Fix host connections on link-local IPv6 addresses

Link-local IPv6 addresses are valid on all interfaces and thus need an
interface specifier / scope id, e.g. fe80::1%eth0.

This commit adds scope ids for initial host connections only. While not
optimal, this is probably enough in practise as the link-local addresses
are likely only important when there is no internet connectivity. In
this case, connecting clients directly is less of an advantage.

src/network/C4NetIO.cpp

@@ -244,6 +244,16 @@ bool C4NetIO::HostAddress::IsLoopback() const
 	return false;
 }
 
+bool C4NetIO::HostAddress::IsLocal() const
+{
+	if (gen.sa_family == AF_INET6)
+		return IN6_IS_ADDR_LINKLOCAL(&v6.sin6_addr) != 0;
+	// We don't really care about local 169.256.0.0/16 addresses here as users will either have a
+	// router doing DHCP (which will prevent usage of these addresses) or have a network that
+	// doesn't care about IP and IPv6 link-local addresses will work.
+	return false;
+}
+
 void C4NetIO::HostAddress::SetScopeId(int scopeId)
 {
 	if (gen.sa_family != AF_INET6) return;

src/network/C4NetIO.h

@@ -111,6 +111,7 @@ public:
 		bool IsNull() const;
 		bool IsMulticast() const;
 		bool IsLoopback() const;
+		bool IsLocal() const;
 //		bool IsBroadcast() const;
 
 		StdStrBuf ToString(int flags = 0) const;

src/network/C4Network2.cpp

@@ -310,9 +310,25 @@ C4Network2::InitResult C4Network2::InitClient(const class C4Network2Address *pAd
 	for (int i = 0; i < iAddrCount; i++)
 		if (!pAddrs[i].isIPNull())
 		{
+			auto addr = pAddrs[i].getAddr();
+			std::vector<C4NetIO::addr_t> addrs;
+			if (addr.IsLocal())
+			{
+				// Local IPv6 addresses need a scope id.
+				for (auto& id : Clients.GetLocal()->getInterfaceIDs())
+				{
+					addr.SetScopeId(id);
+					addrs.push_back(addr);
+				}
+			}
+			else
+				addrs.push_back(addr);
 			// connection
-			if (!NetIO.Connect(pAddrs[i].getAddr(), pAddrs[i].getProtocol(), HostCore, szPassword))
-				continue;
+			int cnt = 0;
+			for (auto& a : addrs)
+				if (NetIO.Connect(a, pAddrs[i].getProtocol(), HostCore, szPassword))
+					cnt++;
+			if (cnt == 0) continue;
 			// format for message
 			if (strAddresses.getLength())
 				strAddresses.Append(", ");

src/network/C4Network2Client.cpp

@@ -231,6 +231,8 @@ void C4Network2Client::AddLocalAddrs(int16_t iPortTCP, int16_t iPortUDP)
 					addr.SetPort(iPortUDP);
 					AddAddr(C4Network2Address(addr, P_UDP), false);
 				}
+				if (addr.GetScopeId())
+					InterfaceIDs.insert(addr.GetScopeId());
 			}
 		}
 	}
@@ -257,6 +259,8 @@ void C4Network2Client::AddLocalAddrs(int16_t iPortTCP, int16_t iPortUDP)
 				addr.SetPort(iPortUDP);
 				AddAddr(C4Network2Address(addr, P_UDP), false);
 			}
+			if (addr.GetScopeId())
+				InterfaceIDs.insert(addr.GetScopeId());
 		}
 	}
 	freeifaddrs(addrs);

src/network/C4Network2Client.h

@@ -57,6 +57,9 @@ protected:
 	int32_t AddrAttempts[C4ClientMaxAddr];
 	int32_t iAddrCnt;
 
+	// interface ids
+	std::set<int> InterfaceIDs;
+
 	// status
 	C4Network2ClientStatus eStatus;
 
@@ -88,6 +91,8 @@ public:
 	int32_t     getAddrCnt()    const { return iAddrCnt; }
 	const C4Network2Address &getAddr(int32_t i) const { return Addr[i]; }
 
+	const std::set<int> &getInterfaceIDs() const { return InterfaceIDs; }
+
 	C4Network2ClientStatus getStatus() const { return eStatus; }
 	bool        hasJoinData()   const { return getStatus() != NCS_Joining; }
 	bool        isChasing()     const { return getStatus() == NCS_Chasing; }