Other end of a socket...

["Phil Hall" <hallp@xxxxxxxx>]

Here's an example of how to determine the port in use at the other end of a
socket connection...



#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>
#include <netdb.h>

int main(void)
{
  int    theSocket, structLen;
  short  thePort = 0;
  struct servent *se;
  struct sockaddr_in  rmtAddr;
  struct sockaddr_in  lclAddr;
  char                myInetAddr[256] = "127.0.0.1";

    se = getservbyname( "telnet", "tcp");
    if (se)
    {
        thePort = htons(se->s_port);
    }

    memset(&rmtAddr, 0, sizeof(rmtAddr));
    rmtAddr.sin_family      = AF_INET;
    rmtAddr.sin_addr.s_addr = inet_addr(myInetAddr);
    rmtAddr.sin_port        = htons(thePort);

    if ( (theSocket = socket(AF_INET, SOCK_STREAM, 0 )) < 0 )
    {
        printf("Could not open socket\n");
        return -1;
    }

    if (connect(theSocket, (struct sockaddr *) &rmtAddr,
        sizeof(rmtAddr)) < 0 )
    {
        printf("Cannot connect to telnet Server\n");
        close(theSocket);
        return -1;
    }

    /*-- let's get the local socket info --*/
    memset(&lclAddr, 0, sizeof(lclAddr));
    structLen = sizeof(lclAddr);

    if (getsockname( theSocket, (struct sockaddr *)&lclAddr, &structLen) <
0 )
    {
        printf("Failed to get local socket info\n");
        close(theSocket);
        return -1;
    }
    else
    {
        printf("Connected to server's remote port %d, using local port
%d\n",
                rmtAddr.sin_port, lclAddr.sin_port);
    }

    close(theSocket);
    return 0;
}


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