.NET: Use IA2AClientFactory to create A2AClient

dotnet/agent-framework-dotnet.slnx

@@ -289,6 +289,7 @@
     <Project Path="samples/02-agents/A2A/A2AAgent_AsFunctionTools/A2AAgent_AsFunctionTools.csproj" />
     <Project Path="samples/02-agents/A2A/A2AAgent_PollingForTaskCompletion/A2AAgent_PollingForTaskCompletion.csproj" />
     <Project Path="samples/02-agents/A2A/A2AAgent_StreamReconnection/A2AAgent_StreamReconnection.csproj" />
+    <Project Path="samples/02-agents/A2A/A2AAgent_ProtocolSelection/A2AAgent_ProtocolSelection.csproj" />
   </Folder>  
   <Folder Name="/Samples/05-end-to-end/">
     <Project Path="samples/05-end-to-end/AgentWithPurview/AgentWithPurview.csproj" />

dotnet/samples/02-agents/A2A/A2AAgent_ProtocolSelection/A2AAgent_ProtocolSelection.csproj

@@ -0,0 +1,19 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFrameworks>net10.0</TargetFrameworks>
+
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="A2A" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\..\..\src\Microsoft.Agents.AI.A2A\Microsoft.Agents.AI.A2A.csproj" />
+  </ItemGroup>
+
+</Project>

dotnet/samples/02-agents/A2A/A2AAgent_ProtocolSelection/Program.cs

@@ -0,0 +1,36 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+// This sample demonstrates how to select the A2A protocol binding (HTTP+JSON vs JSON-RPC) when
+// creating an AIAgent from an A2A agent card using A2AClientOptions.PreferredBindings.
+
+using A2A;
+using Microsoft.Agents.AI;
+
+var a2aAgentHost = Environment.GetEnvironmentVariable("A2A_AGENT_HOST") ?? throw new InvalidOperationException("A2A_AGENT_HOST is not set.");
+
+// Initialize an A2ACardResolver to get an A2A agent card.
+A2ACardResolver agentCardResolver = new(new Uri(a2aAgentHost));
+
+// Get the agent card
+AgentCard agentCard = await agentCardResolver.GetAgentCardAsync();
+
+// Use A2AClientOptions to explicitly select the HTTP+JSON protocol binding.
+// This tells the A2A client factory to prefer the HTTP+JSON interface when the agent card
+// advertises multiple supported interfaces.
+A2AClientOptions options = new()
+{
+    PreferredBindings = [ProtocolBindingNames.HttpJson]
+};
+
+// To prefer JSON-RPC instead, use:
+// A2AClientOptions options = new()
+// {
+//     PreferredBindings = [ProtocolBindingNames.JsonRpc]
+// };
+
+// Create an instance of the AIAgent for an existing A2A agent, using the specified protocol binding.
+AIAgent agent = agentCard.AsAIAgent(options: options);
+
+// Invoke the agent and output the text result.
+AgentResponse response = await agent.RunAsync("Tell me a joke about a pirate.");
+Console.WriteLine(response);

dotnet/samples/02-agents/A2A/A2AAgent_ProtocolSelection/README.md

@@ -0,0 +1,27 @@
+# A2A Agent Protocol Selection
+
+This sample demonstrates how to select the A2A protocol binding when creating an `AIAgent` from an A2A agent card.
+
+A2A agents can expose multiple interfaces with different protocol bindings (e.g., HTTP+JSON, JSON-RPC). By default, `AsAIAgent()` prefers HTTP+JSON with JSON-RPC as a fallback. This sample shows how to use `A2AClientOptions.PreferredBindings` to explicitly control which protocol binding is used.
+
+The sample:
+
+- Connects to an A2A agent server specified in the `A2A_AGENT_HOST` environment variable
+- Configures `A2AClientOptions` to prefer the HTTP+JSON protocol binding
+- Creates an `AIAgent` from the resolved agent card using the specified binding
+- Sends a message to the agent and displays the response
+
+## Prerequisites
+
+Before you begin, ensure you have the following prerequisites:
+
+- .NET 10.0 SDK or later
+- An A2A agent server running and accessible via HTTP
+
+**Note**: These samples need to be run against a valid A2A server. If no A2A server is available, they can be run against the echo-agent that can be spun up locally by following the guidelines at: https://github.com/a2aproject/a2a-dotnet/blob/main/samples/AgentServer/README.md
+
+Set the following environment variable:
+
+```powershell
+$env:A2A_AGENT_HOST="http://localhost:5000"  # Replace with your A2A agent server host
+```

dotnet/samples/02-agents/A2A/README.md

@@ -3,7 +3,7 @@
 These samples demonstrate how to work with Agent-to-Agent (A2A) specific features in the Agent Framework.
 
 For other samples that demonstrate how to use AIAgent instances,
-see the [Getting Started With Agents](../../02-agents/Agents/README.md) samples.
+see the [Getting Started With Agents](../Agents/README.md) samples.
 
 ## Prerequisites
 
@@ -16,6 +16,7 @@ See the README.md for each sample for the prerequisites for that sample.
 |[A2A Agent As Function Tools](./A2AAgent_AsFunctionTools/)|This sample demonstrates how to represent an A2A agent as a set of function tools, where each function tool corresponds to a skill of the A2A agent, and register these function tools with another AI agent so it can leverage the A2A agent's skills.|
 |[A2A Agent Polling For Task Completion](./A2AAgent_PollingForTaskCompletion/)|This sample demonstrates how to poll for long-running task completion using continuation tokens with an A2A agent.|
 |[A2A Agent Stream Reconnection](./A2AAgent_StreamReconnection/)|This sample demonstrates how to reconnect to an A2A agent's streaming response using continuation tokens, allowing recovery from stream interruptions.|
+|[A2A Agent Protocol Selection](./A2AAgent_ProtocolSelection/)|This sample demonstrates how to select the A2A protocol binding (HTTP+JSON vs JSON-RPC) when creating an AIAgent from an A2A agent card using A2AClientOptions.|
 
 ## Running the samples from the console
 

dotnet/samples/02-agents/README.md

@@ -19,3 +19,4 @@ The getting started samples demonstrate the fundamental concepts and functionali
 | [Declarative Agents](./DeclarativeAgents) | Loading and executing AI agents from YAML configuration files |
 | [AG-UI](./AGUI/README.md) | Getting started with AG-UI (Agent UI Protocol) servers and clients |
 | [Dev UI](./DevUI/README.md) | Interactive web interface for testing and debugging AI agents during development |
+| [A2A Agents](./A2A/README.md) | Working with Agent-to-Agent (A2A) specific features |

dotnet/src/Microsoft.Agents.AI.A2A/A2AAgent.cs

@@ -27,7 +27,7 @@ public sealed class A2AAgent : AIAgent
 {
     private static readonly AIAgentMetadata s_agentMetadata = new("a2a");
 
-    private readonly A2AClient _a2aClient;
+    private readonly IA2AClient _a2aClient;
     private readonly string? _id;
     private readonly string? _name;
     private readonly string? _description;
@@ -41,7 +41,7 @@ public sealed class A2AAgent : AIAgent
     /// <param name="name">The the name of the agent.</param>
     /// <param name="description">The description of the agent.</param>
     /// <param name="loggerFactory">Optional logger factory to use for logging.</param>
-    public A2AAgent(A2AClient a2aClient, string? id = null, string? name = null, string? description = null, ILoggerFactory? loggerFactory = null)
+    public A2AAgent(IA2AClient a2aClient, string? id = null, string? name = null, string? description = null, ILoggerFactory? loggerFactory = null)
     {
         _ = Throw.IfNull(a2aClient);
 
@@ -224,7 +224,7 @@ protected override async IAsyncEnumerable<AgentResponseUpdate> RunCoreStreamingA
     /// <inheritdoc/>
     public override object? GetService(Type serviceType, object? serviceKey = null)
         => base.GetService(serviceType, serviceKey)
-           ?? (serviceType == typeof(A2AClient) ? this._a2aClient
+           ?? (serviceType == typeof(IA2AClient) ? this._a2aClient
             : serviceType == typeof(AIAgentMetadata) ? s_agentMetadata
             : null);
 

dotnet/src/Microsoft.Agents.AI.A2A/Extensions/A2AAgentCardExtensions.cs

@@ -1,7 +1,5 @@
 // Copyright (c) Microsoft. All rights reserved.
 
-using System;
-using System.Linq;
 using System.Net.Http;
 using Microsoft.Agents.AI;
 using Microsoft.Extensions.Logging;
@@ -26,16 +24,15 @@ public static class A2AAgentCardExtensions
     /// </remarks>
     /// <param name="card">The <see cref="AgentCard" /> to use for the agent creation.</param>
     /// <param name="httpClient">The <see cref="HttpClient"/> to use for HTTP requests.</param>
+    /// <param name="options">
+    /// Optional <see cref="A2AClientOptions"/> controlling protocol binding preference.
+    /// When not provided, defaults to preferring HTTP+JSON first, with JSON-RPC as fallback.
+    /// </param>
     /// <param name="loggerFactory">The logger factory for enabling logging within the agent.</param>
     /// <returns>An <see cref="AIAgent"/> instance backed by the A2A agent.</returns>
-    public static AIAgent AsAIAgent(this AgentCard card, HttpClient? httpClient = null, ILoggerFactory? loggerFactory = null)
+    public static AIAgent AsAIAgent(this AgentCard card, HttpClient? httpClient = null, A2AClientOptions? options = null, ILoggerFactory? loggerFactory = null)
     {
-        // TODO: Refactor to support interface selection from card.SupportedInterfaces.
-        var url = card.SupportedInterfaces?.FirstOrDefault()?.Url
-            ?? throw new InvalidOperationException("The AgentCard does not have any SupportedInterfaces with a URL.");
-
-        // Create the A2A client using the agent URL from the card.
-        var a2aClient = new A2AClient(new Uri(url), httpClient);
+        var a2aClient = A2AClientFactory.Create(card, httpClient, options);
 
         return a2aClient.AsAIAgent(name: card.Name, description: card.Description, loggerFactory: loggerFactory);
     }

dotnet/src/Microsoft.Agents.AI.A2A/Extensions/A2ACardResolverExtensions.cs

@@ -34,14 +34,18 @@ public static class A2ACardResolverExtensions
     /// </remarks>
     /// <param name="resolver">The <see cref="A2ACardResolver" /> to use for the agent creation.</param>
     /// <param name="httpClient">The <see cref="HttpClient"/> to use for HTTP requests.</param>
+    /// <param name="options">
+    /// Optional <see cref="A2AClientOptions"/> controlling protocol binding preference.
+    /// When not provided, defaults to preferring HTTP+JSON first, with JSON-RPC as fallback.
+    /// </param>
     /// <param name="loggerFactory">The logger factory for enabling logging within the agent.</param>
     /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
     /// <returns>An <see cref="AIAgent"/> instance backed by the A2A agent.</returns>
-    public static async Task<AIAgent> GetAIAgentAsync(this A2ACardResolver resolver, HttpClient? httpClient = null, ILoggerFactory? loggerFactory = null, CancellationToken cancellationToken = default)
+    public static async Task<AIAgent> GetAIAgentAsync(this A2ACardResolver resolver, HttpClient? httpClient = null, A2AClientOptions? options = null, ILoggerFactory? loggerFactory = null, CancellationToken cancellationToken = default)
     {
         // Obtain the agent card from the resolver.
         var agentCard = await resolver.GetAgentCardAsync(cancellationToken).ConfigureAwait(false);
 
-        return agentCard.AsAIAgent(httpClient, loggerFactory);
+        return agentCard.AsAIAgent(httpClient, options, loggerFactory);
     }
 }

dotnet/src/Microsoft.Agents.AI.A2A/Extensions/A2AClientExtensions.cs

@@ -7,7 +7,7 @@
 namespace A2A;
 
 /// <summary>
-/// Provides extension methods for <see cref="A2AClient"/>
+/// Provides extension methods for <see cref="IA2AClient"/>
 /// to simplify the creation of A2A agents.
 /// </summary>
 /// <remarks>
@@ -29,12 +29,12 @@ public static class A2AClientExtensions
     /// <see href="https://github.com/a2aproject/A2A/blob/main/docs/topics/agent-discovery.md#3-direct-configuration--private-discovery">Direct Configuration / Private Discovery</see>
     /// discovery mechanism.
     /// </remarks>
-    /// <param name="client">The <see cref="A2AClient" /> to use for the agent.</param>
+    /// <param name="client">The <see cref="IA2AClient" /> to use for the agent.</param>
     /// <param name="id">The unique identifier for the agent.</param>
     /// <param name="name">The the name of the agent.</param>
     /// <param name="description">The description of the agent.</param>
     /// <param name="loggerFactory">Optional logger factory for enabling logging within the agent.</param>
     /// <returns>An <see cref="AIAgent"/> instance backed by the A2A agent.</returns>
-    public static AIAgent AsAIAgent(this A2AClient client, string? id = null, string? name = null, string? description = null, ILoggerFactory? loggerFactory = null) =>
+    public static AIAgent AsAIAgent(this IA2AClient client, string? id = null, string? name = null, string? description = null, ILoggerFactory? loggerFactory = null) =>
         new A2AAgent(client, id, name, description, loggerFactory);
 }

dotnet/tests/Microsoft.Agents.AI.A2A.UnitTests/A2AAgentTests.cs

@@ -55,6 +55,21 @@ public void Constructor_WithNullA2AClient_ThrowsArgumentNullException() =>
         // Act & Assert
         Assert.Throws<ArgumentNullException>(() => new A2AAgent(null!));
 
+    [Fact]
+    public void Constructor_WithIA2AClient_InitializesCorrectly()
+    {
+        // Arrange
+        IA2AClient ia2aClient = this._a2aClient;
+
+        // Act
+        var agent = new A2AAgent(ia2aClient, "ia2a-id", "IA2A Agent", "An agent from IA2AClient");
+
+        // Assert
+        Assert.Equal("ia2a-id", agent.Id);
+        Assert.Equal("IA2A Agent", agent.Name);
+        Assert.Equal("An agent from IA2AClient", agent.Description);
+    }
+
     [Fact]
     public void Constructor_WithDefaultParameters_UsesBaseProperties()
     {
@@ -1371,19 +1386,33 @@ public async Task RunStreamingAsync_WithInvalidSessionType_ThrowsInvalidOperatio
     #region GetService Method Tests
 
     /// <summary>
-    /// Verify that GetService returns A2AClient when requested.
+    /// Verify that GetService returns IA2AClient when requested.
     /// </summary>
     [Fact]
-    public void GetService_RequestingA2AClient_ReturnsA2AClient()
+    public void GetService_RequestingIA2AClient_ReturnsA2AClient()
     {
         // Arrange & Act
-        var result = this._agent.GetService(typeof(A2AClient));
+        var result = this._agent.GetService(typeof(IA2AClient));
 
         // Assert
         Assert.NotNull(result);
         Assert.Same(this._a2aClient, result);
     }
 
+    /// <summary>
+    /// Verify that GetService returns null when requesting the concrete A2AClient type
+    /// since the agent now exposes IA2AClient instead.
+    /// </summary>
+    [Fact]
+    public void GetService_RequestingConcreteA2AClient_ReturnsNull()
+    {
+        // Arrange & Act
+        var result = this._agent.GetService(typeof(A2AClient));
+
+        // Assert
+        Assert.Null(result);
+    }
+
     /// <summary>
     /// Verify that GetService returns AIAgentMetadata when requested.
     /// </summary>
@@ -1458,10 +1487,10 @@ public void GetService_RequestingAIAgentType_ReturnsBaseImplementation()
     /// Verify that GetService calls base.GetService() first but continues to derived logic when base returns null.
     /// </summary>
     [Fact]
-    public void GetService_RequestingA2AClientWithServiceKey_CallsBaseFirstThenDerivedLogic()
+    public void GetService_RequestingIA2AClientWithServiceKey_CallsBaseFirstThenDerivedLogic()
     {
-        // Arrange & Act - Request A2AClient with a service key (base.GetService will return null due to serviceKey)
-        var result = this._agent.GetService(typeof(A2AClient), "some-key");
+        // Arrange & Act - Request IA2AClient with a service key (base.GetService will return null due to serviceKey)
+        var result = this._agent.GetService(typeof(IA2AClient), "some-key");
 
         // Assert
         Assert.NotNull(result);