Add mimeType validation to ImageContentBlock.FromBytes and AudioContentBlock.FromBytes

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

Author: Copilot

src/ModelContextProtocol.Core/Protocol/ContentBlock.cs

@@ -391,9 +391,12 @@ public sealed class ImageContentBlock : ContentBlock
     /// <remarks>
     /// This method stores the provided bytes as <see cref="DecodedData"/> and encodes them to base64 UTF-8 bytes for <see cref="Data"/>.
     /// </remarks>
-    /// <exception cref="InvalidOperationException"></exception>
+    /// <exception cref="ArgumentNullException"><paramref name="mimeType"/> is <see langword="null"/>.</exception>
+    /// <exception cref="ArgumentException"><paramref name="mimeType"/> is empty or composed entirely of whitespace.</exception>
     public static ImageContentBlock FromBytes(ReadOnlyMemory<byte> bytes, string mimeType)
     {
+        Throw.IfNullOrWhiteSpace(mimeType);
+
         ReadOnlyMemory<byte> data = EncodingUtilities.EncodeToBase64Utf8(bytes);
 
         return new()
@@ -476,9 +479,12 @@ public sealed class AudioContentBlock : ContentBlock
     /// <remarks>
     /// This method stores the provided bytes as <see cref="DecodedData"/> and encodes them to base64 UTF-8 bytes for <see cref="Data"/>.
     /// </remarks>
-    /// <exception cref="InvalidOperationException"></exception>
+    /// <exception cref="ArgumentNullException"><paramref name="mimeType"/> is <see langword="null"/>.</exception>
+    /// <exception cref="ArgumentException"><paramref name="mimeType"/> is empty or composed entirely of whitespace.</exception>
     public static AudioContentBlock FromBytes(ReadOnlyMemory<byte> bytes, string mimeType)
     {
+        Throw.IfNullOrWhiteSpace(mimeType);
+
         ReadOnlyMemory<byte> data = EncodingUtilities.EncodeToBase64Utf8(bytes);
 
         return new()

tests/ModelContextProtocol.Tests/Protocol/ContentBlockTests.cs

@@ -225,4 +225,22 @@ public void ToolUseContentBlock_SerializationRoundTrip()
         Assert.Equal("Paris", result.Input.GetProperty("city").GetString());
         Assert.Equal("metric", result.Input.GetProperty("units").GetString());
     }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData(" ")]
+    public void ImageContentBlock_FromBytes_ThrowsForNullOrWhiteSpaceMimeType(string? mimeType)
+    {
+        Assert.ThrowsAny<ArgumentException>(() => ImageContentBlock.FromBytes((byte[])[1, 2, 3], mimeType!));
+    }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData(" ")]
+    public void AudioContentBlock_FromBytes_ThrowsForNullOrWhiteSpaceMimeType(string? mimeType)
+    {
+        Assert.ThrowsAny<ArgumentException>(() => AudioContentBlock.FromBytes((byte[])[1, 2, 3], mimeType!));
+    }
 }