semantic kernel exposing services using A2A (server and client)

Semantic kernel hasn't natively provide full support for A2A or atleast not proper yet So i am using these 2 libraries here to do all the hard work. There is no agent llm added in this post - you need to add in those code.

dotnet add package A2A

dotnet add package A2A.AspNetCore

The server side code 

using A2A;

using A2A.AspNetCore;

using AgentServer;

var builder = WebApplication.CreateBuilder(args);

var baseUrl = "http://localhost:5000";

builder.Services.AddA2AAgent<EchoAgent>(EchoAgent.GetAgentCard($"{baseUrl}/echo"));

var agentType ="echo";

var app = builder.Build();  

app.UseHttpsRedirection();

app.MapGet("/health", () => Results.Ok(new { Status = "Healthy", Timestamp = DateTimeOffset.UtcNow }));

// Map A2A endpoints using DI-registered services

var path = agentType.ToLowerInvariant() switch

{

    "echo" => "/echo",

    "echotasks" => "/echotasks",

    "researcher" => "/researcher",

    "speccompliance" => "/speccompliance",

    _ => "/agent",

};

app.MapA2A(path);

// For spec compliance, also map at root for well-known agent card discovery

if (agentType.Equals("speccompliance", StringComparison.OrdinalIgnoreCase))

{

    var card = app.Services.GetRequiredService<AgentCard>();

    app.MapWellKnownAgentCard(card);

}

app.Run();

And you can view the your agent card here: http://localhost:5000/echo/.well-known/agent-card.json

The client side code - please create another project and then place this code in there. Be careful about the "/echo/" missing the slash can turn into a disaster :) 

using A2A;

using System.Text.Json;

// 2. Create agent card resolver

A2ACardResolver agentCardResolver = new(new Uri("http://localhost:5000/echo/"));

// 3. Get agent card

AgentCard agentCard = await agentCardResolver.GetAgentCardAsync();

JsonSerializerOptions s_indentedOptions = new(A2AJsonUtilities.DefaultOptions)

{

        WriteIndented = true

};

// 4. Display agent details

Console.WriteLine("\nAgent card details:");

Console.WriteLine(JsonSerializer.Serialize(agentCard, s_indentedOptions));

A2AClient agentClient = new(new Uri(agentCard.SupportedInterfaces[0].Url));

// 3. Create a message to send to the agent

Message userMessage = new()

{

    Role = Role.User,

    MessageId = Guid.NewGuid().ToString(),

    Parts = [Part.FromText("Hello from the message-based communication sample! Please echo this message.")]

};

// 4. Send the message using non-streaming API

await EchoMessage.SendMessageAsync(agentClient, userMessage);

public class EchoMessage

{

    public static async Task SendMessageAsync(A2AClient agentClient, Message userMessage)

    {

        Console.WriteLine("\nNon-Streaming Message Communication");

        Console.WriteLine($" Sending message via non-streaming API: {userMessage.Parts[0].Text}");

        // Send the message and get the response

        SendMessageResponse response = await agentClient.SendMessageAsync(new SendMessageRequest { Message = userMessage });

        // Display the response

        Console.WriteLine($" Received complete response from agent: {response.Message!.Parts[0].Text}");

    }

}

If all works successfully, then you will get this output