Added file-type detection

Author: linkdotnet

src/LinkDotNet.Blog.Web/Features/Components/PreviewImage.razor

@@ -1,11 +1,12 @@
+@using Microsoft.AspNetCore.StaticFiles
 @if (string.IsNullOrEmpty(PreviewImageUrlFallback))
 {
     <img src="@PreviewImageUrl" alt="Preview image blogpost" loading="@LazyLoadTag"/>
 }
 else
 {
     <picture>
-        <source srcset="@PreviewImageUrl" />
+        <source srcset="@PreviewImageUrl" type="@GetMimeType()"/>
         <img src="@PreviewImageUrlFallback" alt="Preview image blogpost" loading="@LazyLoadTag"/>
     </picture>
 }
@@ -21,4 +22,20 @@ else
     public bool LazyLoadImage { get; set; }
 
     private string LazyLoadTag => LazyLoadImage ? "lazy" : "eager";
+
+    private static readonly FileExtensionContentTypeProvider Provider = new();
+
+    static PreviewImage()
+    {
+        if (!Provider.Mappings.Keys.Contains(".avif"))
+        {
+            Provider.Mappings.Add(".avif", "image/avif");
+        }
+    }
+
+    private string GetMimeType()
+    {
+        Provider.TryGetContentType(PreviewImageUrl, out var contentType);
+        return contentType;
+    }
 }

tests/LinkDotNet.Blog.UnitTests/Web/Features/Components/PreviewImageTests.cs

@@ -68,4 +68,20 @@ public void ShouldSetLazyLoadBehaviorNoFallback(bool lazyLoad, string expectedLa
 
         image.Attributes.FirstOrDefault(a => a.Name == "loading").Value.Should().Be(expectedLazy);
     }
+
+    [Theory]
+    [InlineData("http://localhost/image.png", "image/png")]
+    [InlineData("http://localhost/image.webp", "image/webp")]
+    [InlineData("http://localhost/image.avif", "image/avif")]
+    public void ShouldDetectFileTypes(string fileName, string mimeType)
+    {
+        var cut = RenderComponent<PreviewImage>(ps => ps
+            .Add(p => p.PreviewImageUrl, fileName)
+            .Add(p => p.PreviewImageUrlFallback, "not empty"));
+
+        var picture = cut.Find("picture");
+
+        var source = picture.Children[0] as IHtmlSourceElement;
+        source.Type.Should().Be(mimeType);
+    }
 }