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Introduce new mDNS API, add mDNS client example

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Sergio R. Caprile committed 2026-03-06 11:27:22 -03:00
1 parent abe19d2367
commit 2a7fa4cb68
11 files changed
+303 -92
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src/dns.c
+70 -19
View File
@@ -63,7 +63,7 @@ static size_t mg_dns_parse_name_depth(const uint8_t *s, size_t len, size_t ofs,
if (j < tolen) to[j] = '\0'; // Zero-terminate this chunk
// MG_INFO(("--> [%s]", to));
}
if (tolen > 0) to[tolen - 1] = '\0'; // Make sure make sure it is nul-term
if (tolen > 0) to[tolen - 1] = '\0'; // Make sure it is nul-term
return i;
}
@@ -134,12 +134,12 @@ bool mg_dns_parse(const uint8_t *buf, size_t len, struct mg_dns_message *dm) {
mg_dns_parse_name(buf, len, ofs, dm->name, sizeof(dm->name));
ofs += n;
if (rr.alen == 4 && rr.atype == 1 && rr.aclass == 1) {
if (rr.alen == 4 && rr.atype == MG_DNS_RTYPE_A && rr.aclass == 1) {
dm->addr.is_ip6 = false;
memcpy(&dm->addr.addr.ip, &buf[ofs - 4], 4);
dm->resolved = true;
break; // Return success
} else if (rr.alen == 16 && rr.atype == 28 && rr.aclass == 1) {
} else if (rr.alen == 16 && rr.atype == MG_DNS_RTYPE_AAAA && rr.aclass == 1) {
dm->addr.is_ip6 = true;
memcpy(&dm->addr.addr.ip, &buf[ofs - 16], 16);
dm->resolved = true;
@@ -335,7 +335,7 @@ static uint8_t *build_mysrv_name(struct mg_str *name, uint8_t *p,
static uint8_t *build_ptr_record(struct mg_str *name, uint8_t *p, uint16_t o) {
uint16_t offset = mg_htons(o);
memcpy(p, mdns_answer, sizeof(mdns_answer));
p[1] = 12; // overwrite record type
p[1] = MG_DNS_RTYPE_PTR; // overwrite record type
p += sizeof(mdns_answer);
p[-1] = (uint8_t) name->len +
3; // overwrite response length, label length + label + offset
@@ -351,7 +351,7 @@ static uint8_t *build_srv_record(struct mg_str *name, uint8_t *p,
uint16_t port = mg_htons(r->port);
uint16_t offset = mg_htons(o);
memcpy(p, mdns_answer, sizeof(mdns_answer));
p[1] = 33; // overwrite record type
p[1] = MG_DNS_RTYPE_SRV; // overwrite record type
p += sizeof(mdns_answer);
p[-1] = (uint8_t) name->len + 9; // overwrite response length (4+2+1+2)
*p++ = 0; // priority
@@ -369,7 +369,7 @@ static uint8_t *build_srv_record(struct mg_str *name, uint8_t *p,
static uint8_t *build_txt_record(uint8_t *p, struct mg_dnssd_record *r) {
uint16_t len = mg_htons((uint16_t) r->txt.len);
memcpy(p, mdns_answer, sizeof(mdns_answer));
p[1] = 16; // overwrite record type
p[1] = MG_DNS_RTYPE_TXT; // overwrite record type
p += sizeof(mdns_answer);
memcpy(p - 2, &len, 2); // overwrite response length
memcpy(p, r->txt.buf, r->txt.len), p += r->txt.len; // copy record verbatim
@@ -378,12 +378,10 @@ static uint8_t *build_txt_record(uint8_t *p, struct mg_dnssd_record *r) {
// RFC-6762 16: case-insensitivity --> RFC-1034, 1035
static void handle_mdns_record(struct mg_connection *c) {
static void handle_mdns_query(struct mg_connection *c) {
struct mg_dns_header *qh = (struct mg_dns_header *) c->recv.buf;
struct mg_dns_rr rr;
size_t n;
// flags -> !resp, opcode=0 => query; ignore other opcodes and responses
if (c->recv.len <= 12 || (qh->flags & mg_htons(0xF800)) != 0) return;
// Parse first question, offset 12 is header size
n = mg_dns_parse_rr(c->recv.buf, c->recv.len, 12, true, &rr);
MG_VERBOSE(("mDNS request parsed, result=%d", (int) n));
@@ -410,7 +408,7 @@ static void handle_mdns_record(struct mg_connection *c) {
name[name_len -= 6] = '\0'; // remove .local
MG_VERBOSE(("RR %u %u %s", (unsigned int) rr.atype,
(unsigned int) rr.aclass, name));
if (rr.atype == 1) { // A
if (rr.atype == MG_DNS_RTYPE_A) {
// TODO(): ensure c->fn_data ends in \0
// if we have a name to match, go; otherwise users will match and fill
// req.r.name and set req.is_resp
@@ -418,17 +416,15 @@ static void handle_mdns_record(struct mg_connection *c) {
return;
req.is_resp = (c->fn_data != NULL);
req.reqname = mg_str_n(name, name_len);
mg_call(c, MG_EV_MDNS_A, &req);
} else // users have to match the request to something in their db, then
// fill req.r and set req.is_resp
if (rr.atype == 12) { // PTR
if (rr.atype == MG_DNS_RTYPE_PTR) {
if (strcmp("_services._dns-sd._udp", name) == 0) req.is_listing = true;
MG_DEBUG(
("PTR request for %s", req.is_listing ? "services listing" : name));
req.reqname = mg_str_n(name, name_len);
mg_call(c, MG_EV_MDNS_PTR, &req);
} else if (rr.atype == 33 || rr.atype == 16) { // SRV or TXT
MG_DEBUG(("%s request for %s", rr.atype == 33 ? "SRV" : "TXT", name));
} else if (rr.atype == MG_DNS_RTYPE_SRV || rr.atype == MG_DNS_RTYPE_TXT) {
MG_DEBUG(("%s request for %s", rr.atype == MG_DNS_RTYPE_SRV ? "SRV" : "TXT", name));
// if possible, check it starts with our name, users will check it ends
// in a service name they handle
if (c->fn_data != NULL) {
@@ -442,10 +438,11 @@ static void handle_mdns_record(struct mg_connection *c) {
} else {
req.reqname = mg_str_n(name, name_len);
}
mg_call(c, rr.atype == 33 ? MG_EV_MDNS_SRV : MG_EV_MDNS_TXT, &req);
} else { // unhandled record
return;
}
req.rr = &rr;
mg_call(c, MG_EV_MDNS_REQ, &req);
if (!req.is_resp) return;
respname = req.respname.buf != NULL ? &req.respname : &defname;
@@ -459,7 +456,7 @@ static void handle_mdns_record(struct mg_connection *c) {
// range 20-120 ms.
// TODO():
return;
} else if (rr.atype == 12) { // PTR requested, serve PTR + SRV + TXT + A
} else if (rr.atype == MG_DNS_RTYPE_PTR) { // serve PTR + SRV + TXT + A
// TODO(): RFC-6762 6: each responder SHOULD delay its response by a
// random amount of time selected with uniform random distribution in the
// range 20-120 ms. Response to PTR is local_name._myservice._tcp.local
@@ -485,10 +482,10 @@ static void handle_mdns_record(struct mg_connection *c) {
memcpy(p, &offset, 2); // point to target name, in record
*p |= 0xC0, p += 2;
p = build_a_record(c, p);
} else if (rr.atype == 16) { // TXT requested
} else if (rr.atype == MG_DNS_RTYPE_TXT) {
p = build_srv_name(p, req.r);
p = build_txt_record(p, req.r);
} else if (rr.atype == 33) { // SRV requested, serve SRV + A
} else if (rr.atype == MG_DNS_RTYPE_SRV) { // serve SRV + A
uint8_t *o, *aux;
uint16_t offset;
if (respname->buf == NULL || respname->len == 0) return;
@@ -514,6 +511,52 @@ static void handle_mdns_record(struct mg_connection *c) {
}
}
static void handle_mdns_response(struct mg_connection *c) {
struct mg_dns_header *rh = (struct mg_dns_header *) c->recv.buf;
struct mg_dns_rr rr;
size_t n;
// Parse first response, offset 12 is header size
n = mg_dns_parse_rr(c->recv.buf, c->recv.len, 12, false, &rr);
MG_VERBOSE(("mDNS response parsed, result=%d", (int) n));
if (n > 0) {
// RFC-6762 Appendix C, RFC2181 11: m(n + 1-63), max 255 + 0x0
char name[256];
uint8_t name_len;
struct mg_mdns_resp resp;
memset(&resp, 0, sizeof(resp));
if (rh->num_answers > mg_htons(1)) MG_DEBUG(("ignoring > 1 answers"));
mg_dns_parse_name(c->recv.buf, c->recv.len, 12, name, sizeof(name));
name_len = (uint8_t) strlen(name); // verify it ends in .local
MG_VERBOSE(("RR %u %u %s", (unsigned int) rr.atype, (unsigned int) rr.aclass, name));
if (rr.alen == 4 && rr.atype == MG_DNS_RTYPE_A && (rr.aclass & 0x7FFF) == 1) {
resp.addr.is_ip6 = false;
memcpy(resp.addr.addr.ip, (char *)(rh + 1) + n - 4, 4);
MG_DEBUG(("A response from %.*s = %M", name_len, name, mg_print_ip, &resp.addr));
// } else if (rr.alen == 16 && rr.atype == MG_DNS_RTYPE_AAAA && (rr.aclass & 0x7FFF) == 1) {
// resp.addr.is_ip6 = true;
// memcpy(resp.addr.addr.ip, (char *)(rh + 1) + n - 16], 16);
// MG_DEBUG(("AAAA response from %.*s = %M", name_len, name, mg_print_ip, &resp.addr));
} else {
return;
}
resp.name = mg_str_n(name, name_len);
resp.rr = &rr;
mg_call(c, MG_EV_MDNS_RESP, &resp);
}
}
static void handle_mdns_record(struct mg_connection *c) {
struct mg_dns_header *h = (struct mg_dns_header *) c->recv.buf;
if (c->recv.len <= 12) return;
if ((h->flags & mg_htons(0xF800)) == 0) {
// flags -> !resp, opcode=0 => query; ignore other opcodes
handle_mdns_query(c);
} else if ((h->flags & mg_htons(0xF800)) == mg_htons(0x8000)) {
// flags -> resp, opcode=0 => response; ignore other opcodes
handle_mdns_response(c);
}
}
static void mdns_cb(struct mg_connection *c, int ev, void *ev_data) {
if (ev == MG_EV_READ) {
handle_mdns_record(c);
@@ -532,3 +575,11 @@ struct mg_connection *mg_mdns_listen(struct mg_mgr *mgr, mg_event_handler_t fn,
mg_multicast_add(c, (char *) "224.0.0.251");
return c;
}
bool mg_mdns_query(struct mg_connection *c, const char *name, unsigned int rtype) {
struct mg_str name_;
name_.buf = (char *)name, name_.len = strlen(name);
mg_multicast_restore(c, (uint8_t *) &c->loc);
(void) rtype;
return mg_dns_send(c, &name_, 0, false);
}
src/dns.h
+18 -2
View File
@@ -3,6 +3,13 @@
#include "net.h"
#include "str.h"
#define MG_DNS_RTYPE_A 1
#define MG_DNS_RTYPE_PTR 12
#define MG_DNS_RTYPE_TXT 16
#define MG_DNS_RTYPE_AAAA 28
#define MG_DNS_RTYPE_SRV 33
// Mongoose sends DNS queries that contain only one question:
// either A (IPv4) or AAAA (IPv6) address lookup.
// Therefore, we expect zero or one answer.
@@ -38,18 +45,26 @@ struct mg_dnssd_record {
uint16_t port; // SRV record port
};
// mDNS request
// mDNS request and response data structs passed to event handlers
struct mg_mdns_req {
struct mg_dns_rr *rr;
struct mg_dnssd_record *r;
struct mg_str reqname; // requested name in RR
struct mg_str respname; // actual name in response
struct mg_str respname; // actual name to use in response
struct mg_addr addr;
bool is_listing;
bool is_resp;
bool is_unicast;
};
struct mg_mdns_resp {
struct mg_dns_rr *rr;
// TODO(scaprile )struct mg_str srvcproto; struct mg_str txt; uint16_t port; ?
struct mg_str name;
struct mg_addr addr;
// TODO(scaprile); bool has_A; bool has_PTR; bool has_SRV; bool has_TXT; ?
};
void mg_resolve(struct mg_connection *, const char *url);
void mg_resolve_cancel(struct mg_connection *);
bool mg_dns_parse(const uint8_t *buf, size_t len, struct mg_dns_message *);
@@ -58,3 +73,4 @@ size_t mg_dns_parse_rr(const uint8_t *buf, size_t len, size_t ofs,
struct mg_connection *mg_mdns_listen(struct mg_mgr *mgr, mg_event_handler_t fn,
void *fn_data);
bool mg_mdns_query(struct mg_connection *, const char *, unsigned int);
src/event.h
+2 -4
View File
@@ -27,9 +27,7 @@ enum {
MG_EV_MQTT_OPEN, // MQTT CONNACK received int *connack_status_code
MG_EV_SNTP_TIME, // SNTP time received uint64_t *epoch_millis
MG_EV_WAKEUP, // mg_wakeup() data received struct mg_str *data
MG_EV_MDNS_A, // mDNS A record request struct mg_mdns_req *
MG_EV_MDNS_PTR, // mDNS PTR record request struct mg_mdns_req *
MG_EV_MDNS_SRV, // mDNS SRV record request struct mg_mdns_req *
MG_EV_MDNS_TXT, // mDNS TXT record request struct mg_mdns_req *
MG_EV_MDNS_REQ, // mDNS request struct mg_mdns_req *
MG_EV_MDNS_RESP, // mDNS response struct mg_mdns_resp *
MG_EV_USER // Starting ID for user events
};