UDP client/server c - c

Question

I have been looking everywhere for an answer. I am new to coding in C and would have loved it if my Professor would have allowed us to choose the language, but I digress. I am running Oracle V-Box locally running Ubuntu client and a Ubuntu server. I compile the code below on both the server and the client, with a few warnings. I run the code on the server (seems fine) and then on the client. The client is asking to send over a PDF file just like I did with the TCP socket transfer (which worked great). I also have Wireshark running on the client and server, and it looks like the request is sent out from the client but the server doesn't do anything and just sits on both ends without pulling the file over. Not sure if it is the code or something else.
/* Echo server using UDP */
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#define SERVER_UDP_PORT 2466
#define MAXLEN 4096
int main(int argc, char **argv)
{
int sd, client_len, port, n;
char buf[MAXLEN];
struct sockaddr_in server, client;
switch(argc) {
case 1:
port = SERVER_UDP_PORT;
break;
case 2:
port = atoi(argv[1]);
break;
default:
fprintf(stderr, "Usage: %s [port]\n", argv[0]);
exit(1);
}
/* Create a datagram socket */
if ((sd = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
fprintf(stderr, "Can't create a socket\n");
exit(1);
}
/* Bind an address to the socket */
bzero((char *)&server, sizeof(server));
server.sin_family = AF_INET;
server.sin_port = htons(port);
server.sin_addr.s_addr = htonl(INADDR_ANY);
if (bind(sd, (struct sockaddr *)&server,
sizeof(server)) == -1) {
fprintf(stderr, "Can't bind name to socket\n");
exit(1);
}
while (1) {
client_len = sizeof(client);
if ((n = recvfrom(sd, buf, MAXLEN, 0,
(struct sockaddr *)&client, &client_len)) < 0) {
fprintf(stderr, "Can't receive datagram\n");
exit(1);
}
if (sendto(sd, buf, n, 0,
(struct sockaddr *)&client, client_len) != n) {
fprintf(stderr, "Can't send datagram\n");
exit(1);
}
}
close(sd);
return(0);
}
This is the client code
// UDP Echo Client
#include <stdio.h>
#include <string.h>
#include <sys/time.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#define SERVER_UDP_PORT 2466
#define MAXLEN 4096
#define DEFLEN 64
long delay(struct timeval t1, struct timeval t2)
{
long d;
d = (t2.tv_sec - t1.tv_sec) * 1000;
d += ((t2.tv_usec - t1.tv_usec + 500) / 1000);
return(d);
}
int main(int argc, char **argv)
{
int data_size = DEFLEN, port = SERVER_UDP_PORT;
int i, j, sd, server_len;
char *pname, *host, rbuf[MAXLEN], sbuf[MAXLEN];
struct hostent *hp;
struct sockaddr_in server;
struct timeval start, end;
unsigned long address;
pname = argv[0];
argc--;
argv++;
if (argc > 0 && (strcmp(*argv, "-s") == 0)) {
if (--argc > 0 && (data_size = atoi(*++argv))) {
argc--;
argv++;
}
else {
fprintf(stderr,
"Usage: %s [-s data_size] host [port]\n", pname);
exit(1);
}
}
if (argc > 0) {
host = *argv;
if (--argc > 0)
port = atoi(*++argv);
}
else {
fprintf(stderr,
"Usage: %s [-s data_size] host [port]\n", pname);
exit(1);
}
if ((sd = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
fprintf(stderr, "Can't create a socket\n");
exit(1);
}
bzero((char *)&server, sizeof(server));
server.sin_family = AF_INET;
server.sin_port = htons(port);
if ((hp = gethostbyname(host)) == NULL) {
fprintf(stderr, "Can't get server's IP address\n");
exit(1);
}
bcopy(hp->h_addr, (char *) &server.sin_addr, hp->h_length);
if (data_size > MAXLEN) {
fprintf(stderr, "Data is too big\n");
exit(1);
}
for (i = 0; i < data_size; i++) {
j = (i < 26) ? i : i % 26;
sbuf[i] = 'a' + j;
} // construct data to send to the server
gettimeofday(&start, NULL); /* start delay measurement */
server_len = sizeof(server);
if (sendto(sd, sbuf, data_size, 0, (struct sockaddr *)
&server, server_len) == -1) {
fprintf(stderr, "sendto error\n");
exit(1);
}
if (recvfrom(sd, rbuf, MAXLEN, 0, (struct sockaddr *)
&server, &server_len) < 0) {
fprintf(stderr, "recvfrom error\n");
exit(1);
}
gettimeofday(&end, NULL); /* end delay measurement */
if (strncmp(sbuf, rbuf, data_size) != 0)
printf("Data is corrupted\n");
close(sd);
return(0);
}
Once I compile I run the code on Server normally:
./udp_server
and just sits waiting from the client.
Once I compile I run the code on Client:
./udp_client -s 1500 10.0.2.11 2466 > test.pdf
I run this which is (./udp_client -s data_rate server_IP Server_Port > (output to file on desktop of client))
This just produces a blank page. It should have a few pages of text and pics.
I also am getting the send out from client on Wireshark but no reply from server.
This is what i am getting when i run STRACE from terminal
strace ./udp_server

Answer 1

I think you just forgot to print out the received data in the client:
if (strncmp(sbuf, rbuf, data_size) != 0)
printf("Data is corrupted\n");
close(sd);
printf(rbuf); // <----
return(0);
Your client code currently only prints out error messages. If everything works, it won't produce any output.