Merge bitcoin/bitcoin#20018: p2p: ProcessAddrFetch(-seednode) is unnecessary if -connect is specified

2555a3950f0304b7af7609c1e6c696993c50ac72 p2p: ProcessAddrFetch(-seednode) is unnecessary if -connect is specified (Dhruv Mehta)

Pull request description:

  If the user runs: `bitcoind -connect=X -seednode=Y`, I _think_ it is safe to ignore `-seednode`. A more populated `addrman` (via `getaddr` calls to peers in `-seednode`) is not useful in this configuration: `addrman` entries are used to initiate new outbound connections when slots are open, or to open feeler connections and keep `addrman` from getting stale. This is all done in a part of `ThreadOpenConnections` (below [this line](https://github.com/bitcoin/bitcoin/blob/master/src/net.cpp#L1803)) which is never executed when `-connect` is supplied. With `-connect`, `ThreadOpenConnections` will run [this loop](https://github.com/bitcoin/bitcoin/blob/master/src/net.cpp#L1785) and exit thread execution when interrupted.

  Reviewers may also find it relevant that when `-connect` is used, we [soft disable](https://github.com/bitcoin/bitcoin/blob/master/src/init.cpp#L800) `-dnsseed` in init.cpp perhaps for the same reason i.e. seeding is not useful with `-connect`.

  Running `ProcessAddrFetch` does not seem to have downside except developer confusion AFAICT. I was confused by this and felt it might affect other new bitcoiners too. If there is strong preference to not remove the line, I'd also be happy to just leave a comment there mentioning `ADDR_FETCH`/`-seednode` is irrelevant when used with `-connect`.

  If this change is accepted, the node will still make `getaddr` calls to peers in `-connect` and expand `addrman`. However, disabling those `getaddr` calls would leak information about the node's configuration.

ACKs for top commit:
  mzumsande:
    Code Review ACK 2555a3950f0304b7af7609c1e6c696993c50ac72
  achow101:
    ACK 2555a3950f0304b7af7609c1e6c696993c50ac72
  vasild:
    ACK 2555a3950f0304b7af7609c1e6c696993c50ac72

Tree-SHA512: 9187a0cff58db8edeca7e15379b1c121e7ebe8c38fb82f69e3dae8846ee94c92a329d79025e0f023c7579b2d86e7dbf756e4e30e90a72236bfcd2c00714180b3

1 files changed, 7 insertions, 0 deletions

diff --git a/src/init.cpp b/src/init.cpp
index 551f98f15a..fd97cd21da 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -1825,6 +1825,13 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
         if (connect.size() != 1 || connect[0] != "0") {
             connOptions.m_specified_outgoing = connect;
         }
+        if (!connOptions.m_specified_outgoing.empty() && !connOptions.vSeedNodes.empty()) {
+            LogPrintf("-seednode is ignored when -connect is used\n");
+        }
+
+        if (args.IsArgSet("-dnsseed") && args.GetBoolArg("-dnsseed", DEFAULT_DNSSEED) && args.IsArgSet("-proxy")) {
+            LogPrintf("-dnsseed is ignored when -connect is used and -proxy is specified\n");
+        }
     }
 
     const std::string& i2psam_arg = args.GetArg("-i2psam", "");