From 90be8354d47f995f592ee4ce67b7348098a13b17 Mon Sep 17 00:00:00 2001
From: xyzconstant <263061129+xyzconstant@users.noreply.github.com>
Date: Tue, 21 Apr 2026 00:25:15 -0300
Subject: [PATCH 1/2] test: regression for ~ProxyClient destroy after peer
 disconnect

Reproduces bitcoin-core/libmultiprocess#219 by saving a callback on
the server then disconnecting before cleanup completes, so the
server-side `~ProxyClient` runs its remote destroy call against a dead
connection.

Without the fix in the next commit, the throw escapes the noexcept
destructor and aborts mptest.
---
 test/mp/test/test.cpp | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/test/mp/test/test.cpp b/test/mp/test/test.cpp
index d91edb40..b259790b 100644
--- a/test/mp/test/test.cpp
+++ b/test/mp/test/test.cpp
@@ -427,6 +427,32 @@ KJ_TEST("Calling async IPC method, with server disconnect after cleanup")
     }
 }
 
+KJ_TEST("Destroying ProxyClient<> with destroy method after peer disconnect")
+{
+    // Regression test for bitcoin-core/libmultiprocess#219 where
+    // ~ProxyClientBase would call std::terminate if the remote destroy RPC
+    // failed during teardown.
+    //
+    // Save a callback on the server so it holds a ProxyClient<FooCallback>
+    // pointing back to this side, then disconnect. When the server is torn
+    // down, the ProxyClient<FooCallback> destructor issues a destroy RPC over
+    // the now dead connection; without the bugfix the exception escapes the
+    // noexcept destructor and aborts the process.
+
+    TestSetup setup{/*client_owns_connection=*/false};
+    ProxyClient<messages::FooInterface>* foo = setup.client.get();
+    foo->initThreadMap();
+
+    class Callback : public FooCallback
+    {
+    public:
+        int call(int arg) override { return arg; }
+    };
+
+    foo->saveCallback(std::make_shared<Callback>());
+    setup.client_disconnect();
+}
+
 KJ_TEST("Make simultaneous IPC calls on single remote thread")
 {
     TestSetup setup;

From 6de92e1c7324c4748d05687372256a5051c97bb4 Mon Sep 17 00:00:00 2001
From: xyzconstant <263061129+xyzconstant@users.noreply.github.com>
Date: Tue, 21 Apr 2026 00:25:15 -0300
Subject: [PATCH 2/2] proxy-client: tolerate exceptions from remote destroy
 during cleanup

Fixes bitcoin-core/libmultiprocess#219
---
 include/mp/proxy-io.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/mp/proxy-io.h b/include/mp/proxy-io.h
index d7b9f0e5..09465c04 100644
--- a/include/mp/proxy-io.h
+++ b/include/mp/proxy-io.h
@@ -538,7 +538,12 @@ ProxyClientBase<Interface, Impl>::ProxyClientBase(typename Interface::Client cli
         // the remote object, waiting for it to be deleted server side. If the
         // capnp interface does not define a destroy method, this will just call
         // an empty stub defined in the ProxyClientBase class and do nothing.
-        Sub::destroy(*this);
+        // Exceptions are caught and logged rather than propagated because
+        // ~ProxyClientBase is noexcept and the peer may be gone by the time
+        // this runs.
+        if (kj::runCatchingExceptions([&]{ Sub::destroy(*this); }) != nullptr) {
+            MP_LOG(*m_context.loop, Log::Warning) << "Remote destroy call failed during cleanup. Continuing.";
+        }
 
         // FIXME: Could just invoke removed addCleanup fn here instead of duplicating code
         m_context.loop->sync([&]() {