5 files changed, 780 insertions, 1 deletions

diff --git a/src/OSSupport/CMakeLists.txt b/src/OSSupport/CMakeLists.txt
index 6f609c519..81b37ef0e 100644
--- a/src/OSSupport/CMakeLists.txt
+++ b/src/OSSupport/CMakeLists.txt
@@ -18,6 +18,7 @@ SET (SRCS
 	ServerHandleImpl.cpp
 	StackTrace.cpp
 	TCPLinkImpl.cpp
+	UDPEndpointImpl.cpp
 )
 
 SET (HDRS
@@ -36,6 +37,7 @@ SET (HDRS
 	ServerHandleImpl.h
 	StackTrace.h
 	TCPLinkImpl.h
+	UDPEndpointImpl.h
 )
 
 if(NOT MSVC)
diff --git a/src/OSSupport/HostnameLookup.cpp b/src/OSSupport/HostnameLookup.cpp
index 3a2997ffd..0944153be 100644
--- a/src/OSSupport/HostnameLookup.cpp
+++ b/src/OSSupport/HostnameLookup.cpp
@@ -69,12 +69,24 @@ void cHostnameLookup::Callback(int a_ErrCode, evutil_addrinfo * a_Addr, void * a
 			case AF_INET:  // IPv4
 			{
 				sockaddr_in * sin = reinterpret_cast<sockaddr_in *>(a_Addr->ai_addr);
+				if (!Self->m_Callbacks->OnNameResolvedV4(Self->m_Hostname, sin))
+				{
+					// Callback indicated that the IP shouldn't be serialized to a string, just continue with the next address:
+					HasResolved = true;
+					continue;
+				}
 				evutil_inet_ntop(AF_INET, &(sin->sin_addr), IP, sizeof(IP));
 				break;
 			}
 			case AF_INET6:  // IPv6
 			{
 				sockaddr_in6 * sin = reinterpret_cast<sockaddr_in6 *>(a_Addr->ai_addr);
+				if (!Self->m_Callbacks->OnNameResolvedV6(Self->m_Hostname, sin))
+				{
+					// Callback indicated that the IP shouldn't be serialized to a string, just continue with the next address:
+					HasResolved = true;
+					continue;
+				}
 				evutil_inet_ntop(AF_INET6, &(sin->sin6_addr), IP, sizeof(IP));
 				break;
 			}
diff --git a/src/OSSupport/Network.h b/src/OSSupport/Network.h
index e883dfb29..5dd596223 100644
--- a/src/OSSupport/Network.h
+++ b/src/OSSupport/Network.h
@@ -130,6 +130,64 @@ public:
 
 
 
+/** Interface that provides methods available on UDP communication endpoints. */
+class cUDPEndpoint
+{
+public:
+	/** Interface for the callbacks for events that can happen on the endpoint. */
+	class cCallbacks
+	{
+	public:
+		// Force a virtual destructor in all descendants:
+		virtual ~cCallbacks() {}
+
+		/** Called when an error occurs on the endpoint. */
+		virtual void OnError(int a_ErrorCode, const AString & a_ErrorMsg) = 0;
+
+		/** Called when there is an incoming datagram from a remote host. */
+		virtual void OnReceivedData(const char * a_Data, size_t a_Size, const AString & a_RemoteHost, UInt16 a_RemotePort) = 0;
+	};
+
+
+	// Force a virtual destructor for all descendants:
+	virtual ~cUDPEndpoint() {}
+
+	/** Closes the underlying socket.
+	Note that there still might be callbacks in-flight after this method returns. */
+	virtual void Close(void) = 0;
+
+	/** Returns true if the endpoint is open. */
+	virtual bool IsOpen(void) const = 0;
+
+	/** Returns the local port to which the underlying socket is bound. */
+	virtual UInt16 GetPort(void) const = 0;
+
+	/** Sends the specified payload in a single UDP datagram to the specified host+port combination.
+	Note that in order to send to a broadcast address, you need to call EnableBroadcasts() first. */
+	virtual bool Send(const AString & a_Payload, const AString & a_Host, UInt16 a_Port) = 0;
+
+	/** Marks the socket as capable of sending broadcast, using whatever OS API is needed.
+	Without this call, sending to a broadcast address using Send() may fail. */
+	virtual void EnableBroadcasts(void) = 0;
+
+protected:
+	/** The callbacks used for various events on the endpoint. */
+	cCallbacks & m_Callbacks;
+
+
+	/** Creates a new instance of an endpoint, with the specified callbacks. */
+	cUDPEndpoint(cCallbacks & a_Callbacks):
+		m_Callbacks(a_Callbacks)
+	{
+	}
+};
+
+typedef SharedPtr<cUDPEndpoint> cUDPEndpointPtr;
+
+
+
+
+
 class cNetwork
 {
 public:
@@ -183,9 +241,22 @@ public:
 
 		/** Called when the hostname is successfully resolved into an IP address.
 		May be called multiple times if a name resolves to multiple addresses.
-		a_IP may be either an IPv4 or an IPv6 address with their proper formatting. */
+		a_IP may be either an IPv4 or an IPv6 address with their proper formatting.
+		Each call to OnNameResolved() is preceded by a call to either OnNameResolvedV4() or OnNameResolvedV6(). */
 		virtual void OnNameResolved(const AString & a_Name, const AString & a_IP) = 0;
 
+		/** Called when the hostname is successfully resolved into an IPv4 address.
+		May be called multiple times if a name resolves to multiple addresses.
+		Each call to OnNameResolvedV4 is followed by OnNameResolved with the IP address serialized to a string.
+		If this callback returns false, the OnNameResolved() call is skipped for this address. */
+		virtual bool OnNameResolvedV4(const AString & a_Name, const sockaddr_in * a_IP) { return true; }
+
+		/** Called when the hostname is successfully resolved into an IPv6 address.
+		May be called multiple times if a name resolves to multiple addresses.
+		Each call to OnNameResolvedV4 is followed by OnNameResolved with the IP address serialized to a string.
+		If this callback returns false, the OnNameResolved() call is skipped for this address. */
+		virtual bool OnNameResolvedV6(const AString & a_Name, const sockaddr_in6 * a_IP) { return true; }
+
 		/** Called when an error is encountered while resolving.
 		If an error is reported, the OnFinished() callback is not called. */
 		virtual void OnError(int a_ErrorCode, const AString & a_ErrorMsg) = 0;
@@ -242,6 +313,11 @@ public:
 		const AString & a_IP,
 		cResolveNameCallbacksPtr a_Callbacks
 	);
+
+	/** Opens up an UDP endpoint for sending and receiving UDP datagrams on the specified port.
+	If a_Port is 0, the OS is free to assign any port number it likes to the endpoint.
+	Returns the endpoint object that can be interacted with. */
+	static cUDPEndpointPtr CreateUDPEndpoint(UInt16 a_Port, cUDPEndpoint::cCallbacks & a_Callbacks);
 };
 
 
diff --git a/src/OSSupport/UDPEndpointImpl.cpp b/src/OSSupport/UDPEndpointImpl.cpp
new file mode 100644
index 000000000..ece521ab8
--- /dev/null
+++ b/src/OSSupport/UDPEndpointImpl.cpp
@@ -0,0 +1,608 @@
+
+// UDPEndpointImpl.cpp
+
+// Implements the cUDPEndpointImpl class representing an implementation of an endpoint in UDP communication
+
+#include "Globals.h"
+#include "UDPEndpointImpl.h"
+#include "NetworkSingleton.h"
+
+
+
+
+
+////////////////////////////////////////////////////////////////////////////////
+// Globals:
+
+static bool IsValidSocket(evutil_socket_t a_Socket)
+{
+	#ifdef _WIN32
+		return (a_Socket != INVALID_SOCKET);
+	#else  // _WIN32
+		return (a_Socket >= 0);
+	#endif  // else _WIN32
+}
+
+
+
+
+
+/** Converts a_SrcAddr in IPv4 format to a_DstAddr in IPv6 format (using IPv4-mapped IPv6). */
+static void ConvertIPv4ToMappedIPv6(sockaddr_in & a_SrcAddr, sockaddr_in6 & a_DstAddr)
+{
+	memset(&a_DstAddr, 0, sizeof(a_DstAddr));
+	a_DstAddr.sin6_family = AF_INET6;
+	a_DstAddr.sin6_addr.s6_addr[10] = 0xff;
+	a_DstAddr.sin6_addr.s6_addr[11] = 0xff;
+	a_DstAddr.sin6_addr.s6_addr[12] = static_cast<Byte>((a_SrcAddr.sin_addr.s_addr >>  0) & 0xff);
+	a_DstAddr.sin6_addr.s6_addr[13] = static_cast<Byte>((a_SrcAddr.sin_addr.s_addr >>  8) & 0xff);
+	a_DstAddr.sin6_addr.s6_addr[14] = static_cast<Byte>((a_SrcAddr.sin_addr.s_addr >> 16) & 0xff);
+	a_DstAddr.sin6_addr.s6_addr[15] = static_cast<Byte>((a_SrcAddr.sin_addr.s_addr >> 24) & 0xff);
+	a_DstAddr.sin6_port = a_SrcAddr.sin_port;
+}
+
+
+
+
+
+////////////////////////////////////////////////////////////////////////////////
+// cUDPSendAfterLookup:
+
+/** A hostname-to-IP resolver callback that sends the data stored within to the resolved IP address.
+This is used for sending UDP datagrams to hostnames, so that the cUDPEndpoint::Send() doesn't block.
+Instead an instance of this callback is queued for resolving and the data is sent once the IP is resolved. */
+class cUDPSendAfterLookup:
+	public cNetwork::cResolveNameCallbacks
+{
+public:
+	cUDPSendAfterLookup(const AString & a_Data, UInt16 a_Port, evutil_socket_t a_MainSock, evutil_socket_t a_SecondSock, bool a_IsMainSockIPv6):
+		m_Data(a_Data),
+		m_Port(a_Port),
+		m_MainSock(a_MainSock),
+		m_SecondSock(a_SecondSock),
+		m_IsMainSockIPv6(a_IsMainSockIPv6),
+		m_HasIPv4(false),
+		m_HasIPv6(false)
+	{
+	}
+
+protected:
+	/** The data to send after the hostname is resolved. */
+	AString m_Data;
+
+	/** The port to which to send the data. */
+	UInt16 m_Port;
+
+	/** The primary socket to use for sending. */
+	evutil_socket_t m_MainSock;
+
+	/** The secondary socket to use for sending, if needed by the OS. */
+	evutil_socket_t m_SecondSock;
+
+	/** True if m_MainSock is an IPv6 socket. */
+	bool m_IsMainSockIPv6;
+
+	/** The IPv4 address resolved, if any. */
+	sockaddr_in m_AddrIPv4;
+
+	/** Set to true if the name resolved to an IPv4 address. */
+	bool m_HasIPv4;
+
+	/** The IPv6 address resolved, if any. */
+	sockaddr_in6 m_AddrIPv6;
+
+	/** Set to true if the name resolved to an IPv6 address. */
+	bool m_HasIPv6;
+
+
+	// cNetwork::cResolveNameCallbacks overrides:
+	virtual void OnNameResolved(const AString & a_Name, const AString & a_PI) override
+	{
+		// Not needed
+	}
+
+	virtual bool OnNameResolvedV4(const AString & a_Name, const sockaddr_in * a_IP) override
+	{
+		if (!m_HasIPv4)
+		{
+			m_AddrIPv4 = *a_IP;
+			m_AddrIPv4.sin_port = htons(m_Port);
+			m_HasIPv4 = true;
+		}
+
+		// Don't want OnNameResolved() callback
+		return false;
+	}
+
+	virtual bool OnNameResolvedV6(const AString & a_Name, const sockaddr_in6 * a_IP) override
+	{
+		if (!m_HasIPv6)
+		{
+			m_AddrIPv6 = *a_IP;
+			m_AddrIPv6.sin6_port = htons(m_Port);
+			m_HasIPv6 = true;
+		}
+
+		// Don't want OnNameResolved() callback
+		return false;
+	}
+
+	virtual void OnFinished(void) override
+	{
+		// Send the actual data, through the correct socket and using the correct resolved address:
+		if (m_IsMainSockIPv6)
+		{
+			if (m_HasIPv6)
+			{
+				sendto(m_MainSock, m_Data.data(), static_cast<socklen_t>(m_Data.size()), 0, reinterpret_cast<const sockaddr *>(&m_AddrIPv6), static_cast<socklen_t>(sizeof(m_AddrIPv6)));
+			}
+			else if (m_HasIPv4)
+			{
+				// If the secondary socket is valid, it is an IPv4 socket, so use that:
+				if (m_SecondSock != -1)
+				{
+					sendto(m_SecondSock, m_Data.data(), static_cast<socklen_t>(m_Data.size()), 0, reinterpret_cast<const sockaddr *>(&m_AddrIPv4), static_cast<socklen_t>(sizeof(m_AddrIPv4)));
+				}
+				else
+				{
+					// Need an address conversion from IPv4 to IPv6-mapped-IPv4:
+					ConvertIPv4ToMappedIPv6(m_AddrIPv4, m_AddrIPv6);
+					sendto(m_MainSock, m_Data.data(), static_cast<socklen_t>(m_Data.size()), 0, reinterpret_cast<const sockaddr *>(&m_AddrIPv6), static_cast<socklen_t>(sizeof(m_AddrIPv6)));
+				}
+			}
+			else
+			{
+				LOGD("UDP endpoint queued sendto: Name not resolved");
+				return;
+			}
+		}
+		else  // m_IsMainSockIPv6
+		{
+			// Main socket is IPv4 only, only allow IPv4 dst address:
+			if (!m_HasIPv4)
+			{
+				LOGD("UDP endpoint queued sendto: Name not resolved to IPv4 for an IPv4-only socket");
+				return;
+			}
+			sendto(m_MainSock, m_Data.data(), static_cast<socklen_t>(m_Data.size()), 0, reinterpret_cast<const sockaddr *>(&m_AddrIPv4), static_cast<socklen_t>(sizeof(m_AddrIPv4)));
+		}
+	}
+
+	virtual void OnError(int a_ErrorCode, const AString & a_ErrorMsg) override
+	{
+		// Nothing needed
+	}
+};
+
+
+
+
+
+////////////////////////////////////////////////////////////////////////////////
+// cUDPEndpointImpl:
+
+cUDPEndpointImpl::cUDPEndpointImpl(UInt16 a_Port, cUDPEndpoint::cCallbacks & a_Callbacks):
+	super(a_Callbacks),
+	m_Port(0),
+	m_MainSock(-1),
+	m_IsMainSockIPv6(true),
+	m_SecondarySock(-1),
+	m_MainEvent(nullptr),
+	m_SecondaryEvent(nullptr)
+{
+	Open(a_Port);
+}
+
+
+
+
+
+void cUDPEndpointImpl::Close(void)
+{
+	if (m_Port == 0)
+	{
+		// Already closed
+		return;
+	}
+
+	// Close the LibEvent handles:
+	if (m_MainEvent != nullptr)
+	{
+		event_free(m_MainEvent);
+		m_MainEvent = nullptr;
+	}
+	if (m_SecondaryEvent != nullptr)
+	{
+		event_free(m_SecondaryEvent);
+		m_SecondaryEvent = nullptr;
+	}
+
+	// Close the OS sockets:
+	evutil_closesocket(m_MainSock);
+	m_MainSock = -1;
+	evutil_closesocket(m_SecondarySock);
+	m_SecondarySock = -1;
+
+	// Mark as closed:
+	m_Port = 0;
+}
+
+
+
+
+
+bool cUDPEndpointImpl::IsOpen(void) const
+{
+	return (m_Port != 0);
+}
+
+
+
+
+
+UInt16 cUDPEndpointImpl::GetPort(void) const
+{
+	return m_Port;
+}
+
+
+
+
+
+bool cUDPEndpointImpl::Send(const AString & a_Payload, const AString & a_Host, UInt16 a_Port)
+{
+	// If a_Host is an IP address, send the data directly:
+	sockaddr_storage sa;
+	int salen = static_cast<int>(sizeof(sa));
+	memset(&sa, 0, sizeof(sa));
+	if (evutil_parse_sockaddr_port(a_Host.c_str(), reinterpret_cast<sockaddr *>(&sa), &salen) != 0)
+	{
+		// a_Host is a hostname, we need to do a lookup first:
+		auto queue = std::make_shared<cUDPSendAfterLookup>(a_Payload, a_Port, m_MainSock, m_SecondarySock, m_IsMainSockIPv6);
+		return cNetwork::HostnameToIP(a_Host, queue);
+	}
+
+	// a_Host is an IP address and has been parsed into "sa"
+	// Insert the correct port and send data:
+	int NumSent;
+	switch (sa.ss_family)
+	{
+		case AF_INET:
+		{
+			reinterpret_cast<sockaddr_in *>(&sa)->sin_port = htons(a_Port);
+			if (m_IsMainSockIPv6)
+			{
+				if (IsValidSocket(m_SecondarySock))
+				{
+					// The secondary socket, which is always IPv4, is present:
+					NumSent = static_cast<int>(sendto(m_SecondarySock, a_Payload.data(), static_cast<socklen_t>(a_Payload.size()), 0, reinterpret_cast<const sockaddr *>(&sa), static_cast<socklen_t>(salen)));
+				}
+				else
+				{
+					// Need to convert IPv4 to IPv6 address before sending:
+					sockaddr_in6 IPv6;
+					ConvertIPv4ToMappedIPv6(*reinterpret_cast<sockaddr_in *>(&sa), IPv6);
+					NumSent = static_cast<int>(sendto(m_MainSock, a_Payload.data(), static_cast<socklen_t>(a_Payload.size()), 0, reinterpret_cast<const sockaddr *>(&IPv6), static_cast<socklen_t>(sizeof(IPv6))));
+				}
+			}
+			else
+			{
+				NumSent = static_cast<int>(sendto(m_MainSock, a_Payload.data(), static_cast<socklen_t>(a_Payload.size()), 0, reinterpret_cast<const sockaddr *>(&sa), static_cast<socklen_t>(salen)));
+			}
+			break;
+		}
+
+		case AF_INET6:
+		{
+			reinterpret_cast<sockaddr_in6 *>(&sa)->sin6_port = htons(a_Port);
+			NumSent = static_cast<int>(sendto(m_MainSock, a_Payload.data(), static_cast<socklen_t>(a_Payload.size()), 0, reinterpret_cast<const sockaddr *>(&sa), static_cast<socklen_t>(salen)));
+			break;
+		}
+		default:
+		{
+			LOGD("UDP sendto: Invalid address family for address \"%s\".", a_Host.c_str());
+			return false;
+		}
+	}
+	return (NumSent > 0);
+}
+
+
+
+
+
+void cUDPEndpointImpl::EnableBroadcasts(void)
+{
+	ASSERT(IsOpen());
+
+	// Enable broadcasts on the main socket:
+	// Some OSes use ints, others use chars, so we try both
+	int broadcastInt = 1;
+	char broadcastChar = 1;
+	// (Note that Windows uses const char * for option values, while Linux uses const void *)
+	if (setsockopt(m_MainSock, SOL_SOCKET, SO_BROADCAST, reinterpret_cast<const char *>(&broadcastInt), sizeof(broadcastInt)) == -1)
+	{
+		if (setsockopt(m_MainSock, SOL_SOCKET, SO_BROADCAST, &broadcastChar, sizeof(broadcastChar)) == -1)
+		{
+			int err = EVUTIL_SOCKET_ERROR();
+			LOGWARNING("Cannot enable broadcasts on port %d: %d (%s)", m_Port, err, evutil_socket_error_to_string(err));
+			return;
+		}
+
+		// Enable broadcasts on the secondary socket, if opened (use char, it worked for primary):
+		if (IsValidSocket(m_SecondarySock))
+		{
+			if (setsockopt(m_SecondarySock, SOL_SOCKET, SO_BROADCAST, &broadcastChar, sizeof(broadcastChar)) == -1)
+			{
+				int err = EVUTIL_SOCKET_ERROR();
+				LOGWARNING("Cannot enable broadcasts on port %d (secondary): %d (%s)", m_Port, err, evutil_socket_error_to_string(err));
+			}
+		}
+		return;
+	}
+
+	// Enable broadcasts on the secondary socket, if opened (use int, it worked for primary):
+	if (IsValidSocket(m_SecondarySock))
+	{
+		if (setsockopt(m_SecondarySock, SOL_SOCKET, SO_BROADCAST, reinterpret_cast<const char *>(&broadcastInt), sizeof(broadcastInt)) == -1)
+		{
+			int err = EVUTIL_SOCKET_ERROR();
+			LOGWARNING("Cannot enable broadcasts on port %d (secondary): %d (%s)", m_Port, err, evutil_socket_error_to_string(err));
+		}
+	}
+}
+
+
+
+
+
+void cUDPEndpointImpl::Open(UInt16 a_Port)
+{
+	ASSERT(m_Port == 0);  // Must not be already open
+
+	// Make sure the cNetwork internals are innitialized:
+	cNetworkSingleton::Get();
+
+	// Set up the main socket:
+	// It should listen on IPv6 with IPv4 fallback, when available; IPv4 when IPv6 is not available.
+	bool NeedsTwoSockets = false;
+	m_IsMainSockIPv6 = true;
+	m_MainSock = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP);
+
+	int err;
+	if (!IsValidSocket(m_MainSock))
+	{
+		// Failed to create IPv6 socket, create an IPv4 one instead:
+		m_IsMainSockIPv6 = false;
+		err = EVUTIL_SOCKET_ERROR();
+		LOGD("Failed to create IPv6 MainSock: %d (%s)", err, evutil_socket_error_to_string(err));
+		m_MainSock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
+		if (!IsValidSocket(m_MainSock))
+		{
+			err = EVUTIL_SOCKET_ERROR();
+			m_Callbacks.OnError(err, Printf("Cannot create UDP socket for port %d: %s", a_Port, evutil_socket_error_to_string(err)));
+			return;
+		}
+
+		// Allow the port to be reused right after the socket closes:
+		if (evutil_make_listen_socket_reuseable(m_MainSock) != 0)
+		{
+			err = EVUTIL_SOCKET_ERROR();
+			LOG("UDP Port %d cannot be made reusable: %d (%s). Restarting the server might not work.",
+				a_Port, err, evutil_socket_error_to_string(err)
+			);
+		}
+
+		// Bind to all interfaces:
+		sockaddr_in name;
+		memset(&name, 0, sizeof(name));
+		name.sin_family = AF_INET;
+		name.sin_port = ntohs(a_Port);
+		if (bind(m_MainSock, reinterpret_cast<const sockaddr *>(&name), sizeof(name)) != 0)
+		{
+			err = EVUTIL_SOCKET_ERROR();
+			m_Callbacks.OnError(err, Printf("Cannot bind UDP port %d: %s", a_Port, evutil_socket_error_to_string(err)));
+			evutil_closesocket(m_MainSock);
+			return;
+		}
+	}
+	else
+	{
+		// IPv6 socket created, switch it into "dualstack" mode:
+		UInt32 Zero = 0;
+		#ifdef _WIN32
+			// WinXP doesn't support this feature, so if the setting fails, create another socket later on:
+			int res = setsockopt(m_MainSock, IPPROTO_IPV6, IPV6_V6ONLY, reinterpret_cast<const char *>(&Zero), sizeof(Zero));
+			err = EVUTIL_SOCKET_ERROR();
+			NeedsTwoSockets = ((res == SOCKET_ERROR) && (err == WSAENOPROTOOPT));
+		#else
+			setsockopt(m_MainSock, IPPROTO_IPV6, IPV6_V6ONLY, reinterpret_cast<const char *>(&Zero), sizeof(Zero));
+		#endif
+
+		// Allow the port to be reused right after the socket closes:
+		if (evutil_make_listen_socket_reuseable(m_MainSock) != 0)
+		{
+			err  = EVUTIL_SOCKET_ERROR();
+			LOG("UDP Port %d cannot be made reusable: %d (%s). Restarting the server might not work.",
+				a_Port, err, evutil_socket_error_to_string(err)
+			);
+		}
+
+		// Bind to all interfaces:
+		sockaddr_in6 name;
+		memset(&name, 0, sizeof(name));
+		name.sin6_family = AF_INET6;
+		name.sin6_port = ntohs(a_Port);
+		if (bind(m_MainSock, reinterpret_cast<const sockaddr *>(&name), sizeof(name)) != 0)
+		{
+			err = EVUTIL_SOCKET_ERROR();
+			m_Callbacks.OnError(err, Printf("Cannot bind to UDP port %d: %s", a_Port, evutil_socket_error_to_string(err)));
+			evutil_closesocket(m_MainSock);
+			return;
+		}
+	}
+	if (evutil_make_socket_nonblocking(m_MainSock) != 0)
+	{
+		err = EVUTIL_SOCKET_ERROR();
+		m_Callbacks.OnError(err, Printf("Cannot make socket on UDP port %d nonblocking: %s", a_Port, evutil_socket_error_to_string(err)));
+		evutil_closesocket(m_MainSock);
+		return;
+	}
+	m_MainEvent = event_new(cNetworkSingleton::Get().GetEventBase(), m_MainSock, EV_READ | EV_PERSIST, RawCallback, this);
+	event_add(m_MainEvent, nullptr);
+
+	// Read the actual port number on which the socket is listening:
+	{
+		sockaddr_storage name;
+		socklen_t namelen = static_cast<socklen_t>(sizeof(name));
+		getsockname(m_MainSock, reinterpret_cast<sockaddr *>(&name), &namelen);
+		switch (name.ss_family)
+		{
+			case AF_INET:
+			{
+				sockaddr_in * sin = reinterpret_cast<sockaddr_in *>(&name);
+				m_Port = ntohs(sin->sin_port);
+				break;
+			}
+			case AF_INET6:
+			{
+				sockaddr_in6 * sin6 = reinterpret_cast<sockaddr_in6 *>(&name);
+				m_Port = ntohs(sin6->sin6_port);
+				break;
+			}
+		}
+	}
+
+	// If we don't need to create another socket, bail out now:
+	if (!NeedsTwoSockets)
+	{
+		return;
+	}
+
+	// If a secondary socket is required (WinXP dual-stack), create it here:
+	LOGD("Creating a second UDP socket for IPv4");
+	m_SecondarySock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
+
+	if (!IsValidSocket(m_SecondarySock))
+	{
+		// Don't report as an error, the primary socket is working
+		err = EVUTIL_SOCKET_ERROR();
+		LOGD("Socket creation failed for secondary UDP socket for port %d: %d, %s", m_Port, err, evutil_socket_error_to_string(err));
+		return;
+	}
+
+	// Allow the port to be reused right after the socket closes:
+	if (evutil_make_listen_socket_reuseable(m_SecondarySock) != 0)
+	{
+		// Don't report as an error, the primary socket is working
+		err = EVUTIL_SOCKET_ERROR();
+		LOGD("UDP Port %d cannot be made reusable (second socket): %d (%s). Restarting the server might not work.",
+			a_Port, err, evutil_socket_error_to_string(err)
+		);
+		evutil_closesocket(m_SecondarySock);
+		m_SecondarySock = -1;
+		return;
+	}
+
+	// Make the secondary socket nonblocking:
+	if (evutil_make_socket_nonblocking(m_SecondarySock) != 0)
+	{
+		// Don't report as an error, the primary socket is working
+		err = EVUTIL_SOCKET_ERROR();
+		LOGD("evutil_make_socket_nonblocking() failed for secondary UDP socket: %d, %s", err, evutil_socket_error_to_string(err));
+		evutil_closesocket(m_SecondarySock);
+		m_SecondarySock = -1;
+		return;
+	}
+
+	// Bind to all IPv4 interfaces:
+	sockaddr_in name;
+	memset(&name, 0, sizeof(name));
+	name.sin_family = AF_INET;
+	name.sin_port = ntohs(m_Port);
+	if (bind(m_SecondarySock, reinterpret_cast<const sockaddr *>(&name), sizeof(name)) != 0)
+	{
+		// Don't report as an error, the primary socket is working
+		err = EVUTIL_SOCKET_ERROR();
+		LOGD("Cannot bind secondary socket to UDP port %d: %d (%s)", m_Port, err, evutil_socket_error_to_string(err));
+		evutil_closesocket(m_SecondarySock);
+		m_SecondarySock = -1;
+		return;
+	}
+
+	m_SecondaryEvent = event_new(cNetworkSingleton::Get().GetEventBase(), m_SecondarySock, EV_READ | EV_PERSIST, RawCallback, this);
+	event_add(m_SecondaryEvent, nullptr);
+}
+
+
+
+
+
+void cUDPEndpointImpl::RawCallback(evutil_socket_t a_Socket, short a_What, void * a_Self)
+{
+	cUDPEndpointImpl * Self = reinterpret_cast<cUDPEndpointImpl *>(a_Self);
+	Self->Callback(a_Socket, a_What);
+}
+
+
+
+
+
+void cUDPEndpointImpl::Callback(evutil_socket_t a_Socket, short a_What)
+{
+	if ((a_What & EV_READ) != 0)
+	{
+		// Receive datagram from the socket:
+		char buf[64 KiB];
+		socklen_t buflen = static_cast<socklen_t>(sizeof(buf));
+		sockaddr_storage sa;
+		socklen_t salen = static_cast<socklen_t>(sizeof(sa));
+		auto len = recvfrom(a_Socket, buf, buflen, 0, reinterpret_cast<sockaddr *>(&sa), &salen);
+		if (len >= 0)
+		{
+			// Convert the remote IP address to a string:
+			char RemoteHost[128];
+			UInt16 RemotePort;
+			switch (sa.ss_family)
+			{
+				case AF_INET:
+				{
+					auto sin = reinterpret_cast<sockaddr_in *>(&sa);
+					evutil_inet_ntop(sa.ss_family, &sin->sin_addr, RemoteHost, sizeof(RemoteHost));
+					RemotePort = ntohs(sin->sin_port);
+					break;
+				}
+				case AF_INET6:
+				{
+					auto sin = reinterpret_cast<sockaddr_in6 *>(&sa);
+					evutil_inet_ntop(sa.ss_family, &sin->sin6_addr, RemoteHost, sizeof(RemoteHost));
+					RemotePort = ntohs(sin->sin6_port);
+					break;
+				}
+				default:
+				{
+					return;
+				}
+			}
+
+			// Call the callback:
+			m_Callbacks.OnReceivedData(buf, static_cast<size_t>(len), RemoteHost, RemotePort);
+		}
+	}
+}
+
+
+
+
+
+////////////////////////////////////////////////////////////////////////////////
+// cNetwork API:
+
+cUDPEndpointPtr cNetwork::CreateUDPEndpoint(UInt16 a_Port, cUDPEndpoint::cCallbacks & a_Callbacks)
+{
+	return std::make_shared<cUDPEndpointImpl>(a_Port, a_Callbacks);
+}
+
+
+
+
diff --git a/src/OSSupport/UDPEndpointImpl.h b/src/OSSupport/UDPEndpointImpl.h
new file mode 100644
index 000000000..75942b0cf
--- /dev/null
+++ b/src/OSSupport/UDPEndpointImpl.h
@@ -0,0 +1,81 @@
+
+// UDPEndpointImpl.h
+
+// Declares the cUDPEndpointImpl class representing an implementation of an endpoint in UDP communication
+
+
+
+
+
+#pragma once
+
+#include "Network.h"
+#include <event2/event.h>
+
+
+
+
+
+// fwd:
+class cUDPEndpointImpl;
+typedef SharedPtr<cUDPEndpointImpl> cUDPEndpointImplPtr;
+
+
+
+
+
+class cUDPEndpointImpl:
+	public cUDPEndpoint
+{
+	typedef cUDPEndpoint super;
+
+public:
+	/** Creates a new instance of the endpoint, with the specified callbacks.
+	Tries to open on the specified port; if it fails, the endpoint is left in the "closed" state.
+	If a_Port is 0, the OS is free to assign any port number it likes to the endpoint. */
+	cUDPEndpointImpl(UInt16 a_Port, cUDPEndpoint::cCallbacks & a_Callbacks);
+
+	// cUDPEndpoint overrides:
+	virtual void Close(void) override;
+	virtual bool IsOpen(void) const override;
+	virtual UInt16 GetPort(void) const override;
+	virtual bool Send(const AString & a_Payload, const AString & a_Host, UInt16 a_Port) override;
+	virtual void EnableBroadcasts(void) override;
+
+protected:
+	/** The local port on which the endpoint is open.
+	If this is zero, it means the endpoint is closed - either opening has failed, or it has been closed explicitly. */
+	UInt16 m_Port;
+
+	/** The primary underlying OS socket. */
+	evutil_socket_t m_MainSock;
+
+	/** True if m_MainSock is in the IPv6 namespace (needs IPv6 addresses for sending). */
+	bool m_IsMainSockIPv6;
+
+	/** The secondary OS socket (if primary doesn't support dualstack). */
+	evutil_socket_t m_SecondarySock;
+
+	/** The LibEvent handle for the primary socket. */
+	event * m_MainEvent;
+
+	/** The LibEvent handle for the secondary socket. */
+	event * m_SecondaryEvent;
+
+
+	/** Creates and opens the socket on the specified port.
+	If a_Port is 0, the OS is free to assign any port number it likes to the endpoint.
+	If the opening fails, the OnError() callback is called and the endpoint is left "closed" (IsOpen() returns false). */
+	void Open(UInt16 a_Port);
+
+	/** The callback that LibEvent calls when an event occurs on one of the sockets.
+	Calls Callback() on a_Self. */
+	static void RawCallback(evutil_socket_t a_Socket, short a_What, void * a_Self);
+
+	/** The callback that is called when an event occurs on one of the sockets. */
+	void Callback(evutil_socket_t a_Socket, short a_What);
+};
+
+
+
+