Byte-array builder

ByteArrayBuilder.cs

public class ByteArrayBuilder
{
    private byte[] _buffer;
    public int Length { get; set; }

    public ByteArrayBuilder()
    {
        _buffer = new byte[4096];
        Length = 0;
    }

    public ByteArrayBuilder Append(byte b)
    {
        if (GetUnusedBufferLength() == 0)
        {
            _buffer = IncreaseCapacity(_buffer, _buffer.Length * 2);
        }
        _buffer[Length] = b;
        Length++;
        return this;
    }

    public ByteArrayBuilder Append(byte[] buffer)
    {
        var unusedBufferLength = GetUnusedBufferLength();
        if (unusedBufferLength < buffer.Length)
        {
            _buffer = IncreaseCapacity(_buffer, _buffer.Length + buffer.Length);
        }
        Array.Copy(buffer, 0, _buffer, Length, buffer.Length);
        Length += buffer.Length;
        return this;
    }

    public byte[] ToArray()
    {
        var unusedBufferLength = GetUnusedBufferLength();
        if (unusedBufferLength == 0)
        {
            return _buffer;
        }
        var result = new byte[Length];
        Array.Copy(_buffer, result, result.Length);
        return result;
    }

    private int GetUnusedBufferLength()
    {
        return _buffer.Length - Length;
    }

    private static byte[] IncreaseCapacity(byte[] buffer, int targetLength)
    {
        var result = new byte[targetLength];
        Array.Copy(buffer, result, buffer.Length);
        return result;
    }
}