net, refactor: pass reference for peer address in GetReachabilityFrom

The address of the peer always exists (because addr is a member of
CNode), so it was not possible to pass a nullptr before.
Also remove NET_UNKNOWN, which is unused now.

Author: mzumsande

src/net.cpp

@@ -165,7 +165,7 @@ bool GetLocal(CService& addr, const CNode& peer)
         for (const auto& entry : mapLocalHost)
         {
             int nScore = entry.second.nScore;
-            int nReachability = entry.first.GetReachabilityFrom(&peer.addr);
+            int nReachability = entry.first.GetReachabilityFrom(peer.addr);
             if (nReachability > nBestReachability || (nReachability == nBestReachability && nScore > nBestScore))
             {
                 addr = CService(entry.first, entry.second.nPort);

src/netaddress.cpp

@@ -723,19 +723,16 @@ std::vector<unsigned char> CNetAddr::GetAddrBytes() const
 
 // private extensions to enum Network, only returned by GetExtNetwork,
 // and only used in GetReachabilityFrom
-static const int NET_UNKNOWN = NET_MAX + 0;
-static const int NET_TEREDO  = NET_MAX + 1;
-int static GetExtNetwork(const CNetAddr *addr)
+static const int NET_TEREDO = NET_MAX;
+int static GetExtNetwork(const CNetAddr& addr)
 {
-    if (addr == nullptr)
-        return NET_UNKNOWN;
-    if (addr->IsRFC4380())
+    if (addr.IsRFC4380())
         return NET_TEREDO;
-    return addr->GetNetwork();
+    return addr.GetNetwork();
 }
 
 /** Calculates a metric for how reachable (*this) is from a given partner */
-int CNetAddr::GetReachabilityFrom(const CNetAddr *paddrPartner) const
+int CNetAddr::GetReachabilityFrom(const CNetAddr& paddrPartner) const
 {
     enum Reachability {
         REACH_UNREACHABLE,
@@ -750,7 +747,7 @@ int CNetAddr::GetReachabilityFrom(const CNetAddr *paddrPartner) const
     if (!IsRoutable() || IsInternal())
         return REACH_UNREACHABLE;
 
-    int ourNet = GetExtNetwork(this);
+    int ourNet = GetExtNetwork(*this);
     int theirNet = GetExtNetwork(paddrPartner);
     bool fTunnel = IsRFC3964() || IsRFC6052() || IsRFC6145();
 
@@ -790,7 +787,6 @@ int CNetAddr::GetReachabilityFrom(const CNetAddr *paddrPartner) const
         case NET_IPV6:    return REACH_IPV6_WEAK;
         case NET_IPV4:    return REACH_IPV4;
         }
-    case NET_UNKNOWN:
     case NET_UNROUTABLE:
     default:
         switch(ourNet) {

src/netaddress.h

@@ -203,7 +203,7 @@ class CNetAddr
     bool HasLinkedIPv4() const;
 
     std::vector<unsigned char> GetAddrBytes() const;
-    int GetReachabilityFrom(const CNetAddr* paddrPartner = nullptr) const;
+    int GetReachabilityFrom(const CNetAddr& paddrPartner) const;
 
     explicit CNetAddr(const struct in6_addr& pipv6Addr, const uint32_t scope = 0);
     bool GetIn6Addr(struct in6_addr* pipv6Addr) const;

src/test/fuzz/netaddress.cpp

@@ -84,7 +84,7 @@ FUZZ_TARGET(netaddress)
     (void)CServiceHash(0, 0)(service);
 
     const CNetAddr other_net_addr = ConsumeNetAddr(fuzzed_data_provider);
-    (void)net_addr.GetReachabilityFrom(&other_net_addr);
+    (void)net_addr.GetReachabilityFrom(other_net_addr);
     (void)sub_net.Match(other_net_addr);
 
     const CService other_service{net_addr, fuzzed_data_provider.ConsumeIntegral<uint16_t>()};