Test each address returned in the getaddrinfo() call and stop blindly preferring IPv4

Fixes NAT64 on iOS 12 and probably other obscure configurations

src/Connection.c

@@ -213,7 +213,7 @@ int LiStartConnection(PSERVER_INFORMATION serverInfo, PSTREAM_CONFIGURATION stre
 
     Limelog("Resolving host name...");
     ListenerCallbacks.stageStarting(STAGE_NAME_RESOLUTION);
-    err = resolveHostName(serverInfo->address, &RemoteAddr, &RemoteAddrLen);
+    err = resolveHostName(serverInfo->address, AF_UNSPEC, 47984, &RemoteAddr, &RemoteAddrLen);
     if (err != 0) {
         Limelog("failed: %d\n", err);
         ListenerCallbacks.stageFailed(STAGE_NAME_RESOLUTION, err);

src/PlatformSockets.c

@@ -1,6 +1,8 @@
 #include "PlatformSockets.h"
 #include "Limelight-internal.h"
 
+#define TEST_PORT_TIMEOUT_SEC 3
+
 #define RCV_BUFFER_SIZE_MIN  32767
 #define RCV_BUFFER_SIZE_STEP 16384
 
@@ -282,43 +284,53 @@ int enableNoDelay(SOCKET s) {
     return 0;
 }
 
-int resolveHostName(const char* host, struct sockaddr_storage* addr, SOCKADDR_LEN* addrLen)
+int resolveHostName(const char* host, int family, int tcpTestPort, struct sockaddr_storage* addr, SOCKADDR_LEN* addrLen)
 {
 #ifndef __vita__
-    struct addrinfo hints, *res;
+    struct addrinfo hints, *res, *currentAddr;
     int err;
 
-    // We must first try IPv4-only because GFE doesn't listen on IPv6,
-    // so we'll only want to use an IPv6 address if it's the only address we have.
-    // For NAT64 networks, the IPv4 address resolution will fail but the IPv6 address
-    // will give us working connectivity to the host. All other networks will use IPv4
-    // addresses.
     memset(&hints, 0, sizeof(hints));
-    hints.ai_family = AF_INET;
+    hints.ai_family = family;
     hints.ai_flags = AI_ADDRCONFIG;
+    hints.ai_socktype = SOCK_STREAM;
+    hints.ai_protocol = IPPROTO_TCP;
     err = getaddrinfo(host, NULL, &hints, &res);
-    if (err != 0 || res == NULL) {
-        memset(&hints, 0, sizeof(hints));
-        hints.ai_family = AF_UNSPEC;
-        hints.ai_flags = AI_ADDRCONFIG;
-        err = getaddrinfo(host, NULL, &hints, &res);
-        if (err != 0) {
-            Limelog("getaddrinfo() failed: %d\n", err);
-            return err;
-        }
-
-        if (res == NULL) {
-            Limelog("getaddrinfo() returned success without addresses\n");
-            return -1;
-        }
+    if (err != 0) {
+        Limelog("getaddrinfo(%s) failed: %d\n", host, err);
+        return err;
+    }
+    else if (res == NULL) {
+        Limelog("getaddrinfo(%s) returned success without addresses\n", host);
+        return -1;
     }
     
-    // Use the first address in the list
-    memcpy(addr, res->ai_addr, res->ai_addrlen);
-    *addrLen = res->ai_addrlen;
+    for (currentAddr = res; currentAddr != NULL; currentAddr = currentAddr->ai_next) {
+        // Use the test port to ensure this address is working
+        if (tcpTestPort != 0) {
+            SOCKET testSocket = connectTcpSocket((struct sockaddr_storage*)currentAddr->ai_addr,
+                                                 currentAddr->ai_addrlen,
+                                                 tcpTestPort,
+                                                 TEST_PORT_TIMEOUT_SEC);
+            if (testSocket == INVALID_SOCKET) {
+                // Try the next address
+                continue;
+            }
+            else {
+                closeSocket(testSocket);
+            }
+        }
         
+        memcpy(addr, currentAddr->ai_addr, currentAddr->ai_addrlen);
+        *addrLen = currentAddr->ai_addrlen;
+        
+        freeaddrinfo(res);
+        return 0;
+    }
+
+    Limelog("No working addresses found for host: %s\n", host);
     freeaddrinfo(res);
-    return 0;
+    return -1;
 #else
     struct hostent *phost = gethostbyname(host);
     if (!phost) {

src/PlatformSockets.h

@@ -72,7 +72,7 @@ typedef socklen_t SOCKADDR_LEN;
 #define URLSAFESTRING_LEN (INET6_ADDRSTRLEN+2)
 void addrToUrlSafeString(struct sockaddr_storage* addr, char* string);
 
-int resolveHostName(const char* host, struct sockaddr_storage* addr, SOCKADDR_LEN* addrLen);
+int resolveHostName(const char* host, int family, int tcpTestPort, struct sockaddr_storage* addr, SOCKADDR_LEN* addrLen);
 SOCKET connectTcpSocket(struct sockaddr_storage* dstaddr, SOCKADDR_LEN addrlen, unsigned short port, int timeoutSec);
 SOCKET bindUdpSocket(int addrfamily, int bufferSize);
 int enableNoDelay(SOCKET s);

src/SimpleStun.c

@@ -52,18 +52,12 @@ int LiFindExternalAddressIP4(const char* stunServer, unsigned short stunPort, un
         char buf[1024];
     } resp;
 
-    err = resolveHostName(stunServer, &stunAddr, &stunAddrLen);
+    err = resolveHostName(stunServer, AF_INET, 0, &stunAddr, &stunAddrLen);
     if (err != 0) {
         Limelog("Failed to resolve STUN server: %d\n", err);
         return err;
     }
 
-    // We must use IPv4 to talk to the STUN server to get our IPv4 address back
-    if (stunAddr.ss_family != AF_INET) {
-        Limelog("STUN server was not reachable over IPv4\n");
-        return -1;
-    }
-
     sock = bindUdpSocket(AF_INET, 2048);
     if (sock == INVALID_SOCKET) {
         err = LastSocketFail();