Add stream extensions for Span<T>

src/ImageSharp/Common/Extensions/StreamExtensions.cs

@@ -1,7 +1,7 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
-using System.Buffers;
+using System;
 using System.IO;
 
 namespace SixLabors.ImageSharp
@@ -11,6 +11,33 @@ namespace SixLabors.ImageSharp
     /// </summary>
     internal static class StreamExtensions
     {
+#if NETCOREAPP2_1
+        /// <summary>
+        /// Writes data from a stream into the provided buffer.
+        /// </summary>
+        /// <param name="stream">The stream.</param>
+        /// <param name="buffer">The buffer.</param>
+        /// <param name="offset">The offset within the buffer to begin writing.</param>
+        /// <param name="count">The number of bytes to write to the stream.</param>
+        public static void Write(this Stream stream, Span<byte> buffer, int offset, int count)
+        {
+            stream.Write(buffer.Slice(offset, count));
+        }
+
+        /// <summary>
+        /// Reads data from a stream into the provided buffer.
+        /// </summary>
+        /// <param name="stream">The stream.</param>
+        /// <param name="buffer">The buffer..</param>
+        /// <param name="offset">The offset within the buffer where the bytes are read into.</param>
+        /// <param name="count">The number of bytes, if available, to read.</param>
+        /// <returns>The actual number of bytes read.</returns>
+        public static int Read(this Stream stream, Span<byte> buffer, int offset, int count)
+        {
+            return stream.Read(buffer.Slice(offset, count));
+        }
+#endif
+
         /// <summary>
         /// Skips the number of bytes in the given stream.
         /// </summary>

src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs

@@ -73,18 +73,12 @@ namespace SixLabors.ImageSharp.Formats.Bmp
 #endif
             fileHeader.WriteTo(buffer);
 
-#if NETCOREAPP2_1
-            stream.Write(buffer.Slice(0, BmpFileHeader.Size));
-#else
             stream.Write(buffer, 0, BmpFileHeader.Size);
-#endif
+
             infoHeader.WriteTo(buffer);
 
-#if NETCOREAPP2_1
-            stream.Write(buffer.Slice(0, 40));
-#else
             stream.Write(buffer, 0, 40);
-#endif
+
             this.WriteImage(stream, image.Frames.RootFrame);
 
             stream.Flush();

src/ImageSharp/Formats/Gif/LzwDecoder.cs

@@ -239,11 +239,8 @@ namespace SixLabors.ImageSharp.Formats.Gif
                 return 0;
             }
 
-#if NETCOREAPP2_1
-            int count = this.stream.Read(buffer.Slice(0, bufferSize));
-#else
             int count = this.stream.Read(buffer, 0, bufferSize);
-#endif
+
             return count != bufferSize ? 0 : bufferSize;
         }