.Net: Fix Labels Implementation in Vertex AI to Use Dictionary<string, string> (#12636)

### Description
This pull request addresses issue #12633 by updating the Labels property
in the `GeminiPromptExecutionSettings` and `GeminiRequest` classes to
use a `Dictionary<string, string>` instead of a string. This change
aligns the implementation with the Vertex AI API requirements, which
expect labels to be sent as key-value pairs in JSON format.

Fixes #12633

---------

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

Author: 3 people

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

@@ -528,14 +528,14 @@ public void LabelsFromPromptReturnsAsExpected()
         var prompt = "prompt-example";
         var executionSettings = new GeminiPromptExecutionSettings
         {
-            Labels = "Key1:Value1"
+            Labels = new Dictionary<string, string> { { "key1", "value1" }, { "key2", "value2" } }
         };
 
         // Act
         var request = GeminiRequest.FromPromptAndExecutionSettings(prompt, executionSettings);
 
         // Assert
-        Assert.NotNull(request.Configuration);
+        Assert.NotNull(request.Labels);
         Assert.Equal(executionSettings.Labels, request.Labels);
     }
 
@@ -569,7 +569,7 @@ public void LabelsFromChatHistoryReturnsAsExpected()
         chatHistory.AddUserMessage("user-message2");
         var executionSettings = new GeminiPromptExecutionSettings
         {
-            Labels = "Key1:Value1"
+            Labels = new Dictionary<string, string> { { "key1", "value1" }, { "key2", "value2" } }
         };
 
         // Act

dotnet/src/Connectors/Connectors.Google.UnitTests/Services/GoogleAIGeminiChatCompletionServiceTests.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 using System;
+using System.Collections.Generic;
 using System.IO;
 using System.Net.Http;
 using System.Text;
@@ -69,15 +70,13 @@ public async Task RequestCachedContentWorksCorrectlyAsync(string? cachedContent)
         }
     }
 
-    [Theory]
-    [InlineData(null)]
-    [InlineData("key:value")]
-    [InlineData("")]
-    public async Task RequestLabelsWorksCorrectlyAsync(string? labels)
+    [Fact]
+    public async Task RequestLabelsWorksCorrectlyAsync()
     {
         // Arrange
         string model = "fake-model";
         var sut = new GoogleAIGeminiChatCompletionService(model, "key", httpClient: this._httpClient);
+        var labels = new Dictionary<string, string> { { "key1", "value1" }, { "key2", "value2" } };
 
         // Act
         var result = await sut.GetChatMessageContentAsync("my prompt", new GeminiPromptExecutionSettings { Labels = labels });
@@ -87,19 +86,28 @@ public async Task RequestLabelsWorksCorrectlyAsync(string? labels)
         Assert.NotNull(this._messageHandlerStub.RequestContent);
 
         var requestBody = UTF8Encoding.UTF8.GetString(this._messageHandlerStub.RequestContent);
-        if (labels is not null)
-        {
-            Assert.Contains($"\"labels\":\"{labels}\"", requestBody);
-        }
-        else
-        {
-            // Then no quality is provided, it should not be included in the request body
-            Assert.DoesNotContain("labels", requestBody);
-        }
+        Assert.Contains("\"labels\":{\"key1\":\"value1\",\"key2\":\"value2\"}", requestBody);
+    }
+
+    [Fact]
+    public async Task RequestLabelsNullWorksCorrectlyAsync()
+    {
+        // Arrange
+        string model = "fake-model";
+        var sut = new GoogleAIGeminiChatCompletionService(model, "key", httpClient: this._httpClient);
+
+        // Act
+        var result = await sut.GetChatMessageContentAsync("my prompt", new GeminiPromptExecutionSettings { Labels = null });
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.NotNull(this._messageHandlerStub.RequestContent);
+
+        var requestBody = UTF8Encoding.UTF8.GetString(this._messageHandlerStub.RequestContent);
+        Assert.DoesNotContain("labels", requestBody);
     }
 
     [Theory]
-    [InlineData(null, false)]
     [InlineData(0, true)]
     [InlineData(500, true)]
     [InlineData(2048, true)]

dotnet/src/Connectors/Connectors.Google.UnitTests/Services/VertexAIGeminiChatCompletionServiceTests.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 using System;
+using System.Collections.Generic;
 using System.IO;
 using System.Net.Http;
 using System.Text;
@@ -80,15 +81,13 @@ public async Task RequestCachedContentWorksCorrectlyAsync(string? cachedContent)
         }
     }
 
-    [Theory]
-    [InlineData(null)]
-    [InlineData("key:value")]
-    [InlineData("")]
-    public async Task RequestLabelsWorksCorrectlyAsync(string? labels)
+    [Fact]
+    public async Task RequestLabelsWorksCorrectlyAsync()
     {
         // Arrange
         string model = "fake-model";
-        var sut = new GoogleAIGeminiChatCompletionService(model, "key", httpClient: this._httpClient);
+        var sut = new VertexAIGeminiChatCompletionService(model, () => new ValueTask<string>("key"), "location", "project", httpClient: this._httpClient);
+        var labels = new Dictionary<string, string> { { "key1", "value1" }, { "key2", "value2" } };
 
         // Act
         var result = await sut.GetChatMessageContentAsync("my prompt", new GeminiPromptExecutionSettings { Labels = labels });
@@ -98,15 +97,25 @@ public async Task RequestLabelsWorksCorrectlyAsync(string? labels)
         Assert.NotNull(this._messageHandlerStub.RequestContent);
 
         var requestBody = UTF8Encoding.UTF8.GetString(this._messageHandlerStub.RequestContent);
-        if (labels is not null)
-        {
-            Assert.Contains($"\"labels\":\"{labels}\"", requestBody);
-        }
-        else
-        {
-            // Then no quality is provided, it should not be included in the request body
-            Assert.DoesNotContain("labels", requestBody);
-        }
+        Assert.Contains("\"labels\":{\"key1\":\"value1\",\"key2\":\"value2\"}", requestBody);
+    }
+
+    [Fact]
+    public async Task RequestLabelsNullWorksCorrectlyAsync()
+    {
+        // Arrange
+        string model = "fake-model";
+        var sut = new VertexAIGeminiChatCompletionService(model, () => new ValueTask<string>("key"), "location", "project", httpClient: this._httpClient);
+
+        // Act
+        var result = await sut.GetChatMessageContentAsync("my prompt", new GeminiPromptExecutionSettings { Labels = null });
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.NotNull(this._messageHandlerStub.RequestContent);
+
+        var requestBody = UTF8Encoding.UTF8.GetString(this._messageHandlerStub.RequestContent);
+        Assert.DoesNotContain("labels", requestBody);
     }
 
     [Theory]

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

@@ -48,7 +48,7 @@ internal sealed class GeminiRequest
 
     [JsonPropertyName("labels")]
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
-    public string? Labels { get; set; }
+    public IDictionary<string, string>? Labels { get; set; }
 
     public void AddFunction(GeminiFunction function)
     {
@@ -450,7 +450,12 @@ private static void AddSafetySettings(GeminiPromptExecutionSettings executionSet
     private static void AddAdditionalBodyFields(GeminiPromptExecutionSettings executionSettings, GeminiRequest request)
     {
         request.CachedContent = executionSettings.CachedContent;
-        request.Labels = executionSettings.Labels;
+
+        if (executionSettings.Labels is not null)
+        {
+            request.Labels = executionSettings.Labels;
+        }
+
         if (executionSettings.ThinkingConfig is not null)
         {
             request.Configuration ??= new ConfigurationElement();

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

@@ -28,7 +28,7 @@ public sealed class GeminiPromptExecutionSettings : PromptExecutionSettings
     private string? _responseMimeType;
     private object? _responseSchema;
     private string? _cachedContent;
-    private string? _labels;
+    private IDictionary<string, string>? _labels;
     private IList<GeminiSafetySetting>? _safetySettings;
     private GeminiToolCallBehavior? _toolCallBehavior;
     private GeminiThinkingConfig? _thinkingConfig;
@@ -147,9 +147,12 @@ public IList<GeminiSafetySetting>? SafetySettings
     /// Gets or sets the labels.
     /// </summary>
     /// <value>
-    /// Metadata that can be added to the API call in the format of key-value pairs.
+    /// The labels with user-defined metadata for the request. It is used for billing and reporting only.
+    /// label keys and values can be no longer than 63 characters (Unicode codepoints) and can only contain lowercase letters, numeric characters, underscores, and dashes. International characters are allowed. label values are optional. label keys must start with a letter.
     /// </value>
-    public string? Labels
+    [JsonPropertyName("labels")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public IDictionary<string, string>? Labels
     {
         get => this._labels;
         set

dotnet/src/IntegrationTests/Connectors/Google/Gemini/GeminiChatCompletionTests.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 using System;
+using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using System.Net.Http;
@@ -600,4 +601,34 @@ public async Task GoogleAIChatReturnsResponseWorksWithThinkingBudgetAsync()
         Assert.NotNull(streamResponses[0].Content);
         Assert.NotNull(responses[0].Content);
     }
+
+    [RetryTheory(Skip = "This test is for manual verification.")]
+    [InlineData(ServiceType.VertexAI)] // GoogleAI does not support labels yet
+    public async Task GoogleAIChatReturnsResponseWorksWithLabelsAsync(ServiceType serviceType)
+    {
+        // Arrange
+        ChatHistory chatHistory = [];
+        chatHistory.AddUserMessage("Hello, I'm Brandon, how are you?");
+        chatHistory.AddAssistantMessage("I'm doing well, thanks for asking.");
+        chatHistory.AddUserMessage("Call me by my name and expand this abbreviation: LLM");
+
+        var sut = this.GetChatService(serviceType);
+
+        var settings = new GeminiPromptExecutionSettings
+        {
+            Labels = new Dictionary<string, string>()
+            {
+                ["label1"] = "value1",
+                ["label2"] = "value2"
+            }
+        };
+
+        // Act
+        var streamResponses = await sut.GetStreamingChatMessageContentsAsync(chatHistory, settings).ToListAsync();
+        var responses = await sut.GetChatMessageContentsAsync(chatHistory, settings);
+
+        // Assert
+        Assert.NotNull(streamResponses[0].Content);
+        Assert.NotNull(responses[0].Content);
+    }
 }