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// Copyright (c) All contributors. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.
using System;
using System.Buffers;
using System.Collections.Generic;
using System.IO;
using System.Runtime.CompilerServices;
using System.Threading;
using System.Threading.Tasks;
using Nerdbank.Streams;
namespace MessagePack
{
public partial class MessagePackStreamReader : IDisposable
{
/// <summary>
/// Reads the next messagepack array and produces each element individually.
/// </summary>
/// <param name="cancellationToken">A cancellation token.</param>
/// <returns>
/// A task whose result is the next whole data structure from the stream, or <c>null</c> if the stream ends.
/// The returned sequence is valid until this <see cref="MessagePackStreamReader"/> is disposed or
/// until this method is called again, whichever comes first.
/// </returns>
/// <remarks>
/// When <c>null</c> is the result of the returned task,
/// any extra bytes read (between the last complete message and the end of the stream) will be available via the <see cref="RemainingBytes"/> property.
/// </remarks>
public async IAsyncEnumerable<ReadOnlySequence<byte>> ReadArrayAsync([EnumeratorCancellation] CancellationToken cancellationToken)
{
this.RecycleLastMessage();
cancellationToken.ThrowIfCancellationRequested();
int length;
while (!this.TryReadArrayHeader(out length))
{
if (!await this.TryReadMoreDataAsync(cancellationToken).ConfigureAwait(false))
{
throw new EndOfStreamException("The stream ended before an array header could be found.");
}
}
for (int i = 0; i < length; i++)
{
var element = await this.ReadAsync(cancellationToken).ConfigureAwait(false);
if (element.HasValue)
{
yield return element.Value;
}
else
{
throw new EndOfStreamException("Stream ended before all elements were read.");
}
}
}
/// <summary>
/// Reads an array header from <see cref="ReadData"/> if there are enough bytes to do so.
/// </summary>
/// <param name="length">Receives the length of the array, if its header could be read.</param>
/// <returns><c>true</c> if the array header was found and complete; <c>false</c> if there were insufficient bytes to read the header.</returns>
/// <exception cref="MessagePackSerializationException">Thrown if the next msgpack structure is not an array header.</exception>
private bool TryReadArrayHeader(out int length)
{
if (this.ReadData.Length > 0)
{
var reader = new MessagePackReader(this.ReadData);
if (reader.TryReadArrayHeader(out length))
{
this.endOfLastMessage = reader.Position;
return true;
}
}
length = 0;
return false;
}
}
}
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