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ce6164ca206001e6e6d404a3a9b2adbbf656026a
mongoose/src/dns.c
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#include "dns.h"
#include "log.h"
#include "str.h"
#include "timer.h"
#include "util.h"
struct dns_data {
struct dns_data *next;
struct mg_connection *c;
int64_t expire;
uint16_t txnid;
};
static struct dns_data *s_reqs; // Active DNS requests
static void mg_sendnsreq(struct mg_connection *, struct mg_str *, int,
struct mg_dns *, bool);
static void mg_dns_free(struct dns_data *d) {
LIST_DELETE(struct dns_data, &s_reqs, d);
free(d);
}
void mg_resolve_cancel(struct mg_connection *c) {
struct dns_data *tmp, *d;
for (d = s_reqs; d != NULL; d = tmp) {
tmp = d->next;
if (d->c == c) mg_dns_free(d);
}
}
static size_t mg_dns_parse_name_depth(const uint8_t *s, size_t len, size_t ofs,
char *to, size_t tolen, int depth) {
size_t i = 0, j = 0;
if (tolen > 0) to[0] = '\0';
if (depth > 5) return 0;
while (ofs + i + 1 < len) {
size_t n = s[ofs + i];
if (n == 0) {
i++;
break;
}
if (n & 0xc0) {
size_t ptr = (((n & 0x3f) << 8) | s[ofs + i + 1]); // 12 is hdr len
if (ptr + 1 < len && (s[ptr] & 0xc0) == 0 &&
mg_dns_parse_name_depth(s, len, ptr, to, tolen, depth + 1) == 0)
return 0;
i += 2;
break;
}
if (ofs + i + n + 1 >= len) return 0;
if (j > 0) {
if (j < tolen) to[j] = '.';
j++;
}
if (j + n < tolen) memcpy(&to[j], &s[ofs + i + 1], n);
j += n;
i += n + 1;
if (j < tolen) to[j] = '\0'; // Zero-terminate this chunk
}
if (tolen > 0) to[tolen - 1] = '\0'; // Make sure make sure it is nul-term
return i;
}
static size_t mg_dns_parse_name(const uint8_t *s, size_t n, size_t ofs,
char *dst, size_t dstlen) {
return mg_dns_parse_name_depth(s, n, ofs, dst, dstlen, 0);
}
size_t mg_dns_parse_rr(const uint8_t *buf, size_t len, size_t ofs,
bool is_question, struct mg_dns_rr *rr) {
const uint8_t *s = buf + ofs, *e = &buf[len];
memset(rr, 0, sizeof(*rr));
if (len < sizeof(struct mg_dns_header)) return 0; // Too small
if (len > 512) return 0; // Too large, we don't expect that
if (s >= e) return 0; // Overflow
if ((rr->nlen = (uint16_t) mg_dns_parse_name(buf, len, ofs, NULL, 0)) == 0)
return 0;
s += rr->nlen + 4;
if (s > e) return 0;
rr->atype = (uint16_t) (((uint16_t) s[-4] << 8) | s[-3]);
rr->aclass = (uint16_t) (((uint16_t) s[-2] << 8) | s[-1]);
if (is_question) return (size_t) (rr->nlen + 4);
s += 6;
if (s > e) return 0;
rr->alen = (uint16_t) (((uint16_t) s[-2] << 8) | s[-1]);
if (s + rr->alen > e) return 0;
return (size_t) (rr->nlen + rr->alen + 10);
}
bool mg_dns_parse(const uint8_t *buf, size_t len, struct mg_dns_message *dm) {
const struct mg_dns_header *h = (struct mg_dns_header *) buf;
struct mg_dns_rr rr;
size_t i, n, ofs = sizeof(*h);
memset(dm, 0, sizeof(*dm));
if (len < sizeof(*h)) return 0; // Too small, headers dont fit
if (mg_ntohs(h->num_questions) > 1) return 0; // Sanity
if (mg_ntohs(h->num_answers) > 10) return 0; // Sanity
dm->txnid = mg_ntohs(h->txnid);
for (i = 0; i < mg_ntohs(h->num_questions); i++) {
if ((n = mg_dns_parse_rr(buf, len, ofs, true, &rr)) == 0) return false;
// LOG(LL_INFO, ("Q %zu %zu", ofs, n));
ofs += n;
}
for (i = 0; i < mg_ntohs(h->num_answers); i++) {
// LOG(LL_INFO, ("A -- %zu %zu %s", ofs, n, dm->name));
if ((n = mg_dns_parse_rr(buf, len, ofs, false, &rr)) == 0) return false;
mg_dns_parse_name(buf, len, ofs, dm->name, sizeof(dm->name));
ofs += n;
if (rr.alen == 4 && rr.atype == 1 && rr.aclass == 1) {
dm->addr.is_ip6 = false;
memcpy(&dm->addr.ip, &buf[ofs - 4], 4);
dm->resolved = true;
break; // Return success
} else if (rr.alen == 16 && rr.atype == 28 && rr.aclass == 1) {
dm->addr.is_ip6 = true;
memcpy(&dm->addr.ip6, &buf[ofs - 16], 16);
dm->resolved = true;
break; // Return success
}
}
return true;
}
static void dns_cb(struct mg_connection *c, int ev, void *ev_data,
void *fn_data) {
struct dns_data *d, *tmp;
if (ev == MG_EV_POLL) {
int64_t now = *(int64_t *) ev_data;
for (d = s_reqs; d != NULL; d = tmp) {
tmp = d->next;
// LOG(LL_DEBUG, ("%lu %lu dns poll", d->expire, now));
if (now > d->expire) mg_error(d->c, "DNS timeout");
}
} else if (ev == MG_EV_READ) {
struct mg_dns_message dm;
int resolved = 0;
if (mg_dns_parse(c->recv.buf, c->recv.len, &dm) == false) {
char *s = mg_hexdump(c->recv.buf, c->recv.len);
LOG(LL_ERROR, ("Unexpected DNS response:\n%s\n", s));
free(s);
} else {
LOG(LL_VERBOSE_DEBUG, ("%s %d", dm.name, dm.resolved));
for (d = s_reqs; d != NULL; d = tmp) {
tmp = d->next;
// LOG(LL_INFO, ("d %p %hu %hu", d, d->txnid, dm.txnid));
if (dm.txnid != d->txnid) continue;
if (d->c->is_resolving) {
d->c->is_resolving = 0;
if (dm.resolved) {
#if MG_ENABLE_LOG
char buf[100];
#endif
dm.addr.port = d->c->peer.port; // Save port
d->c->peer = dm.addr; // Copy resolved address
LOG(LL_DEBUG, ("%lu %s resolved to %s", d->c->id, dm.name,
mg_ntoa(&d->c->peer, buf, sizeof(buf))));
mg_connect_resolved(d->c);
#if MG_ENABLE_IPV6
} else if (dm.addr.is_ip6 == false && dm.name[0] != '\0') {
struct mg_str x = mg_str(dm.name);
mg_sendnsreq(d->c, &x, c->mgr->dnstimeout, &c->mgr->dns6, true);
#endif
} else {
mg_error(d->c, "%s DNS lookup failed", dm.name);
}
} else {
LOG(LL_ERROR, ("%lu already resolved", d->c->id));
}
mg_dns_free(d);
resolved = 1;
}
}
if (!resolved) LOG(LL_ERROR, ("stray DNS reply"));
c->recv.len = 0;
} else if (ev == MG_EV_CLOSE) {
for (d = s_reqs; d != NULL; d = tmp) {
tmp = d->next;
mg_dns_free(d);
}
}
(void) fn_data;
}
static void mg_dns_send(struct mg_connection *c, const struct mg_str *name,
uint16_t txnid, bool ipv6) {
struct {
struct mg_dns_header header;
uint8_t data[256];
} pkt;
size_t i, n;
memset(&pkt, 0, sizeof(pkt));
pkt.header.txnid = mg_htons(txnid);
pkt.header.flags = mg_htons(0x100);
pkt.header.num_questions = mg_htons(1);
for (i = n = 0; i < sizeof(pkt.data) - 5; i++) {
if (name->ptr[i] == '.' || i >= name->len) {
pkt.data[n] = (uint8_t) (i - n);
memcpy(&pkt.data[n + 1], name->ptr + n, i - n);
n = i + 1;
}
if (i >= name->len) break;
}
memcpy(&pkt.data[n], "\x00\x00\x01\x00\x01", 5); // A query
n += 5;
if (ipv6) pkt.data[n - 3] = 0x1c; // AAAA query
// memcpy(&pkt.data[n], "\xc0\x0c\x00\x1c\x00\x01", 6); // AAAA query
// n += 6;
mg_send(c, &pkt, sizeof(pkt.header) + n);
#if 0
// Immediately after A query, send AAAA query. Whatever reply comes first,
// we'll use it. Note: we cannot send two queries in a single packet.
// https://stackoverflow.com/questions/4082081/requesting-a-and-aaaa-records-in-single-dns-query
pkt.data[n - 3] = 0x1c; // AAAA query
mg_send(c, &pkt, sizeof(pkt.header) + n);
#endif
}
static void mg_sendnsreq(struct mg_connection *c, struct mg_str *name, int ms,
struct mg_dns *dnsc, bool ipv6) {
struct dns_data *d = NULL;
if (dnsc->url == NULL) {
mg_error(c, "DNS server URL is NULL. Call mg_mgr_init()");
} else if (dnsc->c == NULL) {
dnsc->c = mg_connect(c->mgr, dnsc->url, NULL, NULL);
if (dnsc->c != NULL) {
dnsc->c->pfn = dns_cb;
snprintf(dnsc->c->label, sizeof(dnsc->c->label), "%s", "DNS");
// dnsc->c->is_hexdumping = 1;
}
}
if (dnsc->c == NULL) {
mg_error(c, "resolver");
} else if ((d = (struct dns_data *) calloc(1, sizeof(*d))) == NULL) {
mg_error(c, "resolve OOM");
} else {
#if MG_ENABLE_LOG
char buf[100];
#endif
d->txnid = s_reqs ? (uint16_t) (s_reqs->txnid + 1) : 1;
d->next = s_reqs;
s_reqs = d;
d->expire = mg_millis() + (int64_t) ms;
d->c = c;
c->is_resolving = 1;
LOG(LL_VERBOSE_DEBUG,
("%lu resolving %.*s @ %s, txnid %hu", c->id, (int) name->len,
name->ptr, mg_ntoa(&dnsc->c->peer, buf, sizeof(buf)), d->txnid));
mg_dns_send(dnsc->c, name, d->txnid, ipv6);
}
}
void mg_resolve(struct mg_connection *c, struct mg_str *name, int ms) {
if (mg_aton(*name, &c->peer)) {
// name is an IP address, do not fire name resolution
mg_connect_resolved(c);
} else {
// name is not an IP, send DNS resolution request
mg_sendnsreq(c, name, ms, &c->mgr->dns4, false);
}
}
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