.Net: Add responseMimeType Parameter to GeminiPromptExecutionSettings…

… for Enhanced Output Control. (#9870)

### Motivation and Context

**Why is this change required?**
The absence of the `responseMimeType` property in .NET prevented users
from leveraging structured output formats available in the Gemini API,
causing unintended behavior in scenarios requiring JSON or controlled
output.

**What problem does it solve?**
Adds flexibility for developers by enabling control over MIME type
responses, particularly for JSON data parsing and classification tasks.

**What scenario does it contribute to?**
- Requests with structured response needs, such as JSON objects or
controlled classification outputs.
- Seamless migration and parity with the Python SDK's `responseMimeType`
support.

Fixes #9863 

### Description

This PR adds support for the optional `responseMimeType` parameter to
the `GeminiPromptExecutionSettings` class, allowing for better control
over the output response format in Gemini API calls. This change
addresses the missing ability to specify MIME types for valid JSON,
plain text, or enumerated outputs.

### Contribution Checklist

- [Y] The code builds clean without any errors or warnings
- [Y] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [Y] All unit tests pass, and I have added new tests where possible
- [Y] I didn't break anyone 😄

Co-authored-by: Adit Sheth <[email protected]>

dotnet/src/Connectors/Connectors.Google.UnitTests/Core/Gemini/Clients/GeminiChatGenerationTests.cs

@@ -237,7 +237,8 @@ public async Task ShouldUsePromptExecutionSettingsAsync()
             MaxTokens = 102,
             Temperature = 0.45,
             TopP = 0.6,
-            AudioTimestamp = true
+            AudioTimestamp = true,
+            ResponseMimeType = "application/json"
         };
 
         // Act
@@ -249,6 +250,7 @@ public async Task ShouldUsePromptExecutionSettingsAsync()
         Assert.Equal(executionSettings.MaxTokens, geminiRequest.Configuration!.MaxOutputTokens);
         Assert.Equal(executionSettings.Temperature, geminiRequest.Configuration!.Temperature);
         Assert.Equal(executionSettings.AudioTimestamp, geminiRequest.Configuration!.AudioTimestamp);
+        Assert.Equal(executionSettings.ResponseMimeType, geminiRequest.Configuration!.ResponseMimeType);
         Assert.Equal(executionSettings.TopP, geminiRequest.Configuration!.TopP);
     }
 

dotnet/src/Connectors/Connectors.Google.UnitTests/Core/Gemini/GeminiRequestTests.cs

@@ -24,7 +24,8 @@ public void FromPromptItReturnsWithConfiguration()
             Temperature = 1.5,
             MaxTokens = 10,
             TopP = 0.9,
-            AudioTimestamp = true
+            AudioTimestamp = true,
+            ResponseMimeType = "application/json"
         };
 
         // Act
@@ -35,6 +36,7 @@ public void FromPromptItReturnsWithConfiguration()
         Assert.Equal(executionSettings.Temperature, request.Configuration.Temperature);
         Assert.Equal(executionSettings.MaxTokens, request.Configuration.MaxOutputTokens);
         Assert.Equal(executionSettings.AudioTimestamp, request.Configuration.AudioTimestamp);
+        Assert.Equal(executionSettings.ResponseMimeType, request.Configuration.ResponseMimeType);
         Assert.Equal(executionSettings.TopP, request.Configuration.TopP);
     }
 
@@ -87,7 +89,8 @@ public void FromChatHistoryItReturnsWithConfiguration()
             Temperature = 1.5,
             MaxTokens = 10,
             TopP = 0.9,
-            AudioTimestamp = true
+            AudioTimestamp = true,
+            ResponseMimeType = "application/json"
         };
 
         // Act
@@ -98,6 +101,7 @@ public void FromChatHistoryItReturnsWithConfiguration()
         Assert.Equal(executionSettings.Temperature, request.Configuration.Temperature);
         Assert.Equal(executionSettings.MaxTokens, request.Configuration.MaxOutputTokens);
         Assert.Equal(executionSettings.AudioTimestamp, request.Configuration.AudioTimestamp);
+        Assert.Equal(executionSettings.ResponseMimeType, request.Configuration.ResponseMimeType);
         Assert.Equal(executionSettings.TopP, request.Configuration.TopP);
     }
 

dotnet/src/Connectors/Connectors.Google.UnitTests/GeminiPromptExecutionSettingsTests.cs

@@ -27,6 +27,7 @@ public void ItCreatesGeminiExecutionSettingsWithCorrectDefaults()
         Assert.Null(executionSettings.CandidateCount);
         Assert.Null(executionSettings.SafetySettings);
         Assert.Null(executionSettings.AudioTimestamp);
+        Assert.Null(executionSettings.ResponseMimeType);
         Assert.Equal(GeminiPromptExecutionSettings.DefaultTextMaxTokens, executionSettings.MaxTokens);
     }
 
@@ -41,6 +42,7 @@ public void ItUsesExistingGeminiExecutionSettings()
             TopK = 20,
             CandidateCount = 3,
             AudioTimestamp = true,
+            ResponseMimeType = "application/json",
             StopSequences = ["foo", "bar"],
             MaxTokens = 128,
             SafetySettings =
@@ -67,7 +69,8 @@ public void ItCreatesGeminiExecutionSettingsFromExtensionDataSnakeCase()
             {
                 { "max_tokens", 1000 },
                 { "temperature", 0 },
-                { "audio_timestamp", true }
+                { "audio_timestamp", true },
+                { "response_mimetype", "application/json" }
             }
         };
 

dotnet/src/Connectors/Connectors.Google/Core/Gemini/Models/GeminiRequest.cs

@@ -248,7 +248,8 @@ private static void AddConfiguration(GeminiPromptExecutionSettings executionSett
             MaxOutputTokens = executionSettings.MaxTokens,
             StopSequences = executionSettings.StopSequences,
             CandidateCount = executionSettings.CandidateCount,
-            AudioTimestamp = executionSettings.AudioTimestamp
+            AudioTimestamp = executionSettings.AudioTimestamp,
+            ResponseMimeType = executionSettings.ResponseMimeType
         };
     }
 
@@ -287,5 +288,9 @@ internal sealed class ConfigurationElement
         [JsonPropertyName("audioTimestamp")]
         [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
         public bool? AudioTimestamp { get; set; }
+
+        [JsonPropertyName("responseMimeType")]
+        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+        public string? ResponseMimeType { get; set; }
     }
 }

dotnet/src/Connectors/Connectors.Google/GeminiPromptExecutionSettings.cs

@@ -24,6 +24,7 @@ public sealed class GeminiPromptExecutionSettings : PromptExecutionSettings
     private int? _candidateCount;
     private IList<string>? _stopSequences;
     private bool? _audioTimestamp;
+    private string? _responseMimeType;
     private IList<GeminiSafetySetting>? _safetySettings;
     private GeminiToolCallBehavior? _toolCallBehavior;
 
@@ -187,6 +188,24 @@ public bool? AudioTimestamp
         }
     }
 
+    /// <summary>
+    /// The output response MIME type of the generated candidate text.
+    /// The following MIME types are supported:
+    /// 1. application/json: JSON response in the candidates.
+    /// 2. text/plain (default): Plain text output.
+    /// 3. text/x.enum: For classification tasks, output an enum value as defined in the response schema.
+    /// </summary>
+    [JsonPropertyName("response_mimetype")]
+    public string? ResponseMimeType
+    {
+        get => this._responseMimeType;
+        set
+        {
+            this.ThrowIfFrozen();
+            this._responseMimeType = value;
+        }
+    }
+
     /// <inheritdoc />
     public override void Freeze()
     {
@@ -223,7 +242,8 @@ public override PromptExecutionSettings Clone()
             StopSequences = this.StopSequences is not null ? new List<string>(this.StopSequences) : null,
             SafetySettings = this.SafetySettings?.Select(setting => new GeminiSafetySetting(setting)).ToList(),
             ToolCallBehavior = this.ToolCallBehavior?.Clone(),
-            AudioTimestamp = this.AudioTimestamp
+            AudioTimestamp = this.AudioTimestamp,
+            ResponseMimeType = this.ResponseMimeType
         };
     }