Change ByteString to use memory and support unsafe create without copy
diff --git a/csharp/src/Google.Protobuf/ByteStringAsync.cs b/csharp/src/Google.Protobuf/ByteStringAsync.cs
new file mode 100644
index 0000000..8bf8add
--- /dev/null
+++ b/csharp/src/Google.Protobuf/ByteStringAsync.cs
@@ -0,0 +1,64 @@
+#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc. All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+// * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+// * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Google.Protobuf
+{
+ /// <summary>
+ /// SecuritySafeCritical attribute can not be placed on types with async methods.
+ /// This class has ByteString's async methods so it can be marked with SecuritySafeCritical.
+ /// </summary>
+ internal static class ByteStringAsync
+ {
+#if !NET35
+ internal static async Task<ByteString> FromStreamAsyncCore(Stream stream, CancellationToken cancellationToken)
+ {
+ int capacity = stream.CanSeek ? checked((int)(stream.Length - stream.Position)) : 0;
+ var memoryStream = new MemoryStream(capacity);
+ // We have to specify the buffer size here, as there's no overload accepting the cancellation token
+ // alone. But it's documented to use 81920 by default if not specified.
+ await stream.CopyToAsync(memoryStream, 81920, cancellationToken);
+#if NETSTANDARD1_1 || NETSTANDARD2_0
+ byte[] bytes = memoryStream.ToArray();
+#else
+ // Avoid an extra copy if we can.
+ byte[] bytes = memoryStream.Length == memoryStream.Capacity ? memoryStream.GetBuffer() : memoryStream.ToArray();
+#endif
+ return ByteString.AttachBytes(bytes);
+ }
+#endif
+ }
+}
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