tests improvements:

- add failing tests for BmpDecoder
- more sophisticated and verbose buffer capacity configurator

src/ImageSharp/Advanced/AdvancedImageExtensions.cs

@@ -96,7 +96,7 @@ namespace SixLabors.ImageSharp.Advanced
             IMemoryGroup<TPixel> mg = source.GetPixelMemoryGroup();
             if (mg.Count > 1)
             {
-                throw new InvalidOperationException($"GetPixelSpan is invalid, since the backing buffer of this {source.Width}x{source.Height} sized image is discontiguos!");
+                throw new InvalidOperationException($"GetPixelSpan is invalid, since the backing buffer of this {source.Width}x{source.Height} sized image is discontiguous!");
             }
 
             return mg.Single().Span;

src/ImageSharp/Formats/Bmp/BmpDecoder.cs

@@ -1,7 +1,8 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using System.IO;
+using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Bmp
@@ -32,7 +33,20 @@ namespace SixLabors.ImageSharp.Formats.Bmp
         {
             Guard.NotNull(stream, nameof(stream));
 
-            return new BmpDecoderCore(configuration, this).Decode<TPixel>(stream);
+            var decoder = new BmpDecoderCore(configuration, this);
+
+            try
+            {
+                return decoder.Decode<TPixel>(stream);
+            }
+            catch (InvalidMemoryOperationException ex)
+            {
+                Size dims = decoder.Dimensions;
+
+                // TODO: use InvalidImageContentException here, if we decide to define it
+                // https://github.com/SixLabors/ImageSharp/issues/1110
+                throw new ImageFormatException($"Can not decode image. Failed to allocate buffers for possibly degenerate dimensions: {dims.Width}x{dims.Height}.", ex);
+            }
         }
 
         /// <inheritdoc />

src/ImageSharp/Formats/Bmp/BmpDecoderCore.cs

@@ -114,6 +114,8 @@ namespace SixLabors.ImageSharp.Formats.Bmp
             this.options = options;
         }
 
+        public Size Dimensions => new Size(this.infoHeader.Width, this.infoHeader.Height);
+
         /// <summary>
         /// Decodes the image from the specified this._stream and sets
         /// the data to image.

src/ImageSharp/Formats/Jpeg/JpegDecoder.cs

@@ -34,7 +34,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
 
                 // TODO: use InvalidImageContentException here, if we decide to define it
                 // https://github.com/SixLabors/ImageSharp/issues/1110
-                throw new ImageFormatException($"Can not decode the image having degenerate dimensions of {w}x{h}.", ex);
+                throw new ImageFormatException($"Can not decode image. Failed to allocate buffers for possibly degenerate dimensions: {w}x{h}.", ex);
             }
         }
 

tests/ImageSharp.Tests/Advanced/AdvancedImageExtensionsTests.cs

@@ -25,7 +25,7 @@ namespace SixLabors.ImageSharp.Tests.Advanced
             public void OwnedMemory_PixelDataIsCorrect<TPixel>(TestImageProvider<TPixel> provider)
                 where TPixel : struct, IPixel<TPixel>
             {
-                provider.LimitAllocatorBufferCapacity();
+                provider.LimitAllocatorBufferCapacity().InPixels(200);
 
                 using Image<TPixel> image = provider.GetImage();
 
@@ -106,7 +106,7 @@ namespace SixLabors.ImageSharp.Tests.Advanced
         public void GetPixelRowMemory_PixelDataIsCorrect<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : struct, IPixel<TPixel>
         {
-            provider.LimitAllocatorBufferCapacity();
+            provider.LimitAllocatorBufferCapacity().InPixels(200);
 
             using Image<TPixel> image = provider.GetImage();
 
@@ -147,7 +147,7 @@ namespace SixLabors.ImageSharp.Tests.Advanced
         public void GetPixelRowSpan_ShouldReferenceSpanOfMemory<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : struct, IPixel<TPixel>
         {
-            provider.LimitAllocatorBufferCapacity();
+            provider.LimitAllocatorBufferCapacity().InPixels(200);
 
             using Image<TPixel> image = provider.GetImage();
 

tests/ImageSharp.Tests/Formats/Bmp/BmpDecoderTests.cs

@@ -50,7 +50,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Bmp
 
                 if (!string.IsNullOrEmpty(nonContiguousBuffersStr))
                 {
-                    provider.LimitAllocatorBufferCapacity();
+                    provider.LimitAllocatorBufferCapacity().InPixels(100);
                 }
 
                 using Image<TPixel> image = provider.GetImage(BmpDecoder);
@@ -77,7 +77,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Bmp
         public void BmpDecoder_DegenerateMemoryRequest_ShouldTranslateTo_ImageFormatException<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : struct, IPixel<TPixel>
         {
-            provider.LimitAllocatorBufferCapacity(100);
+            provider.LimitAllocatorBufferCapacity().InPixels(10);
             ImageFormatException ex = Assert.Throws<ImageFormatException>(provider.GetImage);
             Assert.IsType<InvalidMemoryOperationException>(ex.InnerException);
         }
@@ -253,11 +253,18 @@ namespace SixLabors.ImageSharp.Tests.Formats.Bmp
         }
 
         [Theory]
-        [WithFile(RLE8, PixelTypes.Rgba32)]
-        [WithFile(RLE8Inverted, PixelTypes.Rgba32)]
-        public void BmpDecoder_CanDecode_RunLengthEncoded_8Bit<TPixel>(TestImageProvider<TPixel> provider)
+        [WithFile(RLE8, PixelTypes.Rgba32, false)]
+        [WithFile(RLE8Inverted, PixelTypes.Rgba32, false)]
+        [WithFile(RLE8, PixelTypes.Rgba32, true)]
+        [WithFile(RLE8Inverted, PixelTypes.Rgba32, true)]
+        public void BmpDecoder_CanDecode_RunLengthEncoded_8Bit<TPixel>(TestImageProvider<TPixel> provider, bool enforceDiscontiguousBuffers)
             where TPixel : struct, IPixel<TPixel>
         {
+            if (enforceDiscontiguousBuffers)
+            {
+                provider.LimitAllocatorBufferCapacity().InBytes(100);
+            }
+
             using (Image<TPixel> image = provider.GetImage(new BmpDecoder { RleSkippedPixelHandling = RleSkippedPixelHandling.FirstColorOfPalette }))
             {
                 image.DebugSave(provider);
@@ -266,12 +273,20 @@ namespace SixLabors.ImageSharp.Tests.Formats.Bmp
         }
 
         [Theory]
-        [WithFile(RLE24, PixelTypes.Rgba32)]
-        [WithFile(RLE24Cut, PixelTypes.Rgba32)]
-        [WithFile(RLE24Delta, PixelTypes.Rgba32)]
-        public void BmpDecoder_CanDecode_RunLengthEncoded_24Bit<TPixel>(TestImageProvider<TPixel> provider)
+        [WithFile(RLE24, PixelTypes.Rgba32, false)]
+        [WithFile(RLE24Cut, PixelTypes.Rgba32, false)]
+        [WithFile(RLE24Delta, PixelTypes.Rgba32, false)]
+        [WithFile(RLE24, PixelTypes.Rgba32, true)]
+        [WithFile(RLE24Cut, PixelTypes.Rgba32, true)]
+        [WithFile(RLE24Delta, PixelTypes.Rgba32, true)]
+        public void BmpDecoder_CanDecode_RunLengthEncoded_24Bit<TPixel>(TestImageProvider<TPixel> provider, bool enforceNonContiguous)
             where TPixel : struct, IPixel<TPixel>
         {
+            if (enforceNonContiguous)
+            {
+                provider.LimitAllocatorBufferCapacity().InBytes(50);
+            }
+
             using (Image<TPixel> image = provider.GetImage(new BmpDecoder { RleSkippedPixelHandling = RleSkippedPixelHandling.Black }))
             {
                 image.DebugSave(provider);

tests/ImageSharp.Tests/Formats/Jpg/JpegDecoderTests.Baseline.cs

@@ -26,7 +26,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
 
                 if (!string.IsNullOrEmpty(nonContiguousBuffersStr))
                 {
-                    provider.LimitAllocatorBufferCapacity();
+                    provider.LimitAllocatorBufferCapacity().InBytes(200);
                 }
 
                 using Image<TPixel> image = provider.GetImage(JpegDecoder);

tests/ImageSharp.Tests/Formats/Jpg/JpegDecoderTests.Progressive.cs

@@ -26,7 +26,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
 
                 if (!string.IsNullOrEmpty(nonContiguousBuffersStr))
                 {
-                    provider.LimitAllocatorBufferCapacity();
+                    provider.LimitAllocatorBufferCapacity().InBytes(200);
                 }
 
                 using Image<TPixel> image = provider.GetImage(JpegDecoder);

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

@@ -111,7 +111,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
         public void DegenerateMemoryRequest_ShouldTranslateTo_ImageFormatException<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : struct, IPixel<TPixel>
         {
-            provider.LimitAllocatorBufferCapacity(100);
+            provider.LimitAllocatorBufferCapacity().InBytes(10);
             ImageFormatException ex = Assert.Throws<ImageFormatException>(provider.GetImage);
             this.Output.WriteLine(ex.Message);
             Assert.IsType<InvalidMemoryOperationException>(ex.InnerException);

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

@@ -93,7 +93,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
                 ? ImageComparer.TolerantPercentage(0.1f)
                 : ImageComparer.TolerantPercentage(5f);
 
-            provider.LimitAllocatorBufferCapacity();
+            provider.LimitAllocatorBufferCapacity().InBytes(200);
             TestJpegEncoderCore(provider, subsample, 100, comparer);
         }
 

tests/ImageSharp.Tests/Formats/Tga/TgaDecoderTests.cs

@@ -204,7 +204,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tga
         public void TgaDecoder_DegenerateMemoryRequest_ShouldTranslateTo_ImageFormatException<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : struct, IPixel<TPixel>
         {
-            provider.LimitAllocatorBufferCapacity(100);
+            provider.LimitAllocatorBufferCapacity().InPixels(10);
             ImageFormatException ex = Assert.Throws<ImageFormatException>(provider.GetImage);
             Assert.IsType<InvalidMemoryOperationException>(ex.InnerException);
         }
@@ -219,7 +219,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tga
             {
                 TestImageProvider<TPixel> provider = BasicSerializer.Deserialize<TestImageProvider<TPixel>>(providerDump);
 
-                provider.LimitAllocatorBufferCapacity();
+                provider.LimitAllocatorBufferCapacity().InPixels(200);
 
                 using Image<TPixel> image = provider.GetImage(new TgaDecoder());
                 image.DebugSave(provider, testOutputDetails: nonContiguousBuffersStr);

tests/ImageSharp.Tests/Formats/Tga/TgaEncoderTests.cs

@@ -128,7 +128,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tga
         public void Encode_WorksWithDiscontiguousBuffers<TPixel>(TestImageProvider<TPixel> provider, TgaBitsPerPixel bitsPerPixel)
             where TPixel : struct, IPixel<TPixel>
         {
-            provider.LimitAllocatorBufferCapacity(10000);
+            provider.LimitAllocatorBufferCapacity().InPixels(100);
             TestTgaEncoderCore(provider, bitsPerPixel, TgaCompression.RunLength);
         }
 

tests/ImageSharp.Tests/TestUtilities/TestImageExtensions.cs

@@ -666,13 +666,12 @@ namespace SixLabors.ImageSharp.Tests
             }
         }
 
-        internal static void LimitAllocatorBufferCapacity<TPixel>(
-            this TestImageProvider<TPixel> provider,
-            int bufferCapacityInPixels = 40000) // 200 x 200
+        internal static AllocatorBufferCapacityConfigurator LimitAllocatorBufferCapacity<TPixel>(
+            this TestImageProvider<TPixel> provider)
             where TPixel : struct, IPixel<TPixel>
         {
             var allocator = (ArrayPoolMemoryAllocator)provider.Configuration.MemoryAllocator;
-            allocator.BufferCapacityInBytes = Unsafe.SizeOf<TPixel>() * bufferCapacityInPixels;
+            return new AllocatorBufferCapacityConfigurator(allocator, Unsafe.SizeOf<TPixel>());
         }
 
         internal static Image<Rgba32> ToGrayscaleImage(this Buffer2D<float> buffer, float scale)
@@ -734,4 +733,32 @@ namespace SixLabors.ImageSharp.Tests
             }
         }
     }
+
+    internal class AllocatorBufferCapacityConfigurator
+    {
+        private readonly ArrayPoolMemoryAllocator allocator;
+        private readonly int pixelSizeInBytes;
+
+        public AllocatorBufferCapacityConfigurator(ArrayPoolMemoryAllocator allocator, int pixelSizeInBytes)
+        {
+            this.allocator = allocator;
+            this.pixelSizeInBytes = pixelSizeInBytes;
+        }
+
+        /// <summary>
+        /// Set the maximum buffer capacity to (areaDimensionBytes x areaDimensionBytes) bytes.
+        /// </summary>
+        public void InBytes(int areaDimensionBytes)
+        {
+            this.allocator.BufferCapacityInBytes = areaDimensionBytes * areaDimensionBytes;
+        }
+
+        /// <summary>
+        /// Set the maximum buffer capacity to (areaDimensionPixels x areaDimensionPixels x size of the pixel) bytes.
+        /// </summary>
+        public void InPixels(int areaDimensionPixels)
+        {
+            this.allocator.BufferCapacityInBytes = areaDimensionPixels * areaDimensionPixels * this.pixelSizeInBytes;
+        }
+    }
 }