Socket Destination Port Problem

Hi everybody,

I have an application where two different socket connections run in order to communicate with a machine. Over the first one (UDP) I send a request packet to ask for data and over the other one connection (TCP) I receive the data.
I repeat this procedure two times that is, I request a block of data and when it's finished I request a second one.By the first time it works without problems but by the second time I discovered with wireshark that the request packet is sent to another port (not over the original port). I know I haven't made changes between the first request call and the second one because I have a function where I initialize all connections at the beginning and it works for the first transmission.

Could the operative system change the destination port?

Can anyone help me?

Thank you very much

no, OS will not change port for you

why not to use same connection?

Hi,

I must use different connections (design requirements...)

try to post some code (a relevant minimal example), there is surely something that changes between the two requests.

Hi again,

Now I can describe the problem better

I have a tcp server that wait for data in the recv function after accept. I receive data buffer of 1500 bytes but I don't receive only one buffer. I receive more. The first time the socket receives something port=2000 (so it's right) but the second time and successively port=49154. Something is wrong with the receive function...

Code:

AcceptSocket = accept(socketInTCP, NULL, NULL);		 
		 if (AcceptSocket == INVALID_SOCKET)
		 {	 
			
			 printf("Server: WSA:\n");
			
		 }
		 else
		 {   
			 printf("Server: Client Connected!\n");
			 //Receive Packages from Client
			 while(run_tcpserver)
			 {  	bytesRecv = recv(AcceptSocket, recvbuf, sizeof(recvbuf), 0);
				if (bytesRecv > 0)
				{if(ctr1==1)
					{	
						WaitForSingleObject(mutex_req,INFINITE);
						//The first time it receives port = 2000
					}
				 
                                 //the second time and successively port =49154
                                 ctr1=0;
				 ofstream outfile(outputfile, ios::out |ios::ate | ios::binary);//open
				 rcv_data=rcv_data+bytesRecv;
				 cout << "\xd" << rcv_data;
				 
				 outfile.write (var, sizeof(var));
				 outfile.close();
				 memset(recvbuf,0,sizeof(recvbuf));
				 
                                 if(rcv_data==(length_dummy*4))
					{
						ReleaseMutex(mutex_req);
						
					}

have anyone any ideas??

I do not see where you do anything with the recv_buf

I don't know. but the destination port is wrong after successively recv...

that is my question....

now I have this code

Code:

while(AcceptSocket==SOCKET_ERROR)
{
   Acceptsocket=accept(socketInTCP,NULL;NULL)
}
socketInTCP=AcceptSocket
while(run_tcpserver)
		{  //comprobar length_dummy, abrir fichero, blucle, cerra fichero
			bytesRecv = recv(socketInTCP, recvbuf, sizeof(recvbuf), 0);
			if (bytesRecv > 0)
				{if(ctr1==1)
					{	
						
						p=ntohs(clientService.sin_port);
						cout << "port the first time it receives:" << p << "\n";
						m=0;
						
						
					}
					ctr1=0;
					port_array[m]=ntohs(clientService.sin_port);
					m++;

					ofstream outfile(outputfile, ios::out |ios::ate | ios::binary);//open
					rcv_data=rcv_data+bytesRecv;
					cout << "\xd" << rcv_data;
   					

				 outfile.write (var, sizeof(var));
				 outfile.close();
				 memset(recvbuf,0,sizeof(recvbuf));
				 if(rcv_data==(length_dummy*4))
					{
						
						ReleaseMutex(req_mutex);
					}
			 
			}
	}

the first time p=2000

and

the second time

port_array[0]=2000
but
port_array[1]=49154.....

I don't understand why after the TCP connection the destination port of my UDP connection is changed...but I have made debugging and I know that it occurs...

Sorry, I wrote something wrong,

the first time it receives port=2000

but the second time=49154 and not 2000

Originally Posted by radeberger

I don't understand why after the TCP connection the destination port of my UDP connection is changed...but I have made debugging and I know that it occurs...

It seems somethere you have a memory overrun

I think it's a synchronization problem because I use a mutex for the screen and I think something is wrong but I can't see it....

what would you recommend me to synchronize the cout on the screen? a mutex or a semaphore?

Originally Posted by radeberger

what would you recommend me to synchronize the cout on the screen? a mutex or a semaphore?

what do you want to synchronize cout with?

If you are using MS multi-threaded library - cout is alrady synchronized

I don't want that two threads print out something on the screen at the same time