sample5.cs

async Task ProcessLinesAsync(Socket socket)
{
    var pipe = new Pipe();
    Task writing = FillPipeAsync(socket, pipe.Writer);
    Task reading = ReadPipeAsync(pipe.Reader);

    return Task.WhenAll(reading, writing);
}

async Task FillPipeAsync(Socket socket, PipeWriter writer)
{
    const int minimumBufferSize = 512;

    while (true)
    {
        // Allocate at least 512 bytes from the PipeWriter
        Memory<byte> memory = writer.GetMemory(minimumBufferSize);
        try 
        {
            int bytesRead = await socket.ReceiveAsync(memory, SocketFlags.None);
            if (bytesRead == 0)
            {
                break;
            }
            // Tell the PipeWriter how much was read from the Socket
            writer.Advance(bytesRead);
        }
        catch (Exception ex)
        {
            LogError(ex);
            break;
        }

        // Make the data available to the PipeReader
        FlushResult result = await writer.FlushAsync();

        if (result.IsCompleted)
        {
            break;
        }
    }

    // Tell the PipeReader that there's no more data coming
    writer.Complete();
}

async Task ReadPipeAsync(PipeReader reader)
{
    while (true)
    {
        ReadResult result = await reader.ReadAsync();

        ReadOnlySequence<byte> buffer = result.Buffer;
        SequencePosition? position = null;

        do 
        {
            // Look for a EOL in the buffer
            position = buffer.PositionOf((byte)'\n');

            if (position != null)
            {
                // Process the line
                ProcessLine(buffer.Slice(0, position.Value));
                
                // Skip the line + the \n character (basically position)
                buffer = buffer.Slice(buffer.GetPosition(1, position.Value));
            }
        }
        while (position != null);

        // Tell the PipeReader how much of the buffer we have consumed
        reader.AdvanceTo(buffer.Start, buffer.End);

        // Stop reading if there's no more data coming
        if (result.IsCompleted)
        {
            break;
        }
    }

    // Mark the PipeReader as complete
    reader.Complete();
}

Line 1 contains an error: it should not use the async keyword since it returns an unawaited Task directly.