Listen to DNS requests - c

Question

I'm trying to listen to DNS request of browsers on my localhost.
I've wrote this code:
WSADATA wsaData;
unsigned char hostname[100];
int sockfd;
struct addrinfo hints, *servinfo, *p;
int rv;
int numbytes;
struct sockaddr_storage their_addr;
char buf[1000];
socklen_t addr_len;
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC; // set to AF_INET to force IPv4
hints.ai_socktype = SOCK_DGRAM;
hints.ai_flags = AI_PASSIVE; // use my IP
if (WSAStartup(MAKEWORD(2,0), &wsaData) != 0)
{
fprintf(stderr, "WSAStartup failed.\n");
exit(1);
}
if ((rv = getaddrinfo(NULL, "53", &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
return 1;
}
// loop through all the results and bind to the first we can
for(p = servinfo; p != NULL; p = p->ai_next) {
if ((sockfd = socket(AF_INET, SOCK_DGRAM,IPPROTO_UDP)) == -1) {
perror("listener: socket");
continue;
}
if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
closesocket(sockfd);
perror("listener: bind");
continue;
}
break;
}
if (p == NULL) {
fprintf(stderr, "listener: failed to bind socket\n");
return 2;
}
freeaddrinfo(servinfo);
printf("listener: waiting to recvfrom...\n");
addr_len = sizeof their_addr;
if ((numbytes = recvfrom(sockfd, buf, 1000-1 , 0,(struct sockaddr *)&their_addr, &addr_len)) == -1) {
perror("recvfrom");
exit(1);
printf("listener: packet is %d bytes long\n", numbytes);
buf[numbytes] = '\0';
printf("listener: packet contains \"%s\"\n", buf);
}
closesocket(sockfd);
I get some weird packets of 39 bytes with some characters I can't read...And it's always getting packets on 53 also when not surfing to anything, is this not the good way to listen to dns requests?
I've changed my DNS Ip to 127.0.0.1 on windows.
Kind regards,

Answer 1

DNS is not a text-based protocol like HTTP, you are supposed to decode the packets. Look into RFC 1035 for details.

Answer 2

I've parsed like this:
pointer = substring( buffer, 14, numbytes-18);
//printf("Substring: %s \n",pointer);
//printf("listener: packet contains \"%x\"\n", buffer);
for( i = 0; i < strlen(pointer); i++)
{
// Indien kleiner als 32 dan moet het een . worden
if(pointer[i] < 32)
result[i] = '.';
// Indien groeter als 32 en kleiner als 127 is het een char
else if(pointer[i] > 32 && pointer[i] < 127)
result[i] = (char)(pointer[i]);
else
continue;
}
result[i] = '\0';
Then in your result you have something like "www.google.com".