[protocol] Remove unused CADDR_TIME_VERSION

Add comments to CAddress serialization code explaining why
it's no longer needed.

src/protocol.h

@@ -371,7 +371,13 @@ class CAddress : public CService
             READWRITE(nVersion);
         }
         if ((s.GetType() & SER_DISK) ||
-            (nVersion >= CADDR_TIME_VERSION && !(s.GetType() & SER_GETHASH))) {
+            (nVersion != INIT_PROTO_VERSION && !(s.GetType() & SER_GETHASH))) {
+            // The only time we serialize a CAddress object without nTime is in
+            // the initial VERSION messages which contain two CAddress records.
+            // At that point, the serialization version is INIT_PROTO_VERSION.
+            // After the version handshake, serialization version is >=
+            // MIN_PEER_PROTO_VERSION and all ADDR messages are serialized with
+            // nTime.
             READWRITE(obj.nTime);
         }
         READWRITE(Using<CustomUintFormatter<8>>(obj.nServices));

src/version.h

@@ -20,10 +20,6 @@ static const int GETHEADERS_VERSION = 31800;
 //! disconnect from peers older than this proto version
 static const int MIN_PEER_PROTO_VERSION = GETHEADERS_VERSION;
 
-//! nTime field added to CAddress, starting with this version;
-//! if possible, avoid requesting addresses nodes older than this
-static const int CADDR_TIME_VERSION = 31402;
-
 //! BIP 0031, pong message, is enabled for all versions AFTER this one
 static const int BIP0031_VERSION = 60000;
 

test/functional/test_framework/messages.py

@@ -207,17 +207,19 @@ def __init__(self):
         self.ip = "0.0.0.0"
         self.port = 0
 
-    def deserialize(self, f, with_time=True):
+    def deserialize(self, f, *, with_time=True):
         if with_time:
+            # VERSION messages serialize CAddress objects without time
             self.time = struct.unpack("<i", f.read(4))[0]
         self.nServices = struct.unpack("<Q", f.read(8))[0]
         self.pchReserved = f.read(12)
         self.ip = socket.inet_ntoa(f.read(4))
         self.port = struct.unpack(">H", f.read(2))[0]
 
-    def serialize(self, with_time=True):
+    def serialize(self, *, with_time=True):
         r = b""
         if with_time:
+            # VERSION messages serialize CAddress objects without time
             r += struct.pack("<i", self.time)
         r += struct.pack("<Q", self.nServices)
         r += self.pchReserved
@@ -973,10 +975,10 @@ def deserialize(self, f):
         self.nServices = struct.unpack("<Q", f.read(8))[0]
         self.nTime = struct.unpack("<q", f.read(8))[0]
         self.addrTo = CAddress()
-        self.addrTo.deserialize(f, False)
+        self.addrTo.deserialize(f, with_time=False)
 
         self.addrFrom = CAddress()
-        self.addrFrom.deserialize(f, False)
+        self.addrFrom.deserialize(f, with_time=False)
         self.nNonce = struct.unpack("<Q", f.read(8))[0]
         self.strSubVer = deser_string(f)
 
@@ -996,8 +998,8 @@ def serialize(self):
         r += struct.pack("<i", self.nVersion)
         r += struct.pack("<Q", self.nServices)
         r += struct.pack("<q", self.nTime)
-        r += self.addrTo.serialize(False)
-        r += self.addrFrom.serialize(False)
+        r += self.addrTo.serialize(with_time=False)
+        r += self.addrFrom.serialize(with_time=False)
         r += struct.pack("<Q", self.nNonce)
         r += ser_string(self.strSubVer)
         r += struct.pack("<i", self.nStartingHeight)