Windows recvfrom doesn't support MSG_TRUNC, so we're using dummy buffer with max size as alternative for peeking actual size of the next pending message.

Core/HLE/proAdhoc.cpp

@@ -60,6 +60,8 @@ uint16_t portOffset;
 uint32_t minSocketTimeoutUS;
 uint32_t fakePoolSize                 = 0;
 SceNetAdhocMatchingContext * contexts = NULL;
+char* dummyPeekBuf64k                 = NULL;
+int dummyPeekBuf64kSize               = 65536;
 int one                               = 1;
 bool friendFinderRunning              = false;
 SceNetAdhocctlPeerInfo * friends      = NULL;
@@ -1908,12 +1910,7 @@ u_long getAvailToRecv(int sock, int udpBufferSize) {
 		return 0;
 
 	if (udpBufferSize > 0 && n > 0) {
-		// TODO: Cap number of bytes of full DGRAM message(s) up to buffer size
-		char buf[8];
-		// Each recv can only received one message, not sure how to read the next pending msg without actually receiving the first one
-		err = recvfrom(sock, buf, sizeof(buf), MSG_PEEK | MSG_NOSIGNAL | MSG_TRUNC, NULL, NULL);
-		if (err >= 0)
-			return (u_long)err;
+		// TODO: Cap number of bytes of full DGRAM message(s) up to buffer size, but may cause Warriors Orochi 2 to get FPS drops
 	}
 	return n;
 }

Core/HLE/proAdhoc.h

@@ -917,6 +917,8 @@ extern int defaultWlanChannel; // Default WLAN Channel for Auto, JPCSP uses 11
 
 extern uint32_t fakePoolSize;
 extern SceNetAdhocMatchingContext * contexts;
+extern char* dummyPeekBuf64k;
+extern int dummyPeekBuf64kSize;
 extern int one;                 
 extern bool friendFinderRunning;
 extern SceNetAdhocctlPeerInfo * friends;

Core/HLE/sceNet.cpp

@@ -203,6 +203,7 @@ void __NetInit() {
 	g_adhocServerIP.in.sin_port = htons(SERVER_PORT); //27312 // Maybe read this from config too
 	g_adhocServerIP.in.sin_addr.s_addr = INADDR_NONE;
 
+	dummyPeekBuf64k = (char*)malloc(dummyPeekBuf64kSize);
 	InitLocalhostIP();
 
 	SceNetEtherAddr mac;
@@ -235,6 +236,8 @@ void __NetShutdown() {
 
 	// Since PortManager supposed to be general purpose for whatever port forwarding PPSSPP needed, may be we shouldn't clear & restore ports in here? it will be cleared and restored by PortManager's destructor when exiting PPSSPP anyway
 	__UPnPShutdown();
+
+	free(dummyPeekBuf64k);
 }
 
 static void __UpdateApctlHandlers(u32 oldState, u32 newState, u32 flag, u32 error) {

Core/HLE/sceNetAdhoc.cpp

@@ -412,9 +412,11 @@ int DoBlockingPdpRecv(int uid, AdhocSocketRequest& req, s64& result) {
 	memset(&sin, 0, sizeof(sin));
 	socklen_t sinlen = sizeof(sin);
 
-	// On Windows: Using MSG_TRUNC can sometimes getting socket error WSAEOPNOTSUPP, may be the socket wasn't ready to received anything right after created & binded?
-	int ret = recvfrom(uid, (char*)req.buffer, *req.length, MSG_PEEK | MSG_NOSIGNAL | MSG_TRUNC, (sockaddr*)&sin, &sinlen);
+	// On Windows: MSG_TRUNC are not supported on recvfrom (socket error WSAEOPNOTSUPP), so we use dummy buffer as an alternative
+	int ret = recvfrom(uid, dummyPeekBuf64k, dummyPeekBuf64kSize, MSG_PEEK | MSG_NOSIGNAL, (sockaddr*)&sin, &sinlen);
 	int sockerr = errno;
+	if (ret > 0 && *req.length > 0)
+		memcpy(req.buffer, dummyPeekBuf64k, std::min(ret, *req.length));
 
 	// Note: UDP must not be received partially, otherwise leftover data in socket's buffer will be discarded
 	if (ret >= 0 && ret <= *req.length) {
@@ -453,7 +455,7 @@ int DoBlockingPdpRecv(int uid, AdhocSocketRequest& req, s64& result) {
 		result = 0;
 	}
 	// On Windows: recvfrom on UDP can get error WSAECONNRESET when previous sendto's destination is unreachable (or destination port is not bound yet), may need to disable SIO_UDP_CONNRESET error
-	else if (sockerr == EAGAIN || sockerr == EWOULDBLOCK || sockerr == ECONNRESET || sockerr == EOPNOTSUPP) {
+	else if (sockerr == EAGAIN || sockerr == EWOULDBLOCK || sockerr == ECONNRESET) {
 		u64 now = (u64)(time_now_d() * 1000000.0);
 		if (req.timeout == 0 || now - req.startTime <= req.timeout) {
 			// Try again later
@@ -1691,8 +1693,11 @@ static int sceNetAdhocPdpRecv(int id, void *addr, void * port, void *buf, void *
 				
 				// Receive Data. PDP always sent in full size or nothing(failed), recvfrom will always receive in full size as requested (blocking) or failed (non-blocking). If available UDP data is larger than buffer, excess data is lost.
 				// Should peek first for the available data size if it's more than len return ERROR_NET_ADHOC_NOT_ENOUGH_SPACE along with required size in len to prevent losing excess data
-				// On Windows: Using MSG_TRUNC can sometimes getting socket error WSAEOPNOTSUPP, may be the socket wasn't ready to received anything right after created & binded?
-				received = recvfrom(pdpsocket.id, (char*)buf, *len, MSG_PEEK | MSG_NOSIGNAL | MSG_TRUNC, (sockaddr*)&sin, &sinlen);
+				// On Windows: MSG_TRUNC are not supported on recvfrom (socket error WSAEOPNOTSUPP), so we use dummy buffer as an alternative
+				received = recvfrom(pdpsocket.id, dummyPeekBuf64k, dummyPeekBuf64kSize, MSG_PEEK | MSG_NOSIGNAL, (sockaddr*)&sin, &sinlen);
+				if (received > 0 && *len > 0)
+					memcpy(buf, dummyPeekBuf64k, std::min(received, *len));
+
 				if (received != SOCKET_ERROR && *len < received) {
 					WARN_LOG(SCENET, "sceNetAdhocPdpRecv[%i:%u]: Peeked %u/%u bytes from %s:%u\n", id, getLocalPort(pdpsocket.id), received, *len, inet_ntoa(sin.sin_addr), ntohs(sin.sin_port));
 					*len = received;
@@ -1722,7 +1727,7 @@ static int sceNetAdhocPdpRecv(int id, void *addr, void * port, void *buf, void *
 				error = errno;
 
 				// On Windows: recvfrom on UDP can get error WSAECONNRESET when previous sendto's destination is unreachable (or destination port is not bound), may need to disable SIO_UDP_CONNRESET
-				if (received == SOCKET_ERROR && (error == EAGAIN || error == EWOULDBLOCK || error == ECONNRESET || error == EOPNOTSUPP)) {
+				if (received == SOCKET_ERROR && (error == EAGAIN || error == EWOULDBLOCK || error == ECONNRESET)) {
 					if (flag == 0) {
 						// Simulate blocking behaviour with non-blocking socket
 						u64 threadSocketId = ((u64)__KernelGetCurThread()) << 32 | pdpsocket.id;