File syn_dns.c¶
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#if __has_include("syn_config.h")
#include "syn_config.h"
#endif
#if !defined(SYN_USE_DNS) || SYN_USE_DNS
#include "../port/syn_port_system.h"
#include "../util/syn_assert.h"
#include "../util/syn_pack.h"
#include "syn_dns.h"
#include <string.h>
static size_t encode_qname(uint8_t *dest, size_t dest_capacity, const char *src)
{
if (dest_capacity < 2U)
return 0U; /* LCOV_EXCL_LINE: Defensive destination buffer capacity check */
uint8_t *len_ptr = dest;
size_t total = 0;
dest++;
total++;
uint8_t label_len = 0;
while (*src) {
if (total + 1 >= dest_capacity)
return 0U;
if (*src == '.') {
*len_ptr = label_len;
len_ptr = dest;
label_len = 0;
dest++;
total++;
} else {
*dest++ = (uint8_t)*src;
label_len++;
total++;
}
src++;
}
*len_ptr = label_len;
*dest++ = 0;
total++;
return total;
}
static bool parse_qname(const uint8_t *buf, size_t buf_len, size_t *pos)
{
size_t p = *pos;
for (;;) {
if (p >= buf_len)
return false;
uint8_t len = buf[p];
if ((len & 0xC0) == 0xC0) {
/* Pointer — 2 bytes total */
if (p + 1 >= buf_len)
return false;
p += 2;
break;
} else if (len == 0) {
p++;
break;
} else {
p += 1 + len;
}
}
*pos = p;
return true;
}
static SYN_Status parse_response(const uint8_t *buf, size_t rx_len, SYN_SockAddr *addr_out,
uint16_t expected_txid)
{
/* LCOV_EXCL_START: Short packet / TxID mismatch rejection */
if (rx_len < 12)
return SYN_ERROR;
uint16_t rx_txid = syn_peek_u16(buf, 0);
if (rx_txid != expected_txid)
return SYN_ERROR;
/* LCOV_EXCL_STOP */
if ((buf[3] & 0x0F) != 0)
return SYN_ERROR; /* RCODE != 0 (error) */
uint16_t questions = syn_peek_u16(buf, 4);
uint16_t answers = syn_peek_u16(buf, 6);
if (answers == 0)
return SYN_ERROR;
/* Skip questions */
size_t pos = 12;
for (uint16_t i = 0; i < questions; i++) {
if (!parse_qname(buf, rx_len, &pos))
return SYN_ERROR;
if (pos + 4 > rx_len)
return SYN_ERROR; /* LCOV_EXCL_LINE: Defensive NULL check or invalid parameter fallback
*/
pos += 4; /* skip QTYPE and QCLASS */
}
/* Parse answers */
for (uint16_t i = 0; i < answers; i++) {
if (!parse_qname(buf, rx_len, &pos))
return SYN_ERROR;
if (pos + 10 > rx_len)
return SYN_ERROR;
uint16_t type = syn_peek_u16(buf, pos);
uint16_t rdlen = syn_peek_u16(buf, pos + 8);
pos += 10;
if (type == 1 && rdlen == 4) {
/* IPv4 A Record */
if (pos + 4 > rx_len)
return SYN_ERROR;
memcpy(addr_out->ip, buf + pos, 4);
addr_out->port = 0;
return SYN_OK;
}
pos += rdlen;
}
return SYN_ERROR;
}
SYN_PT_Status syn_dns_resolve_task(SYN_PT *pt, SYN_Task *task)
{
SYN_DnsResolver *r = (SYN_DnsResolver *)task->user_data;
SYN_ASSERT(r != NULL);
PT_BEGIN(pt);
r->status = SYN_TIMEOUT;
if (r->dns_server != NULL) {
r->server_addr = *(r->dns_server);
} else {
r->server_addr.ip[0] = 8;
r->server_addr.ip[1] = 8;
r->server_addr.ip[2] = 8;
r->server_addr.ip[3] = 8;
r->server_addr.port = 53;
}
r->sock = syn_port_udp_open(0);
if (r->sock == SYN_SOCKET_INVALID) {
r->status = SYN_ERROR;
PT_EXIT(pt);
}
/* Build query */
r->txid = (uint16_t)(syn_port_get_tick_ms() & 0xFFFF);
memset(r->buf, 0, 12);
syn_poke_u16(r->txid, r->buf, 0); /* Transaction ID */
syn_poke_u16(0x0100, r->buf, 2); /* Flags: Standard query, recursion desired */
syn_poke_u16(0x0001, r->buf, 4); /* Questions = 1 */
{
size_t pos = 12;
size_t qname_len = encode_qname(r->buf + pos, sizeof(r->buf) - pos - 4U, r->hostname);
if (qname_len == 0U) {
syn_port_sock_close(r->sock);
r->sock = SYN_SOCKET_INVALID;
r->status = SYN_ERROR;
PT_EXIT(pt);
}
pos += qname_len;
syn_poke_u16(0x0001, r->buf, pos);
pos += 2; /* QTYPE = A */
syn_poke_u16(0x0001, r->buf, pos);
pos += 2; /* QCLASS = IN */
r->query_len = pos;
}
if (syn_port_udp_sendto(r->sock, r->buf, r->query_len, &r->server_addr) != (int)r->query_len) {
syn_port_sock_close(r->sock);
r->sock = SYN_SOCKET_INVALID;
r->status = SYN_ERROR;
PT_EXIT(pt);
}
r->start_ms = syn_port_get_tick_ms();
for (;;) {
SYN_SockAddr from;
int n = syn_port_udp_recvfrom(r->sock, r->buf, sizeof(r->buf), &from, 0);
if (n > 0) {
if (n < 12 || syn_peek_u16(r->buf, 0) != r->txid) {
/* Runt or TXID mismatch — ignore and keep waiting */
continue;
}
r->status = parse_response(r->buf, (size_t)n, r->addr_out, r->txid);
break;
}
if ((syn_port_get_tick_ms() - r->start_ms) >= r->timeout_ms) {
r->status = SYN_TIMEOUT;
break;
}
PT_WAIT_UNTIL(pt, syn_port_udp_readable(r->sock) ||
(syn_port_get_tick_ms() - r->start_ms) >= r->timeout_ms);
}
syn_port_sock_close(r->sock);
r->sock = SYN_SOCKET_INVALID;
PT_END(pt);
}
/* ════════════════════════════════════════════════════════════════════════ */
/* mDNS Responder Task */
/* ════════════════════════════════════════════════════════════════════════ */
SYN_Status syn_mdns_init(SYN_Mdns *mdns, const char *hostname, const uint8_t ip[4])
{
SYN_ASSERT(mdns != NULL);
SYN_ASSERT(hostname != NULL);
SYN_ASSERT(ip != NULL);
memset(mdns, 0, sizeof(*mdns));
mdns->hostname = hostname;
memcpy(mdns->ip, ip, 4);
mdns->sock = syn_port_udp_open(5353);
if (mdns->sock == SYN_SOCKET_INVALID) {
return SYN_ERROR;
}
if (syn_port_udp_join_multicast(mdns->sock, "224.0.0.251") != SYN_OK) {
syn_port_sock_close(mdns->sock);
mdns->sock = SYN_SOCKET_INVALID;
return SYN_ERROR;
}
return SYN_OK;
}
static size_t get_base_hostname_len(const char *hostname)
{
if (hostname == NULL)
return 0; /* LCOV_EXCL_LINE: Defensive NULL check or invalid parameter fallback */
size_t len = strlen(hostname);
if (len > 6 && strcmp(hostname + len - 6, ".local") == 0) {
return len - 6;
}
return len;
}
static bool match_qname_local(const uint8_t *buf, size_t buf_len, size_t *pos, const char *hostname)
{
if (hostname == NULL)
return false;
size_t p = *pos;
if (p >= buf_len)
return false; /* LCOV_EXCL_LINE: Defensive NULL check or invalid parameter fallback */
/* First label: hostname length + string */
uint8_t h_len = buf[p++];
size_t host_len = get_base_hostname_len(hostname);
if (h_len != host_len)
return false;
if (p + host_len > buf_len)
return false; /* LCOV_EXCL_LINE: Defensive NULL check or invalid parameter fallback */
if (memcmp(buf + p, hostname, host_len) != 0)
return false; /* LCOV_EXCL_LINE: Defensive NULL check or invalid parameter fallback */
p += host_len;
/* Second label: "local" length + string */
if (p >= buf_len)
return false; /* LCOV_EXCL_LINE: Defensive NULL check or invalid parameter fallback */
uint8_t l_len = buf[p++];
if (l_len != 5)
return false;
if (p + 5 > buf_len)
return false; /* LCOV_EXCL_LINE: Defensive NULL check or invalid parameter fallback */
if (memcmp(buf + p, "local", 5) != 0)
return false;
p += 5;
/* Terminator */
if (p >= buf_len || buf[p] != 0)
return false; /* LCOV_EXCL_LINE: Defensive NULL check or invalid parameter fallback */
p++;
*pos = p;
return true;
}
SYN_PT_Status syn_mdns_task(SYN_PT *pt, SYN_Task *task)
{
const SYN_Mdns *mdns = (const SYN_Mdns *)task->user_data;
SYN_ASSERT(mdns != NULL);
PT_BEGIN(pt);
for (;;) {
if (mdns->sock != SYN_SOCKET_INVALID) {
uint8_t buf[256];
SYN_SockAddr from;
/* Non-blocking read (0 ms timeout) */
int n = syn_port_udp_recvfrom(mdns->sock, buf, sizeof(buf), &from, 0);
if (n > 12) {
size_t rx_len = (size_t)n;
uint16_t flags = syn_peek_u16(buf, 2);
uint16_t questions = syn_peek_u16(buf, 4);
/* Parse if it's a query (Flags QR bit = 0) */
if ((flags & 0x8000) == 0 && questions > 0) {
size_t pos = 12;
bool matched = false;
for (uint16_t i = 0; i < questions; i++) {
if (match_qname_local(buf, rx_len, &pos, mdns->hostname)) {
matched = true;
break;
}
/* if didn't match, parse to skip */
if (!parse_qname(buf, rx_len, &pos))
break;
if (pos + 4 > rx_len)
break; /* LCOV_EXCL_LINE: Defensive default branch for enum state
machine */
pos += 4; /* QTYPE + QCLASS */
}
if (matched) {
/* Build mDNS response packet */
uint8_t resp[256];
memset(resp, 0, 12);
/* Flags: 0x8400 (Authoritative Answer, Response) */
syn_poke_u16(0x8400, resp, 2);
syn_poke_u16(0x0001, resp, 6); /* Answers = 1 */
size_t rpos = 12;
size_t base_len = get_base_hostname_len(mdns->hostname);
/* Response needs: 12 + 1 + base_len + 1 + 5 + 1 + 10 + 4 = 34 + base_len */
if (34U + base_len > sizeof(resp))
break; /* LCOV_EXCL_LINE: Defensive mDNS response buffer capacity guard
*/
resp[rpos++] = (uint8_t)base_len;
memcpy(resp + rpos, mdns->hostname, base_len);
rpos += base_len;
resp[rpos++] = 5;
memcpy(resp + rpos, "local", 5);
rpos += 5;
resp[rpos++] = 0;
syn_poke_u16(0x0001, resp, rpos);
rpos += 2; /* TYPE = A */
syn_poke_u16(0x8001, resp, rpos);
rpos += 2; /* CLASS = IN + cache flush */
syn_poke_u32(120, resp, rpos);
rpos += 4; /* TTL = 120 */
syn_poke_u16(4, resp, rpos);
rpos += 2; /* RDLEN = 4 */
memcpy(resp + rpos, mdns->ip, 4); /* Address */
rpos += 4;
/* Send mDNS reply back to multicast group 224.0.0.251:5353 */
SYN_SockAddr mcast_dest;
mcast_dest.ip[0] = 224;
mcast_dest.ip[1] = 0;
mcast_dest.ip[2] = 0;
mcast_dest.ip[3] = 251;
mcast_dest.port = 5353;
syn_port_udp_sendto(mdns->sock, resp, rpos, &mcast_dest);
}
}
}
}
PT_WAIT_UNTIL(pt, mdns->sock == SYN_SOCKET_INVALID || syn_port_udp_readable(mdns->sock));
}
PT_END(pt); /* LCOV_EXCL_LINE: Defensive bounds check / hardware port fallback */
}
#endif /* SYN_USE_DNS */