DearFTP/DearFTP/Connection/Commands/StoreCommand.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net.Sockets;
using System.Text;

namespace DearFTP.Connection.Commands
{
    class StoreCommand : ICommand
    {
        public const int BufferSize = 4096;

        public string[] Aliases { get; } = new string[]
        {
            "APPE",
            "STOR",
            "STOU"
        };

        public void Execute(Session session, FtpStream stream, string alias, string argument)
        {
            var dataConnection = session.DataConnection;

            if (!dataConnection.IsAvailable)
            {
                stream.Send(ResponseCode.DataConnectionOpenError, "Passive mode not activated.");
                return;
            }

            string path = alias.ToUpper() == "STOU" ? Path.GetRandomFileName() : argument;

            var (navigablePath, realPath) = session.NavigablePath.GetNewSystemFilePath(path);

            if (realPath == null)
            {
                stream.Send(ResponseCode.FileUnavailable, "Invalid destination path.");
                return;
            }

            if (Directory.Exists(realPath))
            {
                stream.Send(ResponseCode.FileUnavailable, "A directory with this name already exists.");
                return;
            }

            if (!session.WritablesShares.Contains(navigablePath.CurrentShare))
            {
                stream.Send(ResponseCode.FileUnavailable, "You don't have write access to this file.");
                return;
            }

            stream.Send(ResponseCode.FileStatusOK, "Waiting file.");

            ReceiveFile(dataConnection.Stream, realPath, alias.ToUpper() == "APPE");

            dataConnection.Close();

            stream.Send(ResponseCode.CloseDataConnection, "File received.");
        }

        private void ReceiveFile(NetworkStream stream, string path, bool append)
        {
            using (var file = File.Open(path, append ? FileMode.Append : FileMode.Create))
            {
                Span<byte> buffer = stackalloc byte[BufferSize];
                int readBytes;

                while ((readBytes = stream.Read(buffer)) > 0)
                {
                    if (readBytes < BufferSize)
                    {
                        file.Write(buffer.Slice(0, readBytes));
                    }
                    else
                    {
                        file.Write(buffer);
                    }
                }
            }
        }
    }
}