net: Prevent node from binding to the same CService

Currently, if the user inadvertently starts the node with duplicate bind options,
such as `-bind=0.0.0.0 -bind=0.0.0.0`, it will cause a fatal error with the
misleading message "Bitcoin Core is probably already running".

This commit adds early validation to detect duplicate bindings across all binding
configurations (-bind, -whitebind, and onion bindings) before attempting to bind.
When duplicates are detected, the node terminates with a clear, specific error
message: "Duplicate binding configuration for address <addr>. Please check your
-bind, -bind=...=onion and -whitebind settings."

The validation catches duplicates both within the same option type (e.g.,
`-bind=X -bind=X`) and across different types (e.g., `-bind=X -whitebind=Y@X`),
helping users identify and fix configuration mistakes.

src/init.cpp

@@ -1233,6 +1233,40 @@ bool CheckHostPortOptions(const ArgsManager& args) {
     return true;
 }
 
+/**
+ * @brief Checks for duplicate bindings across all binding configurations.
+ *
+ * @param[in] conn_options Connection options containing the binding vectors to check
+ * @return std::optional<CService> containing the first duplicate found, or std::nullopt if no duplicates
+ */
+static std::optional<CService> CheckBindingConflicts(const CConnman::Options& conn_options)
+{
+    std::set<CService> seen;
+
+    // Check all whitelisted bindings
+    for (const auto& wb : conn_options.vWhiteBinds) {
+        if (!seen.insert(wb.m_service).second) {
+            return wb.m_service;
+        }
+    }
+
+    // Check regular bindings
+    for (const auto& bind : conn_options.vBinds) {
+        if (!seen.insert(bind).second) {
+            return bind;
+        }
+    }
+
+    // Check onion bindings
+    for (const auto& onion_bind : conn_options.onion_binds) {
+        if (!seen.insert(onion_bind).second) {
+            return onion_bind;
+        }
+    }
+
+    return std::nullopt;
+}
+
 // A GUI user may opt to retry once with do_reindex set if there is a failure during chainstate initialization.
 // The function therefore has to support re-entry.
 static ChainstateLoadResult InitAndLoadChainstate(
@@ -2142,6 +2176,13 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
 
     connOptions.m_i2p_accept_incoming = args.GetBoolArg("-i2pacceptincoming", DEFAULT_I2P_ACCEPT_INCOMING);
 
+    if (auto conflict = CheckBindingConflicts(connOptions)) {
+        return InitError(strprintf(
+            _("Duplicate binding configuration for address %s. "
+                "Please check your -bind, -bind=...=onion and -whitebind settings."),
+                    conflict->ToStringAddrPort()));
+    }
+
     if (!node.connman->Start(scheduler, connOptions)) {
         return false;
     }

test/functional/feature_bind_extra.py

@@ -3,10 +3,12 @@
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """
-Test starting bitcoind with -bind and/or -bind=...=onion and confirm
-that bind happens on the expected ports.
+Test starting bitcoind with -bind and/or -bind=...=onion, confirm that
+it binds to the expected ports, and verify that duplicate or conflicting
+-bind/-whitebind configurations are rejected with a descriptive error.
 """
 
+from itertools import combinations_with_replacement
 from test_framework.netutil import (
     addr_to_hex,
     get_bind_addrs,
@@ -14,13 +16,13 @@ from test_framework.netutil import (
 from test_framework.test_framework import (
     BitcoinTestFramework,
 )
+from test_framework.test_node import ErrorMatch
 from test_framework.util import (
     assert_equal,
     p2p_port,
     rpc_port,
 )
 
-
 class BindExtraTest(BitcoinTestFramework):
     def set_test_params(self):
         self.setup_clean_chain = True
@@ -87,5 +89,14 @@ class BindExtraTest(BitcoinTestFramework):
             binds = set(filter(lambda e: e[1] != rpc_port(i), binds))
             assert_equal(binds, set(expected_services))
 
+        self.stop_node(0)
+
+        addr = "127.0.0.1:11012"
+        for opt1, opt2 in combinations_with_replacement([f"-bind={addr}", f"-bind={addr}=onion", f"-whitebind=noban@{addr}"], 2):
+            self.nodes[0].assert_start_raises_init_error(
+                        [opt1, opt2],
+                        "Error: Duplicate binding configuration",
+                        match=ErrorMatch.PARTIAL_REGEX)
+
 if __name__ == '__main__':
     BindExtraTest(__file__).main()