net: save the network type explicitly in CNetAddr

Before this change, we would analyze the contents of `CNetAddr::ip[16]`
in order to tell which type is an address. Change this by introducing a
new member `CNetAddr::m_net` that explicitly tells the type of the
address.

This is necessary because in BIP155 we will not be able to tell the
address type by just looking at its raw representation (e.g. both TORv3
and I2P are "seemingly random" 32 bytes).

As a side effect of this change we no longer need to store IPv4
addresses encoded as IPv6 addresses - we can store them in proper 4
bytes (will be done in a separate commit). Also the code gets
somewhat simplified - instead of
`memcmp(ip, pchIPv4, sizeof(pchIPv4)) == 0` we can use
`m_net == NET_IPV4`.

Co-authored-by: Carl Dong <contact@carldong.me>

1 files changed, 37 insertions, 2 deletions

diff --git a/src/netaddress.h b/src/netaddress.h
index 11c5ae1d53..0365907d44 100644
--- a/src/netaddress.h
+++ b/src/netaddress.h
@@ -49,10 +49,17 @@ enum Network
     NET_MAX,
 };
 
-/** IP address (IPv6, or IPv4 using mapped IPv6 range (::FFFF:0:0/96)) */
+/**
+ * Network address.
+ */
 class CNetAddr
 {
     protected:
+        /**
+         * Network to which this address belongs.
+         */
+        Network m_net{NET_IPV6};
+
         unsigned char ip[16]; // in network byte order
         uint32_t scopeId{0}; // for scoped/link-local ipv6 addresses
 
@@ -62,6 +69,14 @@ class CNetAddr
         void SetIP(const CNetAddr& ip);
 
         /**
+         * Set from a legacy IPv6 address.
+         * Legacy IPv6 address may be a normal IPv6 address, or another address
+         * (e.g. IPv4) disguised as IPv6. This encoding is used in the legacy
+         * `addr` encoding.
+         */
+        void SetLegacyIPv6(const uint8_t ipv6[16]);
+
+        /**
          * Set raw IPv4 or IPv6 address (in network byte order)
          * @note Only NET_IPV4 and NET_IPV6 are allowed for network.
          */
@@ -122,7 +137,27 @@ class CNetAddr
         friend bool operator!=(const CNetAddr& a, const CNetAddr& b) { return !(a == b); }
         friend bool operator<(const CNetAddr& a, const CNetAddr& b);
 
-        SERIALIZE_METHODS(CNetAddr, obj) { READWRITE(obj.ip); }
+        /**
+         * Serialize to a stream.
+         */
+        template <typename Stream>
+        void Serialize(Stream& s) const
+        {
+            s << ip;
+        }
+
+        /**
+         * Unserialize from a stream.
+         */
+        template <typename Stream>
+        void Unserialize(Stream& s)
+        {
+            unsigned char ip_temp[sizeof(ip)];
+            s >> ip_temp;
+            // Use SetLegacyIPv6() so that m_net is set correctly. For example
+            // ::FFFF:0102:0304 should be set as m_net=NET_IPV4 (1.2.3.4).
+            SetLegacyIPv6(ip_temp);
+        }
 
         friend class CSubNet;
 };