NAME passaround --- listens and forwards UDP packets according to message contents. SYNOPSIS

passaround [-v] [-n number] [-m message] port

DESCRIPTION

Passaround listens on the port given in the command line for UDP packets and forwards the packet as instructed by the packet contents. Packet content is a character sequence (not a string!) of format: host(:host)* or the empty string. If the empty string, there is nothing to pass on. Else the first host name is removed from the string, and the remainder of the string (properly formatted) is sent to the named host. OPTIONS

-m Take as the "message" the first received message -n forward number packets to forward, then exit. Default is 1; 0 for loop forever. -v verbose ARGUMENTS

Port, the port number to listen on, and to send to. The from port can be ephemeral.

OUTPUT Without the verbose option the output should be strictly one line for each send and receive, in the order of occurrence: R: host:port |message-as-received| S: host:port |message-as-sent| Host and port refer to the send-to, on S, and the received from, on R. For host, please print the IP address. Going from IP to hostname is called reverse IP lookup, and reverse records are not always available.

Please help to fill the if(msg) and while part. Thank you!

#include #include #include #include #include #include #include #include #include #include #include

#define LOCALHOST "localhost" #define MAXMSGLEN 2048 #define N_REPEAT_DEFAULT 1

#define USAGE_MESSAGE "usage: passaround [-v] [-n num] [-m message] port"

int g_verbose = 0 ;

int main(int argc, char * argv[]) { int ch ; int the_port = 0 ; int n_repeat = N_REPEAT_DEFAULT ; char * msg = NULL ; int is_forever = 0 ;

assert(sizeof(short)==2) ;

while ((ch = getopt(argc, argv, "vm:n:")) != -1) { switch(ch) { case 'n': n_repeat = atoi(optarg) ; break ; case 'v': g_verbose = 1 ; break ; case 'm': msg = strdup(optarg) ; break ; case '?': default: printf("%s ",USAGE_MESSAGE) ; return 0 ; } } argc -= optind; argv += optind;

if ( argc!= 1 ) { printf("%s ",USAGE_MESSAGE) ; exit(0) ; }

the_port = atoi(*argv) ;

assert(the_port) ;

is_forever = (n_repeat == 0) ;

if ( msg ) {

// parse and send // and print S: host:port |message|

free(msg) ; n_repeat-- ; // a packet sent }

while( is_forever || n_repeat ) {

// listen for a packet // print R: host:port |message|

// if something to send, { // parse and send // and print S: host:port |message| // }

n_repeat-- ; } return 0 ; }