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// MIT License, Copyright (c) 2020 Marvin Borner
// TODO: Less magic, auto xld splitting
// TODO: DNS cache
#include <def.h>
#include <libnet/net.h>
#include <libnet/socket.h>
#include <mem.h>
#include <print.h>
#include <random.h>
#include <str.h>
static u32 dns_ip_addr = ip(1, 1, 1, 1);
struct dns_packet {
u16 qid;
u16 flags;
u16 questions;
u16 answers;
u16 authorities;
u16 additional;
u8 data[];
} PACKED;
static u32 part_count(const char *name)
{
u32 cnt = 0;
for (u32 i = 0; i < strlen(name); i++) {
if (name[i] == '.')
cnt++;
}
return cnt + 1;
}
static u32 part_len(const char *name, u32 index)
{
const char *data = name;
u32 cnt = 0;
for (u32 i = 0; i < strlen(name); i++) {
if (cnt == index) {
data += i;
break;
}
if (name[i] == '.')
cnt++;
}
for (cnt = 0; cnt < strlen(data); cnt++) {
if (data[cnt] == '.' || data[cnt] == '\0')
break;
}
return cnt;
}
static void dns_make_packet(struct dns_packet *packet, const char *name)
{
packet->qid = htons(rand());
packet->flags = htons(0x0100); // Standard query
packet->questions = htons(1);
packet->answers = htons(0);
packet->authorities = htons(0);
packet->additional = htons(0);
u8 *data = packet->data;
u32 cnt = 0;
for (u32 i = 0; i < part_count(name) * 2; i += 2) {
data[cnt] = part_len(name, i / 2);
memcpy(&data[cnt + 1], &name[cnt], data[cnt]);
cnt += data[cnt] + 1;
}
packet->data[cnt + 0] = 0x00; // Name end
packet->data[cnt + 2] = 0x01; // A
packet->data[cnt + 4] = 0x01; // IN
}
static u32 dns_handle_packet(struct dns_packet *packet)
{
u16 flags = htons(packet->flags);
u8 reply_code = flags & 0xf;
if (reply_code != DNS_NOERROR) {
printf("DNS error: %d\n", reply_code);
return 0;
}
u8 *start = &packet->data[1] + strlen((char *)&packet->data[1]);
printf("TTL of %s: %ds\n", &packet->data[1], (u32)start[14]);
u8 *ip = &start[17];
printf("IP: %d.%d.%d.%d\n", ip[0], ip[1], ip[2], ip[3]);
return ip(ip[0], ip[1], ip[2], ip[3]);
}
u32 dns_request(const char *name)
{
struct socket *socket = net_open(S_UDP);
if (!socket || !net_connect(socket, dns_ip_addr, 53, NET_TIMEOUT) || part_count(name) == 1)
return 0;
u32 length = sizeof(struct dns_packet) + strlen(name) + part_count(name) + 4;
struct dns_packet *packet = malloc(length);
memset(packet, 0, length);
dns_make_packet(packet, name);
net_send(socket, packet, length);
free(packet);
u8 buf[1024] = { 0 };
int l = net_receive(socket, buf, 1024, NET_TIMEOUT);
net_close(socket);
if (l > 0)
return dns_handle_packet((void *)buf);
else
return 0;
}
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