From 1adb635ec641dc1b20f79726c2a20a4e75558b60 Mon Sep 17 00:00:00 2001
From: Kittywhiskers Van Gogh <63189531+kwvg@users.noreply.github.com>
Date: Fri, 22 Jul 2022 13:54:35 -0400
Subject: [PATCH] merge bitcoin#25678: skip querying dns seeds if -onlynet
 disables IPv4 and IPv6

---
 src/init.cpp                           | 18 ++++++++++++++++++
 src/net.cpp                            |  9 +++++++--
 test/functional/feature_config_args.py |  3 ++-
 3 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/src/init.cpp b/src/init.cpp
index 7c2dc4e766..8462295dce 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -973,6 +973,17 @@ void InitParameterInteraction(ArgsManager& args)
             LogPrintf("%s: parameter interaction: -whitelistforcerelay=1 -> setting -whitelistrelay=1\n", __func__);
     }
 
+    if (args.IsArgSet("-onlynet")) {
+        const auto onlynets = args.GetArgs("-onlynet");
+        bool clearnet_reachable = std::any_of(onlynets.begin(), onlynets.end(), [](const auto& net) {
+            const auto n = ParseNetwork(net);
+            return n == NET_IPV4 || n == NET_IPV6;
+        });
+        if (!clearnet_reachable && args.SoftSetBoolArg("-dnsseed", false)) {
+            LogPrintf("%s: parameter interaction: -onlynet excludes IPv4 and IPv6 -> setting -dnsseed=0\n", __func__);
+        }
+    }
+
     int64_t nPruneArg = args.GetArg("-prune", 0);
     if (nPruneArg > 0) {
         if (args.SoftSetBoolArg("-disablegovernance", true)) {
@@ -1678,6 +1689,13 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     // 2.1. -onlynet is not given or
     // 2.2. -onlynet=cjdns is given
 
+    // Requesting DNS seeds entails connecting to IPv4/IPv6, which -onlynet options may prohibit:
+    // If -dnsseed=1 is explicitly specified, abort. If it's left unspecified by the user, we skip
+    // the DNS seeds by adjusting -dnsseed in InitParameterInteraction.
+    if (args.GetBoolArg("-dnsseed", DEFAULT_DNSSEED) == true && !IsReachable(NET_IPV4) && !IsReachable(NET_IPV6)) {
+        return InitError(strprintf(_("Incompatible options: -dnsseed=1 was explicitly specified, but -onlynet forbids connections to IPv4/IPv6")));
+    };
+
     // Check for host lookup allowed before parsing any network related parameters
     fNameLookup = args.GetBoolArg("-dns", DEFAULT_NAME_LOOKUP);
 
diff --git a/src/net.cpp b/src/net.cpp
index 4d16d43fab..10cda21d0b 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -2648,15 +2648,20 @@ void CConnman::ThreadOpenConnections(const std::vector<std::string> connect, CDe
                 LOCK2(m_addr_fetches_mutex, m_added_nodes_mutex);
                 if (m_addr_fetches.empty() && m_added_nodes.empty()) {
                     add_fixed_seeds_now = true;
-                    LogPrintf("Adding fixed seeds as -dnsseed=0, -addnode is not provided and all -seednode(s) attempted\n");
+                    LogPrintf("Adding fixed seeds as -dnsseed=0 (or IPv4/IPv6 connections are disabled via -onlynet), -addnode is not provided and all -seednode(s) attempted\n");
                 }
             }
 
             if (add_fixed_seeds_now) {
+                std::vector<CAddress> seed_addrs{ConvertSeeds(Params().FixedSeeds())};
+                seed_addrs.erase(std::remove_if(seed_addrs.begin(), seed_addrs.end(),
+                                               [](const CAddress& addr) { return !IsReachable(addr); }),
+                                seed_addrs.end());
                 CNetAddr local;
                 local.SetInternal("fixedseeds");
-                addrman.Add(ConvertSeeds(Params().FixedSeeds()), local);
+                addrman.Add(seed_addrs, local);
                 add_fixed_seeds = false;
+                LogPrintf("Added %d fixed seeds from reachable networks.\n", seed_addrs.size());
             }
         }
 
diff --git a/test/functional/feature_config_args.py b/test/functional/feature_config_args.py
index 28abf73e23..3413263dd7 100755
--- a/test/functional/feature_config_args.py
+++ b/test/functional/feature_config_args.py
@@ -181,11 +181,12 @@ class ConfArgsTest(BitcoinTestFramework):
         with self.nodes[0].assert_debug_log(expected_msgs=[
                 "Loaded 0 addresses from peers.dat",
                 "DNS seeding disabled",
-                "Adding fixed seeds as -dnsseed=0, -addnode is not provided and all -seednode(s) attempted\n",
+                "Adding fixed seeds as -dnsseed=0 (or IPv4/IPv6 connections are disabled via -onlynet), -addnode is not provided and all -seednode(s) attempted\n",
         ]):
             self.start_node(0, extra_args=['-dnsseed=0', '-fixedseeds=1'])
         assert time.time() - start < 60
         self.stop_node(0)
+        self.nodes[0].assert_start_raises_init_error(['-dnsseed=1', '-onlynet=i2p', '-i2psam=127.0.0.1:7656'], "Error: Incompatible options: -dnsseed=1 was explicitly specified, but -onlynet forbids connections to IPv4/IPv6")
 
         # No peers.dat exists and dns seeds are disabled.
         # We expect the node will not add fixed seeds when explicitly disabled.