mdns: Fix/Update Windows mdns code

This syncs the application side with the updates in the mdns.h file
from: https://github.com/mjansson/mdns/
and does things according to the specs. (build up info from both A, AAAA and
SRV records), not just assuming that the DNS server is the host.

Signed-off-by: Robin Getz <[email protected]>

Author: rgetz

dns_sd_windows.c

@@ -2,11 +2,11 @@
 /*
  * libiio - Library for interfacing industrial I/O (IIO) devices
  *
- * Copyright (C) 2014-2020 Analog Devices, Inc.
+ * Copyright (C) 2014-2022 Analog Devices, Inc.
  * Author: Adrian Suciu <[email protected]>
  *
- * Based on https://github.com/mjansson/mdns/blob/ce2e4f789f06429008925ff8f18c22036e60201e/mdns.c
- * which is Licensed under Public Domain
+ * Based on https://github.com/mjansson/mdns/blob/main/mdns.c
+ * which should be sync'ed with the mdns.h file and is Licensed under Public Domain
  */
 
 #include <stdio.h>
@@ -47,6 +47,50 @@ static bool is_localhost4(const struct sockaddr_in *saddr)
 		saddr->sin_addr.S_un.S_un_b.s_b4 == 1;
 }
 
+static struct dns_sd_discovery_data *new_discovery_data(struct dns_sd_discovery_data *dd)
+{
+	struct dns_sd_discovery_data *d;
+
+	d = zalloc(sizeof(*d));
+	if (!d)
+		return NULL;
+
+	if (dd)
+		d->lock = dd->lock;
+
+	return d;
+}
+
+static mdns_string_t ip_address_to_string(char *buffer, size_t capacity,
+					  const struct sockaddr *addr, size_t addrlen)
+{
+	char host[NI_MAXHOST] = { 0 };
+	char service[NI_MAXSERV] = { 0 };
+	int ret, len = 0;
+	ret = getnameinfo((const struct sockaddr *)addr, (socklen_t)addrlen, host,
+			NI_MAXHOST, service, NI_MAXSERV, NI_NUMERICSERV | NI_NUMERICHOST);
+
+	if (ret == 0) {
+		if (addr->sa_family == AF_INET6 &&
+				((struct sockaddr_in6 *)addr)->sin6_port != 0 &&
+				strncmp(service, "5353", sizeof("5353")))
+			len = snprintf(buffer, capacity, "[%s]:%s", host, service);
+		else if (((struct sockaddr_in *)addr)->sin_port != 0 &&
+				strncmp(service, "5353", sizeof("5353")))
+			len = snprintf(buffer, capacity, "%s:%s", host, service);
+		else
+			len = snprintf(buffer, capacity, "%s", host);
+	}
+
+	if (len >= (int)capacity)
+		len = (int)capacity - 1;
+	mdns_string_t str;
+	str.str = buffer;
+	str.length = len;
+
+	return str;
+}
+
 static int open_client_sockets(int *sockets, unsigned int max_sockets)
 {
 	IP_ADAPTER_UNICAST_ADDRESS *unicast;
@@ -130,6 +174,14 @@ static int open_client_sockets(int *sockets, unsigned int max_sockets)
 	return num_sockets;
 }
 
+/* We should get:
+ *  - "service" record (SRV) specifying host (name) and port
+ *  - IPv4 "address" record (A) specifying IPv4 address of a given host
+ *  - IPv6 "address" record (AAAA) specifying IPv6 address of a given host
+ * It's this routine that gets called, and needs to stitch things together
+ * The DNS host doesn't necessary need to be the acutal host (but for
+ * mdns - it usually is.
+ */
 static int query_callback(int sock, const struct sockaddr *from, size_t addrlen,
 			  mdns_entry_type_t entry, uint16_t query_id,
 			  uint16_t rtype, uint16_t rclass, uint32_t ttl,
@@ -140,52 +192,155 @@ static int query_callback(int sock, const struct sockaddr *from, size_t addrlen,
 {
 	struct dns_sd_discovery_data *dd = user_data;
 	char addrbuffer[64];
-	char servicebuffer[64];
+	char entrybuffer[256];
 	char namebuffer[256];
 	mdns_record_srv_t srv;
+	bool found = false;
+
+	mdns_string_t entrystr, fromaddrstr;
 
 	if (!dd) {
 		IIO_ERROR("DNS SD: Missing info structure. Stop browsing.\n");
 		goto quit;
 	}
 
-	if (rtype != MDNS_RECORDTYPE_SRV)
+	if (rtype != MDNS_RECORDTYPE_SRV && rtype != MDNS_RECORDTYPE_A &&
+			rtype != MDNS_RECORDTYPE_AAAA)
 		goto quit;
 
-	getnameinfo(from, (socklen_t)addrlen, addrbuffer, NI_MAXHOST,
-		    servicebuffer, NI_MAXSERV, NI_NUMERICSERV | NI_NUMERICHOST);
-
-	srv = mdns_record_parse_srv(data, size, name_offset, name_length,
-				    namebuffer, sizeof(namebuffer));
-	IIO_DEBUG("%s : SRV %.*s priority %d weight %d port %d\n", addrbuffer,
-		  MDNS_STRING_FORMAT(srv.name), srv.priority, srv.weight, srv.port);
-
-	/* Go to the last element in the list */
-	while (dd->next)
-		dd = dd->next;
-
-	if (srv.name.length > 1)
-	{
-		dd->hostname = malloc(srv.name.length);
-		if (!dd->hostname)
-			return -ENOMEM;
+	if (entry != MDNS_ENTRYTYPE_ANSWER)
+		goto quit;
 
-		iio_strlcpy(dd->hostname, srv.name.str, srv.name.length);
-	}
+	entrystr = mdns_string_extract(data, size, &name_offset,
+			entrybuffer, sizeof(entrybuffer));
 
-	iio_strlcpy(dd->addr_str, addrbuffer, DNS_SD_ADDRESS_STR_MAX);
-	dd->port = srv.port;
+	if (!strstr(entrystr.str, "_iio._tcp.local"))
+		goto quit;
 
-	IIO_DEBUG("DNS SD: added %s (%s:%d)\n",
-		  dd->hostname, dd->addr_str, dd->port);
+	fromaddrstr = ip_address_to_string(addrbuffer, sizeof(addrbuffer),
+			from, addrlen);
+
+	iio_mutex_lock(dd->lock);
+	if (rtype == MDNS_RECORDTYPE_SRV) {
+		srv = mdns_record_parse_srv(data, size, record_offset, record_length,
+			namebuffer, sizeof(namebuffer));
+		IIO_DEBUG("%.*s : %.*s SRV %.*s priority %d weight %d port %d\n",
+			MDNS_STRING_FORMAT(fromaddrstr), MDNS_STRING_FORMAT(entrystr),
+			MDNS_STRING_FORMAT(srv.name), srv.priority, srv.weight, srv.port);
+
+		/* find a match based on name/port/ipv[46] & update it, otherwise add it */
+		while (dd->next) {
+			if (dd->hostname &&
+			    !strncmp(dd->hostname, srv.name.str, srv.name.length - 1) &&
+			    (!dd->port || dd->port == srv.port) &&
+			    dd->found == (from->sa_family != AF_INET)) {
+				dd->port = srv.port;
+				IIO_DEBUG("DNS SD: updated SRV %s (%s port:%hu)\n",
+						dd->hostname, dd->addr_str, dd->port);
+				found = true;
+			}
+			dd = dd->next;
+		}
+		if (!found) {
+			/* new hostname and port */
+			if (srv.name.length > 1) {
+				dd->hostname = iio_strndup(srv.name.str,
+						srv.name.length - 1);
+				if (!dd->hostname)
+					goto mem_fail;
+			}
 
-	/* A list entry was filled, prepare new item on the list */
-	dd->next = zalloc(sizeof(*dd->next));
-	if (!dd->next)
-		IIO_ERROR("DNS SD mDNS Resolver : memory failure\n");
+			iio_strlcpy(dd->addr_str, fromaddrstr.str, fromaddrstr.length + 1);
+			dd->port = srv.port;
+			dd->found = (from->sa_family != AF_INET);
+			IIO_DEBUG("DNS SD: added SRV %s (%s port:%d)\n",
+				dd->hostname, dd->addr_str, dd->port);
 
+			/* A list entry was filled, prepare new item on the list */
+			dd->next = new_discovery_data(dd);
+			if (!dd->next)
+				goto mem_fail;
+		}
+	} else if (rtype == MDNS_RECORDTYPE_A) {
+		struct sockaddr_in addr;
+		mdns_string_t addrstr;
+
+		mdns_record_parse_a(data, size, record_offset, record_length, &addr);
+		addrstr = ip_address_to_string(namebuffer, sizeof(namebuffer),
+				(struct sockaddr *) &addr, sizeof(addr));
+		IIO_DEBUG("%.*s : %.*s A %.*s\n", MDNS_STRING_FORMAT(fromaddrstr),
+			MDNS_STRING_FORMAT(entrystr), MDNS_STRING_FORMAT(addrstr));
+
+		/* find a match based on name/ipv4 or 6 & update it, otherwise add it */
+		while (dd->next) {
+			if (dd->hostname &&
+			    !strncmp(dd->hostname, entrystr.str, entrystr.length - 1) &&
+			    !dd->found) {
+				iio_strlcpy(dd->addr_str, addrstr.str, addrstr.length + 1);
+				IIO_DEBUG("DNS SD: updated A %s (%s port:%hu)\n",
+						dd->hostname, dd->addr_str, dd->port);
+				found = true;
+			}
+			dd = dd->next;
+		}
+		if (!found) {
+			dd->hostname = iio_strndup(entrystr.str, entrystr.length - 1);
+			if (!dd->hostname)
+				goto mem_fail;
+			iio_strlcpy(dd->addr_str, addrstr.str, addrstr.length + 1);
+			dd->found = 0;
+
+			/* A list entry was filled, prepare new item on the list */
+			dd->next = new_discovery_data(dd);
+			if (!dd->next)
+				goto mem_fail;
+		}
+	}
+#ifdef HAVE_IPV6
+	else if (rtype == MDNS_RECORDTYPE_AAAA) {
+		struct sockaddr_in6 addr;
+		mdns_string_t addrstr;
+
+		mdns_record_parse_aaaa(data, size, record_offset, record_length, &addr);
+		addrstr = ip_address_to_string(namebuffer, sizeof(namebuffer),
+				(struct sockaddr *) &addr, sizeof(addr));
+		IIO_DEBUG("%.*s : %.*s AAAA %.*s\n", MDNS_STRING_FORMAT(fromaddrstr),
+			MDNS_STRING_FORMAT(entrystr), MDNS_STRING_FORMAT(addrstr));
+
+		/* find a match based on name/port/ipv[46] & update it, otherwise add it */
+		while (dd->next) {
+			if (dd->hostname &&
+			    !strncmp(dd->hostname, entrystr.str, entrystr.length - 1) &&
+			    dd->found) {
+				iio_strlcpy(dd->addr_str, addrstr.str, addrstr.length + 1);
+				IIO_DEBUG("DNS SD: updated AAAA %s (%s port:%hu)\n",
+						dd->hostname, dd->addr_str, dd->port);
+				found = true;
+			}
+			dd = dd->next;
+		}
+		if (!found) {
+			dd->hostname = iio_strndup(entrystr.str, entrystr.length - 1);
+			if (!dd->hostname)
+				goto mem_fail;
+			iio_strlcpy(dd->addr_str, addrstr.str, addrstr.length + 1);
+			dd->found = 1;
+
+			/* A list entry was filled, prepare new item on the list */
+			dd->next = new_discovery_data(dd);
+			if (!dd->next)
+				goto mem_fail;
+		}
+	}
+#endif /* HAVE_IPV6 */
+	iio_mutex_unlock(dd->lock);
 quit:
 	return 0;
+
+mem_fail:
+	iio_mutex_unlock(dd->lock);
+	IIO_ERROR("DNS SD mDNS Resolver : memory failure\n");
+	return -ENOMEM;
 }
 
 int dnssd_find_hosts(struct dns_sd_discovery_data **ddata)
@@ -202,15 +357,16 @@ int dnssd_find_hosts(struct dns_sd_discovery_data **ddata)
 	int ret = -ENOMEM;
 
 	if (WSAStartup(versionWanted, &wsaData)) {
-		printf("Failed to initialize WinSock\n");
+		IIO_ERROR("Failed to initialize WinSock\n");
 		return -WSAGetLastError();
 	}
 
 	IIO_DEBUG("DNS SD: Start service discovery.\n");
 
-	d = zalloc(sizeof(*d));
+	d = new_discovery_data(NULL);
 	if (!d)
 		goto out_wsa_cleanup;
+
 	/* pass the structure back, so it can be freed if err */
 	*ddata = d;
 
@@ -241,23 +397,24 @@ int dnssd_find_hosts(struct dns_sd_discovery_data **ddata)
 		ret = mdns_query_send(sockets[isock], MDNS_RECORDTYPE_PTR,
 				      service, sizeof(service)-1, buffer,
 				      capacity, 0);
-		if (ret <= 0)
+		if (ret < 0)
 			IIO_ERROR("Failed to send mDNS query: errno %d\n", errno);
 
 		transaction_id[isock] = ret;
 	}
 
-	/* This is a simple implementation that loops for 10 seconds or as long as we get replies
-	 * A real world implementation would probably use select, poll or similar syscall to wait
-	 * until data is available on a socket and then read it */
+	/* This is a simple implementation that loops as long as we get replies
+	 * A better implementation would probably use select, poll or similar
+	 * syscall to wait until data is available on a socket and then read it
+	 */
 	IIO_DEBUG("Reading mDNS query replies\n");
 
 	for (i = 0; i < 10; i++) {
 		do {
 			records = 0;
 
 			for (isock = 0; isock < num_sockets; isock++) {
-				if (transaction_id[isock] <= 0)
+				if (transaction_id[isock] < 0)
 					continue;
 
 				records += mdns_query_recv(sockets[isock],