C UDP client server not working - c

Question

So I have one UDP server that returns the hour or the date to the client with the following code:
#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <netdb.h>
#include <time.h>
void main(int argc, char *argv[]) {
struct addrinfo hints;
struct addrinfo *res;
struct sockaddr_storage cli;
time_t rawtime;
struct tm* timeinfo;
char tbuffer[9];
char buf[81], host[NI_MAXHOST], serv[NI_MAXSERV];
hints.ai_family = AF_UNSPEC; /* Allow IPv4 or IPv6 */
hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
hints.ai_flags = AI_PASSIVE; /* For wildcard IP address */
hints.ai_protocol = 0; /* Any protocol */
getaddrinfo(argv[1], argv[2], &hints, &res);
int sd = socket(res->ai_family, res->ai_socktype, 0);
bind(sd, (struct sockaddr *)res->ai_addr, res->ai_addrlen);
freeaddrinfo(res);
while(1) {
socklen_t clen = sizeof(cli);
int c = recvfrom(sd, buf, 80, 0, (struct sockaddr*) &cli, &clen);
buf[c] = '\0';
getnameinfo((struct sockaddr*) &cli, clen, host, NI_MAXHOST, serv, NI_MAXSERV, NI_NUMERICHOST);
time(&rawtime);
timeinfo = localtime(&rawtime);
if(buf[0] == 't') {
printf("%ld bytes de %s:%s\n", c, host, serv);
ssize_t chars = strftime(tbuffer, sizeof(tbuffer), "%T", timeinfo);
sendto(sd, tbuffer, chars, 0, (struct sockaddr *)&cli, clen);
} else if(buf[0] == 'd') {
printf("%ld bytes de %s:%s\n", c, host, serv);
ssize_t chars = strftime(tbuffer, sizeof(tbuffer), "%D", timeinfo);
sendto(sd, tbuffer, chars, 0, (struct sockaddr *)&cli, clen);
} else if(buf[0] == 'q') {
printf("Saliendo...\n");
exit(EXIT_SUCCESS);
} else {
printf("Comando no soportado %s", buf);
}
}
}
To test the code I was using ./server <IPServerAddres> <PortAddress> on the server side and nc -u <IpServerAddress> <PortServer> on the client side (another machine).
Now I want to create the UDP client UDP and do the same without using nc, just writing ./client <IPServerAddres> <PortAddress> <command> where command can be t for time d for date and q for quit, just like in the server.
Here is the code of the client program:
#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <netdb.h>
#include <time.h>
int main(int argc, char *argv[]) {
struct addrinfo hints;
struct addrinfo *res, *resp;
int sd, j, s;
size_t len;
ssize_t nread, nwrite;
char buf[500];
if (argc < 3) {
fprintf(stderr, "Usage: %s host port command...\n", argv[0]);
exit(EXIT_FAILURE);
}
memset(&hints, 0, sizeof(struct addrinfo));
hints.ai_family = AF_UNSPEC; /* Allow IPv4 or IPv6 */
hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
hints.ai_flags = 0;
hints.ai_protocol = 0; /* Any protocol */
getaddrinfo(argv[1], argv[2], &hints, &res);
for(resp = res; resp != NULL; resp = resp->ai_next) {
sd = socket(resp->ai_family, resp->ai_socktype, resp->ai_protocol);
if(sd == -1) {
perror("socket()");
continue;
}
if(connect(sd, resp->ai_addr, resp->ai_addrlen) == -1) {
perror("socket()");
} else {
break;
}
close(sd);
}
freeaddrinfo(res);
for(j = 3; j < argc; j++) {
len = strlen(argv[j]) + 1;
nwrite = write(sd, argv[j], len);
if(nwrite == -1) perror("write()");
nread = read(sd, buf, 500);
buf[nread] = 0;
if(nread == -1) perror("read()");
printf("Recibidos %ld bytes: %s\n", (long) nread, buf);
}
exit(EXIT_SUCCESS);
}
The problem is that when I try to run my client program I got no response, so I guess is in a infinite loop or something like that.
Any help will be apreciated, I'm learning C so I'm sorry for the mistakes, thank you.
EDITED: Corrected the break in the for loop in case connect() returns something different than -1.

Answer 1

The problem is in your calculation of the length of the message to send:
len = strlen(argv[j] + 1);
This gets the length of the string starting from the second character. You want:
len = strlen(argv[j]) + 1;
This gives you the string length plus 1 for the null terminator.
Also, after reading the response, you'll need to null-terminate what you got back:
buf[nread] = 0;