.NET: Fix A2A conversion routines to ignore unknown content types instead of throwing exceptions (#1154)

* Initial plan

* Update A2A conversion routines to ignore unknown content types

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

* Fix dotnet format

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
Co-authored-by: Stephen Toub <stoub@microsoft.com>
Co-authored-by: SergeyMenshykh <68852919+SergeyMenshykh@users.noreply.github.com>

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

@@ -159,7 +159,7 @@ internal sealed class A2AAgent : AIAgent
                 RawRepresentation = message,
                 Role = ChatRole.Assistant,
                 MessageId = message.MessageId,
-                Contents = [.. message.Parts.Select(part => part.ToAIContent())],
+                Contents = [.. message.Parts.Select(part => part.ToAIContent()).OfType<AIContent>()],
                 AdditionalProperties = message.Metadata.ToAdditionalProperties(),
             };
         }

dotnet/src/Microsoft.Agents.AI.A2A/Extensions/A2AAIContentExtensions.cs

@@ -1,6 +1,5 @@
 // Copyright (c) Microsoft. All rights reserved.
 
-using System;
 using System.Collections.Generic;
 using A2A;
 
@@ -22,7 +21,11 @@ internal static class A2AAIContentExtensions
 
         foreach (var content in contents)
         {
-            (parts ??= []).Add(content.ToA2APart());
+            var part = content.ToA2APart();
+            if (part is not null)
+            {
+                (parts ??= []).Add(part);
+            }
         }
 
         return parts;
@@ -32,12 +35,13 @@ internal static class A2AAIContentExtensions
     ///  Converts a <see cref="AIContent"/> to a <see cref="Part"/> object."/>
     /// </summary>
     /// <param name="content">AI content to convert.</param>
-    /// <returns>The corresponding A2A <see cref="Part"/> object.</returns>
-    internal static Part ToA2APart(this AIContent content) =>
+    /// <returns>The corresponding A2A <see cref="Part"/> object, or null if the content type is not supported.</returns>
+    internal static Part? ToA2APart(this AIContent content) =>
         content switch
         {
             TextContent textContent => new TextPart { Text = textContent.Text },
             HostedFileContent hostedFileContent => new FilePart { File = new FileWithUri { Uri = hostedFileContent.FileId } },
-            _ => throw new NotSupportedException($"Unsupported content type: {content.GetType().Name}."),
+            // Ignore unknown content types (FunctionCallContent, FunctionResultContent, etc.)
+            _ => null,
         };
 }

dotnet/src/Microsoft.Agents.AI.A2A/Extensions/A2AArtifactExtensions.cs

@@ -16,7 +16,11 @@ internal static class A2AArtifactExtensions
 
         foreach (var part in artifact.Parts)
         {
-            (aiContents ??= []).Add(part.ToAIContent());
+            var content = part.ToAIContent();
+            if (content is not null)
+            {
+                (aiContents ??= []).Add(content);
+            }
         }
 
         return new ChatMessage(ChatRole.Assistant, aiContents)

dotnet/src/Microsoft.Agents.AI.A2A/Extensions/A2AMessageExtensions.cs

@@ -16,7 +16,11 @@ internal static class A2AMessageExtensions
 
         foreach (var part in message.Parts)
         {
-            (aiContents ??= []).Add(part.ToAIContent());
+            var content = part.ToAIContent();
+            if (content is not null)
+            {
+                (aiContents ??= []).Add(content);
+            }
         }
 
         return new ChatMessage(ChatRole.Assistant, aiContents)

dotnet/src/Microsoft.Agents.AI.A2A/Extensions/A2APartExtensions.cs

@@ -1,6 +1,5 @@
 // Copyright (c) Microsoft. All rights reserved.
 
-using System;
 using Microsoft.Extensions.AI;
 
 namespace A2A;
@@ -14,8 +13,8 @@ internal static class A2APartExtensions
     /// Converts an A2A <see cref="Part"/> to an <see cref="AIContent"/>.
     /// </summary>
     /// <param name="part">The A2A part to convert.</param>
-    /// <returns>The corresponding <see cref="AIContent"/>.</returns>
-    internal static AIContent ToAIContent(this Part part) =>
+    /// <returns>The corresponding <see cref="AIContent"/>, or null if the part type is not supported.</returns>
+    internal static AIContent? ToAIContent(this Part part) =>
         part switch
         {
             TextPart textPart => new TextContent(textPart.Text)
@@ -30,6 +29,7 @@ internal static class A2APartExtensions
                 AdditionalProperties = filePart.Metadata.ToAdditionalProperties()
             },
 
-            _ => throw new NotSupportedException($"Part type '{part.GetType().Name}' is not supported.")
+            // Ignore unknown part types (DataPart, etc.)
+            _ => null
         };
 }

dotnet/src/Microsoft.Agents.AI.Hosting.A2A/Converters/MessageConverter.cs

@@ -160,7 +160,8 @@ internal static class MessageConverter
                 RawRepresentation = textPart,
                 AdditionalProperties = textPart.Metadata?.ToAdditionalPropertiesDictionary()
             },
-            FilePart or DataPart or _ => throw new NotSupportedException($"Part type '{part.GetType().Name}' is not supported. Only TextPart is supported.")
+            // Ignore unknown content types (FilePart, DataPart, etc.)
+            _ => null
         };
 
     /// <summary>
@@ -234,7 +235,8 @@ internal static class MessageConverter
             {
                 Text = textContent.Text
             },
-            _ => throw new NotSupportedException($"Content type '{content.GetType().Name}' is not supported.")
+            // Ignore unknown content types (FunctionCallContent, FunctionResultContent, etc.)
+            _ => null
         };
 
     private static AdditionalPropertiesDictionary? ToAdditionalPropertiesDictionary(this Dictionary<string, JsonElement> metadata)

dotnet/tests/Microsoft.Agents.AI.A2A.UnitTests/Extensions/A2AAIContentExtensionsTests.cs

@@ -1,6 +1,5 @@
 // Copyright (c) Microsoft. All rights reserved.
 
-using System;
 using System.Collections.Generic;
 using A2A;
 using Microsoft.Extensions.AI;
@@ -49,14 +48,16 @@ public sealed class A2AAIContentExtensionsTests
     }
 
     [Fact]
-    public void ToA2APart_WithUnsupportedContentType_ThrowsNotSupportedException()
+    public void ToA2APart_WithUnsupportedContentType_ReturnsNull()
     {
         // Arrange
         var unsupportedContent = new MockAIContent();
 
-        // Act & Assert
-        var exception = Assert.Throws<NotSupportedException>(unsupportedContent.ToA2APart);
-        Assert.Equal("Unsupported content type: MockAIContent.", exception.Message);
+        // Act
+        var result = unsupportedContent.ToA2APart();
+
+        // Assert
+        Assert.Null(result);
     }
 
     [Fact]
@@ -106,6 +107,37 @@ public sealed class A2AAIContentExtensionsTests
         Assert.Equal("https://example.com/file2.txt", secondFileWithUri.Uri);
     }
 
+    [Fact]
+    public void ToA2AParts_WithMixedSupportedAndUnsupportedContent_IgnoresUnsupportedContent()
+    {
+        // Arrange
+        var contents = new List<AIContent>
+        {
+            new TextContent("First text"),
+            new MockAIContent(), // Unsupported - should be ignored
+            new HostedFileContent("https://example.com/file.txt"),
+            new MockAIContent(), // Unsupported - should be ignored
+            new TextContent("Second text")
+        };
+
+        // Act
+        var result = contents.ToA2AParts();
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.Equal(3, result.Count);
+
+        var firstTextPart = Assert.IsType<TextPart>(result[0]);
+        Assert.Equal("First text", firstTextPart.Text);
+
+        var filePart = Assert.IsType<FilePart>(result[1]);
+        var fileWithUri = Assert.IsType<FileWithUri>(filePart.File);
+        Assert.Equal("https://example.com/file.txt", fileWithUri.Uri);
+
+        var secondTextPart = Assert.IsType<TextPart>(result[2]);
+        Assert.Equal("Second text", secondTextPart.Text);
+    }
+
     // Mock class for testing unsupported scenarios
     private sealed class MockAIContent : AIContent;
 }

dotnet/tests/Microsoft.Agents.AI.A2A.UnitTests/Extensions/A2APartExtensionsTests.cs

@@ -1,6 +1,5 @@
 // Copyright (c) Microsoft. All rights reserved.
 
-using System;
 using System.Collections.Generic;
 using System.Text.Json;
 using A2A;
@@ -80,14 +79,16 @@ public sealed class A2APartExtensionsTests
     }
 
     [Fact]
-    public void ToAIContent_WithCustomPartType_ThrowsNotSupportedException()
+    public void ToAIContent_WithCustomPartType_ReturnsNull()
     {
         // Arrange
         var customPart = new MockPart();
 
-        // Act & Assert
-        var exception = Assert.Throws<NotSupportedException>(customPart.ToAIContent);
-        Assert.Equal("Part type 'MockPart' is not supported.", exception.Message);
+        // Act
+        var result = customPart.ToAIContent();
+
+        // Assert
+        Assert.Null(result);
     }
 
     // Mock class for testing unsupported scenarios

dotnet/tests/Microsoft.Agents.AI.Hosting.A2A.Tests/Converters/MessageConverterTests.cs

@@ -228,13 +228,16 @@ public class MessageConverterTests
     }
 
     [Fact]
-    public void ToA2AMessage_ChatMessageWithUnsupportedContent_ThrowsNotSupportedException()
+    public void ToA2AMessage_ChatMessageWithUnsupportedContent_IgnoresUnsupportedContent()
     {
         var unsupportedContent = new DataContent(new byte[] { 1, 2, 3 }, "image/png");
         var chatMessage = new ChatMessage(ChatRole.User, [unsupportedContent]);
 
-        var exception = Assert.Throws<NotSupportedException>(chatMessage.ToA2AMessage);
-        Assert.Contains("Content type 'DataContent' is not supported", exception.Message);
+        var result = chatMessage.ToA2AMessage();
+
+        // Should create a message but ignore the unsupported content
+        Assert.NotNull(result);
+        Assert.Empty(result.Parts);
     }
 
     [Fact]
@@ -389,7 +392,7 @@ public class MessageConverterTests
     }
 
     [Fact]
-    public void ConvertPartToAIContent_FilePart_ThrowsNotSupportedException()
+    public void ConvertPartToAIContent_FilePart_IgnoresUnsupportedPart()
     {
         var filePart = new FilePart();
         var message = new AgentMessage
@@ -399,12 +402,15 @@ public class MessageConverterTests
             Parts = [filePart]
         };
 
-        var exception = Assert.Throws<NotSupportedException>(() => new List<AgentMessage> { message }.ToChatMessages());
-        Assert.Contains("Part type 'FilePart' is not supported", exception.Message);
+        var result = new List<AgentMessage> { message }.ToChatMessages();
+
+        // Should return empty collection since FilePart is ignored
+        Assert.NotNull(result);
+        Assert.Empty(result);
     }
 
     [Fact]
-    public void ConvertPartToAIContent_DataPart_ThrowsNotSupportedException()
+    public void ConvertPartToAIContent_DataPart_IgnoresUnsupportedPart()
     {
         var dataPart = new DataPart();
         var message = new AgentMessage
@@ -414,8 +420,11 @@ public class MessageConverterTests
             Parts = [dataPart]
         };
 
-        var exception = Assert.Throws<NotSupportedException>(() => new List<AgentMessage> { message }.ToChatMessages());
-        Assert.Contains("Part type 'DataPart' is not supported", exception.Message);
+        var result = new List<AgentMessage> { message }.ToChatMessages();
+
+        // Should return empty collection since DataPart is ignored
+        Assert.NotNull(result);
+        Assert.Empty(result);
     }
 
     [Fact]
@@ -529,4 +538,57 @@ public class MessageConverterTests
         var chatMessage = result.First();
         Assert.Null(chatMessage.AdditionalProperties);
     }
+
+    [Fact]
+    public void ConvertPartToAIContent_MixedPartsWithUnsupported_IgnoresUnsupportedParts()
+    {
+        var message = new AgentMessage
+        {
+            MessageId = "test",
+            Role = MessageRole.User,
+            Parts = [
+                new TextPart { Text = "First part" },
+                new DataPart(), // Unsupported - should be ignored
+                new TextPart { Text = "Second part" },
+                new FilePart() // Unsupported - should be ignored
+            ]
+        };
+
+        var result = new List<AgentMessage> { message }.ToChatMessages();
+
+        Assert.NotNull(result);
+        Assert.Single(result);
+
+        var chatMessage = result.First();
+        Assert.Equal(2, chatMessage.Contents.Count);
+
+        var firstContent = Assert.IsType<TextContent>(chatMessage.Contents[0]);
+        Assert.Equal("First part", firstContent.Text);
+
+        var secondContent = Assert.IsType<TextContent>(chatMessage.Contents[1]);
+        Assert.Equal("Second part", secondContent.Text);
+    }
+
+    [Fact]
+    public void ToA2AMessage_MixedContentWithUnsupported_IgnoresUnsupportedContent()
+    {
+        var contents = new List<AIContent>
+        {
+            new TextContent("First text"),
+            new DataContent(new byte[] { 1, 2, 3 }, "image/png"), // Unsupported - should be ignored
+            new TextContent("Second text")
+        };
+        var chatMessage = new ChatMessage(ChatRole.User, contents);
+
+        var result = chatMessage.ToA2AMessage();
+
+        Assert.NotNull(result);
+        Assert.Equal(2, result.Parts.Count);
+
+        var firstPart = Assert.IsType<TextPart>(result.Parts[0]);
+        Assert.Equal("First text", firstPart.Text);
+
+        var secondPart = Assert.IsType<TextPart>(result.Parts[1]);
+        Assert.Equal("Second text", secondPart.Text);
+    }
 }