Sending big files in socket programming c#

Question

I want to send big files with socket in c#. File can be transferred but when I want to open it, I see it is damaged. What's the problem? I broke the file to 2KB in array in client code and send it. Then, in server code, I received it and put it in byte array and convert to file.

server code:

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

namespace MyServer
{
    class Program
    {
        static void Main(string[] args)
        {
            bool full = false;
            byte[] data = new byte[2049];
            byte[] bsize = new byte[2048];
            List<byte> bytes = new List<byte>();
            IPEndPoint ipep = new IPEndPoint(IPAddress.Any, 9050);
            Socket newsock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            newsock.Bind(ipep);
            newsock.Listen(100);
            Console.WriteLine("Wating For Client ...");
            Socket client = newsock.Accept();
            IPEndPoint clientep = (IPEndPoint)client.RemoteEndPoint;
            Console.WriteLine("Connected with {0} at port {1}",clientep.Address,clientep.Port);
            Console.Write("Enter the name of file:  ");
            string Address = Console.ReadLine();
            client.Receive(bsize);
            int size = BitConverter.ToInt32(bsize, 0);
            byte[] bytes2 = new byte[size];
            int k = 0;
            while (true)
            {
                client.Receive(data);
                for(int i = k,j=0; i < k + 2048 && j<2048; i++,j++)
                {
                    if (i == size)
                    {
                        full = true;
                        break;
                    }
                    bytes2[i] = data[j];
                    //bytes.Insert(i,data[j]);
                }
                k += 2048;
                if (full == true)
                    break;
                /*if (bytes.Count >= size)
                    break;*/
            }
            File.WriteAllBytes(@"G:\"+Address,bytes2 /*bytes.ToArray()*/);
            Console.WriteLine("Disconnected from Client {0}",clientep.Address);
            client.Close();
            newsock.Close();
            Console.ReadKey();
        }
    }
}

client code:

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

namespace MyClient
{
    class Program
    {
        static void Main(string[] args)
        {
            int reza = 0;
            IPEndPoint ipep = new IPEndPoint(IPAddress.Parse("192.168.0.2"), 9050);
            Socket server = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            try
            {
                server.Connect(ipep);
            }
            catch (SocketException e)
            {
                Console.WriteLine("Unable to connect to Server");
                Console.WriteLine(e.ToString());
                Console.ReadKey();
                return;
            }
            Console.Write("Enter Address Of File:");
            string Address = Console.ReadLine();
            FileStream File = new FileStream(Address, FileMode.Open, FileAccess.Read);
            byte[] bytes = System.IO.File.ReadAllBytes(@Address);
            File.Close();
            byte[] data = new byte[2048];
            byte[] Size = BitConverter.GetBytes(bytes.Length);
            server.Send(Size, Size.Length, SocketFlags.None);
            for (int i = 0; i <= bytes.Length; i +=2048)
            {
                int k = i + 2048;
                for(int j=i,d=0 ;j< k && j<bytes.Length; j++,d++)
                {
                    data[d] = bytes[j];
                    reza++;
                }
                if (reza == 2048)
                {
                    server.Send(data, data.Length, SocketFlags.None);
                    Console.Write("*");
                    reza = 0;
                }
                else
                {
                    server.Send(data, reza, SocketFlags.None);
                    Console.WriteLine("*");
                }
            }
            Console.WriteLine("Disconnecting from server ...");
            server.Shutdown(SocketShutdown.Both);
            server.Close();
            Console.ReadKey();
        }
    }
}

What happens when you compare two files in a hex editor? Do they look completely different? Try sending a file smaller than 2KB and compare them. — Alexey, Jan 14 '16 at 13:28
I compare them they are different and when transfer smaller than 2KB file all of bytes are Zero!!!!!!! — R.MSZD, Jan 14 '16 at 14:13

jgauffin · Answer 1 · 2016-01-14T14:24:58.817

The problem is that you ignore the return value from Receive(). There is no guarantee what-so-ever that your buffer will be completely filled.

The return value tells you how much data that the socket actually read from the network. Adjust your receiving code so it's taken into account. Same goes for the send. If the internal socket buffer gets full it will report less bytes sent than you have requested to send.

Other than that, I suggest you start to give your variables meaningful names. Your code is not very readable as is.

Here is a better receive routine:

var fileBuffer = new byte[size];
var receiveBuffer = new byte[2048];
var bytesLeftToReceive = size;
var fileOffset = 0;

while (bytesLeftToReceive > 0)
{
    //receive
    var bytesRead = client.Receive(receiveBuffer);
    if (bytesRead == 0) 
        throw new InvalidOperationException("Remote endpoint disconnected");

    //if the socket is used for other things after the file transfer
    //we need to make sure that we do not copy that data
    //to the file
    int bytesToCopy = Math.Min(bytesRead, bytesLeftToReceive);

    // copy data from our socket buffer to the file buffer.
    Buffer.BlockCopy(receiveBuffer, 0, bytesLeftToReceive, fileBuffer, fileOffset);

    //move forward in the file buffer
    fileOffset += bytesToCopy;

    //update our tracker.
    bytesLeftToReceive -= bytesToCopy;
}

However, since you are transferring large files, isn't it better to write it directly to a file stream?

var stream = File.Create(@"C:\path\to\file.dat");
var receiveBuffer = new byte[2048];
var bytesLeftToReceive = size;

while (bytesLeftToReceive > 0)
{
    //receive
    var bytesRead = client.Receive(receiveBuffer);
    if (bytesRead == 0) 
        throw new InvalidOperationException("Remote endpoint disconnected");

    //if the socket is used for other things after the file transfer
    //we need to make sure that we do not copy that data
    //to the file
    int bytesToCopy = Math.Min(bytesRead, bytesLeftToReceive);

    // write to file
    stream.Write(receiveBuffer, 0, bytesToCopy);

    //update our tracker.
    bytesLeftToReceive -= bytesToCopy;
}

On the send side I would do something like this:

// read directly from the file to reduce memory usage.
var fileName = @"....";
using (var file = File.OpenRead(fileName))
{
    var sendBuffer = new byte[2048];
    var fileSize = BitConverter.GetBytes((int)file.Length);
    server.Send(fileSize, fileSize.Length, SocketFlags.None);

    var bytesLeftToTransmit = fileSize;
    while (bytesLeftToTransmit > 0)
    {
        var dataToSend = file.Read(sendBuffer, 0, sendBuffer.Length);
        bytesLeftToTransmit -= dataToSend;

        //loop until the socket have sent everything in the buffer.
        var offset=0;
        while (dataToSend > 0)
        {
            var bytesSent = socket.Send(sendBuffer, offset, dataToSend);
            dataToSend -= bytesSent;
            offset += bytesSent;
        }
    }
}

Finally you have a Socket.SendFile which have been optimized to send files. You can invoke it at any time for an open socket.

_"The problem is that you ignore the return value from Receive()"_ - every. socket. question. ever. — CodeCaster, Jan 14 '16 at 14:22
i am beginner and i don't understand your code! :( can you fix my code?! — R.MSZD, Jan 14 '16 at 14:52
then I strongly suggest that you paste it into a Visual Studio console application to study and learn it. .. or stop using sockets.. — jgauffin, Jan 14 '16 at 15:01
Can someone tell me, how the receiver know the "size" of the file sent? Do we first send another message which tells the datatype and filesize first? And then we send the file afteward? — Fandi Susanto, Jul 16 '17 at 11:48

Sending big files in socket programming c#

1 Answers1

Linked