ggpo: resolve the peer host name (#2514)

GGPO parses the peer address with inet_pton() only, so a host name in
the Peer field silently becomes 0.0.0.0 and the session never syncs,
without any error. Resolve non-numeric addresses with getaddrinfo()
before handing them to GGPO, and fail with a clear message when the
name cannot be resolved.

Co-authored-by: unjordi <[email protected]>
[ci skip]

core/network/ggpo.cpp

@@ -25,6 +25,7 @@
 #include "cfg/option.h"
 #include "oslib/oslib.h"
 #include "oslib/i18n.h"
+#include "net_platform.h"
 #include <algorithm>
 
 namespace ggpo
@@ -595,6 +596,25 @@ void startSession(int localPort, int localPlayerNum)
 		peerPort = atoi(config::NetworkServer.get().substr(colon + 1).c_str());
 	}
 	player.type = GGPO_PLAYERTYPE_REMOTE;
+	// GGPO only takes a dotted IPv4 address: resolve host names here
+	in_addr peerAddr;
+	if (inet_pton(AF_INET, peerIp.c_str(), &peerAddr) != 1)
+	{
+		addrinfo hints {};
+		hints.ai_family = AF_INET;
+		hints.ai_socktype = SOCK_DGRAM;
+		addrinfo *result = nullptr;
+		if (getaddrinfo(peerIp.c_str(), nullptr, &hints, &result) != 0 || result == nullptr)
+		{
+			stopSession();
+			throw FlycastException(strprintf(i18n::T("GGPO: unknown peer address %s"), peerIp.c_str()));
+		}
+		char address[INET_ADDRSTRLEN];
+		inet_ntop(AF_INET, &((sockaddr_in *)result->ai_addr)->sin_addr, address, sizeof(address));
+		freeaddrinfo(result);
+		NOTICE_LOG(NETWORK, "GGPO: peer %s resolved to %s", peerIp.c_str(), address);
+		peerIp = address;
+	}
 	strcpy(player.u.remote.ip_address, peerIp.c_str());
 	player.u.remote.port = peerPort;
 	player.player_num = (1 - localPlayerNum) + 1;