How to set up two UDP sockets in one executable? - c

Question

I am new to the topic of network communication, but would like to set up an UDP server client connection, with one participant continuously broadcasting data whether anyone is listening in on it or not and two participants that start receiving and storing these information whenever they are ready to do so (It's fine if they miss what has been sent before that point). The idea is that there is no other communication than one participant sending data (fire and forget) and two participants receiving them, without any form of feedback to the sending part. For now I would like to get it running on my local host, but would like to use it on a network.
I have been looking into a solution for quite some time now and decided to have a client broadcast the file stream continuously on two separate ports so, so that the receiving two servers can bind to a port respectively without blocking each other (If there is a better way, I am open for suggestions).
So far I have been able to set up this kind of communication with one client and one server, following these instructions. However, when I try to set up a second socket in my client executable, I always receive the error message Invalid argument once I reach the sendto() part.
Seeing as I have not been able to find a solution myself, yet I would like to ask for some help.
My code so far consists of the
Client:
/** set up socket_1 properties */
struct addrinfo hints;
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC; // set to AF_INET to force IPv4
hints.ai_socktype = SOCK_DGRAM;
hints.ai_flags = AI_PASSIVE; // use my IP
/** Read address information of incoming connection */
int status;
struct addrinfo *servinfo;
if ((status = getaddrinfo(NULL, MYPORT, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(status));
return 1;
}
/** loop through all the results and bind to the first we can */
int sockfd;
struct addrinfo *p;
for ( p = servinfo; p != NULL; p = p->ai_next ) {
if ((sockfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol)) == -1) {
perror("listener: socket");
continue;
}
// /** Allow the reuse of a socket */
// if ( setsockopt( sockfd, SOL_SOCKET, SO_REUSEADDR, &(int){ 1 }, sizeof(int) ) == -1 ){
// printf("[ERROR]: Failed setting reusable socket %s.\n", strerror( errno ) );
// exit(1);
// }
// /** Allow the reuse of a socket */
// if ( setsockopt( sockfd, SOL_SOCKET, SO_REUSEPORT, &(int){ 1 }, sizeof(int) ) == -1 ){
// printf("[ERROR]: Failed setting reusable socket %s.\n", strerror( errno ) );
// exit(1);
// }
break;
}
if (p == NULL) {
printf("[ERROR]: Failed to bind broadcaster socket 1: %s.\n", strerror(errno) );
return 2;
}
/** set up socket_2 */
// ( reuse socket_1 hints and change the port number )
/** Read address information of incoming connection */
int status_2;
struct addrinfo *servinfo_2;
if ((status_2 = getaddrinfo(NULL, MYPORT_2, &hints, &servinfo_2)) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(status_2));
return 1;
}
/** loop through all the results and bind to the first we can */
int sockfd_2;
struct addrinfo *p_2;
for ( p_2 = servinfo_2; p_2 != NULL; p_2 = p_2->ai_next ) {
if ((sockfd_2 = socket(p_2->ai_family, p_2->ai_socktype, p_2->ai_protocol)) == -1) {
perror("listener: socket");
continue;
}
// /** Allow the reuse of a socket */
// if ( setsockopt( sockfd, SOL_SOCKET, SO_REUSEADDR, &(int){ 1 }, sizeof(int) ) == -1 ){
// printf("[ERROR]: Failed setting reusable socket %s.\n", strerror( errno ) );
// exit(1);
// }
// /** Allow the reuse of a socket */
// if ( setsockopt( sockfd, SOL_SOCKET, SO_REUSEPORT, &(int){ 1 }, sizeof(int) ) == -1 ){
// printf("[ERROR]: Failed setting reusable socket %s.\n", strerror( errno ) );
// exit(1);
// }
break;
}
if (p_2 == NULL) {
printf("[ERROR]: Failed to bind broadcaster socket 2: %s.\n", strerror(errno) );
return 2;
}
...
some file read/write related stuff
...
while ( /* some condition */ )
{
if ( ( readBytes = pread( fd, buf, BUFFER_SIZE, offset ) ) == -1 ){
printf("[ERROR]: %s.\n", strerror(errno) );
free( buf );
close( fd );
close( sockfd );
exit(1);
}
// the next line is generating the error message
if ( ( numbytes = sendto( sockfd, buf, readBytes, 0, p->ai_addr, p->ai_addrlen ) ) == -1 )
{
perror("sender_1: sendo.\n");
free( buf );
close( fd );
close( sockfd );
exit(1);
}
if ( ( numbytes = sendto( sockfd_2, buf, readBytes, 0, p_2->ai_addr, p_2->ai_addrlen ) ) == -1 )
{
perror("sender_2: sendo.\n");
free( buf );
close( fd );
close( sockfd_2 );
exit(1);
}
}
.
.
.
free( buf );
freeaddrinfo(servinfo);
freeaddrinfo(servinfo_2);
printf( "Broadcasting complete.\n" );
/** Clean what is not necessary anymore */
close( fd );
close( sockfd );
return 0;
}
I tried to add the reuse port and IP functionality to make sure that there is nothing blocking the setup of the new socket, but this did not solve my problem
My server side seems to work fine, but just in case I will post it here, too:
int main(int argc, char **argv)
{
if (argc < 2){
printf("Please provide image Name ID.\n");
exit(1);
}
struct addrinfo hints;
struct addrinfo *servinfo = NULL; // will point to getaddrinfo() results
memset(&hints, 0, sizeof hints); // make sure struct is empty
hints.ai_family = AF_UNSPEC; // don't care if IPv4 or IPv6
hints.ai_socktype = SOCK_DGRAM; // Use UDP protocol
hints.ai_flags = AI_PASSIVE;
int res;
if ((res = getaddrinfo( NULL, argv[1]/* SERVERPORT*/, &hints, &servinfo )) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(res));
return 1;
}
/** Get socket file descriptor */
int sockfd;
struct addrinfo *p = NULL;
// loop through all the results and make a socket
for(p = servinfo; p != NULL; p = p->ai_next) {
if ((sockfd = socket(p->ai_family, p->ai_socktype,
p->ai_protocol)) == -1) {
perror("talker: socket");
continue;
}
/** Allow the reuse of an IP */
if ( setsockopt( sockfd, SOL_SOCKET, SO_REUSEADDR, &(int){ 1 }, sizeof(int) ) == -1 ){
printf("[ERROR]: Failed setting reusable socket %s.\n", strerror( errno ) );
exit(1);
}
/** Allow the reuse of a socket */
if ( setsockopt( sockfd, SOL_SOCKET, SO_REUSEPORT, &(int){ 1 }, sizeof(int) ) == -1 ){
printf("[ERROR]: Failed setting reusable socket %s.\n", strerror( errno ) );
exit(1);
}
/** Bind found socket to desired port */
if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
close(sockfd);
printf("[ERROR]: Failed to bind socket to desired port: %s.\n", strerror( errno ) );
continue;
}
break;
}
struct timeval read_timeout;
read_timeout.tv_sec = 30;
read_timeout.tv_usec = 500;
if ( setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, &read_timeout, sizeof read_timeout) < 0 ){
printf( "[ERROR]: %s.\n", strerror(errno) );
}
...
some file read/write stuff
...
while ( ( numbytes = recvfrom(sockfd, buf, BUFFER_SIZE, 0, (struct sockaddr *)&their_addr, &addr_len ) ) != -1)
{
.
.
.
}
printf("Done broadcasting.\n");
freeaddrinfo(servinfo);
close(sockfd);
return 0;
}
It would be much appreciated if anybody could provide me some help or point me into the right direction where to look for a solution.
Best regards