Extend capabilities of Address class

src/client/game.cpp

@@ -1621,7 +1621,8 @@ bool Game::connectToServer(const GameStartData &start_data,
 	try {
 		connect_address.Resolve(start_data.address.c_str());
 
-		if (connect_address.isZero()) { // i.e. INADDR_ANY, IN6ADDR_ANY
+		if (connect_address.isAny()) {
+			// replace with localhost IP
 			if (connect_address.isIPv6()) {
 				IPv6AddressBytes addr_bytes;
 				addr_bytes.bytes[15] = 1;

src/network/address.cpp

@@ -84,7 +84,7 @@ Address::Address(const IPv6AddressBytes *ipv6_bytes, u16 port)
 }
 
 // Equality (address family, IP and port must be equal)
-bool Address::operator==(const Address &other)
+bool Address::operator==(const Address &other) const
 {
 	if (other.m_addr_family != m_addr_family || other.m_port != m_port)
 		return false;
@@ -101,44 +101,60 @@ bool Address::operator==(const Address &other)
 	return false;
 }
 
-void Address::Resolve(const char *name)
+void Address::Resolve(const char *name, Address *fallback)
 {
 	if (!name || name[0] == 0) {
 		if (m_addr_family == AF_INET)
 			setAddress(static_cast<u32>(0));
 		else if (m_addr_family == AF_INET6)
 			setAddress(static_cast<IPv6AddressBytes*>(nullptr));
+		if (fallback)
+			*fallback = Address();
 		return;
 	}
 
-	struct addrinfo *resolved, hints;
+	const auto &copy_from_ai = [] (const struct addrinfo *ai, Address *to) {
+		if (ai->ai_family == AF_INET) {
+			struct sockaddr_in *t = (struct sockaddr_in *)ai->ai_addr;
+			to->m_addr_family = AF_INET;
+			to->m_address.ipv4 = t->sin_addr;
+		} else if (ai->ai_family == AF_INET6) {
+			struct sockaddr_in6 *t = (struct sockaddr_in6 *)ai->ai_addr;
+			to->m_addr_family = AF_INET6;
+			to->m_address.ipv6 = t->sin6_addr;
+		} else {
+			to->m_addr_family = 0;
+		}
+	};
+
+	struct addrinfo hints;
 	memset(&hints, 0, sizeof(hints));
 
-	// Setup hints
+	// set a type, so every unique address is only returned once
+	hints.ai_socktype = SOCK_DGRAM;
 	if (g_settings->getBool("enable_ipv6")) {
 		// AF_UNSPEC allows both IPv6 and IPv4 addresses to be returned
 		hints.ai_family = AF_UNSPEC;
 	} else {
 		hints.ai_family = AF_INET;
 	}
+	hints.ai_flags = AI_ADDRCONFIG;
 
 	// Do getaddrinfo()
-	int e = getaddrinfo(name, NULL, &hints, &resolved);
+	struct addrinfo *resolved = nullptr;
+	int e = getaddrinfo(name, nullptr, &hints, &resolved);
 	if (e != 0)
 		throw ResolveError(gai_strerror(e));
+	assert(resolved);
 
 	// Copy data
-	if (resolved->ai_family == AF_INET) {
-		struct sockaddr_in *t = (struct sockaddr_in *)resolved->ai_addr;
-		m_addr_family = AF_INET;
-		m_address.ipv4 = t->sin_addr;
-	} else if (resolved->ai_family == AF_INET6) {
-		struct sockaddr_in6 *t = (struct sockaddr_in6 *)resolved->ai_addr;
-		m_addr_family = AF_INET6;
-		m_address.ipv6 = t->sin6_addr;
-	} else {
-		m_addr_family = 0;
+	copy_from_ai(resolved, this);
+	if (fallback) {
+		*fallback = Address();
+		if (resolved->ai_next)
+			copy_from_ai(resolved->ai_next, fallback);
 	}
+
 	freeaddrinfo(resolved);
 }
 
@@ -151,28 +167,11 @@ std::string Address::serializeString() const
 	return str;
 }
 
-struct in_addr Address::getAddress() const
-{
-	return m_address.ipv4;
-}
-
-struct in6_addr Address::getAddress6() const
-{
-	return m_address.ipv6;
-}
-
-u16 Address::getPort() const
-{
-	return m_port;
-}
-
-bool Address::isZero() const
+bool Address::isAny() const
 {
 	if (m_addr_family == AF_INET) {
 		return m_address.ipv4.s_addr == 0;
-	}
-
-	if (m_addr_family == AF_INET6) {
+	} else if (m_addr_family == AF_INET6) {
 		static const char zero[16] = {0};
 		return memcmp(m_address.ipv6.s6_addr, zero, 16) == 0;
 	}
@@ -218,18 +217,19 @@ void Address::print(std::ostream& s) const
 
 bool Address::isLocalhost() const
 {
-	if (isIPv6()) {
+	if (m_addr_family == AF_INET6) {
 		static const u8 localhost_bytes[] = {
 				0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1};
 		static const u8 mapped_ipv4_localhost[] = {
 				0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff, 0x7f, 0, 0, 0};
 
-		auto addr = m_address.ipv6.s6_addr;
+		auto *addr = m_address.ipv6.s6_addr;
 
 		return memcmp(addr, localhost_bytes, 16) == 0 ||
 			memcmp(addr, mapped_ipv4_localhost, 13) == 0;
-	}
-
+	} else if (m_addr_family == AF_INET) {
 		auto addr = ntohl(m_address.ipv4.s_addr);
 		return (addr >> 24) == 0x7f;
+	}
+	return false;
 }

src/network/address.h

@@ -47,21 +47,29 @@ public:
 	Address(u8 a, u8 b, u8 c, u8 d, u16 port);
 	Address(const IPv6AddressBytes *ipv6_bytes, u16 port);
 
-	bool operator==(const Address &address);
-	bool operator!=(const Address &address) { return !(*this == address); }
+	bool operator==(const Address &address) const;
+	bool operator!=(const Address &address) const { return !(*this == address); }
 
-	struct in_addr getAddress() const;
-	struct in6_addr getAddress6() const;
-	u16 getPort() const;
 	int getFamily() const { return m_addr_family; }
+	bool isValid() const { return m_addr_family != 0; }
 	bool isIPv6() const { return m_addr_family == AF_INET6; }
-	bool isZero() const;
+	struct in_addr getAddress() const { return m_address.ipv4; }
+	struct in6_addr getAddress6() const { return m_address.ipv6; }
+	u16 getPort() const { return m_port; }
+
 	void print(std::ostream &s) const;
 	std::string serializeString() const;
+
+	// Is this an address that binds to all interfaces (like INADDR_ANY)?
+	bool isAny() const;
+	// Is this an address referring to the local host?
 	bool isLocalhost() const;
 
-	// Resolve() may throw ResolveError (address is unchanged in this case)
-	void Resolve(const char *name);
+	// `name`: hostname or numeric IP
+	// `fallback`: fallback IP to try gets written here
+	// any empty name resets the IP to the "any address"
+	// may throw ResolveError (address is unchanged in this case)
+	void Resolve(const char *name, Address *fallback = nullptr);
 
 	void setAddress(u32 address);
 	void setAddress(u8 a, u8 b, u8 c, u8 d);
@@ -75,5 +83,6 @@ private:
 		struct in_addr ipv4;
 		struct in6_addr ipv6;
 	} m_address;
-	u16 m_port = 0; // Port is separate from sockaddr structures
+	// port is separate from in_addr structures
+	u16 m_port = 0;
 };

src/unittest/test_address.cpp

@@ -32,14 +32,36 @@ public:
 
 	void runTests(IGameDef *gamedef);
 
+	void testBasic();
 	void testIsLocalhost();
+	void testResolve();
 };
 
 static TestAddress g_test_instance;
 
 void TestAddress::runTests(IGameDef *gamedef)
 {
+	TEST(testBasic);
 	TEST(testIsLocalhost);
+	TEST(testResolve);
+}
+
+void TestAddress::testBasic()
+{
+	Address tmp;
+
+	UASSERT(!tmp.isValid());
+	UASSERTEQ(int, tmp.getFamily(), 0);
+
+	tmp = Address(static_cast<u32>(0), 0);
+	UASSERT(tmp.isValid());
+	UASSERTEQ(int, tmp.getFamily(), AF_INET);
+	UASSERT(tmp.isAny());
+
+	tmp = Address(static_cast<IPv6AddressBytes*>(nullptr), 0);
+	UASSERT(tmp.isValid());
+	UASSERTEQ(int, tmp.getFamily(), AF_INET6);
+	UASSERT(tmp.isAny());
 }
 
 void TestAddress::testIsLocalhost()
@@ -65,3 +87,33 @@ void TestAddress::testIsLocalhost()
 	memcpy(ipv6Bytes->bytes, &ipv6RawAddr[0], 16);
 	UASSERT(!Address(ipv6Bytes.get(), 0).isLocalhost())
 }
+
+void TestAddress::testResolve()
+{
+	// Empty test
+	{
+		Address tmp(1, 2, 3, 4, 5);
+		tmp.Resolve("");
+
+		UASSERT(tmp.isValid());
+		UASSERT(tmp.isAny());
+	}
+
+	// Localhost test
+	Address result, fallback;
+	result.Resolve("localhost", &fallback);
+
+	UASSERT(result.isValid());
+	UASSERT(result.isLocalhost());
+
+	if (fallback.isValid()) {
+		UASSERT(fallback.isLocalhost());
+
+		// the result should be ::1 and 127.0.0.1 so the fallback addr should be
+		// of a different family
+		UASSERTCMP(int, !=, result.getFamily(), fallback.getFamily());
+	} else if (g_settings->getBool("enable_ipv6")) {
+		warningstream << "Couldn't verify Address::Resolve fallback (no IPv6?)"
+			<< std::endl;
+	}
+}