Merge #13111: Add unloadwallet RPC

fe65bdec2 bugfix: Delete walletView in WalletFrame::removeWallet (João Barbosa)
0b82bac76 bugfix: Remove dangling wallet env instance (João Barbosa)
0ee77b207 ui: Support wallets unloaded dynamically (João Barbosa)
9f9b50d5f doc: Add release notes for unloadwallet RPC (João Barbosa)
ccbf7ae74 test: Wallet methods are disabled when no wallet is loaded (João Barbosa)
4940a20a4 test: Add functional tests for unloadwallet RPC (João Barbosa)
6608c369b rpc: Add unloadwallet RPC (João Barbosa)
537efe19e rpc: Extract GetWalletNameFromJSONRPCRequest from GetWalletForJSONRPCRequest (João Barbosa)

Pull request description:

  This patch adds wallet unload feature via RPC. It also adds UI support for unloaded wallets.

Tree-SHA512: 7c7f9f32f7a2266d2df574aa6b95f993c3dc82736f93304562122beb8756fb28cd22d03866b48f493c747441f22d30e196b098dec435cc25e035633f090351ea

4 files changed, 84 insertions, 13 deletions

diff --git a/src/wallet/db.cpp b/src/wallet/db.cpp
index 410dd5009f..01b8eacccb 100644
--- a/src/wallet/db.cpp
+++ b/src/wallet/db.cpp
@@ -694,8 +694,10 @@ void BerkeleyEnvironment::Flush(bool fShutdown)
             if (mapFileUseCount.empty()) {
                 dbenv->log_archive(&listp, DB_ARCH_REMOVE);
                 Close();
-                if (!fMockDb)
+                if (!fMockDb) {
                     fs::remove_all(fs::path(strPath) / "database");
+                }
+                g_dbenvs.erase(strPath);
             }
         }
     }
@@ -794,5 +796,6 @@ void BerkeleyDatabase::Flush(bool shutdown)
 {
     if (!IsDummy()) {
         env->Flush(shutdown);
+        if (shutdown) env = nullptr;
     }
 }
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index fd9e23cb64..3f2255d042 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -40,12 +40,21 @@
 
 static const std::string WALLET_ENDPOINT_BASE = "/wallet/";
 
-std::shared_ptr<CWallet> GetWalletForJSONRPCRequest(const JSONRPCRequest& request)
+bool GetWalletNameFromJSONRPCRequest(const JSONRPCRequest& request, std::string& wallet_name)
 {
     if (request.URI.substr(0, WALLET_ENDPOINT_BASE.size()) == WALLET_ENDPOINT_BASE) {
         // wallet endpoint was used
-        std::string requestedWallet = urlDecode(request.URI.substr(WALLET_ENDPOINT_BASE.size()));
-        std::shared_ptr<CWallet> pwallet = GetWallet(requestedWallet);
+        wallet_name = urlDecode(request.URI.substr(WALLET_ENDPOINT_BASE.size()));
+        return true;
+    }
+    return false;
+}
+
+std::shared_ptr<CWallet> GetWalletForJSONRPCRequest(const JSONRPCRequest& request)
+{
+    std::string wallet_name;
+    if (GetWalletNameFromJSONRPCRequest(request, wallet_name)) {
+        std::shared_ptr<CWallet> pwallet = GetWallet(wallet_name);
         if (!pwallet) throw JSONRPCError(RPC_WALLET_NOT_FOUND, "Requested wallet does not exist or is not loaded");
         return pwallet;
     }
@@ -66,11 +75,6 @@ bool EnsureWalletIsAvailable(CWallet * const pwallet, bool avoidException)
     if (pwallet) return true;
     if (avoidException) return false;
     if (!HasWallets()) {
-        // Note: It isn't currently possible to trigger this error because
-        // wallet RPC methods aren't registered unless a wallet is loaded. But
-        // this error is being kept as a precaution, because it's possible in
-        // the future that wallet RPC methods might get or remain registered
-        // when no wallets are loaded.
         throw JSONRPCError(
             RPC_METHOD_NOT_FOUND, "Method not found (wallet method is disabled because no wallet is loaded)");
     }
@@ -3053,7 +3057,7 @@ static UniValue listwallets(const JSONRPCRequest& request)
     return obj;
 }
 
-UniValue loadwallet(const JSONRPCRequest& request)
+static UniValue loadwallet(const JSONRPCRequest& request)
 {
     if (request.fHelp || request.params.size() != 1)
         throw std::runtime_error(
@@ -3100,7 +3104,7 @@ UniValue loadwallet(const JSONRPCRequest& request)
     return obj;
 }
 
-UniValue createwallet(const JSONRPCRequest& request)
+static UniValue createwallet(const JSONRPCRequest& request)
 {
     if (request.fHelp || request.params.size() != 1) {
         throw std::runtime_error(
@@ -3147,6 +3151,55 @@ UniValue createwallet(const JSONRPCRequest& request)
     return obj;
 }
 
+static UniValue unloadwallet(const JSONRPCRequest& request)
+{
+    if (request.fHelp || request.params.size() > 1) {
+        throw std::runtime_error(
+            "unloadwallet ( \"wallet_name\" )\n"
+            "Unloads the wallet referenced by the request endpoint otherwise unloads the wallet specified in the argument.\n"
+            "Specifying the wallet name on a wallet endpoint is invalid."
+            "\nArguments:\n"
+            "1. \"wallet_name\"    (string, optional) The name of the wallet to unload.\n"
+            "\nExamples:\n"
+            + HelpExampleCli("unloadwallet", "wallet_name")
+            + HelpExampleRpc("unloadwallet", "wallet_name")
+        );
+    }
+
+    std::string wallet_name;
+    if (GetWalletNameFromJSONRPCRequest(request, wallet_name)) {
+        if (!request.params[0].isNull()) {
+            throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot unload the requested wallet");
+        }
+    } else {
+        wallet_name = request.params[0].get_str();
+    }
+
+    std::shared_ptr<CWallet> wallet = GetWallet(wallet_name);
+    if (!wallet) {
+        throw JSONRPCError(RPC_WALLET_NOT_FOUND, "Requested wallet does not exist or is not loaded");
+    }
+
+    // Release the "main" shared pointer and prevent further notifications.
+    // Note that any attempt to load the same wallet would fail until the wallet
+    // is destroyed (see CheckUniqueFileid).
+    if (!RemoveWallet(wallet)) {
+        throw JSONRPCError(RPC_MISC_ERROR, "Requested wallet already unloaded");
+    }
+    UnregisterValidationInterface(wallet.get());
+
+    // The wallet can be in use so it's not possible to explicitly unload here.
+    // Just notify the unload intent so that all shared pointers are released.
+    // The wallet will be destroyed once the last shared pointer is released.
+    wallet->NotifyUnload();
+
+    // There's no point in waiting for the wallet to unload.
+    // At this point this method should never fail. The unloading could only
+    // fail due to an unexpected error which would cause a process termination.
+
+    return NullUniValue;
+}
+
 static UniValue resendwallettransactions(const JSONRPCRequest& request)
 {
     std::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(request);
@@ -4382,6 +4435,7 @@ static const CRPCCommand commands[] =
     { "wallet",             "settxfee",                         &settxfee,                      {"amount"} },
     { "wallet",             "signmessage",                      &signmessage,                   {"address","message"} },
     { "wallet",             "signrawtransactionwithwallet",     &signrawtransactionwithwallet,  {"hexstring","prevtxs","sighashtype"} },
+    { "wallet",             "unloadwallet",                     &unloadwallet,                  {"wallet_name"} },
     { "wallet",             "walletlock",                       &walletlock,                    {} },
     { "wallet",             "walletpassphrasechange",           &walletpassphrasechange,        {"oldpassphrase","newpassphrase"} },
     { "wallet",             "walletpassphrase",                 &walletpassphrase,              {"passphrase","timeout"} },
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index ca785298fd..6255f28b17 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -79,6 +79,15 @@ std::shared_ptr<CWallet> GetWallet(const std::string& name)
     return nullptr;
 }
 
+// Custom deleter for shared_ptr<CWallet>.
+static void ReleaseWallet(CWallet* wallet)
+{
+    LogPrintf("Releasing wallet %s\n", wallet->GetName());
+    wallet->BlockUntilSyncedToCurrentChain();
+    wallet->Flush();
+    delete wallet;
+}
+
 const uint32_t BIP32_HARDENED_KEY_LIMIT = 0x80000000;
 
 const uint256 CMerkleTx::ABANDON_HASH(uint256S("0000000000000000000000000000000000000000000000000000000000000001"));
@@ -1296,7 +1305,7 @@ void CWallet::BlockUntilSyncedToCurrentChain() {
         LOCK(cs_main);
         const CBlockIndex* initialChainTip = chainActive.Tip();
 
-        if (m_last_block_processed->GetAncestor(initialChainTip->nHeight) == initialChainTip) {
+        if (m_last_block_processed && m_last_block_processed->GetAncestor(initialChainTip->nHeight) == initialChainTip) {
             return;
         }
     }
@@ -4066,7 +4075,9 @@ std::shared_ptr<CWallet> CWallet::CreateWalletFromFile(const std::string& name,
 
     int64_t nStart = GetTimeMillis();
     bool fFirstRun = true;
-    std::shared_ptr<CWallet> walletInstance = std::make_shared<CWallet>(name, WalletDatabase::Create(path));
+    // TODO: Can't use std::make_shared because we need a custom deleter but
+    // should be possible to use std::allocate_shared.
+    std::shared_ptr<CWallet> walletInstance(new CWallet(name, WalletDatabase::Create(path)), ReleaseWallet);
     DBErrors nLoadWalletRet = walletInstance->LoadWallet(fFirstRun);
     if (nLoadWalletRet != DBErrors::LOAD_OK)
     {
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index aacbdf81d6..b829394847 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -1100,6 +1100,9 @@ public:
     //! Flush wallet (bitdb flush)
     void Flush(bool shutdown=false);
 
+    /** Wallet is about to be unloaded */
+    boost::signals2::signal<void ()> NotifyUnload;
+
     /**
      * Address book entry changed.
      * @note called with lock cs_wallet held.