protobuf/csharp/src/Google.Protobuf/ByteStringAsync.cs

#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
            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
    }
}