ipc: Handle bitcoin-wallet disconnections

This fixes an error reported by Antoine Poinsot <darosior@protonmail.com> in
https://github.com/bitcoin-core/libmultiprocess/issues/123 that does not happen
in master, but does happen with https://github.com/bitcoin/bitcoin/pull/10102
applied, where if the child bitcoin-wallet process is killed (either by an
external signal or by Ctrl-C as reported in the issue) the bitcoin-node process
will not shutdown cleanly after that because chain client flush()
calls will fail.

This change fixes the problem by handling ipc::Exception errors thrown during
the flush() calls, and it relies on the fixes to disconnect detection
implemented in https://github.com/bitcoin-core/libmultiprocess/pull/160 to work
effectively.

src/common/args.cpp

@@ -589,6 +589,14 @@ void ArgsManager::AddHiddenArgs(const std::vector<std::string>& names)
     }
 }
 
+void ArgsManager::ClearArgs()
+{
+    LOCK(cs_args);
+    m_settings = {};
+    m_available_args.clear();
+    m_network_only_args.clear();
+}
+
 void ArgsManager::CheckMultipleCLIArgs() const
 {
     LOCK(cs_args);

src/common/args.h

@@ -359,11 +359,7 @@ protected:
     /**
      * Clear available arguments
      */
-    void ClearArgs() {
-        LOCK(cs_args);
-        m_available_args.clear();
-        m_network_only_args.clear();
-    }
+    void ClearArgs();
 
     /**
      * Check CLI command args

src/init.cpp

@@ -33,6 +33,7 @@
 #include <interfaces/ipc.h>
 #include <interfaces/mining.h>
 #include <interfaces/node.h>
+#include <ipc/exception.h>
 #include <kernel/caches.h>
 #include <kernel/context.h>
 #include <key.h>
@@ -298,8 +299,13 @@ void Shutdown(NodeContext& node)
     StopREST();
     StopRPC();
     StopHTTPServer();
-    for (const auto& client : node.chain_clients) {
+    for (auto& client : node.chain_clients) {
+        try {
             client->flush();
+        } catch (const ipc::Exception& e) {
+            LogDebug(BCLog::IPC, "Chain client did not disconnect cleanly: %s", e.what());
+            client.reset();
+        }
     }
     StopMapPort();
 
@@ -374,7 +380,7 @@ void Shutdown(NodeContext& node)
         }
     }
     for (const auto& client : node.chain_clients) {
-        client->stop();
+        if (client) client->stop();
     }
 
 #ifdef ENABLE_ZMQ
@@ -398,6 +404,12 @@ void Shutdown(NodeContext& node)
 
     RemovePidFile(*node.args);
 
+    // If any -ipcbind clients are still connected, disconnect them now so they
+    // do not block shutdown.
+    if (interfaces::Ipc* ipc = node.init->ipc()) {
+        ipc->disconnectIncoming();
+    }
+
     LogPrintf("%s: done\n", __func__);
 }
 

src/interfaces/ipc.h

@@ -59,17 +59,20 @@ public:
     //! true. If this is not a spawned child process, return false.
     virtual bool startSpawnedProcess(int argc, char* argv[], int& exit_status) = 0;
 
-    //! Connect to a socket address and make a client interface proxy object
-    //! using provided callback. connectAddress returns an interface pointer if
-    //! the connection was established, returns null if address is empty ("") or
-    //! disabled ("0") or if a connection was refused but not required ("auto"),
-    //! and throws an exception if there was an unexpected error.
+    //! Connect to a socket address and return a pointer to its Init interface.
+    //! Returns a non-null pointer if the connection was established, returns
+    //! null if address is empty ("") or disabled ("0") or if a connection was
+    //! refused but not required ("auto"), and throws an exception if there was
+    //! an unexpected error.
     virtual std::unique_ptr<Init> connectAddress(std::string& address) = 0;
 
-    //! Connect to a socket address and make a client interface proxy object
-    //! using provided callback. Throws an exception if there was an error.
+    //! Listen on a socket address exposing this process's init interface to
+    //! clients. Throws an exception if there was an error.
     virtual void listenAddress(std::string& address) = 0;
 
+    //! Disconnect any incoming connections that are still connected.
+    virtual void disconnectIncoming() = 0;
+
     //! Add cleanup callback to remote interface that will run when the
     //! interface is deleted.
     template<typename Interface>

src/ipc/capnp/protocol.cpp

@@ -68,6 +68,13 @@ public:
         m_loop->loop();
         m_loop.reset();
     }
+    void disconnectIncoming() override
+    {
+        if (!m_loop) return;
+        m_loop->sync([&] {
+            m_loop->m_incoming_connections.clear();
+        });
+    }
     void addCleanup(std::type_index type, void* iface, std::function<void()> cleanup) override
     {
         mp::ProxyTypeRegister::types().at(type)(iface).cleanup_fns.emplace_back(std::move(cleanup));

src/ipc/interfaces.cpp

@@ -17,6 +17,7 @@
 #include <cstdlib>
 #include <functional>
 #include <memory>
+#include <signal.h>
 #include <stdexcept>
 #include <string.h>
 #include <string>
@@ -26,6 +27,27 @@
 
 namespace ipc {
 namespace {
+#ifndef WIN32
+std::string g_ignore_ctrl_c;
+
+void HandleCtrlC(int)
+{
+    (void)write(STDOUT_FILENO, g_ignore_ctrl_c.data(), g_ignore_ctrl_c.size());
+}
+#endif
+
+void IgnoreCtrlC(std::string message)
+{
+#ifndef WIN32
+    g_ignore_ctrl_c = std::move(message);
+    struct sigaction sa{};
+    sa.sa_handler = HandleCtrlC;
+    sigemptyset(&sa.sa_mask);
+    sa.sa_flags = SA_RESTART;
+    sigaction(SIGINT, &sa, nullptr);
+#endif
+}
+
 class IpcImpl : public interfaces::Ipc
 {
 public:
@@ -53,6 +75,7 @@ public:
         if (!m_process->checkSpawned(argc, argv, fd)) {
             return false;
         }
+        IgnoreCtrlC(strprintf("[%s] SIGINT received — waiting for parent to shut down.\n", m_exe_name));
         m_protocol->serve(fd, m_exe_name, m_init);
         exit_status = EXIT_SUCCESS;
         return true;
@@ -86,6 +109,10 @@ public:
         int fd = m_process->bind(gArgs.GetDataDirNet(), m_exe_name, address);
         m_protocol->listen(fd, m_exe_name, m_init);
     }
+    void disconnectIncoming() override
+    {
+        m_protocol->disconnectIncoming();
+    }
     void addCleanup(std::type_index type, void* iface, std::function<void()> cleanup) override
     {
         m_protocol->addCleanup(type, iface, std::move(cleanup));

src/ipc/protocol.h

@@ -58,6 +58,9 @@ public:
     //! clients and servers independently.
     virtual void serve(int fd, const char* exe_name, interfaces::Init& init, const std::function<void()>& ready_fn = {}) = 0;
 
+    //! Disconnect any incoming connections that are still connected.
+    virtual void disconnectIncoming() = 0;
+
     //! Add cleanup callback to interface that will run when the interface is
     //! deleted.
     virtual void addCleanup(std::type_index type, void* iface, std::function<void()> cleanup) = 0;

src/netbase.h

@@ -121,6 +121,13 @@ public:
         m_reachable.clear();
     }
 
+    void Reset() EXCLUSIVE_LOCKS_REQUIRED(!m_mutex)
+    {
+        AssertLockNotHeld(m_mutex);
+        LOCK(m_mutex);
+        m_reachable = DefaultNets();
+    }
+
     [[nodiscard]] bool Contains(Network net) const EXCLUSIVE_LOCKS_REQUIRED(!m_mutex)
     {
         AssertLockNotHeld(m_mutex);
@@ -142,9 +149,9 @@ public:
     }
 
 private:
-    mutable Mutex m_mutex;
-
-    std::unordered_set<Network> m_reachable GUARDED_BY(m_mutex){
+    static std::unordered_set<Network> DefaultNets()
+    {
+        return {
             NET_UNROUTABLE,
             NET_IPV4,
             NET_IPV6,
@@ -155,6 +162,10 @@ private:
         };
     };
 
+    mutable Mutex m_mutex;
+    std::unordered_set<Network> m_reachable GUARDED_BY(m_mutex){DefaultNets()};
+};
+
 extern ReachableNets g_reachable_nets;
 
 /**

src/rpc/server.cpp

@@ -323,6 +323,12 @@ void SetRPCWarmupStatus(const std::string& newStatus)
     rpcWarmupStatus = newStatus;
 }
 
+void SetRPCWarmupStarting()
+{
+    LOCK(g_rpc_warmup_mutex);
+    fRPCInWarmup = true;
+}
+
 void SetRPCWarmupFinished()
 {
     LOCK(g_rpc_warmup_mutex);

src/rpc/server.h

@@ -30,6 +30,7 @@ void RpcInterruptionPoint();
  */
 void SetRPCWarmupStatus(const std::string& newStatus);
 /* Mark warmup as done.  RPC calls will be processed from now on.  */
+void SetRPCWarmupStarting();
 void SetRPCWarmupFinished();
 
 /* returns the current warmup state.  */

src/test/CMakeLists.txt

@@ -63,6 +63,7 @@ add_executable(test_bitcoin
   net_peer_eviction_tests.cpp
   net_tests.cpp
   netbase_tests.cpp
+  node_init_tests.cpp
   node_warnings_tests.cpp
   orphanage_tests.cpp
   pcp_tests.cpp

src/test/net_tests.cpp

@@ -702,6 +702,7 @@ BOOST_AUTO_TEST_CASE(get_local_addr_for_peer_port)
 
 BOOST_AUTO_TEST_CASE(LimitedAndReachable_Network)
 {
+    g_reachable_nets.Reset();
     BOOST_CHECK(g_reachable_nets.Contains(NET_IPV4));
     BOOST_CHECK(g_reachable_nets.Contains(NET_IPV6));
     BOOST_CHECK(g_reachable_nets.Contains(NET_ONION));

src/test/node_init_tests.cpp

@@ -0,0 +1,49 @@
+// Copyright (c) 2025 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <init.h>
+#include <interfaces/init.h>
+#include <rpc/server.h>
+
+#include <boost/test/unit_test.hpp>
+#include <test/util/setup_common.h>
+
+using node::NodeContext;
+
+BOOST_FIXTURE_TEST_SUITE(node_init_tests, BasicTestingSetup)
+
+//! Custom implementation of interfaces::Init for testing.
+class TestInit : public interfaces::Init
+{
+public:
+    TestInit(NodeContext& node) : m_node(node)
+    {
+        InitContext(m_node);
+        m_node.init = this;
+    }
+    std::unique_ptr<interfaces::Chain> makeChain() override { return interfaces::MakeChain(m_node); }
+    std::unique_ptr<interfaces::WalletLoader> makeWalletLoader(interfaces::Chain& chain) override
+    {
+        return MakeWalletLoader(chain, *Assert(m_node.args));
+    }
+    NodeContext& m_node;
+};
+
+BOOST_AUTO_TEST_CASE(init_test)
+{
+    // Reset logging, config file path, rpc state, reachable nets to avoid errors in AppInitMain
+    LogInstance().DisconnectTestLogger();
+    m_node.args->SetConfigFilePath({});
+    SetRPCWarmupStarting();
+    g_reachable_nets.Reset();
+
+    // Run through initialization and shutdown code.
+    TestInit init{m_node};
+    BOOST_CHECK(AppInitInterfaces(m_node));
+    BOOST_CHECK(AppInitMain(m_node));
+    Interrupt(m_node);
+    Shutdown(m_node);
+}
+
+BOOST_AUTO_TEST_SUITE_END()

src/test/util/setup_common.cpp

@@ -214,7 +214,10 @@ BasicTestingSetup::~BasicTestingSetup()
     } else {
         fs::remove_all(m_path_root);
     }
+    // Clear all arguments except for -datadir, which GUI tests currently rely
+    // on to be set even after the testing setup is destroyed.
     gArgs.ClearArgs();
+    gArgs.ForceSetArg("-datadir", fs::PathToString(m_path_root));
 }
 
 ChainTestingSetup::ChainTestingSetup(const ChainType chainType, TestOpts opts)