Merge #16963: wallet: Fix unique_ptr usage in boost::signals2

6d6a7a8403ae923f189812edebdd95761de0e7f2 gui: Fix duplicate wallet showing up (João Barbosa)
81ea66c30e2953dee24d5b127c28daa0d9452a28 Drop signal CClientUIInterface::LoadWallet (Russell Yanofsky)

Pull request description:

  This PR includes 2 fixes:
   - prevent GUI LoadWallet handlers from crashing on startup when multiple handlers are attached, because the first handler takes ownership of the wallet unique pointer. Now every handler will receive its own unique pointer;

   - prevent showing a wallet twice in the GUI on startup due to a race with `loadwallet`.

  Fixes #16937

ACKs for top commit:
  fjahr:
    code review ACK 6d6a7a8403ae923f189812edebdd95761de0e7f2
  ryanofsky:
    Code review ACK 6d6a7a8403ae923f189812edebdd95761de0e7f2. No changes since last ACK other than rebase due to #17070
  kallewoof:
    Code review ACK 6d6a7a8403ae923f189812edebdd95761de0e7f2

Tree-SHA512: 7f0658c9011f81dfa176a094c2263448ee1d14fda7dc94e8b55ee9c8b81538bd2d1e4bf8a8dbfcd029ebfc9feb6d3cda9dee3f911122df0a4b1e0ca75f653ba4

5 files changed, 21 insertions, 8 deletions

diff --git a/src/interfaces/chain.cpp b/src/interfaces/chain.cpp
index ac640aa35a..ed35e19525 100644
--- a/src/interfaces/chain.cpp
+++ b/src/interfaces/chain.cpp
@@ -338,7 +338,6 @@ public:
     void initMessage(const std::string& message) override { ::uiInterface.InitMessage(message); }
     void initWarning(const std::string& message) override { InitWarning(message); }
     void initError(const std::string& message) override { InitError(message); }
-    void loadWallet(std::unique_ptr<Wallet> wallet) override { ::uiInterface.LoadWallet(wallet); }
     void showProgress(const std::string& title, int progress, bool resume_possible) override
     {
         ::uiInterface.ShowProgress(title, progress, resume_possible);
diff --git a/src/interfaces/chain.h b/src/interfaces/chain.h
index 349af152d5..c42f1a1fa3 100644
--- a/src/interfaces/chain.h
+++ b/src/interfaces/chain.h
@@ -43,7 +43,7 @@ class Wallet;
 //!   asynchronously
 //!   (https://github.com/bitcoin/bitcoin/pull/10973#issuecomment-380101269).
 //!
-//! * The initMessages() and loadWallet() methods which the wallet uses to send
+//! * The initMessage() and showProgress() methods which the wallet uses to send
 //!   notifications to the GUI should go away when GUI and wallet can directly
 //!   communicate with each other without going through the node
 //!   (https://github.com/bitcoin/bitcoin/pull/15288#discussion_r253321096).
@@ -209,9 +209,6 @@ public:
     //! Send init error.
     virtual void initError(const std::string& message) = 0;
 
-    //! Send wallet load notification to the GUI.
-    virtual void loadWallet(std::unique_ptr<Wallet> wallet) = 0;
-
     //! Send progress indicator.
     virtual void showProgress(const std::string& title, int progress, bool resume_possible) = 0;
 
diff --git a/src/interfaces/handler.cpp b/src/interfaces/handler.cpp
index 92601fc4e9..4e235688fe 100644
--- a/src/interfaces/handler.cpp
+++ b/src/interfaces/handler.cpp
@@ -22,6 +22,15 @@ public:
     boost::signals2::scoped_connection m_connection;
 };
 
+class CleanupHandler : public Handler
+{
+public:
+    explicit CleanupHandler(std::function<void()> cleanup) : m_cleanup(std::move(cleanup)) {}
+    ~CleanupHandler() override { if (!m_cleanup) return; m_cleanup(); m_cleanup = nullptr; }
+    void disconnect() override { if (!m_cleanup) return; m_cleanup(); m_cleanup = nullptr; }
+    std::function<void()> m_cleanup;
+};
+
 } // namespace
 
 std::unique_ptr<Handler> MakeHandler(boost::signals2::connection connection)
@@ -29,4 +38,9 @@ std::unique_ptr<Handler> MakeHandler(boost::signals2::connection connection)
     return MakeUnique<HandlerImpl>(std::move(connection));
 }
 
+std::unique_ptr<Handler> MakeHandler(std::function<void()> cleanup)
+{
+    return MakeUnique<CleanupHandler>(std::move(cleanup));
+}
+
 } // namespace interfaces
diff --git a/src/interfaces/handler.h b/src/interfaces/handler.h
index c4c674cac5..46918bc22e 100644
--- a/src/interfaces/handler.h
+++ b/src/interfaces/handler.h
@@ -5,6 +5,7 @@
 #ifndef BITCOIN_INTERFACES_HANDLER_H
 #define BITCOIN_INTERFACES_HANDLER_H
 
+#include <functional>
 #include <memory>
 
 namespace boost {
@@ -30,6 +31,9 @@ public:
 //! Return handler wrapping a boost signal connection.
 std::unique_ptr<Handler> MakeHandler(boost::signals2::connection connection);
 
+//! Return handler wrapping a cleanup function.
+std::unique_ptr<Handler> MakeHandler(std::function<void()> cleanup);
+
 } // namespace interfaces
 
 #endif // BITCOIN_INTERFACES_HANDLER_H
diff --git a/src/interfaces/node.cpp b/src/interfaces/node.cpp
index f2b00377be..7e022dce7a 100644
--- a/src/interfaces/node.cpp
+++ b/src/interfaces/node.cpp
@@ -43,11 +43,10 @@ std::vector<fs::path> ListWalletDir();
 std::vector<std::shared_ptr<CWallet>> GetWallets();
 std::shared_ptr<CWallet> LoadWallet(interfaces::Chain& chain, const std::string& name, std::string& error, std::vector<std::string>& warnings);
 WalletCreationStatus CreateWallet(interfaces::Chain& chain, const SecureString& passphrase, uint64_t wallet_creation_flags, const std::string& name, std::string& error, std::vector<std::string>& warnings, std::shared_ptr<CWallet>& result);
+std::unique_ptr<interfaces::Handler> HandleLoadWallet(interfaces::Node::LoadWalletFn load_wallet);
 
 namespace interfaces {
 
-class Wallet;
-
 namespace {
 
 class NodeImpl : public Node
@@ -286,7 +285,7 @@ public:
     }
     std::unique_ptr<Handler> handleLoadWallet(LoadWalletFn fn) override
     {
-        return MakeHandler(::uiInterface.LoadWallet_connect([fn](std::unique_ptr<Wallet>& wallet) { fn(std::move(wallet)); }));
+        return HandleLoadWallet(std::move(fn));
     }
     std::unique_ptr<Handler> handleNotifyNumConnectionsChanged(NotifyNumConnectionsChangedFn fn) override
     {