recvfrom() not blocking - c

Question

For some reason my recvfrom() function for sockets is not blocking on my server code like it is supposed to. I am making a basic UDP server to create a rolling session key system.
What am I doing wrong here? It continues on after this line (before i put the (n < 1)) and was crashing. I am pretty sure recvfrom() is supposed to stop the execution of the program until it gets something from the client...
int sockfd, portNumber;
socklen_t clilen;
char buffer[BUFFER_LENGTH];
struct sockaddr_in serv_addr, from;
int n;
// Invalid arguments
if (argc < 2)
exit(0);
else if (atoi(argv[1]) > 65535 || atoi(argv[1]) < 1)
exit(0);
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
{
printf("Error opening socket.\n");
exit(0);
}
// Taken from reference
bzero((char *) &serv_addr, sizeof(serv_addr));
portNumber = atoi(argv[1]);
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = INADDR_ANY;
serv_addr.sin_port = htons(portNumber);
if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0)
{
printf("ERROR on binding.\n");
close(sockfd);
exit(0);
}
// Get initial session key request
int fromlen = sizeof(struct sockaddr_in);
n = recvfrom(sockfd, buffer, BUFFER_LENGTH, 0, (struct sockaddr *)&from, &fromlen);
if (n < 0)
{
printf("Error in receiving.\n");
exit(1);
}
Thanks

Answer 1

You're trying to use a stream socket for UDP;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
What you mean to do is probably;
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
Trying to do recvfrom on an unconnected stream socket will most likely return immediately with an error. Next time, you may want to check errno for a hint.