Question

I made a client & server that establishes a TCP connection through sockets, I’m trying to send binary data over the socket but I could only send txt or pdf files, I had no luck with exe files, I use fread and fseek to read the file and split it into a buffer. When I read the whole exe file it gets sent successfully but when I split it, it gets sent corrupted!

I read some books about sockets but I still don’t know much and I have some questions.

is it okay to send the whole file in one send()?? or I should continue with sending it in small chunks?

Also, why exe files get corrupted when I send them in chunks?

Thank you!

Client Code (in c):

int bufSize = 10000;
int sentBytes = 0;


  FILE * pFile;
  long remainingBytes;
  char * buffer;
  size_t result;

  pFile = fopen ( "D:\\file.exe" , "rb" );
  fseek (pFile , 0 , SEEK_END);
  remainingBytes = ftell (pFile);
  rewind (pFile);

int bufferSize = remainingBytes > bufSize ? bufSize : remainingBytes;
buffer = (char*) malloc (sizeof(char)*bufferSize);
send(Socket, (char*)&remainingBytes, 4, 0);

while(remainingBytes > 0)
{
    fseek (pFile , sentBytes , SEEK_SET);
    result = fread(buffer,1,bufferSize,pFile);
    if(bufferSize < remainingBytes)
    {
        send(Socket, buffer, bufferSize, 0);
    }
    else
    {
        send(Socket, buffer, remainingBytes, 0);
        bufferSize = remainingBytes;
    }
    remainingBytes -= bufferSize;
    sentBytes += bufferSize;
}

Server code (in c#)

        try
        {
            int bufferSize = 200;
            int len = 0;
            int receivedBytes = 0;
            int remainingBytes = len;
            byte[] length = new byte[4];
            //byte[] imgBuf = new byte[bufferSize];

            int current = 0;
            List<byte[]> coming = new List<byte[]>();

            sockets[number].Receive(length,4,0);

            len = BitConverter.ToInt32(length, 0);
            remainingBytes = len;

            bufferSize = len < bufferSize ? len : bufferSize;

            while(receivedBytes < len)
            {
                if (remainingBytes > bufferSize)
                {
                    coming.Add(new byte[bufferSize]);
                    //imgBuf = new byte[bufferSize];
                    sockets[number].Receive(coming[current], bufferSize, 0);
                }
                else
                {
                    coming.Add(new byte[remainingBytes]);
                    //imgBuf = new byte[remainingBytes];
                    sockets[number].Receive(coming[current], remainingBytes, 0);
                    bufferSize = remainingBytes;
                }
                remainingBytes -= bufferSize;
                receivedBytes += bufferSize;
                current++;
                //Array.Clear(imgBuf, 0, imgBuf.Length);
            }

            using (var stream = new FileStream(@"C:\receivedFile.exe",FileMode.Create))
            {
                using (var binaryWriter = new BinaryWriter(stream))
                {
                    foreach (byte[] buffer in coming)
                    {
                        binaryWriter.Write(buffer);
                    }
                }

            }
        }
        catch (Exception ex)
        { this.setText(ex.Message, textBox2); }

Edit: Thanks for the help, I got it working 🙂

        try
        {
            int bufferSize = 1024 * 100;
            int len = 0;
            int receivedBytes = 0;
            int remainingBytes = len;
            int reached = 0;

            byte[] length = new byte[4];
            byte[] imgBuf = new byte[bufferSize];

            int current = 0;
            sockets[number].Receive(length,4,0);

            len = BitConverter.ToInt32(length, 0);
            remainingBytes = len;

            bufferSize = len < bufferSize ? len : bufferSize;
            imgBuf = new byte[len];

            while (reached < len)
            {
                reached += sockets[number].Receive(imgBuf, receivedBytes, remainingBytes, 0);
                remainingBytes = len - reached;
                receivedBytes = reached;
                current++;
                //Array.Clear(imgBuf, 0, imgBuf.Length);
            }

            using (var stream = new FileStream(@"C:\putty.exe",FileMode.Create))
            {
                using (var binaryWriter = new BinaryWriter(stream))
                {
                        binaryWriter.Write(imgBuf);
                }
            }
            Array.Clear(imgBuf, 0, imgBuf.Length);
        }
        catch (Exception ex)
        { this.setText(ex.Message, textBox2); }

Answer 1

You don’t check how many bytes you actually received in sockets[number].Receive(coming[current], bufferSize, 0); . It doesn’t have to be equal to the buffer size you have declared.
Additionaly, as said in comments, keeping whole file in memory is not a good idea.