Malformed packet in dns client implementation - c

Question

Hi there for fun i'm developing a tiny dns client on a unix system.
I've read the documentation about dns protocol i wrote a tiny function
int makeQuestion(char* dns_addr,char *name){
int s = socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP);
register int len_name = strlen(name);
if(s<0)
return errno;
struct sockaddr_in address;
bzero(&address,sizeof(address));
address.sin_port = htons(53);
address.sin_addr.s_addr = inet_addr(dns_addr);
dns_header header;
memset(&header,0,sizeof(dns_header));
header.id = htons(getpid());
header.q_count = htons(1);
dns_question quest = {
.qclass = htons(IN),
.qtype = htons(A)
};
register int pack_size = sizeof(dns_header)+len_name+2+sizeof(dns_question);
char *packet = malloc(pack_size);
memcpy(packet,&header,sizeof(dns_header));
for(int i = 0;i<len_name;i++)
*(packet +i +sizeof(dns_header)) = name[i];
packet[len_name+sizeof(dns_header)] = '.';
packet[len_name+sizeof(dns_header)+1] = '\0';
memcpy(packet+sizeof(dns_header)+len_name+2,&quest,sizeof(dns_question));
sendto(s,packet,pack_size,NULL,&address,sizeof(address));
return OK;
}
The structure for the dns header and dns query are declared like:
//DNS header structures
typedef struct dns_header
{
uint16_t id; // identification number
uint8_t rd :1; // recursion desired
uint8_t tc :1; // truncated message
uint8_t aa :1; // authoritive answer
uint8_t opcode :4; // purpose of message
uint8_t qr :1; // query/response flag
uint8_t rcode :4; // response code
uint8_t cd :1; // checking disabled
uint8_t ad :1; // authenticated data
uint8_t z :1; // its z! reserved
uint8_t ra :1; // recursion available
uint16_t q_count; // number of question entries
uint16_t ans_count; // number of answer entries
uint16_t auth_count; // number of authority entries
uint16_t add_count; // number of resource entries
}dns_header;
typedef struct dns_question
{
uint16_t qtype;
uint16_t qclass;
}dns_question;
Now i executed the code while wireshark was running and i saw the packet that seemed to be correct but in the query section wireshark said
Name: <Unknown extended label>
So the question is there is a way i have to use to store the dns name of the queried host in the packet or there is something wrong in the implementation. Sorry for the loosing of time and sorry for my English. Thanks indeed

Answer 1

I solved finally. Studing better the protocoll ( the domain name system) where the reference is at this link a the wrong part was in the section called qname ( the name of the host that in my case the protocoll wasn't able to determinate the size)
So as the document said qname is:
a domain name represented as a sequence of labels, where
each label consists of a length octet followed by that
number of octets. The domain name terminates with the
zero length octet for the null label of the root. Note
that this field may be an odd number of octets; no
padding is used.
So i changed my code to transform www.example.com in 3www7example3com
and everything works