Write exif profile with padding if needed

src/ImageSharp/Formats/Webp/BitWriter/BitWriterBase.cs

@@ -10,11 +10,22 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
 {
     internal abstract class BitWriterBase
     {
+        private const uint MaxDimension = 16777215;
+
+        private const ulong MaxCanvasPixels = 4294967295ul;
+
+        protected const uint ExtendedFileChunkSize = WebpConstants.ChunkHeaderSize + WebpConstants.Vp8XChunkSize;
+
         /// <summary>
         /// Buffer to write to.
         /// </summary>
         private byte[] buffer;
 
+        /// <summary>
+        /// A scratch buffer to reduce allocations.
+        /// </summary>
+        private readonly byte[] scratchBuffer = new byte[4];
+
         /// <summary>
         /// Initializes a new instance of the <see cref="BitWriterBase"/> class.
         /// </summary>
@@ -81,13 +92,25 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
         /// <param name="riffSize">The block length.</param>
         protected void WriteRiffHeader(Stream stream, uint riffSize)
         {
-            Span<byte> buf = stackalloc byte[4];
             stream.Write(WebpConstants.RiffFourCc);
-            BinaryPrimitives.WriteUInt32LittleEndian(buf, riffSize);
-            stream.Write(buf);
+            BinaryPrimitives.WriteUInt32LittleEndian(this.scratchBuffer, riffSize);
+            stream.Write(this.scratchBuffer.AsSpan(0, 4));
             stream.Write(WebpConstants.WebpHeader);
         }
 
+        /// <summary>
+        /// Calculates the exif chunk size.
+        /// </summary>
+        /// <param name="exifBytes">The exif profile bytes.</param>
+        /// <returns>The exif chunk size in bytes.</returns>
+        protected uint ExifChunkSize(byte[] exifBytes)
+        {
+            uint exifSize = (uint)exifBytes.Length;
+            uint exifChunkSize = WebpConstants.ChunkHeaderSize + exifSize + (exifSize & 1);
+
+            return exifChunkSize;
+        }
+
         /// <summary>
         /// Writes the Exif profile to the stream.
         /// </summary>
@@ -97,12 +120,19 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
         {
             DebugGuard.NotNull(exifBytes, nameof(exifBytes));
 
-            Span<byte> buf = stackalloc byte[4];
+            uint size = (uint)exifBytes.Length;
+            Span<byte> buf = this.scratchBuffer.AsSpan(0, 4);
             BinaryPrimitives.WriteUInt32BigEndian(buf, (uint)WebpChunkType.Exif);
             stream.Write(buf);
-            BinaryPrimitives.WriteUInt32LittleEndian(buf, (uint)exifBytes.Length);
+            BinaryPrimitives.WriteUInt32LittleEndian(buf, size);
             stream.Write(buf);
             stream.Write(exifBytes);
+
+            // Add padding byte if needed.
+            if ((size & 1) == 1)
+            {
+                stream.WriteByte(0);
+            }
         }
 
         /// <summary>
@@ -114,14 +144,13 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
         /// <param name="height">The height of the image.</param>
         protected void WriteVp8XHeader(Stream stream, ExifProfile exifProfile, uint width, uint height)
         {
-            int maxDimension = 16777215;
-            if (width > maxDimension || height > maxDimension)
+            if (width > MaxDimension || height > MaxDimension)
             {
-                WebpThrowHelper.ThrowInvalidImageDimensions($"Image width or height exceeds maximum allowed dimension of {maxDimension}");
+                WebpThrowHelper.ThrowInvalidImageDimensions($"Image width or height exceeds maximum allowed dimension of {MaxDimension}");
             }
 
             // The spec states that the product of Canvas Width and Canvas Height MUST be at most 2^32 - 1.
-            if (width * height > 4294967295ul)
+            if (width * height > MaxCanvasPixels)
             {
                 WebpThrowHelper.ThrowInvalidImageDimensions("The product of image width and height MUST be at most 2^32 - 1");
             }
@@ -133,7 +162,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
                 flags |= 8;
             }
 
-            Span<byte> buf = stackalloc byte[4];
+            Span<byte> buf = this.scratchBuffer.AsSpan(0, 4);
             stream.Write(WebpConstants.Vp8XMagicBytes);
             BinaryPrimitives.WriteUInt32LittleEndian(buf, WebpConstants.Vp8XChunkSize);
             stream.Write(buf);

src/ImageSharp/Formats/Webp/BitWriter/Vp8BitWriter.cs

@@ -408,9 +408,9 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
             if (exifProfile != null)
             {
                 isVp8X = true;
-                riffSize += WebpConstants.ChunkHeaderSize + WebpConstants.Vp8XChunkSize;
+                riffSize += ExtendedFileChunkSize;
                 exifBytes = exifProfile.ToByteArray();
-                riffSize += WebpConstants.ChunkHeaderSize + (uint)exifBytes.Length;
+                riffSize += this.ExifChunkSize(exifBytes);
             }
 
             this.Finish();

src/ImageSharp/Formats/Webp/BitWriter/Vp8LBitWriter.cs

@@ -130,16 +130,15 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
         /// <inheritdoc/>
         public override void WriteEncodedImageToStream(Stream stream, ExifProfile exifProfile, uint width, uint height)
         {
-            Span<byte> buffer = stackalloc byte[4];
             bool isVp8X = false;
             byte[] exifBytes = null;
             uint riffSize = 0;
             if (exifProfile != null)
             {
                 isVp8X = true;
-                riffSize += WebpConstants.ChunkHeaderSize + WebpConstants.Vp8XChunkSize;
+                riffSize += ExtendedFileChunkSize;
                 exifBytes = exifProfile.ToByteArray();
-                riffSize += WebpConstants.ChunkHeaderSize + (uint)exifBytes.Length;
+                riffSize += this.ExifChunkSize(exifBytes);
             }
 
             this.Finish();
@@ -161,8 +160,8 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
             stream.Write(WebpConstants.Vp8LMagicBytes);
 
             // Write Vp8 Header.
-            BinaryPrimitives.WriteUInt32LittleEndian(buffer, size);
-            stream.Write(buffer);
+            BinaryPrimitives.WriteUInt32LittleEndian(this.scratchBuffer, size);
+            stream.Write(this.scratchBuffer.AsSpan(0, 4));
             stream.WriteByte(WebpConstants.Vp8LHeaderMagicByte);
 
             // Write the encoded bytes of the image to the stream.

src/ImageSharp/Formats/Webp/WebpEncoderCore.cs

@@ -4,11 +4,9 @@
 using System.IO;
 using System.Threading;
 using SixLabors.ImageSharp.Advanced;
-using SixLabors.ImageSharp.Formats.Bmp;
 using SixLabors.ImageSharp.Formats.Webp.Lossless;
 using SixLabors.ImageSharp.Formats.Webp.Lossy;
 using SixLabors.ImageSharp.Memory;
-using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Webp

tests/ImageSharp.Tests/Formats/WebP/WebpMetaDataTests.cs

@@ -63,6 +63,31 @@ namespace SixLabors.ImageSharp.Tests.Formats.Webp
             }
         }
 
+        [Theory]
+        [InlineData(WebpFileFormatType.Lossy)]
+        [InlineData(WebpFileFormatType.Lossless)]
+        public void Encode_WritesExifWithPadding(WebpFileFormatType fileFormatType)
+        {
+            // arrange
+            using var input = new Image<Rgba32>(25, 25);
+            using var memoryStream = new MemoryStream();
+            var expectedExif = new ExifProfile();
+            string expectedSoftware = "ImageSharp";
+            expectedExif.SetValue(ExifTag.Software, expectedSoftware);
+            input.Metadata.ExifProfile = expectedExif;
+
+            // act
+            input.Save(memoryStream, new WebpEncoder() { FileFormat = fileFormatType });
+            memoryStream.Position = 0;
+
+            // assert
+            using var image = Image.Load<Rgba32>(memoryStream);
+            ExifProfile actualExif = image.Metadata.ExifProfile;
+            Assert.NotNull(actualExif);
+            Assert.Equal(expectedExif.Values.Count, actualExif.Values.Count);
+            Assert.Equal(expectedSoftware, actualExif.GetValue(ExifTag.Software).Value);
+        }
+
         [Theory]
         [WithFile(TestImages.Webp.Lossy.WithExif, PixelTypes.Rgba32)]
         public void EncodeLossyWebp_PreservesExif<TPixel>(TestImageProvider<TPixel> provider)