Add TextContent.MediaType

Author: stephentoub

src/Libraries/Microsoft.Extensions.AI.Abstractions/Contents/TextContent.cs

@@ -1,8 +1,11 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
+using System.Text.Json.Serialization;
+using Microsoft.Shared.Diagnostics;
 
 namespace Microsoft.Extensions.AI;
 
@@ -13,6 +16,7 @@ namespace Microsoft.Extensions.AI;
 public sealed class TextContent : AIContent
 {
     private string? _text;
+    private string? _mediaType;
 
     /// <summary>
     /// Initializes a new instance of the <see cref="TextContent"/> class.
@@ -33,6 +37,27 @@ public string Text
         set => _text = value;
     }
 
+    /// <summary>Gets or sets the text media type (also known as MIME type) of the content.</summary>
+    [JsonPropertyOrder(1)]
+    public string? MediaType
+    {
+        get => _mediaType;
+        set
+        {
+            if (value is not null)
+            {
+                if (!DataUriParser.IsValidMediaType(value.AsSpan(), ref value))
+                {
+                    Throw.ArgumentException(nameof(value), "Invalid media type.");
+                }
+
+                // Don't require a "text/" prefix in order to allow for types like "application/typescript".
+            }
+
+            _mediaType = value;
+        }
+    }
+
     /// <inheritdoc/>
     public override string ToString() => Text;
 

test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/ChatCompletion/ChatResponseUpdateTests.cs

@@ -116,7 +116,7 @@ public void JsonSerialization_Roundtrips()
                 new TextContent("text-1"),
                 new DataContent("http://localhost/image"),
                 new FunctionCallContent("callId1", "fc1"),
-                new DataContent("data"u8.ToArray()),
+                new DataContent("data"u8.ToArray(), "text/plain"),
                 new TextContent("text-2"),
             ],
             RawRepresentation = new object(),

test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/Contents/TextContentTests.cs

@@ -47,4 +47,19 @@ public void Constructor_PropsRoundtrip()
         Assert.Equal(string.Empty, c.Text);
         Assert.Equal(string.Empty, c.ToString());
     }
+
+    [Fact]
+    public void MediaType_ValidValue_Roundtrips()
+    {
+        TextContent c = new("text");
+        Assert.Null(c.MediaType);
+
+        foreach (string? mediaType in new[] { null, "text/plain", "application/typescript", "text/html", null })
+        {
+            c.MediaType = mediaType;
+            Assert.Equal(mediaType, c.MediaType);
+        }
+
+        Assert.Equal("text", c.Text);
+    }
 }