net: decouple state independent service flags from desirable ones

This former one will be moved to the peer manager class in the
following-up commit.

Author: furszy

contrib/seeds/README.md

@@ -4,7 +4,7 @@ Utility to generate the seeds.txt list that is compiled into the client
 (see [src/chainparamsseeds.h](/src/chainparamsseeds.h) and other utilities in [contrib/seeds](/contrib/seeds)).
 
 Be sure to update `PATTERN_AGENT` in `makeseeds.py` to include the current version,
-and remove old versions as necessary (at a minimum when GetDesirableServiceFlags
+and remove old versions as necessary (at a minimum when SeedsServiceFlags()
 changes its default return value, as those are the services which seeds are added
 to addrman with).
 

src/net.cpp

@@ -202,7 +202,7 @@ static std::vector<CAddress> ConvertSeeds(const std::vector<uint8_t> &vSeedsIn)
     while (!s.eof()) {
         CService endpoint;
         s >> endpoint;
-        CAddress addr{endpoint, GetDesirableServiceFlags(NODE_NONE)};
+        CAddress addr{endpoint, SeedsServiceFlags()};
         addr.nTime = rng.rand_uniform_delay(Now<NodeSeconds>() - one_week, -one_week);
         LogPrint(BCLog::NET, "Added hardcoded seed: %s\n", addr.ToStringAddrPort());
         vSeedsOut.push_back(addr);
@@ -2273,7 +2273,7 @@ void CConnman::ThreadDNSAddressSeed()
             AddAddrFetch(seed);
         } else {
             std::vector<CAddress> vAdd;
-            ServiceFlags requiredServiceBits = GetDesirableServiceFlags(NODE_NONE);
+            constexpr ServiceFlags requiredServiceBits{SeedsServiceFlags()};
             std::string host = strprintf("x%x.%s", requiredServiceBits, seed);
             CNetAddr resolveSource;
             if (!resolveSource.SetInternal(host)) {

src/protocol.h

@@ -330,12 +330,17 @@ std::vector<std::string> serviceFlagsToStr(uint64_t flags);
  * guaranteed to not change dependent on state - ie they are suitable for
  * use when describing peers which we know to be desirable, but for which
  * we do not have a confirmed set of service flags.
- *
- * If the NODE_NONE return value is changed, contrib/seeds/makeseeds.py
- * should be updated appropriately to filter for the same nodes.
  */
 ServiceFlags GetDesirableServiceFlags(ServiceFlags services);
 
+/**
+ * State independent service flags.
+ * If the return value is changed, contrib/seeds/makeseeds.py
+ * should be updated appropriately to filter for nodes with
+ * desired service flags (compatible with our new flags).
+ */
+constexpr ServiceFlags SeedsServiceFlags() { return ServiceFlags(NODE_NETWORK | NODE_WITNESS); }
+
 /** Set the current IBD status in order to figure out the desirable service flags */
 void SetServiceFlagsIBDCache(bool status);