Document via tests that image content type is jpeg (#48)

Input content type is omitted.

Author: kzu

src/xAI.Tests/ImageGeneratorTests.cs

@@ -17,7 +17,6 @@ public async Task GenerateImage_WithPrompt_ReturnsImageContent()
         var options = new ImageGenerationOptions
         {
             ResponseFormat = ImageGenerationResponseFormat.Uri,
-            Count = 1
         };
 
         var response = await imageGenerator.GenerateAsync(request, options);
@@ -44,6 +43,7 @@ public async Task GenerateImage_WithEditsToPreviousImage()
         var request = new ImageGenerationRequest("A cat sitting on a tree branch");
         var options = new ImageGenerationOptions
         {
+            MediaType = "image/png",
             ResponseFormat = ImageGenerationResponseFormat.Uri,
             Count = 1
         };
@@ -54,6 +54,8 @@ public async Task GenerateImage_WithEditsToPreviousImage()
         Assert.NotEmpty(response.Contents);
         Assert.Single(response.Contents);
         var image = Assert.IsType<UriContent>(response.Contents.First());
+        // media type in options is ignored and you always get the same jpg
+        Assert.Equal("image/jpg", image.MediaType);
         output.WriteLine($"Generated image URL: {image.Uri}");
 
         var edit = await imageGenerator.GenerateAsync(new ImageGenerationRequest("Edit provided image by adding a batman mask", [image]), options);
@@ -62,6 +64,8 @@ public async Task GenerateImage_WithEditsToPreviousImage()
         Assert.NotEmpty(edit.Contents);
         Assert.Single(edit.Contents);
         image = Assert.IsType<UriContent>(edit.Contents.First());
+        // media type in options is ignored and you always get the same jpg
+        Assert.Equal("image/jpg", image.MediaType);
 
         output.WriteLine($"Edited image URL: {image.Uri}");
     }

src/xAI/GrokImageGenerator.cs

@@ -16,7 +16,6 @@ sealed class GrokImageGenerator : IImageGenerator
     readonly ImageGeneratorMetadata metadata;
     readonly ImageClient imageClient;
     readonly string defaultModelId;
-    readonly GrokClientOptions clientOptions;
 
     internal GrokImageGenerator(GrpcChannel channel, GrokClientOptions clientOptions, string defaultModelId)
         : this(new ImageClient(channel), clientOptions, defaultModelId)
@@ -32,7 +31,6 @@ internal GrokImageGenerator(ImageClient imageClient, string defaultModelId)
     GrokImageGenerator(ImageClient imageClient, GrokClientOptions clientOptions, string defaultModelId)
     {
         this.imageClient = imageClient;
-        this.clientOptions = clientOptions;
         this.defaultModelId = defaultModelId;
         metadata = new ImageGeneratorMetadata("xai", clientOptions.Endpoint, defaultModelId);
     }
@@ -63,9 +61,8 @@ public async Task<ImageGenerationResponse> GenerateAsync(
         }
 
         // Handle image editing if original images are provided
-        if (request.OriginalImages is not null && request.OriginalImages.Any())
+        if (request.OriginalImages?.FirstOrDefault() is { } originalImage)
         {
-            var originalImage = request.OriginalImages.FirstOrDefault();
             if (originalImage is DataContent dataContent)
             {
                 var imageUrl = dataContent.Uri?.ToString();
@@ -91,7 +88,7 @@ public async Task<ImageGenerationResponse> GenerateAsync(
 
         var response = await imageClient.GenerateImageAsync(protocolRequest, cancellationToken: cancellationToken).ConfigureAwait(false);
 
-        return ToImageGenerationResponse(response, options?.MediaType);
+        return ToImageGenerationResponse(response);
     }
 
     /// <inheritdoc />
@@ -103,18 +100,14 @@ public async Task<ImageGenerationResponse> GenerateAsync(
     };
 
     /// <inheritdoc />
-    void IDisposable.Dispose()
-    {
-        // Nothing to dispose. Implementation required for the IImageGenerator interface.
-    }
+    void IDisposable.Dispose() { }
 
     /// <summary>
     /// Converts an xAI <see cref="ImageResponse"/> to a <see cref="ImageGenerationResponse"/>.
     /// </summary>
-    static ImageGenerationResponse ToImageGenerationResponse(ImageResponse response, string? mediaType)
+    static ImageGenerationResponse ToImageGenerationResponse(ImageResponse response)
     {
         var contents = new List<AIContent>();
-        var contentType = mediaType ?? DefaultOutputContentType; // xAI returns JPG by default
 
         foreach (var image in response.Images)
         {
@@ -123,12 +116,12 @@ static ImageGenerationResponse ToImageGenerationResponse(ImageResponse response,
                 case GeneratedImage.ImageOneofCase.Base64:
                     {
                         var imageBytes = Convert.FromBase64String(image.Base64);
-                        contents.Add(new DataContent(imageBytes, contentType));
+                        contents.Add(new DataContent(imageBytes, DefaultOutputContentType));
                         break;
                     }
                 case GeneratedImage.ImageOneofCase.Url:
                     {
-                        contents.Add(new UriContent(new Uri(image.Url), contentType));
+                        contents.Add(new UriContent(new Uri(image.Url), DefaultOutputContentType));
                         break;
                     }
                 default: