implement JpegEncoder cancellation

src/ImageSharp/Formats/Jpeg/JpegEncoderCore.cs

@@ -201,6 +201,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         {
             Guard.NotNull(image, nameof(image));
             Guard.NotNull(stream, nameof(stream));
+            cancellationToken.ThrowIfCancellationRequested();
 
             const ushort max = JpegConstants.MaxLength;
             if (image.Width >= max || image.Height >= max)
@@ -249,7 +250,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
             this.WriteDefineHuffmanTables(componentCount);
 
             // Write the image data.
-            this.WriteStartOfScan(image);
+            this.WriteStartOfScan(image, cancellationToken);
 
             // Write the End Of Image marker.
             this.buffer[0] = JpegConstants.Markers.XFF;
@@ -398,7 +399,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// </summary>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <param name="pixels">The pixel accessor providing access to the image pixels.</param>
-        private void Encode444<TPixel>(Image<TPixel> pixels)
+        /// <param name="cancellationToken">The token to monitor for cancellation.</param>
+        private void Encode444<TPixel>(Image<TPixel> pixels, CancellationToken cancellationToken)
             where TPixel : unmanaged, IPixel<TPixel>
         {
             // TODO: Need a JpegScanEncoder<TPixel> class or struct that encapsulates the scan-encoding implementation. (Similar to JpegScanDecoder.)
@@ -420,6 +422,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
 
             for (int y = 0; y < pixels.Height; y += 8)
             {
+                cancellationToken.ThrowIfCancellationRequested();
                 var currentRows = new RowOctet<TPixel>(pixelBuffer, y);
 
                 for (int x = 0; x < pixels.Width; x += 8)
@@ -945,7 +948,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// </summary>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <param name="image">The pixel accessor providing access to the image pixels.</param>
-        private void WriteStartOfScan<TPixel>(Image<TPixel> image)
+        /// <param name="cancellationToken">The token to monitor for cancellation.</param>
+        private void WriteStartOfScan<TPixel>(Image<TPixel> image, CancellationToken cancellationToken)
             where TPixel : unmanaged, IPixel<TPixel>
         {
             // TODO: Need a JpegScanEncoder<TPixel> class or struct that encapsulates the scan-encoding implementation. (Similar to JpegScanDecoder.)
@@ -955,10 +959,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
             switch (this.subsample)
             {
                 case JpegSubsample.Ratio444:
-                    this.Encode444(image);
+                    this.Encode444(image, cancellationToken);
                     break;
                 case JpegSubsample.Ratio420:
-                    this.Encode420(image);
+                    this.Encode420(image, cancellationToken);
                     break;
             }
 
@@ -972,7 +976,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// </summary>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <param name="pixels">The pixel accessor providing access to the image pixels.</param>
-        private void Encode420<TPixel>(Image<TPixel> pixels)
+        /// <param name="cancellationToken">The token to monitor for cancellation.</param>
+        private void Encode420<TPixel>(Image<TPixel> pixels, CancellationToken cancellationToken)
             where TPixel : unmanaged, IPixel<TPixel>
         {
             // TODO: Need a JpegScanEncoder<TPixel> class or struct that encapsulates the scan-encoding implementation. (Similar to JpegScanDecoder.)
@@ -1000,6 +1005,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
 
             for (int y = 0; y < pixels.Height; y += 16)
             {
+                cancellationToken.ThrowIfCancellationRequested();
                 for (int x = 0; x < pixels.Width; x += 16)
                 {
                     for (int i = 0; i < 4; i++)

tests/ImageSharp.Tests/Formats/Jpg/JpegEncoderTests.cs

@@ -1,8 +1,11 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
 using SixLabors.ImageSharp.Formats.Jpeg;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
@@ -284,5 +287,30 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
             IccProfile values = input.Metadata.IccProfile;
             Assert.Equal(values.Entries, actual.Entries);
         }
+
+        [Theory]
+        [InlineData(JpegSubsample.Ratio420, 0)]
+        [InlineData(JpegSubsample.Ratio420, 3)]
+        [InlineData(JpegSubsample.Ratio420, 10)]
+        [InlineData(JpegSubsample.Ratio444, 0)]
+        [InlineData(JpegSubsample.Ratio444, 3)]
+        [InlineData(JpegSubsample.Ratio444, 10)]
+        public async Task Encode_IsCancellable(JpegSubsample subsample, int cancellationDelayMs)
+        {
+            using var image = new Image<Rgba32>(5000, 5000);
+            using MemoryStream stream = new MemoryStream();
+            var cts = new CancellationTokenSource();
+            if (cancellationDelayMs == 0)
+            {
+                cts.Cancel();
+            }
+            else
+            {
+                cts.CancelAfter(cancellationDelayMs);
+            }
+
+            var encoder = new JpegEncoder() { Subsample = subsample };
+            await Assert.ThrowsAnyAsync<OperationCanceledException>(() => image.SaveAsync(stream, encoder, cts.Token));
+        }
     }
 }

tests/ImageSharp.Tests/Image/ImageTests.SaveAsync.cs

@@ -3,9 +3,9 @@
 
 using System;
 using System.IO;
-
+using System.Threading;
 using Moq;
-
+using SixLabors.ImageSharp.Formats.Bmp;
 using SixLabors.ImageSharp.Formats.Png;
 using SixLabors.ImageSharp.PixelFormats;
 using Xunit;
@@ -90,7 +90,7 @@ namespace SixLabors.ImageSharp.Tests
             [InlineData("test.bmp")]
             [InlineData("test.jpg")]
             [InlineData("test.gif")]
-            public async Task SaveNeverCallsSyncMethods(string filename)
+            public async Task SaveAsync_NeverCallsSyncMethods(string filename)
             {
                 using (var image = new Image<Rgba32>(5, 5))
                 {
@@ -102,6 +102,20 @@ namespace SixLabors.ImageSharp.Tests
                     }
                 }
             }
+
+            [Fact]
+            public async Task SaveAsync_WithNonSeekableStream_IsCancellable()
+            {
+                using var image = new Image<Rgba32>(500, 500);
+                IImageEncoder encoder = new BmpEncoder();
+                using var stream = new MemoryStream();
+                var asyncStream = new AsyncStreamWrapper(stream, () => false);
+                var cts = new CancellationTokenSource();
+                cts.CancelAfter(TimeSpan.FromTicks(1));
+
+                await Assert.ThrowsAnyAsync<TaskCanceledException>(() =>
+                    image.SaveAsync(asyncStream, encoder, cts.Token));
+            }
         }
     }
 }