TCP ZeroWindow Issue C#

Question

i have been writing a file server/client application in c# and it appeared to be working but then i realized the the stream was not being advanced and the client kept failing to receive from the server. so i checked wireshark and saw that my client was emitting TCPZeroWindow flagged packets. Any thoughts? Thanks.

Client :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net;
using System.Net.Sockets;
using System.IO;
namespace PortalClient
{
    class Program
    {
        static string s1;
        static byte[] data03;
        static int int02;
        static string str01;
        static int length;
        static IPEndPoint ipe01;
        static TcpClient tcp01;
        static FileStream s01;
        static string ip01;
        static string port01;
        static string path01;
        static byte[] data01;
        static byte[] data02;
        static byte[] data04;
        static void Main(string[] args)
        {

            while (true)
            {
            label1:
                {
                    try
                    {
                        string version = "V:1.1.4";
                        Console.Title = (" Portal Client " + version);
                        ConsoleColor ccolor1 = new ConsoleColor();
                        ccolor1 = Console.ForegroundColor;
                        Console.ForegroundColor = ConsoleColor.Green;
                        Console.WriteLine();
                        Console.WriteLine("         PORTAL CLIENT " + version);
                        Console.WriteLine();
                        Console.ForegroundColor = ccolor1;
                        data01 = new byte[20];
                        data03 = new byte[100];
                        data04 = new byte[100];
                        Console.Write(" Enter IPv4 address of server : ");
                        ip01 = Console.ReadLine();
                        Console.Write(" Enter port to connect on : ");
                        port01 = Console.ReadLine();
                        ipe01 = new IPEndPoint(IPAddress.Parse(ip01), Convert.ToInt32(port01));
                        tcp01 = new TcpClient();
                        tcp01.ReceiveTimeout = 2500;
                        tcp01.NoDelay = true;
                        Console.WriteLine(" Connecting...");
                        tcp01.Connect(ipe01);
                        Console.WriteLine(" Done.");
                        tcp01.Client.Receive(data04, SocketFlags.None);
                        System.Threading.Thread.Sleep(100);
                        Console.WriteLine(" Server message : " + Encoding.UTF8.GetString(data04));
                        tcp01.Client.Receive(data03, SocketFlags.None);
                        System.Threading.Thread.Sleep(100);
                        Console.WriteLine(" File on server : " + Encoding.UTF8.GetString(data03));
                        tcp01.Client.Receive(data01, SocketFlags.None);
                        System.Threading.Thread.Sleep(100);
                        str01 = Encoding.UTF8.GetString(data01);
                        Console.WriteLine();
                        Console.WriteLine(" file size : " + str01);
                        Console.WriteLine();
                        Console.Write(" Enter the number you see above : ");
                        length = Convert.ToInt32(Console.ReadLine());
                        Console.Write(" Save file as : ");
                        path01 = Console.ReadLine();
                        for (int i = 1; i <= 9000; i++)
                        {
                            if (length % i == 0) { int02 = i; }
                        }
                        if (length < 9000) { int02 = length; }
                        int int03 = length / int02;
                        s01 = File.OpenWrite(@path01);
                        Console.WriteLine(" Receiving file from " + tcp01.Client.RemoteEndPoint.ToString() + "...");
                        tcp01.Client.Send(new byte[1], SocketFlags.None);
                        System.Threading.Thread.Sleep(1000);
                        for (int i = 0; i <= int03; i++)
                        {
                            bool bool1 = false;
                            data02 = new byte[int02];
                            int n = tcp01.Client.Receive(data02, 0, int02, SocketFlags.None);
                            while (n < int02)
                            {
                                Console.WriteLine(" Entered Loop ");
                                int int04 = int02 - n;
                                tcp01.Client.Send(Encoding.UTF8.GetBytes("2"), 0, 1, SocketFlags.None);
                                int int05 = 0;
                                byte[] data05 = new byte[int04];
                                if (int04 >= 1 && int04 <= 9) { s1 = int04 + "xxx"; }
                                if (int04 >= 10 && int04 <= 99) { s1 = int04 + "xx"; }
                                if (int04 >= 100 && int04 <= 999) { s1 = int04 + "x"; }
                                if (int04 >= 1000 && int04 <= 9000) { s1 = int04.ToString(); }
                                tcp01.Client.Send(Encoding.UTF8.GetBytes(s1), 0, 4, SocketFlags.None);
                                int05 = tcp01.Client.Receive(data05, 0, int04, SocketFlags.None);
                                n = n + int05;
                                s01.Write(data05, 0, int05);
                                bool1 = true;
                            }
                            if (bool1 == false)
                            {
                                s01.Write(data02, 0, int02);
                                tcp01.Client.Send(new byte[1], 0, 1, SocketFlags.None);
                            }
                        }
                        System.Threading.Thread.Sleep(1000);
                        s01.Close();
                        Console.WriteLine(" Received all data.");
                        Console.WriteLine(" Press enter to disconnect...");
                        Console.ReadLine();
                        tcp01.Client.Send(new byte[1], SocketFlags.None);
                        System.Threading.Thread.Sleep(1000);
                        Console.WriteLine(" Disconnecting...");
                        tcp01.Close();
                        Console.WriteLine(" Done.");
                    }
                    catch (Exception e)
                    {
                        Console.WriteLine(" Error! : " + e.Message.ToString() + " - " + e.Data.ToString() + " - " + e.TargetSite.ToString()); if (!(tcp01 == null)) { tcp01.Close(); } if (!(s01 == null)) { s01.Close(); goto label1; }
                    }
                }

            }
        }
    }
}

Server :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net;
using System.Net.Sockets;
using System.IO;
namespace PortalServer
{
    class Program
    {
        static long length;
        static int int03;
        static int int02;
        static TcpListener tcp01;
        static TcpClient tcp02;
        static FileStream s01;
        static byte[] data01;
        static byte[] data03;
        static byte[] data04;
        static byte[] data05;
        static string str01;
        static string str02;
        static IPEndPoint ipe01;
        static string port01;
        static void Main(string[] args)
        {
            while (true)
            {
            label1:
                try
                {
                    string version = "V:1.1.4";
                    Console.Title = (" Portal Server " + version);
                    ConsoleColor ccolor1 = new ConsoleColor();
                    ccolor1 = Console.ForegroundColor;
                    Console.ForegroundColor = ConsoleColor.Green;
                    Console.WriteLine();
                    Console.WriteLine("         PORTAL SERVER " + version);
                    Console.WriteLine();
                    Console.ForegroundColor = ccolor1;
                    Console.Write(" Enter port for connecting clients : ");
                    port01 = Console.ReadLine();
                    Console.Write(" Enter path of file to send : ");
                    str01 = Console.ReadLine();
                    ipe01 = new IPEndPoint(IPAddress.Any, Convert.ToInt32(port01));
                    tcp01 = new TcpListener(ipe01);
                    Console.Write(" Enter server message : ");
                    str02 = Console.ReadLine();
                    s01 = File.OpenRead(@str01);
                    length = s01.Length;
                    for (int i = 1; i <= 9000; i++)
                    {
                        if (length % i == 0) { int02 = i; } 
                    }
                    if (length < 9000) { int02 = (int)length;}

                    int03 = (int)length / int02;
                    tcp01.Start();
                    Console.WriteLine(" Server started. Waiting for clients...");
                    tcp02 = tcp01.AcceptTcpClient();
                    tcp02.Client.NoDelay = true;
                    Console.WriteLine(" Client " + tcp02.Client.RemoteEndPoint.ToString() + " connected.");
                    data05 = Encoding.UTF8.GetBytes(str02);
                    tcp02.Client.Send(data05, SocketFlags.None);
                    System.Threading.Thread.Sleep(500);
                    data04 = Encoding.UTF8.GetBytes(str01);
                    tcp02.Client.Send(data04, SocketFlags.None);
                    System.Threading.Thread.Sleep(500);
                    data03 = Encoding.UTF8.GetBytes(length.ToString());
                    tcp02.Client.Send(data03, SocketFlags.None);
                    System.Threading.Thread.Sleep(500);
                    Console.WriteLine(" Waiting for response...");
                    tcp02.Client.Receive(new byte[1], SocketFlags.None);
                    Console.WriteLine(" Received response...");
                    Console.WriteLine(" Sending file to " + tcp02.Client.RemoteEndPoint.ToString() + "...");
                    System.Threading.Thread.Sleep(1);
                    for (int i = 0; i <= int03;i++ )
                    {
                        System.Threading.Thread.Sleep(30);
                        data01 = new byte[int02];
                        s01.Read(data01, 0, data01.Length);
                        int n = tcp02.Client.Send(data01, 0 ,data01.Length, SocketFlags.None);
                        if (n != int02) { throw new Exception("unable to write bytes, insufficient memory."); }
                        byte[] data07 = new byte[1];
                        while (true)
                        {
                            tcp02.Client.Receive(data07,0,1,SocketFlags.None);
                            if (Encoding.UTF8.GetString(data07) == "2") 
                            {
                                byte[] data06 = new byte[4];
                                int b = tcp02.Client.Receive(data06, 0, 4, SocketFlags.None);
                                if (b != 4) { throw new Exception("ex1"); }
                                string s1 = Encoding.UTF8.GetString(data06);
                                s1 = s1.Replace("x", "");
                                int int05 = Convert.ToInt32(s1);
                                int int06 = int02 - int05;
                                byte[] data08 = new byte[int05];
                                Buffer.BlockCopy(data01, int06, data08, 0, int05);
                                tcp02.Client.Send(data08, 0, data08.Length, SocketFlags.None);
                                System.Threading.Thread.Sleep(30);
                            }
                            break;
                        }
                    }
                    System.Threading.Thread.Sleep(1000);
                    s01.Close();
                    Console.WriteLine(" All data sent.");
                    Console.WriteLine(" Waiting for terminate message...");
                    tcp02.Client.Receive(new byte[1], SocketFlags.None);
                    Console.WriteLine(" Received terminate message.");
                    tcp02.Close();
                    Console.WriteLine(" Stopping client and server.");
                    tcp01.Stop();
                    Console.WriteLine(" Done. Restarting.");

                }

                catch (Exception e)
                {
                    Console.WriteLine(" Error! : " + e.Message.ToString() + " - " + e.Data.ToString() + " - " + e.TargetSite.ToString());
                    if (!(tcp02 == null)) { tcp02.Close(); }
                    if (!(tcp01 == null)) { tcp01.Stop(); goto label1; }
                }
            }
        }
    }
}

Answer 1

I used separate threads for the heavy lifting send / receive methods, increased buffer size, increased time between sends, made sure fragmentation was on. works like a charm now.

client :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net;
using System.Net.Sockets;
using System.IO;
using System.ComponentModel;
namespace PortalClient
{
    class Program
    {
        static int partloop;
        static bool bool1;
        static byte[] data05;
        static int int03;
        static int int04;
        static int int05;
        static int numbytesreceived;
        static BackgroundWorker bw1;
        static int bytestoreceive;
        static string s1;
        static byte[] data03;
        static int int02;
        static string str01;
        static int length;
        static IPEndPoint ipe01;
        static TcpClient tcp01;
        static FileStream s01;
        static string ip01;
        static string port01;
        static string path01;
        static byte[] data01;
        static byte[] data02;
        static byte[] data04;
        static void Main(string[] args)
        {
            newvoid();
        }
        static void newvoid()
        {
            while (true)
            {
                try
                {
                    Console.Clear();
                    Console.WindowWidth = 95;
                    string version = "V:1.1.4";
                    Console.Title = (" Portal Client " + version);
                    ConsoleColor ccolor1 = new ConsoleColor();
                    ccolor1 = Console.ForegroundColor;
                    Console.ForegroundColor = ConsoleColor.Green;
                    Console.WriteLine();
                    Console.WriteLine(@"
 __________              __         .__    _________ .__  .__               __   
 \______   \____________/  |______  |  |   \_   ___ \|  | |__| ____   _____/  |_ 
  |     ___/  _ \_  __ \   __\__  \ |  |   /    \  \/|  | |  |/ __ \ /    \   __\
  |    |  (  <_> )  | \/|  |  / __ \|  |__ \     \___|  |_|  \  ___/|   |  \  |  
  |____|   \____/|__|   |__| (____  /____/  \______  /____/__|\___  >___|  /__|  
                                  \/               \/             \/     \/       " + version);
                    Console.WriteLine();
                    Console.ForegroundColor = ccolor1;
                    data01 = new byte[20];
                    data03 = new byte[100];
                    data04 = new byte[100];
                    Console.Write(" Enter IPv4 address of server : ");
                    ip01 = Console.ReadLine();
                    Console.Write(" Enter port to connect on : ");
                    port01 = Console.ReadLine();
                    ipe01 = new IPEndPoint(IPAddress.Parse(ip01), Convert.ToInt32(port01));
                    tcp01 = new TcpClient();
                    Console.WriteLine(" Connecting...");
                    tcp01.Connect(ipe01);
                    Console.WriteLine(" Done.");
                    tcp01.Client.Receive(data04, SocketFlags.None);
                    System.Threading.Thread.Sleep(100);
                    Console.WriteLine(" Server message : " + Encoding.UTF8.GetString(data04));
                    tcp01.Client.Receive(data03, SocketFlags.None);
                    System.Threading.Thread.Sleep(100);
                    Console.WriteLine(" File on server : " + Encoding.UTF8.GetString(data03));
                    tcp01.Client.Receive(data01, SocketFlags.None);
                    System.Threading.Thread.Sleep(100);
                    str01 = Encoding.UTF8.GetString(data01);
                    Console.WriteLine();
                    Console.WriteLine(" file size : " + str01);
                    Console.WriteLine();
                    Console.Write(" Enter the number you see above : ");
                    length = Convert.ToInt32(Console.ReadLine());
                    bytestoreceive = length;
                    Console.Write(" Save file as : ");
                    path01 = Console.ReadLine();
                    for (int i = 1; i <= 60000; i++)
                    {
                        if (length % i == 0) { int02 = i; }
                    }
                    if (length < 60000) { int02 = length; }
                    int03 = length / int02;
                    s01 = File.OpenWrite(@path01);
                    Console.WriteLine(" Receiving file from " + tcp01.Client.RemoteEndPoint.ToString() + "...");
                    tcp01.Client.Send(new byte[1], SocketFlags.None);
                    System.Threading.Thread.Sleep(1000);
                    while (bytestoreceive > 0)
                    {
                        bw1 = new BackgroundWorker();
                        bw1.DoWork += new DoWorkEventHandler(bw1_DoWork);
                        bw1.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw1_RunWorkerCompleted);
                        bool1 = false;
                        numbytesreceived = 0;
                        data02 = new byte[int02];
                        bw1.RunWorkerAsync();
                        while (numbytesreceived == 0) { }
                        while (numbytesreceived < int02)
                        {
                            bw1 = new BackgroundWorker();
                            bw1.DoWork += new DoWorkEventHandler(bw1_DoWork);
                            bw1.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw1_RunWorkerCompleted);
                            bool1 = true;
                            partloop += 1;
                            int04 = int02 - numbytesreceived;
                            tcp01.Client.Send(Encoding.UTF8.GetBytes("2"), 0, 1, SocketFlags.None);
                            int05 = 0;
                            data05 = new byte[int04];
                            if (int04 >= 1 && int04 <= 9) { s1 = int04 + "xxxx"; }
                            if (int04 >= 10 && int04 <= 99) { s1 = int04 + "xxx"; }
                            if (int04 >= 100 && int04 <= 999) { s1 = int04 + "xx"; }
                            if (int04 >= 1000 && int04 <= 9999) { s1 = int04 + "x"; }
                            if (int04 > 10000 && int04 <= 60000) { s1 = int04.ToString(); }
                            tcp01.Client.Send(Encoding.UTF8.GetBytes(s1), 0, 5, SocketFlags.None);
                            bw1.RunWorkerAsync();
                            while (int05 == 0) { }
                            if (int05 == 0) { throw new Exception("ex1"); }
                            numbytesreceived += int05;
                            bytestoreceive -= numbytesreceived;
                            s01.Write(data05, 0, data05.Length);
                            Console.WriteLine(" Received " + (length - bytestoreceive) + " / " + length + " bytes | P.B.R. loops: " + partloop.ToString());
                            Console.SetCursorPosition(0, Console.CursorTop - 1);
                        }

                        if (bool1 == false)
                        {

                            bytestoreceive -= numbytesreceived;
                            s01.Write(data02, 0, int02);
                            tcp01.Client.Send(new byte[1], 0, 1, SocketFlags.None);
                            Console.WriteLine(" Received " + (length - bytestoreceive) + " / " + length + " bytes | P.B.R. loops: " + partloop.ToString());
                            Console.SetCursorPosition(0, Console.CursorTop - 1);
                        }
                    }
                    Console.SetCursorPosition(0, Console.CursorTop + 1);
                    Console.WriteLine();
                    System.Threading.Thread.Sleep(500);
                    s01.Close();
                    Console.WriteLine(" Received all data.");
                    Console.WriteLine(" Press enter to disconnect...");
                    Console.ReadLine();
                    tcp01.Client.Send(new byte[1], SocketFlags.None);
                    System.Threading.Thread.Sleep(1000);
                    Console.WriteLine(" Disconnecting...");
                    tcp01.Close();
                    Console.WriteLine(" Done.");
                }
                catch (Exception e)
                {
                    Console.WriteLine(" Error! : " + e.Message.ToString() + " - " + e.Data.ToString() + " - " + e.TargetSite.ToString());
                    if (!(tcp01 == null)) { tcp01.Close(); }
                    if (!(s01 == null)) { s01.Close(); }
                    Console.Write(" Press enter to continue..."); Console.ReadLine();
                    newvoid();
                }
            }
        }

        static void bw1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            try
            {
                bw1.Dispose();
            }
            catch (Exception e1)
            {
                Console.WriteLine(" Error! : " + e1.Message.ToString() + " - " + e1.Data.ToString() + " - " + e1.TargetSite.ToString());
                if (!(tcp01 == null)) { tcp01.Close(); }
                if (!(s01 == null)) { s01.Close(); }
                Console.Write(" Press enter to continue..."); Console.ReadLine();
                newvoid();
            }
        }

        static void bw1_DoWork(object sender, DoWorkEventArgs e)
        {
            try
            {
                if (bool1 == false)
                {
                    numbytesreceived = tcp01.Client.Receive(data02, 0, int02, SocketFlags.None);
                }
                if (bool1 == true)
                {
                    int05 = tcp01.Client.Receive(data05, 0, int04, SocketFlags.None);
                }
            }
            catch (Exception e2)
            {
                Console.WriteLine(" Error! : " + e2.Message.ToString() + " - " + e2.Data.ToString() + " - " + e2.TargetSite.ToString());
                if (!(tcp01 == null)) { tcp01.Close(); }
                if (!(s01 == null)) { s01.Close(); }
                Console.Write(" Press enter to continue..."); Console.ReadLine();
                newvoid();
            }
        }
    }
}

server:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net;
using System.Net.Sockets;
using System.IO;
using System.ComponentModel;
namespace PortalServer
{
    class Program
    {
        static int bytesresent;
        static BackgroundWorker bw1;
        static int int06;
        static int int05;
        static string string01;
        static int bytesCreceived;
        static byte[] data06;
        static byte[] data07;
        static byte[] data08;
        static int bytessent;
        static bool bool1;
        static int bytestosend;
        static long length;
        static int int03;
        static int int02;
        static TcpListener tcp01;
        static TcpClient tcp02;
        static FileStream s01;
        static byte[] data01;
        static byte[] data03;
        static byte[] data04;
        static byte[] data05;
        static string str01;
        static string str02;
        static IPEndPoint ipe01;
        static string port01;
        static void Main(string[] args)
        {
            newvoid();
        }
        static void newvoid()
        {
            while (true)
            {
                try
                {
                    Console.Clear();
                    Console.WindowWidth = 95;
                    string version = "V:1.1.4";
                    Console.Title = (" Portal Server " + version);
                    ConsoleColor ccolor1 = new ConsoleColor();
                    ccolor1 = Console.ForegroundColor;
                    Console.ForegroundColor = ConsoleColor.Green;
                    Console.WriteLine();
                    Console.WriteLine(@"
 __________              __         .__      _________                                
 \______   \____________/  |______  |  |    /   _____/ ______________  __ ___________ 
  |     ___/  _ \_  __ \   __\__  \ |  |    \_____  \_/ __ \_  __ \  \/ // __ \_  __ \
  |    |  (  <_> )  | \/|  |  / __ \|  |__  /        \  ___/|  | \/\   /\  ___/|  | \/
  |____|   \____/|__|   |__| (____  /____/ /_______  /\___  >__|    \_/  \___  >__|   
                                  \/               \/     \/                 \/       " + version);
                    Console.WriteLine();
                    Console.ForegroundColor = ccolor1;
                    Console.Write(" Enter port for connecting clients : ");
                    port01 = Console.ReadLine();
                    Console.Write(" Enter path of file to send : ");
                    str01 = Console.ReadLine();
                    ipe01 = new IPEndPoint(IPAddress.Any, Convert.ToInt32(port01));
                    tcp01 = new TcpListener(ipe01);
                    Console.Write(" Enter server message : ");
                    str02 = Console.ReadLine();
                    s01 = File.OpenRead(@str01);
                    length = s01.Length;
                    bytestosend = (int)length;
                    for (int i = 1; i <= 60000; i++)
                    {
                        if (length % i == 0) { int02 = i; }
                    }
                    if (length < 60000) { int02 = (int)length; }

                    int03 = (int)length / int02;
                    tcp01.Start();
                    Console.WriteLine(" Server started. Waiting for clients...");
                    tcp02 = tcp01.AcceptTcpClient();
                    Console.WriteLine(" Client " + tcp02.Client.RemoteEndPoint.ToString() + " connected.");
                    data05 = Encoding.UTF8.GetBytes(str02);
                    tcp02.Client.Send(data05, SocketFlags.None);
                    System.Threading.Thread.Sleep(500);
                    data04 = Encoding.UTF8.GetBytes(str01);
                    tcp02.Client.Send(data04, SocketFlags.None);
                    System.Threading.Thread.Sleep(500);
                    data03 = Encoding.UTF8.GetBytes(length.ToString());
                    tcp02.Client.Send(data03, SocketFlags.None);
                    System.Threading.Thread.Sleep(500);
                    Console.WriteLine(" Waiting for response...");
                    tcp02.Client.Receive(new byte[1], SocketFlags.None);
                    Console.WriteLine(" Received response...");
                    Console.WriteLine(" Sending file to " + tcp02.Client.RemoteEndPoint.ToString() + "...");
                    System.Threading.Thread.Sleep(1);
                    while (bytestosend > 0)
                    {
                        System.Threading.Thread.Sleep(50);
                        bool1 = false;
                        bytessent = 0;
                        bw1 = new BackgroundWorker();
                        bw1.DoWork += new DoWorkEventHandler(bw1_DoWork);
                        bw1.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw1_RunWorkerCompleted);
                        data01 = new byte[int02];
                        s01.Read(data01, 0, data01.Length);
                        bw1.RunWorkerAsync();
                        while (bytessent == 0) { }
                        if (bytessent != int02) { throw new Exception("unable to write bytes, insufficient memory."); }
                        while (true)
                        {
                            data07 = new byte[1];
                            tcp02.Client.Receive(data07, 0, 1, SocketFlags.None);
                            if (Encoding.UTF8.GetString(data07) == "2")
                            {
                                bytesresent = 0;
                                bool1 = true;
                                bw1 = new BackgroundWorker();
                                bw1.DoWork += new DoWorkEventHandler(bw1_DoWork);
                                bw1.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw1_RunWorkerCompleted);
                                data06 = new byte[5];
                                bytesCreceived = tcp02.Client.Receive(data06, 0, 5, SocketFlags.None);
                                if (bytesCreceived != 5) { throw new Exception("invalid client response."); }
                                string01 = Encoding.UTF8.GetString(data06);
                                string01 = string01.Replace("x", "");
                                int05 = Convert.ToInt32(string01);
                                int06 = int02 - int05;
                                bytestosend -= int05;
                                data08 = new byte[int05];
                                Buffer.BlockCopy(data01, int06, data08, 0, int05);
                                bw1.RunWorkerAsync();
                                while (bytesresent == 0) { }
                                Console.WriteLine(" Sent " + (length - bytestosend) + " / " + length + " bytes");
                                Console.SetCursorPosition(0, Console.CursorTop - 1);
                                System.Threading.Thread.Sleep(50);
                            }
                            if (Encoding.UTF8.GetString(data07) != "2")
                            {
                                bool1 = false;
                                bytestosend -= bytessent;
                                Console.WriteLine(" Sent " + (length - bytestosend) + " / " + length + " bytes");
                                Console.SetCursorPosition(0, Console.CursorTop - 1);
                                break;
                            }
                        }
                    }
                    Console.SetCursorPosition(0, Console.CursorTop + 1);
                    Console.WriteLine();
                    System.Threading.Thread.Sleep(500);
                    s01.Close();
                    Console.WriteLine(" All data sent.");
                    Console.WriteLine(" Waiting for terminate message...");
                    tcp02.Client.Receive(new byte[1], SocketFlags.None);
                    Console.WriteLine(" Received terminate message.");
                    tcp02.Close();
                    Console.WriteLine(" Stopping client and server.");
                    tcp01.Stop();
                    Console.WriteLine(" Done. Press enter to continue...");
                    Console.ReadLine();
                }

                catch (Exception e)
                {
                    Console.WriteLine(" Error! : " + e.Message.ToString() + " - " + e.Data.ToString() + " - " + e.TargetSite.ToString());
                    if (!(tcp02 == null)) { tcp02.Close(); }
                    if (!(tcp01 == null)) { tcp01.Stop(); }
                    if (!(s01 == null)) { s01.Close(); }
                    Console.Write(" Press enter to continue..."); Console.ReadLine();
                    newvoid();
                }
            }
        }

        static void bw1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            try
            {
                bw1.Dispose();
            }
            catch (Exception e1)
            {
                Console.WriteLine(" Error! : " + e1.Message.ToString() + " - " + e1.Data.ToString() + " - " + e1.TargetSite.ToString());
                if (!(tcp02 == null)) { tcp02.Close(); }
                if (!(tcp01 == null)) { tcp01.Stop(); }
                if (!(s01 == null)) { s01.Close(); }
                Console.Write(" Press enter to continue..."); Console.ReadLine();
                newvoid();
            }
        }

        static void bw1_DoWork(object sender, DoWorkEventArgs e)
        {
            try
            {
                if (bool1 == false)
                {
                    bytessent = tcp02.Client.Send(data01, 0, data01.Length, SocketFlags.None);
                }
                if (bool1 == true)
                {
                    bytesresent = tcp02.Client.Send(data08, 0, data08.Length, SocketFlags.None);
                }
            }
            catch(Exception e2)
            {
                Console.WriteLine(" Error! : " + e2.Message.ToString() + " - " + e2.Data.ToString() + " - " + e2.TargetSite.ToString());
                if (!(tcp02 == null)) { tcp02.Close(); }
                if (!(tcp01 == null)) { tcp01.Stop(); }
                Console.Write(" Press enter to continue..."); Console.ReadLine();
                if (!(s01 == null)) { s01.Close(); }
                newvoid();
            }
        }
    }
}

Answer 2

I've seen this happen if you are not emptying the network buffer correctly at the client end and the TCP window size is reduced to zero as a consequence.

This could be happening with your use of

tcp01.Client.Receive(data04, SocketFlags.None);

which may not be clearing the buffer sufficiently, see MSDN. You want to call Receive continuously until no further data is available.

If you would like a working example as a comparison please see here.