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