init: Inform user of upcoming RDTS softfork and lack of enforcement by this software

Author: luke-jr

src/init.cpp

@@ -1339,6 +1339,54 @@ bool UserProtocolRulesCheck()
     return InitError(strprintf(_("Unknown rule specified in -%s: %s"), CONSENSUSRULES_CONFIG_NAME, rules_requested.front()));
 }
 
+bool UserProtocolRulesConsent()
+{
+    static const std::string CONSENSUSRULES_MISSING{"rdts"};
+    bool require_rdts{false};
+    for (const auto& rulesok : gArgs.GetArgs(CONSENSUSRULES_CONFIG_NAME)) {
+        if (rulesok == CONSENSUSRULES_MISSING) {
+            LogPrintf("User already consented to '%s' consensus rules\n", CONSENSUSRULES_MISSING);
+            require_rdts = true;
+            break;
+        }
+    }
+
+    bilingual_str msg = strprintf(_(
+        "Bitcoin protocol change proposed\n"
+        "\n"
+        "A one-year \"reduced data\" protocol change to the Bitcoin rules, beginning no later than September, has been proposed. "
+        "This upgrade fixes an existential threat to the Bitcoin network.\n"
+        "\n"
+        "Protocol changes require user consent to be effective, and if enforced inconsistently within the community may compromise your security or others'!\n"
+        "\n"
+        "If you do not know what you are doing, you can learn more at %s.\n"
+        "\n"
+        "Note that to reject this softfork, you must implement your own rejection fork.\n"
+        "(You must make a decision either way - old versions are insecure in all scenarios.)\n"
+        "\n"
+        "This release of %s does NOT include the protocol change, and will be insecure when it activates. "
+        "You can download the latest version from %s."
+    ), "https://bitcoinknots.org/learn/2026-rdts",
+        CLIENT_NAME,
+        CLIENT_URL);
+    if (require_rdts) {
+        const bilingual_str msg_config_suffix = strprintf(_(
+            "To run this version, you must remove from your config files: %s"
+        ), CONSENSUSRULES_CONFIG_NAME + "=" + CONSENSUSRULES_MISSING);
+        msg += Untranslated("\n\n") + msg_config_suffix;
+    }
+
+    const bool consent = uiInterface.ThreadSafeQuestion(
+        _("Caution:") + Untranslated(" ") + msg,
+        msg.original
+        , "Caution",
+        require_rdts
+            ? (CClientUIInterface::ICON_WARNING | CClientUIInterface::BTN_ABORT | CClientUIInterface::MODAL)
+            : (CClientUIInterface::MSG_WARNING | CClientUIInterface::BTN_ABORT | CClientUIInterface::DEFAULT_TRUE));
+
+    return consent;
+}
+
 bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
 {
     const ArgsManager& args = *Assert(node.args);
@@ -1404,6 +1452,10 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     g_wallet_init_interface.Construct(node);
     uiInterface.InitWallet();
 
+    if (!(chainparams.IsTestChain() || UserProtocolRulesConsent())) {
+        return false;
+    }
+
     if (!UserProtocolRulesCheck()) {
         return false;
     }

test/functional/feature_config_args.py

@@ -464,6 +464,7 @@ def test_acceptstalefeeestimates_arg_support(self):
         conf_file = self.nodes[0].datadir_path / "bitcoin.conf"
         for chain, chain_name in {("main", ""), ("test", "testnet3"), ("signet", "signet"), ("testnet4", "testnet4")}:
             util.write_config(conf_file, n=0, chain=chain_name, extra_config='acceptstalefeeestimates=1\n')
+            self.nodes[0].expected_stderr_prefix = self.MAINNET_NORMAL_STDERR if (chain_name == '') else ''
             self.nodes[0].assert_start_raises_init_error(expected_msg=f'Error: acceptstalefeeestimates is not supported on {chain} chain.')
         util.write_config(conf_file, n=0, chain="regtest")  # Reset to regtest
 

test/functional/mining_mainnet.py

@@ -44,6 +44,7 @@ def set_test_params(self):
         self.num_nodes = 1
         self.setup_clean_chain = True
         self.chain = "" # main
+        self.MAINNET_NORMAL_STDERR = ''  # because we truncate the message away
 
     def add_options(self, parser):
         parser.add_argument(

test/functional/test_framework/test_framework.py

@@ -243,6 +243,19 @@ def parse_args(self, test_file):
 
         PortSeed.n = self.options.port_seed
 
+        self.MAINNET_NORMAL_STDERR = f'''Caution: Bitcoin protocol change proposed
+
+A one-year "reduced data" protocol change to the Bitcoin rules, beginning no later than September, has been proposed. This upgrade fixes an existential threat to the Bitcoin network.
+
+Protocol changes require user consent to be effective, and if enforced inconsistently within the community may compromise your security or others'!
+
+If you do not know what you are doing, you can learn more at https://bitcoinknots.org/learn/2026-rdts.
+
+Note that to reject this softfork, you must implement your own rejection fork.
+(You must make a decision either way - old versions are insecure in all scenarios.)
+
+This release of {self.config['environment']['CLIENT_NAME']} does NOT include the protocol change, and will be insecure when it activates. You can download the latest version from {self.config['environment']['CLIENT_URL']}.'''
+
     def set_binary_paths(self):
         """Update self.options with the paths of all binaries from environment variables or their default values"""