Use built in stream copy when available (#338)

Author: twsouthwick

DocumentFormat.OpenXml/DocumentFormat.OpenXml.csproj

@@ -60,6 +60,10 @@
         <Compile Include="System\Collections\Generic\IReadOnlyCollection.cs" />
         <Compile Include="System\Reflection\TypeExtensions.cs" />
       </ItemGroup>
+
+      <ItemGroup Condition=" '$(TargetFramework)' == 'net35' ">
+        <Compile Include="System\IO\StreamCopyExtensions.cs" />
+      </ItemGroup>
     </When>
 
     <When Condition=" '$(TargetFramework)' == 'net46' ">

DocumentFormat.OpenXml/Packaging/DataPart.cs

@@ -156,7 +156,7 @@ public void FeedData(Stream sourceStream)
 
             using (Stream targetStream = this.GetStream(FileMode.Create))
             {
-                OpenXmlPart.CopyStream(sourceStream, targetStream);
+                sourceStream.CopyTo(targetStream);
             }
         }
 

DocumentFormat.OpenXml/Packaging/OpenXmlBasePart.cs

@@ -398,7 +398,7 @@ public void FeedData(Stream sourceStream)
 
             using (Stream targetStream = this.GetStream(FileMode.Create))
             {
-                CopyStream(sourceStream, targetStream);
+                sourceStream.CopyTo(targetStream);
             }
         }
 
@@ -845,30 +845,6 @@ internal sealed override PackageRelationship CreateRelationship(Uri targetUri, T
 
         #endregion
 
-        #region private methods
-        internal static void CopyStream(Stream sourceStream, Stream targetStream)
-        {
-            if (sourceStream == null)
-            {
-                throw new ArgumentNullException(nameof(sourceStream));
-            }
-
-            using (BinaryReader sourceReader = new BinaryReader(sourceStream))
-            {
-                byte[] buffer = new byte[4096];
-
-                int num = 0;
-                do
-                {
-                    num = sourceReader.Read(buffer, 0, 4096);
-                    if (num > 0)
-                        targetStream.Write(buffer, 0, num);
-                }
-                while (num > 0);
-            }
-        }
-        #endregion
-
         #region MC Staffs
         internal MarkupCompatibilityProcessSettings MCSettings;
         #endregion

DocumentFormat.OpenXml/Packaging/OpenXmlPackage.cs

@@ -949,7 +949,7 @@ internal void ChangeDocumentTypeInternal<T>() where T : OpenXmlPart
                         throw new OpenXmlPackageException(ExceptionMessages.DocumentTooBig);
                     }
                     memoryStream = new MemoryStream(Convert.ToInt32(mainPartStream.Length));
-                    OpenXmlPart.CopyStream(mainPartStream, memoryStream);
+                    mainPartStream.CopyTo(memoryStream);
                 }
 
                 //

DocumentFormat.OpenXml/System/IO/StreamCopyExtensions.cs

@@ -0,0 +1,31 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+namespace System.IO
+{
+    internal static class StreamCopyExtensions
+    {
+        public static void CopyTo(this Stream source, Stream destination)
+        {
+            const int BufferSize = 4096;
+
+            if (source == null)
+            {
+                throw new ArgumentNullException(nameof(source));
+            }
+
+            if (destination == null)
+            {
+                throw new ArgumentNullException(nameof(destination));
+            }
+
+            var buffer = new byte[BufferSize];
+            int bytesRead;
+
+            while ((bytesRead = source.Read(buffer, 0, BufferSize)) > 0)
+            {
+                destination.Write(buffer, 0, bytesRead);
+            }
+        }
+    }
+}