rpc, cli: improve error message on multiwallet mode

The primary objective is to provide users with clearer
and more informative error messages when encountering
the RPC_WALLET_NOT_SPECIFIED error, which occurs when
multiple wallets are loadad.

This commit also rectifies the error message consistency
by bringing the error message in line with the definition
established in protocol.h ("error when there are multiple
wallets loaded").

src/bitcoin-cli.cpp

@@ -950,7 +950,8 @@ static void ParseError(const UniValue& error, std::string& strPrint, int& nRet)
             strPrint += ("error message:\n" + err_msg.get_str());
         }
         if (err_code.isNum() && err_code.getInt<int>() == RPC_WALLET_NOT_SPECIFIED) {
-            strPrint += "\nTry adding \"-rpcwallet=<filename>\" option to bitcoin-cli command line.";
+            strPrint += " Or for the CLI, specify the \"-rpcwallet=<walletname>\" option before the command";
+            strPrint += " (run \"bitcoin-cli -h\" for help or \"bitcoin-cli listwallets\" to see which wallets are currently loaded).";
         }
     } else {
         strPrint = "error: " + error.write();

src/wallet/rpc/util.cpp

@@ -91,7 +91,7 @@ std::shared_ptr<CWallet> GetWalletForJSONRPCRequest(const JSONRPCRequest& reques
             RPC_WALLET_NOT_FOUND, "No wallet is loaded. Load a wallet using loadwallet or create a new one with createwallet. (Note: A default wallet is no longer automatically created)");
     }
     throw JSONRPCError(RPC_WALLET_NOT_SPECIFIED,
-        "Wallet file not specified (must request wallet RPC through /wallet/<filename> uri-path).");
+        "Multiple wallets are loaded. Please select which wallet to use by requesting the RPC through the /wallet/<walletname> URI path.");
 }
 
 void EnsureWalletIsUnlocked(const CWallet& wallet)

test/functional/interface_bitcoin_cli.py

@@ -30,7 +30,12 @@
 BLOCKS_VALUE_OF_ZERO = 'error: the first argument (number of blocks to generate, default: 1) must be an integer value greater than zero'
 TOO_MANY_ARGS = 'error: too many arguments (maximum 2 for nblocks and maxtries)'
 WALLET_NOT_LOADED = 'Requested wallet does not exist or is not loaded'
-WALLET_NOT_SPECIFIED = 'Wallet file not specified'
+WALLET_NOT_SPECIFIED = (
+    "Multiple wallets are loaded. Please select which wallet to use by requesting the RPC "
+    "through the /wallet/<walletname> URI path. Or for the CLI, specify the \"-rpcwallet=<walletname>\" "
+    "option before the command (run \"bitcoin-cli -h\" for help or \"bitcoin-cli listwallets\" to see "
+    "which wallets are currently loaded)."
+)
 
 
 def cli_get_info_string_to_dict(cli_get_info_string):
@@ -331,6 +336,10 @@ def run_test(self):
             n4 = 10
             blocks = self.nodes[0].getblockcount()
 
+            self.log.info('Test -generate -rpcwallet=<filename> raise RPC error')
+            wallet2_path = f'-rpcwallet={self.nodes[0].wallets_path / wallets[2] / self.wallet_data_filename}'
+            assert_raises_rpc_error(-18, WALLET_NOT_LOADED, self.nodes[0].cli(wallet2_path, '-generate').echo)
+
             self.log.info('Test -generate -rpcwallet with no args')
             generate = self.nodes[0].cli(rpcwallet2, '-generate').send_cli()
             assert_equal(set(generate.keys()), {'address', 'blocks'})

test/functional/wallet_multiwallet.py

@@ -229,7 +229,7 @@ def wallet_file(name):
         assert_raises_rpc_error(-18, "Requested wallet does not exist or is not loaded", wallet_bad.getwalletinfo)
 
         # accessing wallet RPC without using wallet endpoint fails
-        assert_raises_rpc_error(-19, "Wallet file not specified", node.getwalletinfo)
+        assert_raises_rpc_error(-19, "Multiple wallets are loaded. Please select which wallet", node.getwalletinfo)
 
         w1, w2, w3, w4, *_ = wallets
         self.generatetoaddress(node, nblocks=COINBASE_MATURITY + 1, address=w1.getnewaddress(), sync_fun=self.no_op)
@@ -275,7 +275,7 @@ def wallet_file(name):
         loadwallet_name = node.loadwallet(wallet_names[1])
         assert_equal(loadwallet_name['name'], wallet_names[1])
         assert_equal(node.listwallets(), wallet_names[0:2])
-        assert_raises_rpc_error(-19, "Wallet file not specified", node.getwalletinfo)
+        assert_raises_rpc_error(-19, "Multiple wallets are loaded. Please select which wallet", node.getwalletinfo)
         w2 = node.get_wallet_rpc(wallet_names[1])
         w2.getwalletinfo()