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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System.Diagnostics;
namespace System.Buffers
{
/// <summary>
/// Represents a heap-based, array-backed output sink into which <typeparam name="T"/> data can be written.
/// </summary>
public sealed class ArrayBufferWriter<T> : IBufferWriter<T>
{
private T[] _buffer;
private int _index;
private const int DefaultInitialBufferSize = 256;
/// <summary>
/// Creates an instance of an <see cref="ArrayBufferWriter{T}"/>, in which data can be written to,
/// with the default initial capacity.
/// </summary>
public ArrayBufferWriter()
{
_buffer = Array.Empty<T>();
_index = 0;
}
/// <summary>
/// Creates an instance of an <see cref="ArrayBufferWriter{T}"/>, in which data can be written to,
/// with an initial capacity specified.
/// </summary>
/// <param name="initialCapacity">The minimum capacity with which to initialize the underlying buffer.</param>
/// <exception cref="ArgumentException">
/// Thrown when <paramref name="initialCapacity"/> is not positive (i.e. less than or equal to 0).
/// </exception>
public ArrayBufferWriter(int initialCapacity)
{
if (initialCapacity <= 0)
throw new ArgumentException(nameof(initialCapacity));
_buffer = new T[initialCapacity];
_index = 0;
}
/// <summary>
/// Returns the data written to the underlying buffer so far, as a <see cref="ReadOnlyMemory{T}"/>.
/// </summary>
public ReadOnlyMemory<T> WrittenMemory => _buffer.AsMemory(0, _index);
/// <summary>
/// Returns the data written to the underlying buffer so far, as a <see cref="ReadOnlySpan{T}"/>.
/// </summary>
public ReadOnlySpan<T> WrittenSpan => _buffer.AsSpan(0, _index);
/// <summary>
/// Returns the amount of data written to the underlying buffer so far.
/// </summary>
public int WrittenCount => _index;
/// <summary>
/// Returns the total amount of space within the underlying buffer.
/// </summary>
public int Capacity => _buffer.Length;
/// <summary>
/// Returns the amount of space available that can still be written into without forcing the underlying buffer to grow.
/// </summary>
public int FreeCapacity => _buffer.Length - _index;
/// <summary>
/// Clears the data written to the underlying buffer.
/// </summary>
/// <remarks>
/// You must clear the <see cref="ArrayBufferWriter{T}"/> before trying to re-use it.
/// </remarks>
public void Clear()
{
Debug.Assert(_buffer.Length >= _index);
_buffer.AsSpan(0, _index).Clear();
_index = 0;
}
/// <summary>
/// Notifies <see cref="IBufferWriter{T}"/> that <paramref name="count"/> amount of data was written to the output <see cref="Span{T}"/>/<see cref="Memory{T}"/>
/// </summary>
/// <exception cref="ArgumentException">
/// Thrown when <paramref name="count"/> is negative.
/// </exception>
/// <exception cref="InvalidOperationException">
/// Thrown when attempting to advance past the end of the underlying buffer.
/// </exception>
/// <remarks>
/// You must request a new buffer after calling Advance to continue writing more data and cannot write to a previously acquired buffer.
/// </remarks>
public void Advance(int count)
{
if (count < 0)
throw new ArgumentException(nameof(count));
if (_index > _buffer.Length - count)
ThrowInvalidOperationException_AdvancedTooFar(_buffer.Length);
_index += count;
}
/// <summary>
/// Returns a <see cref="Memory{T}"/> to write to that is at least the requested length (specified by <paramref name="sizeHint"/>).
/// If no <paramref name="sizeHint"/> is provided (or it's equal to <code>0</code>), some non-empty buffer is returned.
/// </summary>
/// <exception cref="ArgumentException">
/// Thrown when <paramref name="sizeHint"/> is negative.
/// </exception>
/// <remarks>
/// This will never return an empty <see cref="Memory{T}"/>.
/// </remarks>
/// <remarks>
/// There is no guarantee that successive calls will return the same buffer or the same-sized buffer.
/// </remarks>
/// <remarks>
/// You must request a new buffer after calling Advance to continue writing more data and cannot write to a previously acquired buffer.
/// </remarks>
public Memory<T> GetMemory(int sizeHint = 0)
{
CheckAndResizeBuffer(sizeHint);
Debug.Assert(_buffer.Length > _index);
return _buffer.AsMemory(_index);
}
/// <summary>
/// Returns a <see cref="Span{T}"/> to write to that is at least the requested length (specified by <paramref name="sizeHint"/>).
/// If no <paramref name="sizeHint"/> is provided (or it's equal to <code>0</code>), some non-empty buffer is returned.
/// </summary>
/// <exception cref="ArgumentException">
/// Thrown when <paramref name="sizeHint"/> is negative.
/// </exception>
/// <remarks>
/// This will never return an empty <see cref="Span{T}"/>.
/// </remarks>
/// <remarks>
/// There is no guarantee that successive calls will return the same buffer or the same-sized buffer.
/// </remarks>
/// <remarks>
/// You must request a new buffer after calling Advance to continue writing more data and cannot write to a previously acquired buffer.
/// </remarks>
public Span<T> GetSpan(int sizeHint = 0)
{
CheckAndResizeBuffer(sizeHint);
Debug.Assert(_buffer.Length > _index);
return _buffer.AsSpan(_index);
}
private void CheckAndResizeBuffer(int sizeHint)
{
if (sizeHint < 0)
throw new ArgumentException(nameof(sizeHint));
if (sizeHint == 0)
{
sizeHint = 1;
}
if (sizeHint > FreeCapacity)
{
int growBy = Math.Max(sizeHint, _buffer.Length);
if (_buffer.Length == 0)
{
growBy = Math.Max(growBy, DefaultInitialBufferSize);
}
int newSize = checked(_buffer.Length + growBy);
Array.Resize(ref _buffer, newSize);
}
Debug.Assert(FreeCapacity > 0 && FreeCapacity >= sizeHint);
}
private static void ThrowInvalidOperationException_AdvancedTooFar(int capacity)
{
throw new InvalidOperationException(SR.Format(SR.BufferWriterAdvancedTooFar, capacity));
}
}
}
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