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#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <stdio.h>
#include "dns.h"
struct dns_packet* dns_packet_new(void) {
struct dns_packet *p;
p = malloc(sizeof(struct dns_packet));
assert(p);
p->size = p->rindex = 2*6;
memset(p->data, 0, p->size);
return p;
}
void dns_packet_free(struct dns_packet *p) {
assert(p);
free(p);
}
void dns_packet_set_field(struct dns_packet *p, unsigned index, uint16_t v) {
assert(p && index < 2*6);
((uint16_t*) p->data)[index] = htons(v);
}
uint16_t dns_packet_get_field(struct dns_packet *p, unsigned index) {
assert(p && index < 2*6);
return ntohs(((uint16_t*) p->data)[index]);
}
uint8_t* dns_packet_append_name(struct dns_packet *p, const char *name) {
uint8_t *d, *f = NULL;
assert(p);
for (;;) {
size_t n = strcspn(name, ".");
if (!n || n > 63)
return NULL;
d = dns_packet_extend(p, n+1);
if (!f)
f = d;
d[0] = n;
memcpy(d+1, name, n);
name += n;
/* no trailing dot */
if (!*name)
break;
name ++;
/* trailing dot */
if (!*name)
break;
}
d = dns_packet_extend(p, 1);
d[0] = 0;
return f;
}
uint8_t* dns_packet_append_uint16(struct dns_packet *p, uint16_t v) {
uint8_t *d;
assert(p);
d = dns_packet_extend(p, sizeof(uint16_t));
*((uint16_t*) d) = htons(v);
return d;
}
uint8_t *dns_packet_extend(struct dns_packet *p, size_t l) {
uint8_t *d;
assert(p);
assert(p->size+l <= sizeof(p->data));
d = p->data + p->size;
p->size += l;
return d;
}
uint8_t *dns_packet_append_name_compressed(struct dns_packet *p, const char *name, uint8_t *prev) {
int16_t *d;
signed long k;
assert(p);
if (!prev)
return dns_packet_append_name(p, name);
k = prev - p->data;
if (k < 0 || k >= 0x4000 || (size_t) k >= p->size)
return dns_packet_append_name(p, name);
d = (int16_t*) dns_packet_extend(p, sizeof(uint16_t));
*d = htons((0xC000 | k));
return prev;
}
int dns_packet_check_valid(struct dns_packet *p) {
assert(p);
uint16_t flags;
if (p->size < 12)
return -1;
flags = dns_packet_get_field(p, DNS_FIELD_FLAGS);
if (flags & DNS_FLAG_OPCODE || flags & DNS_FLAG_RCODE)
return -1;
return 0;
}
int dns_packet_check_valid_response(struct dns_packet *p) {
uint16_t flags;
assert(p);
if (dns_packet_check_valid(p) < 0)
return -1;
flags = dns_packet_get_field(p, DNS_FIELD_FLAGS);
if (!(flags & DNS_FLAG_QR))
return -1;
if (dns_packet_get_field(p, DNS_FIELD_QDCOUNT) > 0)
return -1;
return 0;
}
static ssize_t consume_labels(struct dns_packet *p, size_t index, char *ret_name, size_t l) {
ssize_t ret = 0;
int compressed = 0;
int first_label = 1;
assert(p && ret_name && l);
for (;;) {
uint8_t n;
if (index+1 > p->size)
return -1;
n = p->data[index];
if (!n) {
index++;
if (!compressed)
ret++;
if (l < 1)
return -1;
*ret_name = 0;
return ret;
} else if (n <= 63) {
/* Uncompressed label */
index++;
if (!compressed)
ret++;
if (index + n > p->size)
return -1;
if ((size_t) n + 1 > l)
return -1;
if (!first_label) {
*(ret_name++) = '.';
l--;
} else
first_label = 0;
memcpy(ret_name, p->data + index, n);
index += n;
ret_name += n;
l -= n;
if (!compressed)
ret += n;
} else if ((n & 0xC0) == 0xC0) {
/* Compressed label */
if (index+2 > p->size)
return -1;
index = ((size_t) (p->data[index] & ~0xC0)) << 8 | p->data[index+1];
if (!compressed)
ret += 2;
compressed = 1;
} else
return -1;
}
}
int dns_packet_consume_name(struct dns_packet *p, char *ret_name, size_t l) {
ssize_t r;
if ((r = consume_labels(p, p->rindex, ret_name, l)) < 0)
return -1;
p->rindex += r;
return 0;
}
int dns_packet_consume_uint16(struct dns_packet *p, uint16_t *ret_v) {
assert(p && ret_v);
if (p->rindex + sizeof(uint16_t) > p->size)
return -1;
*ret_v = ntohs(*((uint16_t*) (p->data + p->rindex)));
p->rindex += sizeof(uint16_t);
return 0;
}
int dns_packet_consume_uint32(struct dns_packet *p, uint32_t *ret_v) {
assert(p && ret_v);
if (p->rindex + sizeof(uint32_t) > p->size)
return -1;
*ret_v = ntohl(*((uint32_t*) (p->data + p->rindex)));
p->rindex += sizeof(uint32_t);
return 0;
}
int dns_packet_consume_bytes(struct dns_packet *p, void *ret_data, size_t l) {
assert(p && ret_data && l > 0);
if (p->rindex + l > p->size)
return -1;
memcpy(ret_data, p->data + p->rindex, l);
p->rindex += l;
return 0;
}
int dns_packet_consume_seek(struct dns_packet *p, size_t length) {
assert(p && length > 0);
if (p->rindex + length > p->size)
return -1;
p->rindex += length;
return 0;
}
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