permission filter to your kernel using the following code:

// Build the kernel
Kernel kernel = builder.Build();
kernel.FunctionInvocationFilters.Add(new PermissionFilter());

Replace the await SyncPreviousChat(); function call with the following code to update the flow:

AddUserMessage("Find me a flight to Tokyo on the 19");
await GetReply();
GetInput();
await GetReply();

Enter dotnet run in the terminal to test your new filter.

Try denying the approval request. You should see a response similar to the following output:

User: Find me a flight to Tokyo on the 19
Assistant: I found a flight to Tokyo on the 19th of January. The flight is with Air Japan and the price is $1200.
User: Y
System Message: The agent requires an approval to complete this operation. Do you approve (Y/N)
User: N
Assistant: I'm sorry, but I am unable to book the flight for you.

Now you successfully added a function filter service to your kernel. Great work!

Exercise - Add a filter service to the kernel

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