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respondd: delay replies to multicast packages to avoid flooding the server

This commit is contained in:
Ralf Jung 2016-06-23 23:19:06 +02:00
parent 4e2785a34a
commit 87f81d15f2
1 changed files with 41 additions and 3 deletions
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44
net/respondd/src/respondd.c
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@ -48,6 +48,8 @@
#include <sys/types.h>
#include <sys/socket.h>
#define MULTICAST_MAX_DELAY (1*1000*1000) // 1 second
struct provider_list {
struct provider_list *next;
@ -320,19 +322,33 @@ static struct json_object * handle_request(char *request, bool *compress) {
}
}
static void serve(int sock) {
char input[256];
char control[256];
const char *output = NULL;
ssize_t input_bytes, output_bytes;
struct sockaddr_in6 addr;
struct in6_addr destaddr;
struct cmsghdr *cmsg;
socklen_t addrlen = sizeof(addr);
bool compress;
input_bytes = recvfrom(sock, input, sizeof(input)-1, 0, (struct sockaddr *)&addr, &addrlen);
struct iovec iv = {
.iov_base = input,
.iov_len = sizeof(input)-1,
};
struct msghdr mh = {
.msg_name = &addr,
.msg_namelen = sizeof(addr),
.msg_iov = &iv,
.msg_iovlen = 1,
.msg_control = control,
.msg_controllen = sizeof(control),
};
input_bytes = recvmsg(sock, &mh, 0);
if (input_bytes < 0) {
perror("recvfrom failed");
perror("recvmsg failed");
exit(EXIT_FAILURE);
}
@ -342,6 +358,19 @@ static void serve(int sock) {
if (!result)
return;
// Determine destination address
for (cmsg = CMSG_FIRSTHDR(&mh); cmsg != NULL; cmsg = CMSG_NXTHDR(&mh, cmsg))
{
// ignore the control headers that don't match what we want
if (cmsg->cmsg_level != IPPROTO_IPV6 || cmsg->cmsg_type != IPV6_PKTINFO)
continue;
struct in6_pktinfo *pi = CMSG_DATA(cmsg);
destaddr = pi->ipi6_addr;
break;
}
// Now "cmsg != NULL" tests whether we found the destination address at all.
const bool is_multicast = (cmsg != NULL) && destaddr.s6_addr[0] == 0xFF;
const char *str = json_object_to_json_string_ext(result, JSON_C_TO_STRING_PLAIN);
if (compress) {
@ -361,6 +390,10 @@ static void serve(int sock) {
}
if (output) {
if (is_multicast) {
// Wait some random amount of time to avoid spamming the multicast sender from all sides at once.
usleep(rand() % MULTICAST_MAX_DELAY);
}
if (sendto(sock, output, output_bytes, 0, (struct sockaddr *)&addr, addrlen) < 0)
perror("sendto failed");
}
@ -376,6 +409,7 @@ int main(int argc, char **argv) {
struct sockaddr_in6 server_addr = {};
struct in6_addr mgroup_addr;
srand(time(NULL));
sock = socket(PF_INET6, SOCK_DGRAM, 0);
if (sock < 0) {
@ -387,6 +421,10 @@ int main(int argc, char **argv) {
perror("can't set socket to IPv6 only");
exit(EXIT_FAILURE);
}
if (setsockopt(sock, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one))) {
perror("can't set socket to deliver IPV6_PKTINFO control message");
exit(EXIT_FAILURE);
}
server_addr.sin6_family = AF_INET6;
server_addr.sin6_addr = in6addr_any;