Address PR feedback: improve DebuggerDisplay implementations

- Use proper base64 decoding with Base64.IsValid on NET or Convert.FromBase64String
- Add helper method GetBase64LengthDisplay for consistent base64 length display
- Use string literals in DebuggerDisplay attributes where possible
- Put URIs in quotes for better readability
- Use Text ?? "" and Uri ?? "" for null safety in ToString and DebuggerDisplay

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

Author: Copilot

src/ModelContextProtocol.Core/Protocol/BlobResourceContents.cs

@@ -35,10 +35,30 @@ private string DebuggerDisplay
     {
         get
         {
-            // Decode base64 to get actual byte length
-            int byteLength = Blob.Length * 3 / 4;
+            string lengthDisplay;
+            try
+            {
+#if NET
+                if (System.Buffers.Text.Base64.IsValid(System.Text.Encoding.UTF8.GetBytes(Blob), out int decodedLength))
+                {
+                    lengthDisplay = $"{decodedLength} bytes";
+                }
+                else
+                {
+                    lengthDisplay = "invalid base64";
+                }
+#else
+                byte[] decoded = Convert.FromBase64String(Blob);
+                lengthDisplay = $"{decoded.Length} bytes";
+#endif
+            }
+            catch
+            {
+                lengthDisplay = "invalid base64";
+            }
+
             string mimeInfo = MimeType is not null ? $", MimeType = {MimeType}" : "";
-            return $"Uri = {Uri}{mimeInfo}, Length = {byteLength} bytes";
+            return $"Uri = \"{Uri}\"{mimeInfo}, Length = {lengthDisplay}";
         }
     }
 }

src/ModelContextProtocol.Core/Protocol/ContentBlock.cs

@@ -32,6 +32,30 @@ private protected ContentBlock()
     {
     }
 
+    /// <summary>
+    /// Helper method to get the decoded length of base64 data for debugger display.
+    /// </summary>
+    private protected static string GetBase64LengthDisplay(string base64Data)
+    {
+        try
+        {
+#if NET
+            if (System.Buffers.Text.Base64.IsValid(System.Text.Encoding.UTF8.GetBytes(base64Data), out int decodedLength))
+            {
+                return $"{decodedLength} bytes";
+            }
+            return "invalid base64";
+#else
+            byte[] decoded = Convert.FromBase64String(base64Data);
+            return $"{decoded.Length} bytes";
+#endif
+        }
+        catch
+        {
+            return "invalid base64";
+        }
+    }
+
     /// <summary>
     /// When overridden in a derived class, gets the type of content.
     /// </summary>
@@ -356,7 +380,7 @@ public override void Write(Utf8JsonWriter writer, ContentBlock value, JsonSerial
 }
 
 /// <summary>Represents text provided to or from an LLM.</summary>
-[DebuggerDisplay("{DebuggerDisplay,nq}")]
+[DebuggerDisplay("Text = \\\"{Text}\\\"")]
 public sealed class TextContentBlock : ContentBlock
 {
     /// <inheritdoc/>
@@ -369,10 +393,7 @@ public sealed class TextContentBlock : ContentBlock
     public required string Text { get; set; }
 
     /// <inheritdoc/>
-    public override string ToString() => Text;
-
-    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
-    private string DebuggerDisplay => $"Text = \"{Text}\"";
+    public override string ToString() => Text ?? "";
 }
 
 /// <summary>Represents an image provided to or from an LLM.</summary>
@@ -398,15 +419,7 @@ public sealed class ImageContentBlock : ContentBlock
     public required string MimeType { get; set; }
 
     [DebuggerBrowsable(DebuggerBrowsableState.Never)]
-    private string DebuggerDisplay
-    {
-        get
-        {
-            // Decode base64 to get actual byte length
-            int byteLength = Data.Length * 3 / 4;
-            return $"MimeType = {MimeType}, Length = {byteLength} bytes";
-        }
-    }
+    private string DebuggerDisplay => $"MimeType = {MimeType}, Length = {GetBase64LengthDisplay(Data)}";
 }
 
 /// <summary>Represents audio provided to or from an LLM.</summary>
@@ -432,15 +445,7 @@ public sealed class AudioContentBlock : ContentBlock
     public required string MimeType { get; set; }
 
     [DebuggerBrowsable(DebuggerBrowsableState.Never)]
-    private string DebuggerDisplay
-    {
-        get
-        {
-            // Decode base64 to get actual byte length
-            int byteLength = Data.Length * 3 / 4;
-            return $"MimeType = {MimeType}, Length = {byteLength} bytes";
-        }
-    }
+    private string DebuggerDisplay => $"MimeType = {MimeType}, Length = {GetBase64LengthDisplay(Data)}";
 }
 
 /// <summary>Represents the contents of a resource, embedded into a prompt or tool call result.</summary>
@@ -467,14 +472,14 @@ public sealed class EmbeddedResourceBlock : ContentBlock
     public required ResourceContents Resource { get; set; }
 
     [DebuggerBrowsable(DebuggerBrowsableState.Never)]
-    private string DebuggerDisplay => $"Uri = {Resource.Uri}";
+    private string DebuggerDisplay => $"Uri = \"{Resource.Uri}\"";
 }
 
 /// <summary>Represents a resource that the server is capable of reading, included in a prompt or tool call result.</summary>
 /// <remarks>
 /// Resource links returned by tools are not guaranteed to appear in the results of `resources/list` requests.
 /// </remarks>
-[DebuggerDisplay("{DebuggerDisplay,nq}")]
+[DebuggerDisplay("Name = {Name}, Uri = \\\"{Uri}\\\"")]
 public sealed class ResourceLinkBlock : ContentBlock
 {
     /// <inheritdoc/>
@@ -536,9 +541,6 @@ public sealed class ResourceLinkBlock : ContentBlock
     /// </remarks>
     [JsonPropertyName("size")]
     public long? Size { get; set; }
-
-    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
-    private string DebuggerDisplay => $"Name = {Name}, Uri = {Uri}";
 }
 
 /// <summary>Represents a request from the assistant to call a tool.</summary>

src/ModelContextProtocol.Core/Protocol/Icon.cs

@@ -91,7 +91,7 @@ private string DebuggerDisplay
         get
         {
             string mimeInfo = MimeType is not null ? $", MimeType = {MimeType}" : "";
-            return $"Source = {Source}{mimeInfo}";
+            return $"Source = \"{Source}\"{mimeInfo}";
         }
     }
 }

src/ModelContextProtocol.Core/Protocol/TextResourceContents.cs

@@ -20,7 +20,7 @@ namespace ModelContextProtocol.Protocol;
 /// See the <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">schema</see> for more details.
 /// </para>
 /// </remarks>
-[DebuggerDisplay("Uri = {Uri}, Text = \\\"{Text}\\\"")]
+[DebuggerDisplay("Uri = \\\"{Uri}\\\", Text = \\\"{Text}\\\"")]
 public sealed class TextResourceContents : ResourceContents
 {
     /// <summary>
@@ -30,5 +30,5 @@ public sealed class TextResourceContents : ResourceContents
     public required string Text { get; set; }
 
     /// <inheritdoc/>
-    public override string ToString() => Text;
+    public override string ToString() => Text ?? "";
 }