UDP server with poll() - c

Question

I'm coding udp server, which can listen multiple ports. As the method of paralleling I use function poll(). So server get two ports in argc, and then try to listen the range of ports. Then open msg.txt, where saves all the information, which he get from clients. A then waiting for them. But the problem is that with poll(), my server can listen only one port. But if I delete this function, server accept messages from all ports. What can be a problem?Here's my code:
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/select.h>
#include <netdb.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <sys/poll.h>
int set_non_block_mode(int s)
{
int fl = fcntl(s, F_GETFL, 0);
return fcntl(s, F_SETFL, fl | O_NONBLOCK);
}
void s_close(int s)
{
close(s);
}
int sock_err(const char *function, int s)
{
int err = errno;
fprintf(stderr, "%s: socket error: %d\n", function, err);
return -1;
}
struct client
{
char id[30];
int msgs[20];
struct cl *next;
char send[81];
int amount;
int answer;
};
struct client *addnew(struct client *head)
{
struct client *tmp = (struct client *)calloc(1, sizeof(struct client));
memset(tmp->msgs, 0, 20);
memset(tmp->send, '\0', 81);
memset(tmp->id, '\0', 30);
tmp->amount = 0;
tmp->answer = 0;
tmp->next = NULL;
return tmp;
}
struct client *search(struct client *head, unsigned int ip, int port)
{
char str[30];
sprintf(str, "%u.%u.%u.%u:%d", (ip >> 24) & 0xFF, (ip >> 16) & 0xFF, (ip >> 8) & 0xFF, (ip)&0xFF, port);
struct client *tmp = head;
if (tmp!=NULL){
while (1)
{
if (strcmp(tmp->id, str) == 0)
{
return tmp;
}
if(tmp->next==NULL)break;
tmp = tmp->next;
}
tmp->next = addnew(head);
tmp = tmp->next;
strcpy(tmp->id, str);
return tmp;
} else {
tmp = addnew(head);
strcpy(tmp->id, str);
return tmp;
}
}
int parcing(FILE *text, char *buffer, int s, struct sockaddr_in *addr, struct client *head, int port)
{
int flags = MSG_NOSIGNAL;
int addrlen = sizeof(*addr);
unsigned int ip = ntohl((*addr).sin_addr.s_addr);
struct client *tmp = search(head, ip, port);
int n;
memcpy(&n, buffer, 4);
n = ntohl(n);
if (tmp->msgs[n] == 0)
{
tmp->msgs[n] = 1;
tmp->answer++;
n = htonl(n);
memcpy(&tmp->send[4 * tmp->amount], tmp->send, 4 * tmp->amount);
tmp->amount++;
memcpy(tmp->send, &n, 4);
fprintf(text, "%s %d:%d:", tmp->id, buffer[4], buffer[5]);
memcpy(&n, &buffer[6], 2);
n = ntohs(n);
fprintf(text, "%hu ", n);
memcpy(&n, &buffer[8], 2);
n = ntohs(n);
fprintf(text, "%hi ", n);
for (int i = 10; i < 22; i++)
fprintf(text, "%c", buffer[i]);
fprintf(text, " %s\n", &buffer[22]);
sendto(s, tmp->send, 4 * tmp->amount, flags, (struct sockaddr *)addr, addrlen);
if (strcmp(&buffer[22], "stop") == 0)
return 0;
return 1;
}
else
{
sendto(s, tmp->send, 4 * tmp->amount, flags, (struct sockaddr *)addr, addrlen);
}
}
int main(int argc, char *argv[])
{
int i;
int flags = MSG_NOSIGNAL;
int start, end;
if (argc == 3)
{
start = atoi(argv[1]);
end = atoi(argv[2]);
}
else
{
start = atoi(argv[1]);
end = start;
}
//start = 8035;
//end = start;
int AmountOfPorts = end - start + 1;
struct pollfd *pfd = (struct pollfd *)calloc(AmountOfPorts, sizeof(struct pollfd));
int *s = (int *)calloc(AmountOfPorts, sizeof(int));
struct sockaddr_in *addr = (struct sockaddr_in *)calloc(AmountOfPorts, sizeof(struct sockaddr_in));
for (int i = 0; i < AmountOfPorts; i++)
{
s[i] = socket(AF_INET, SOCK_DGRAM, 0);
if (s[i] < 0)
return sock_err("socket", s[i]);
set_non_block_mode(s[i]);
memset(&addr[i], 0, sizeof(addr));
addr[i].sin_family = AF_INET;
addr[i].sin_port = htons(start + i);
addr[i].sin_addr.s_addr = htonl(INADDR_ANY);
if (bind(s[i], (struct sockaddr *)&addr[i], sizeof(addr[i])) < 0)
return sock_err("bind", s[i]);
pfd[i].fd = s[i];
pfd[i].events = POLLIN | POLLOUT;
}
int g = 1;
struct client *head = NULL;
struct client *tmp = NULL;
FILE *text = fopen("msg1.txt", "w");
char buffer[131072] = {0};
int addrlen = 0;
do
{
int ev_cnt = poll(pfd, sizeof(pfd) / sizeof(pfd[0]), 100000);
if (ev_cnt > 0)
{
for (i = 0; i < AmountOfPorts; i++)
{
if (pfd[i].revents & POLLHUP)
{
s_close(s[i]);
}
if (pfd[i].revents & POLLERR)
{
s_close(s[i]);
}
if (pfd[i].revents & POLLIN)
{
addrlen = sizeof(addr[i]);
recvfrom(s[i], buffer, sizeof(buffer), 0, (struct sockaddr *)(&addr[i]), &addrlen);
if (rcv > 0)
{
if (!parcing(text, buffer, s[i], &addr[i], head, start + i))
{
g = 0;
break;
}
}
if (pfd[i].revents & POLLOUT)
{
addrlen = sizeof(addr[i]);
unsigned int ip = ntohl((*addr).sin_addr.s_addr);
tmp = search(head, ip, start+i);
sendto(s[i], tmp->send, 4 * tmp->amount, flags, (struct sockaddr *)&addr[i], addrlen);
}
}
}
}
else
{
}
} while (g);
fclose(text);
for (int i = 0; i < AmountOfPorts; i++)
s_close(s[i]);
return 0;
}

Answer 1

You declare pfd as a pointer to a struct pollfd:
struct pollfd *pfd;
Therefore the following construct will not work as intended (for that to work, pfd would have to be an array: struct pollfd pfd[N]):
sizeof(pfd) / sizeof(pfd[0]) //in call to poll
The above expression could be numerically expressed like this (dependend on your machine and os):
//sizeof(struct pollfd*) / sizeof(struct pollfd)
8 / (4 + 2 + 2) => 8 / 8 => 1
//your expectation:
16 / 8 => 2
That means, poll will listen only to the first pollfd, since the parameter nfds is set to 1.
Note: I didn't fully checked your code, but since you're using pointers (calloc) and sizeof a lot, make sure that you did not made the same mistake at other places. Remember pointer != array.