Rewrite to TryDetectFormat

src/ImageSharp/Formats/Bmp/BmpImageFormatDetector.cs

@@ -2,6 +2,7 @@
 // Licensed under the Six Labors Split License.
 
 using System.Buffers.Binary;
+using System.Diagnostics.CodeAnalysis;
 
 namespace SixLabors.ImageSharp.Formats.Bmp;
 
@@ -14,9 +15,11 @@ public sealed class BmpImageFormatDetector : IImageFormatDetector
     public int HeaderSize => 2;
 
     /// <inheritdoc/>
-    public IImageFormat? DetectFormat(ReadOnlySpan<byte> header)
+    public bool TryDetectFormat(ReadOnlySpan<byte> header, [NotNullWhen(true)] out IImageFormat? format)
     {
-        return this.IsSupportedFileFormat(header) ? BmpFormat.Instance : null;
+        format = this.IsSupportedFileFormat(header) ? BmpFormat.Instance : null;
+
+        return format != null;
     }
 
     private bool IsSupportedFileFormat(ReadOnlySpan<byte> header)
@@ -24,7 +27,8 @@ public sealed class BmpImageFormatDetector : IImageFormatDetector
         if (header.Length >= this.HeaderSize)
         {
             short fileTypeMarker = BinaryPrimitives.ReadInt16LittleEndian(header);
-            return fileTypeMarker == BmpConstants.TypeMarkers.Bitmap || fileTypeMarker == BmpConstants.TypeMarkers.BitmapArray;
+            return fileTypeMarker == BmpConstants.TypeMarkers.Bitmap ||
+                   fileTypeMarker == BmpConstants.TypeMarkers.BitmapArray;
         }
 
         return false;

src/ImageSharp/Formats/Gif/GifImageFormatDetector.cs

@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace SixLabors.ImageSharp.Formats.Gif;
 
 /// <summary>
@@ -12,9 +14,10 @@ public sealed class GifImageFormatDetector : IImageFormatDetector
     public int HeaderSize => 6;
 
     /// <inheritdoc/>
-    public IImageFormat? DetectFormat(ReadOnlySpan<byte> header)
+    public bool TryDetectFormat(ReadOnlySpan<byte> header, [NotNullWhen(true)] out IImageFormat? format)
     {
-        return this.IsSupportedFileFormat(header) ? GifFormat.Instance : null;
+        format = this.IsSupportedFileFormat(header) ? GifFormat.Instance : null;
+        return format != null;
     }
 
     private bool IsSupportedFileFormat(ReadOnlySpan<byte> header)

src/ImageSharp/Formats/IImageFormatDetector.cs

@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace SixLabors.ImageSharp.Formats;
 
 /// <summary>
@@ -18,6 +20,7 @@ public interface IImageFormatDetector
     /// Detect mimetype
     /// </summary>
     /// <param name="header">The <see cref="T:byte[]"/> containing the file header.</param>
-    /// <returns>returns the mime type of detected otherwise returns null</returns>
-    IImageFormat? DetectFormat(ReadOnlySpan<byte> header);
+    /// <param name="format">The mime type of detected otherwise returns null</param>
+    /// <returns>returns true when format was detected otherwise false.</returns>
+    bool TryDetectFormat(ReadOnlySpan<byte> header, [NotNullWhen(true)] out IImageFormat? format);
 }

src/ImageSharp/Formats/Jpeg/JpegImageFormatDetector.cs

@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace SixLabors.ImageSharp.Formats.Jpeg;
 
 /// <summary>
@@ -12,8 +14,11 @@ public sealed class JpegImageFormatDetector : IImageFormatDetector
     public int HeaderSize => 11;
 
     /// <inheritdoc/>
-    public IImageFormat? DetectFormat(ReadOnlySpan<byte> header)
-        => this.IsSupportedFileFormat(header) ? JpegFormat.Instance : null;
+    public bool TryDetectFormat(ReadOnlySpan<byte> header, [NotNullWhen(true)] out IImageFormat? format)
+    {
+        format = this.IsSupportedFileFormat(header) ? JpegFormat.Instance : null;
+        return format != null;
+    }
 
     private bool IsSupportedFileFormat(ReadOnlySpan<byte> header)
         => header.Length >= this.HeaderSize

src/ImageSharp/Formats/Pbm/PbmImageFormatDetector.cs

@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace SixLabors.ImageSharp.Formats.Pbm;
 
 /// <summary>
@@ -16,7 +18,11 @@ public sealed class PbmImageFormatDetector : IImageFormatDetector
     public int HeaderSize => 2;
 
     /// <inheritdoc/>
-    public IImageFormat? DetectFormat(ReadOnlySpan<byte> header) => IsSupportedFileFormat(header) ? PbmFormat.Instance : null;
+    public bool TryDetectFormat(ReadOnlySpan<byte> header, [NotNullWhen(true)] out IImageFormat? format)
+    {
+        format = IsSupportedFileFormat(header) ? PbmFormat.Instance : null;
+        return format != null;
+    }
 
     private static bool IsSupportedFileFormat(ReadOnlySpan<byte> header)
     {

src/ImageSharp/Formats/Png/PngImageFormatDetector.cs

@@ -2,6 +2,7 @@
 // Licensed under the Six Labors Split License.
 
 using System.Buffers.Binary;
+using System.Diagnostics.CodeAnalysis;
 
 namespace SixLabors.ImageSharp.Formats.Png;
 
@@ -14,9 +15,10 @@ public sealed class PngImageFormatDetector : IImageFormatDetector
     public int HeaderSize => 8;
 
     /// <inheritdoc/>
-    public IImageFormat? DetectFormat(ReadOnlySpan<byte> header)
+    public bool TryDetectFormat(ReadOnlySpan<byte> header, [NotNullWhen(true)] out IImageFormat? format)
     {
-        return this.IsSupportedFileFormat(header) ? PngFormat.Instance : null;
+        format = this.IsSupportedFileFormat(header) ? PngFormat.Instance : null;
+        return format != null;
     }
 
     private bool IsSupportedFileFormat(ReadOnlySpan<byte> header)

src/ImageSharp/Formats/Tga/TgaImageFormatDetector.cs

@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace SixLabors.ImageSharp.Formats.Tga;
 
 /// <summary>
@@ -12,9 +14,10 @@ public sealed class TgaImageFormatDetector : IImageFormatDetector
     public int HeaderSize => 16;
 
     /// <inheritdoc/>
-    public IImageFormat? DetectFormat(ReadOnlySpan<byte> header)
+    public bool TryDetectFormat(ReadOnlySpan<byte> header, [NotNullWhen(true)] out IImageFormat? format)
     {
-        return this.IsSupportedFileFormat(header) ? TgaFormat.Instance : null;
+        format = this.IsSupportedFileFormat(header) ? TgaFormat.Instance : null;
+        return format != null;
     }
 
     private bool IsSupportedFileFormat(ReadOnlySpan<byte> header)

src/ImageSharp/Formats/Tiff/TiffImageFormatDetector.cs

@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace SixLabors.ImageSharp.Formats.Tiff;
 
 /// <summary>
@@ -12,14 +14,10 @@ public sealed class TiffImageFormatDetector : IImageFormatDetector
     public int HeaderSize => 8;
 
     /// <inheritdoc/>
-    public IImageFormat? DetectFormat(ReadOnlySpan<byte> header)
+    public bool TryDetectFormat(ReadOnlySpan<byte> header, [NotNullWhen(true)] out IImageFormat? format)
     {
-        if (this.IsSupportedFileFormat(header))
-        {
-            return TiffFormat.Instance;
-        }
-
-        return null;
+        format = this.IsSupportedFileFormat(header) ? TiffFormat.Instance : null;
+        return format != null;
     }
 
     private bool IsSupportedFileFormat(ReadOnlySpan<byte> header)

src/ImageSharp/Formats/Webp/WebpImageFormatDetector.cs

@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace SixLabors.ImageSharp.Formats.Webp;
 
 /// <summary>
@@ -12,8 +14,11 @@ public sealed class WebpImageFormatDetector : IImageFormatDetector
     public int HeaderSize => 12;
 
     /// <inheritdoc />
-    public IImageFormat? DetectFormat(ReadOnlySpan<byte> header)
-        => this.IsSupportedFileFormat(header) ? WebpFormat.Instance : null;
+    public bool TryDetectFormat(ReadOnlySpan<byte> header, [NotNullWhen(true)] out IImageFormat? format)
+    {
+        format = this.IsSupportedFileFormat(header) ? WebpFormat.Instance : null;
+        return format != null;
+    }
 
     private bool IsSupportedFileFormat(ReadOnlySpan<byte> header)
         => header.Length >= this.HeaderSize && IsRiffContainer(header) && IsWebpFile(header);

src/ImageSharp/Image.Decode.cs

@@ -82,8 +82,7 @@ public abstract partial class Image
         {
             if (formatDetector.HeaderSize <= headerSize)
             {
-                IImageFormat attemptFormat = formatDetector.DetectFormat(headersBuffer);
-                if (attemptFormat != null)
+                if (formatDetector.TryDetectFormat(headersBuffer, out IImageFormat attemptFormat))
                 {
                     format = attemptFormat;
                 }

src/ImageSharp/Image.FromBytes.cs

@@ -39,9 +39,7 @@ public abstract partial class Image
 
         foreach (IImageFormatDetector detector in configuration.ImageFormatsManager.FormatDetectors)
         {
-            IImageFormat? f = detector.DetectFormat(data);
-
-            if (f != null)
+            if (detector.TryDetectFormat(data, out IImageFormat? f))
             {
                 return f;
             }

tests/ImageSharp.Tests/Image/MockImageFormatDetector.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Diagnostics.CodeAnalysis;
 using SixLabors.ImageSharp.Formats;
 
 namespace SixLabors.ImageSharp.Tests;
@@ -19,8 +20,10 @@ public class MockImageFormatDetector : IImageFormatDetector
 
     public int HeaderSize => 1;
 
-    public IImageFormat DetectFormat(ReadOnlySpan<byte> header)
+    public bool TryDetectFormat(ReadOnlySpan<byte> header, [NotNullWhen(true)] out IImageFormat? format)
     {
-        return this.localImageFormatMock;
+        format = this.localImageFormatMock;
+
+        return true;
     }
 }

tests/ImageSharp.Tests/TestFormat.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Numerics;
 using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.PixelFormats;
@@ -174,14 +175,11 @@ public class TestFormat : IImageFormatConfigurationModule, IImageFormat
 
         public int HeaderSize => this.testFormat.HeaderSize;
 
-        public IImageFormat DetectFormat(ReadOnlySpan<byte> header)
+        public bool TryDetectFormat(ReadOnlySpan<byte> header, [NotNullWhen(true)] out IImageFormat? format)
         {
-            if (this.testFormat.IsSupportedFileFormat(header))
-            {
-                return this.testFormat;
-            }
+            format = this.testFormat.IsSupportedFileFormat(header) ? this.testFormat : null;
 
-            return null;
+            return format != null;
         }
 
         public TestHeader(TestFormat testFormat) => this.testFormat = testFormat;