Merge pull request #2770 from SixLabors/af/backport-2759-2.1.x

Backport 2759 to 2.1.x

Author: JimBobSquarePants

src/ImageSharp/Formats/Gif/GifDecoder.cs

@@ -23,6 +23,11 @@ public sealed class GifDecoder : IImageDecoder, IGifDecoderOptions, IImageInfoDe
         /// </summary>
         public FrameDecodingMode DecodingMode { get; set; } = FrameDecodingMode.All;
 
+        /// <summary>
+        /// Gets or sets the maximum number of gif frames.
+        /// </summary>
+        public uint MaxFrames { get; set; } = uint.MaxValue;
+
         /// <inheritdoc/>
         public Image<TPixel> Decode<TPixel>(Configuration configuration, Stream stream, CancellationToken cancellationToken)
             where TPixel : unmanaged, IPixel<TPixel>

src/ImageSharp/Formats/Gif/GifDecoderCore.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 
 namespace SixLabors.ImageSharp.Formats.Gif
@@ -24,5 +25,11 @@ public static void ThrowInvalidImageContentException(string errorMessage)
         /// if no inner exception is specified.</param>
         [MethodImpl(InliningOptions.ColdPath)]
         public static void ThrowInvalidImageContentException(string errorMessage, Exception innerException) => throw new InvalidImageContentException(errorMessage, innerException);
+
+        [MethodImpl(InliningOptions.ColdPath)]
+        public static void ThrowNoHeader() => throw new InvalidImageContentException("Gif image does not contain a Logical Screen Descriptor.");
+
+        [MethodImpl(InliningOptions.ColdPath)]
+        public static void ThrowNoData() => throw new InvalidImageContentException("Unable to read Gif image data");
     }
 }

src/ImageSharp/Formats/Gif/GifThrowHelper.cs

@@ -19,5 +19,10 @@ internal interface IGifDecoderOptions
         /// Gets the decoding mode for multi-frame images.
         /// </summary>
         FrameDecodingMode DecodingMode { get; }
+
+        /// <summary>
+        /// Gets or sets the maximum number of gif frames.
+        /// </summary>
+        uint MaxFrames { get; set; }
     }
 }