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#include <arpa/inet.h>
#include <assert.h>
#include <ctype.h>
#include <netdb.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <tb/sv.h>
#include <unistd.h>
#define PORT 53
u16 add_domain_label(u8 *buffer, struct sv label) {
assert(label.length < 64);
u16 size = 0;
u8 ll = label.length;
memcpy(buffer + size, &ll, sizeof(u8));
size += sizeof(u8);
memcpy(buffer + size, label.s, label.length);
size += label.length;
return size;
}
u16 send_domain_request(int sockfd, const char *domain, u16 *id) {
*id = 0;
u8 message[512];
memset(message, 0, sizeof(message));
u16 size = 0;
size += 6 * sizeof(u16); // header
u16 flags = htons(0x0100);
u16 qdcount = htons(1);
memcpy(message, id, sizeof(u16));
memcpy(message + sizeof(u16), &flags, sizeof(u16));
memcpy(message + sizeof(u16) * 2, &qdcount, sizeof(u16));
struct sv labels = C_TO_SV(domain);
for (; !sv_isempty(labels);) {
struct sv label = sv_split_delim(labels, &labels, '.');
size += add_domain_label(message + size, label);
}
size += add_domain_label(message + size, C_TO_SV(""));
u16 query_type = htons(1); // A type
memcpy(message + size, &query_type, sizeof(u16));
size += sizeof(u16);
u16 q_class = htons(1); // IN
memcpy(message + size, &q_class, sizeof(u16));
size += sizeof(u16);
printf("sending: %d\n", size);
write(sockfd, (char *)message, size);
return size;
}
int connect_dns(void) {
int sockfd;
struct sockaddr_in servaddr;
memset(&servaddr, 0, sizeof(servaddr));
servaddr.sin_addr.a[0] = 8;
servaddr.sin_addr.a[1] = 8;
servaddr.sin_addr.a[2] = 8;
servaddr.sin_addr.a[3] = 8;
servaddr.sin_port = htons(PORT);
servaddr.sin_family = AF_INET;
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (connect(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0) {
return -1;
}
return sockfd;
}
/*
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = type;
hints.ai_flags = AI_PASSIVE;
hints.ai_protocol = 0;
hints.ai_canonname = NULL;
hints.ai_addr = NULL;
hints.ai_next = NULL;
*/
u16 service_to_port(const char *service) {
int is_number = 0;
for (int i = 0; service[i]; i++) {
if (isdigit(service[i])) {
is_number = 1;
}
}
if (is_number) {
return htons(atoi(service));
}
#define SERVICE(_name, _port) \
if (0 == strcmp(_name, service)) { \
return htons(_port); \
}
SERVICE("http", 80)
SERVICE("https", 443)
#undef SERVICE
return 0;
}
int getaddrinfo(const char *restrict node, const char *restrict service,
const struct addrinfo *restrict hints,
struct addrinfo **restrict res) {
int sockfd = connect_dns();
if (-1 == sockfd) {
return EAI_AGAIN;
}
// TODO: Use the hints to make decisions about what data to request.
(void)hints;
u16 id;
u16 size = send_domain_request(sockfd, node, &id);
u8 buffer[512];
memset(buffer, 0, sizeof(buffer));
int rc = read(sockfd, buffer, sizeof(buffer));
if (rc < size) {
close(sockfd);
return EAI_FAIL;
}
close(sockfd);
if (0 != memcmp(buffer, &id, sizeof(u16))) {
close(sockfd);
return EAI_FAIL;
}
u16 flags;
memcpy(&flags, buffer + sizeof(u16), sizeof(u16));
flags = ntohs(flags);
if (!(flags & (1 << 15))) { // QR
close(sockfd);
return EAI_FAIL;
}
if (0 != (flags & 0x1F)) { // Error field
close(sockfd);
return EAI_AGAIN;
}
u16 qcount = ntohs(*(u16 *)(buffer + sizeof(u16) * 2));
if (1 != qcount) {
close(sockfd);
return EAI_FAIL;
}
u16 ancount = ntohs(*(u16 *)(buffer + sizeof(u16) * 3));
if (0 == ancount) {
close(sockfd);
return EAI_NONAME; // TODO: Check if this is correct
}
u8 *answer = buffer + size;
u16 answer_length = rc - size;
if (0 == answer_length) {
close(sockfd);
return EAI_FAIL;
}
/*
// get labels
{
u16 offset = ntohs(*(u16 *)answer);
assert(3 == offset >> 14);
offset &= ~(3 << 14);
printf("offset: %d\n", offset);
printf("name: ");
u8 length = buffer[offset];
for (int i = 0; i < length; i++) {
printf("%c", buffer[offset + 1 + i]);
}
printf("\n");
}
*/
for (u16 i = 0; i < answer_length;) {
// type
u16 type = ntohs(*(u16 *)(answer + sizeof(u16)));
u16 class = ntohs(*(u16 *)(answer + sizeof(u16) * 2));
int ignore = 0;
u16 inc = 0;
if (1 != type) {
ignore = 1;
}
if (1 != class) {
ignore = 1;
}
inc += sizeof(u16) * 3;
u16 rdlength = ntohs(*(u16 *)(answer + sizeof(u16) * 3 + sizeof(u32)));
inc += sizeof(u16);
inc += rdlength;
inc += sizeof(u32);
if (4 != rdlength) {
ignore = 1;
}
if (!ignore) {
u32 ip = *(u32 *)(answer + sizeof(u16) * 4 + sizeof(u32));
if (res) {
*res = calloc(1, sizeof(struct addrinfo));
if (!(*res)) {
close(sockfd);
return EAI_MEMORY;
}
struct sockaddr_in *sa = calloc(1, sizeof(struct sockaddr_in));
if (!sa) {
free(*res);
close(sockfd);
return EAI_MEMORY;
}
(*res)->ai_addr = (struct sockaddr *)sa;
sa->sin_addr.s_addr = ip;
sa->sin_port = service_to_port(service);
sa->sin_family = AF_INET;
}
}
i += inc;
answer += inc;
}
return 0;
}
void freeaddrinfo(struct addrinfo *res) {
free(res->ai_addr);
free(res);
}
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