套接字-C中的權限被拒絕

Question

我正在嘗試從C中的DNS服務器獲取MX記錄。我的問題是，每次我調用sendto或recvfrom時，都會出現“權限被拒絕”錯誤。 （IDE-Xcode 4，Mac OS X Lion）到目前為止，在C中還沒有真正做任何事情，但是我需要這樣做。 到目前為止，來自http://www.binarytides.com/blog/dns-query-code-in-c-with-linux-sockets/的 “靈感”：

struct QUESTION
{
unsigned short qtype;
unsigned short qclass;
};

typedef struct
{
unsigned char *name;
struct QUESTION *ques;
} QUERY;

typedef struct
{
unsigned short type;
unsigned short _class;
unsigned int ttl;
unsigned short data_len;
} R_DATA;



int main(int argc, char *argv[]) 
{ 



int sockfd, i;
unsigned char buf[65536],*qname;
struct QUESTION *qinfo = NULL;

struct sockaddr_in dest;

struct dnsheader *dns = NULL;

sockfd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);


dest.sin_family=AF_INET;
dest.sin_port=htons(53);
dest.sin_addr.s_addr= inet_addr("ns1.sil.at");


srand((unsigned)time(NULL)); 
int16_t rand_number = (rand()%1000+1);
printf("generated random number : %i \n", rand_number);


dns = (struct dnsheader *)&buf;
dns->flags = STANDARD_QUERY_FLAGS;
dns->question_count = 1;
dns->transaction_id = rand_number;
dns->answer_rr_count = 0;
dns->additional_rr_count = 0;
dns->nameserver_rr_count = 0;


qname =(unsigned char*)&buf[sizeof(struct dnsheader)];


qinfo =(struct QUESTION*)&buf[sizeof(struct dnsheader) + (strlen((const char*)qname) + 1)]; //fill it

qinfo->qtype = htons( 15 ); // MX = 15
qinfo->qclass = htons(1); 

printf("\nSending Packet...");
if( sendto(sockfd,(char*)buf,sizeof(struct dnsheader) + (strlen((const char*)qname)+1) + sizeof(struct QUESTION),0,(struct sockaddr*)&dest,sizeof(dest)) < 0){
    perror("\nsendto failed");
}
printf("\nDone\n");


i = sizeof dest;
printf("\nReceiving answer...");
if(recvfrom (sockfd,(char*)buf , 65536 , 0 , (struct sockaddr*)&dest , (socklen_t*)&i ) < 0){
    perror("recvfrom failed");
}
printf("Done");

dns = (struct dnsheader*) buf;

print_dns_answers(buf, sizeof((char*)buf));




close(sockfd); 


return 0; 
} 

Answer 1

inet_addr函數采用字符串形式的IP地址，而不是主機名。 嘗試更換"ns1.sil.at"與它的IP地址， "213.129.232.1"

Answer 2

除了@ joni-salonen的答案之外，您還需要綁定套接字。
使用bind函數調用。
它需要一個struct sockaddr_in ，它將標識套接字的本地端。 您可以使用AF_INET系列，端口0和地址INADDR_ANY對其進行初始化。