Windows platform supports reading IPv6 addresses for DNS server. (libevent#1701)

When using libevent on the Windows platform in an IPv6 environment, I found that libevent could not read the DNS server address for IPv6 addresses during DNS initialization, resulting in constant DNS resolution failures. Then, on MSDN, I discovered that the GetNetworkParams interface does not support obtaining IPv6 addresses, and they provided another interface, GetAdaptersAddresses, to obtain both IPv4 and IPv6 addresses. Therefore, I replaced the GetNetworkParams interface with the GetAdaptersAddresses interface. Please review whether this modification can be merged into the master branch.

Reference MSDN documentation:
https://learn.microsoft.com/en-us/windows/win32/api/iphlpapi/nf-iphlpapi-getnetworkparams
https://learn.microsoft.com/en-us/windows/win32/api/iphlpapi/nf-iphlpapi-getadaptersaddresses

Co-authored-by: alphacheng <[email protected]>
Co-authored-by: Azat Khuzhin <[email protected]>
Co-authored-by: Azat Khuzhin <[email protected]>

Author: 3 people

CMakeLists.txt

@@ -830,6 +830,7 @@ set(HDR_PRIVATE
     evrpc-internal.h
     evsignal-internal.h
     evthread-internal.h
+    evdns-internal.h
     ht-internal.h
     http-internal.h
     iocp-internal.h

Makefile.am

@@ -333,6 +333,7 @@ noinst_HEADERS +=				\
 	evrpc-internal.h			\
 	evsignal-internal.h			\
 	evthread-internal.h			\
+	evdns-internal.h			\
 	ht-internal.h				\
 	http-internal.h				\
 	iocp-internal.h				\

evdns-internal.h

@@ -0,0 +1,22 @@
+#ifndef EVDNS_INTERNAL_H_INCLUDED_
+#define EVDNS_INTERNAL_H_INCLUDED_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include "event2/event_struct.h"
+
+#ifdef _WIN32
+
+EVENT2_EXPORT_SYMBOL
+int load_nameservers_with_getadaptersaddresses(struct evdns_base *base);
+
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+

evdns.c

@@ -104,6 +104,7 @@
 #include "ipv6-internal.h"
 #include "util-internal.h"
 #include "evthread-internal.h"
+#include "evdns-internal.h"
 #ifdef _WIN32
 #include <ctype.h>
 #include <winsock2.h>
@@ -4621,21 +4622,20 @@ evdns_nameserver_ip_add_line(struct evdns_base *base, const char *ips) {
 	return 0;
 }
 
-typedef DWORD(WINAPI *GetNetworkParams_fn_t)(FIXED_INFO *, DWORD*);
+typedef DWORD(WINAPI *GetAdaptersAddresses_fn_t)(ULONG, ULONG, PVOID, PIP_ADAPTER_ADDRESSES, PULONG);
 
-/* Use the windows GetNetworkParams interface in iphlpapi.dll to */
+/* Use the windows GetAdaptersAddresses interface in iphlpapi.dll to */
 /* figure out what our nameservers are. */
 static int
-load_nameservers_with_getnetworkparams(struct evdns_base *base)
+load_nameservers_with_getadaptersaddresses_unlocked(struct evdns_base *base)
 {
-	/* Based on MSDN examples and inspection of  c-ares code. */
-	FIXED_INFO *fixed;
+	PIP_ADAPTER_ADDRESSES addresses = NULL;
 	HMODULE handle = 0;
-	ULONG size = sizeof(FIXED_INFO);
+	ULONG size = sizeof(IP_ADAPTER_ADDRESSES);
 	void *buf = NULL;
-	int status = 0, r, added_any;
-	IP_ADDR_STRING *ns;
-	GetNetworkParams_fn_t fn;
+	int status = 0, r, added_any = 0;
+	GetAdaptersAddresses_fn_t fn;
+	IP_ADAPTER_DNS_SERVER_ADDRESS *dnsserver = NULL;
 
 	ASSERT_LOCKED(base);
 	if (!(handle = evutil_load_windows_system_library_(
@@ -4644,48 +4644,59 @@ load_nameservers_with_getnetworkparams(struct evdns_base *base)
 		status = -1;
 		goto done;
 	}
-	if (!(fn = (GetNetworkParams_fn_t) GetProcAddress(handle, "GetNetworkParams"))) {
+	if (!(fn = (GetAdaptersAddresses_fn_t) GetProcAddress(handle, "GetAdaptersAddresses"))) {
 		log(EVDNS_LOG_WARN, "Could not get address of function.");
 		status = -1;
 		goto done;
 	}
 
 	buf = mm_malloc(size);
 	if (!buf) { status = 4; goto done; }
-	fixed = buf;
-	r = fn(fixed, &size);
-	if (r != ERROR_SUCCESS && r != ERROR_BUFFER_OVERFLOW) {
+	addresses = buf;
+	r = fn(AF_UNSPEC, GAA_FLAG_INCLUDE_PREFIX, NULL, addresses, &size);
+	if (r != NO_ERROR && r != ERROR_BUFFER_OVERFLOW) {
 		status = -1;
 		goto done;
 	}
-	if (r != ERROR_SUCCESS) {
+	if (r != NO_ERROR) {
 		mm_free(buf);
 		buf = mm_malloc(size);
 		if (!buf) { status = 4; goto done; }
-		fixed = buf;
-		r = fn(fixed, &size);
-		if (r != ERROR_SUCCESS) {
+		addresses = buf;
+		r = fn(AF_UNSPEC, GAA_FLAG_INCLUDE_PREFIX, NULL, addresses, &size);
+		if (r != NO_ERROR) {
 			log(EVDNS_LOG_DEBUG, "fn() failed.");
 			status = -1;
 			goto done;
 		}
 	}
 
-	EVUTIL_ASSERT(fixed);
-	added_any = 0;
-	ns = &(fixed->DnsServerList);
-	while (ns) {
-		r = evdns_nameserver_ip_add_line(base, ns->IpAddress.String);
-		if (r) {
-			log(EVDNS_LOG_DEBUG,"Could not add nameserver %s to list,error: %d",
-				(ns->IpAddress.String),(int)GetLastError());
-			status = r;
-		} else {
-			++added_any;
-			log(EVDNS_LOG_DEBUG,"Successfully added %s as nameserver",ns->IpAddress.String);
-		}
+	while (addresses) {
+		dnsserver = addresses->FirstDnsServerAddress;
+		while (dnsserver && (addresses->OperStatus == IfOperStatusUp)) {
+			char ip[INET6_ADDRSTRLEN] = {0};
+			if (AF_INET == dnsserver->Address.lpSockaddr->sa_family) {
+				inet_ntop(AF_INET, &((SOCKADDR_IN *)dnsserver->Address.lpSockaddr)->sin_addr, ip, sizeof(ip));
+			} else if (AF_INET6 == dnsserver->Address.lpSockaddr->sa_family) {
+				inet_ntop(AF_INET6, &((SOCKADDR_IN6 *)dnsserver->Address.lpSockaddr)->sin6_addr, ip, sizeof(ip));
+			}
 
-		ns = ns->Next;
+			dnsserver = dnsserver->Next;
+			if (strncmp(ip, "fec0:", 5) == 0) { /* remove ipv6 reserved address */
+				continue;
+			}
+			
+			r = evdns_base_nameserver_ip_add(base, ip);
+			if (r) {
+				log(EVDNS_LOG_DEBUG, "Could not add nameserver %s to list, error: %d", ip, r);
+				status = r;
+			} else {
+				++added_any;
+				log(EVDNS_LOG_DEBUG, "Successfully added %s as nameserver", ip);
+			}
+		}
+		
+		addresses = addresses->Next;
 	}
 
 	if (!added_any) {
@@ -4704,6 +4715,16 @@ load_nameservers_with_getnetworkparams(struct evdns_base *base)
 	return status;
 }
 
+int
+load_nameservers_with_getadaptersaddresses(struct evdns_base *base)
+{
+	int r;
+	EVDNS_LOCK(base);
+	r = load_nameservers_with_getadaptersaddresses_unlocked(base);
+	EVDNS_UNLOCK(base);
+	return r;
+}
+
 static int
 config_nameserver_from_reg_key(struct evdns_base *base, HKEY key, const TCHAR *subkey)
 {
@@ -4803,7 +4824,7 @@ evdns_base_config_windows_nameservers(struct evdns_base *base)
 	if (fname)
 		mm_free(fname);
 
-	if (load_nameservers_with_getnetworkparams(base) == 0) {
+	if (load_nameservers_with_getadaptersaddresses_unlocked(base) == 0) {
 		EVDNS_UNLOCK(base);
 		return 0;
 	}

test/regress_dns.c

@@ -78,6 +78,7 @@
 #include <event2/thread.h>
 #include "log-internal.h"
 #include "evthread-internal.h"
+#include "evdns-internal.h"
 #include "regress.h"
 #include "regress_testutils.h"
 #include "regress_thread.h"
@@ -1200,6 +1201,47 @@ dns_initialize_nameservers_test(void *arg)
 		evdns_base_free(dns, 0);
 }
 
+#ifdef _WIN32
+static void
+windows_dns_initialize_ipv6_nameservers_test(void *arg)
+{
+	struct basic_test_data *data = arg;
+	struct event_base *base = data->base;
+	struct evdns_base *dns = NULL;
+	struct sockaddr_storage ss;
+	int i = 0, count = 0, ipv6_count = 0, size = 0;
+	int sockfd = 0;
+
+	dns = evdns_base_new(base, 0);
+	tt_assert(dns);
+
+	tt_int_op(load_nameservers_with_getadaptersaddresses(dns), ==, 0);
+	count = evdns_base_count_nameservers(dns);
+	tt_int_op(count, >, 0);
+
+	sockfd = socket(AF_INET6, SOCK_DGRAM, 0);
+	if (sockfd < 0) {
+		event_warn("socket(AF_INET6) failed. Skipping test.");
+		tt_skip();
+	}
+	evutil_closesocket(sockfd);
+
+	for (i = 0; i < count; ++i) {
+		size = evdns_base_get_nameserver_addr(dns, i, (struct sockaddr *)&ss, sizeof(ss));
+		tt_int_op(size, >, 0);
+		if (ss.ss_family == AF_INET6) {
+			ipv6_count++;
+		}
+	}
+	/* CI environment does not have IPv6 addresses, so we cannot assert on this one */
+	TT_BLATHER(("Found %i IPv6 addresses", ipv6_count));
+
+end:
+	if (dns)
+		evdns_base_free(dns, 0);
+}
+#endif
+
 static const char *dns_resolvconf_with_one_nameserver =
 	"nameserver 127.0.0.53\n";
 
@@ -3273,6 +3315,12 @@ struct testcase_t dns_testcases[] = {
 
 	{ "initialize_nameservers", dns_initialize_nameservers_test,
 	  TT_FORK|TT_NEED_BASE, &basic_setup, NULL },
+
+#ifdef _WIN32
+	{ "windows_initialize_ipv6_nameservers", windows_dns_initialize_ipv6_nameservers_test,
+	  TT_FORK|TT_NEED_BASE, &basic_setup, NULL },
+#endif
+
 #ifndef _WIN32
 	{"initialize_with_one_inactive_nameserver", dns_initialize_inactive_one_nameserver_test,
 	  TT_FORK | TT_NEED_BASE, &basic_setup, NULL},