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#1 2007-03-08 05:53 PM


Re: UDP echo server


I am trying to write a simple UDP echo server in C.
The server should listen on a specific port and every incoming udp package has to be redirected to another IP-address on the same port. My first try was to write a TCP echo server that simply echos all incoming data on port 6666 using a while loop:

while( (bytesrecv = recv(socketid, buffer, sizeof(buffer), 0)) > 0)
        send(socketid, buffer, bytesrecv, 0);

and it worked. But I think I am to stupid to manage this with an udp socket.
Instead of recv() and send() I use recvfrom() and sendto() with this sockaddr_in struct as parameter. recvfrom() works fine but the sendto() function always returns -1 (Invalid parameter). I think it has something to to with the sockaddr_in struct.

I'd like to post a part of my code but at the moment I cannot access the server my soucecode is on.

Can someone provide me a very simple example?

Thank you very much!!!!!


#2 2007-03-08 08:06 PM

From: Boston, MA
Registered: 2002-06-12
Posts: 3,839

Re: UDP echo server

dg_echo(int sockfd, SA *pcliaddr, socklen_t clilen)
    int         n;
    socklen_t   len;
    char        mesg[MAXLINE];

    for ( ; ; ) {
        len = clilen;
        n = Recvfrom(sockfd, mesg, MAXLINE, 0, pcliaddr, &len);

        Sendto(sockfd, mesg, n, 0, pcliaddr, len);


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