Text Reader Extensions

TextReaderExtensions.cs

using System;
using System.Buffers;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

public static class TextReaderExtensions
{

	public static async IAsyncEnumerable<ReadOnlyMemory<char>> SingleBufferReadAsync(
		this TextReader reader,
		int bufferSize = 4096)
	{
		var pool = MemoryPool<char>.Shared;
		using var A = pool.Rent(bufferSize);
		var buffer = A.Memory;

		while (true)
		{
			var n = await reader.ReadAsync(buffer).ConfigureAwait(false);
			if (n == 0) break;
			yield return n == buffer.Length ? buffer : buffer.Slice(0, n);
		}
	}

	public static async IAsyncEnumerable<ReadOnlyMemory<char>> DualBufferReadAsync(
		this TextReader reader,
		int bufferSize = 4096)
	{
		var pool = MemoryPool<char>.Shared;
		using var A = pool.Rent(bufferSize);
		using var B = pool.Rent(bufferSize);
		var cNext = A.Memory;
		var cCurrent = B.Memory;

		var next = reader.ReadAsync(cNext);
		while (true)
		{
			var n = await next.ConfigureAwait(false);
			if (n == 0) break;

			// Preemptive request before yielding.
			var current = reader.ReadAsync(cCurrent);
			yield return n == cNext.Length ? cNext : cNext.Slice(0, n);

			var swap = cNext;
			cNext = cCurrent;
			cCurrent = swap;
			next = current;
		}
	}

	public static async IAsyncEnumerable<string> PreemptiveReadLineAsync(
		this TextReader reader)
	{
		var next = reader.ReadLineAsync();
		while (true)
		{
			var n = await next.ConfigureAwait(false);
			if (n == null) break;

			// Preemptive request before yielding.
			next = reader.ReadLineAsync();
			yield return n;
		}
	}
}