PinkRooster.EventEmittingFunctionInvokingChatClient

A FunctionInvokingChatClient subclass that emits async events before and after each tool invocation, giving you full observability into the Microsoft.Extensions.AI function-calling pipeline.

Installation

dotnet add package PinkRooster.EventEmittingFunctionInvokingChatClient

Quick Start

using Microsoft.Extensions.AI;

// Build a pipeline with event-emitting function invocation
var pipeline = new ChatClientBuilder(innerClient)
    .Use(client =>
    {
        var funcClient = new EventEmittingFunctionInvokingChatClient(client);

        funcClient.ToolCallStarting += async (sender, e) =>
        {
            Console.WriteLine($"Starting: {e.FunctionName} [{e.CallId}]");
            await Task.CompletedTask;
        };

        funcClient.ToolCallCompleted += async (sender, e) =>
        {
            var icon = e.Succeeded ? "OK" : "FAIL";
            Console.WriteLine($"{icon}: {e.FunctionName} in {e.Duration.TotalMilliseconds:F0}ms");
            await Task.CompletedTask;
        };

        return funcClient;
    })
    .Build();

Features

• ToolCallStarting event fires before each function invocation with function name, arguments, call ID, and iteration info
• ToolCallCompleted event fires after each invocation with result/exception, wall-clock duration, and termination status
• Accurate timing that measures only function execution, excluding event handler overhead
• Thread-safe: works correctly with AllowConcurrentInvocation = true
• Robust error handling in the completed event (handler exceptions never swallow function exceptions)
• Overridable OnCompletedHandlerException for custom error handling in completed event handlers

Event Args

ToolCallStartingEventArgs

Property	Type	Description
FunctionName	string	Name of the function about to be invoked
CallId	string	Unique identifier for this tool call
Arguments	AIFunctionArguments?	Arguments passed to the function
Iteration	int	0-based roundtrip iteration number
FunctionCallIndex	int	0-based index within the current iteration
FunctionCount	int	Total function calls in the current iteration
IsStreaming	bool	Whether this is inside a streaming response
Context	FunctionInvocationContext	Full context for advanced scenarios

ToolCallCompletedEventArgs

Property	Type	Description
FunctionName	string	Name of the function that was invoked
CallId	string	Unique identifier for this tool call
Result	object?	Return value, or null on failure
Exception	Exception?	Exception thrown, or null on success
Duration	TimeSpan	Wall-clock duration (excluding handler time)
Succeeded	bool	Convenience: true when Exception is null
TerminationRequested	bool	Whether the function requested loop termination
Context	FunctionInvocationContext	Full context for advanced scenarios

Example

See the Tavily Research Agent for a full working example that uses this library with the Tavily MCP server to build an interactive research assistant.

License

MIT