Fix misleading "Method not found" multiwallet errors

Raise RPC_WALLET_NOT_SPECIFIED instead of RPC_METHOD_NOT_FOUND when a required
wallet filename was not specified in an RPC call.

Also raise more specific RPC_WALLET_NOT_FOUND error instead of
RPC_INVALID_PARAMETER in case an invalid wallet was specified, for consistency.

src/bitcoin-cli.cpp

@@ -337,6 +337,10 @@ int CommandLineRPC(int argc, char *argv[])
 
                         if (errMsg.isStr())
                             strPrint += "error message:\n"+errMsg.get_str();
+
+                        if (errCode.isNum() && errCode.get_int() == RPC_WALLET_NOT_SPECIFIED) {
+                            strPrint += "\nTry adding \"-rpcwallet=<filename>\" option to bitcoin-cli command line.";
+                        }
                     }
                 } else {
                     // Result

src/rpc/protocol.h

@@ -82,6 +82,8 @@ enum RPCErrorCode
     RPC_WALLET_WRONG_ENC_STATE      = -15, //!< Command given in wrong wallet encryption state (encrypting an encrypted wallet etc.)
     RPC_WALLET_ENCRYPTION_FAILED    = -16, //!< Failed to encrypt the wallet
     RPC_WALLET_ALREADY_UNLOCKED     = -17, //!< Wallet is already unlocked
+    RPC_WALLET_NOT_FOUND            = -18, //!< Invalid wallet specified
+    RPC_WALLET_NOT_SPECIFIED        = -19, //!< No wallet specified (error when there are multiple wallets loaded)
 };
 
 UniValue JSONRPCRequestObj(const std::string& strMethod, const UniValue& params, const UniValue& id);

src/wallet/rpcwallet.cpp

@@ -43,7 +43,7 @@ CWallet *GetWalletForJSONRPCRequest(const JSONRPCRequest& request)
                 return pwallet;
             }
         }
-        throw JSONRPCError(RPC_INVALID_PARAMETER, "Requested wallet does not exist or is not loaded");
+        throw JSONRPCError(RPC_WALLET_NOT_FOUND, "Requested wallet does not exist or is not loaded");
     }
     return ::vpwallets.size() == 1 || (request.fHelp && ::vpwallets.size() > 0) ? ::vpwallets[0] : nullptr;
 }
@@ -57,13 +57,14 @@ std::string HelpRequiringPassphrase(CWallet * const pwallet)
 
 bool EnsureWalletIsAvailable(CWallet * const pwallet, bool avoidException)
 {
-    if (!pwallet) {
-        if (!avoidException)
+    if (pwallet) return true;
+    if (avoidException) return false;
+    if (::vpwallets.empty()) {
+        // Wallet RPC methods are disabled if no wallets are loaded.
         throw JSONRPCError(RPC_METHOD_NOT_FOUND, "Method not found (disabled)");
-        else
-            return false;
     }
-    return true;
+    throw JSONRPCError(RPC_WALLET_NOT_SPECIFIED,
+        "Wallet file not specified (must request wallet RPC through /wallet/<filename> uri-path).");
 }
 
 void EnsureWalletIsUnlocked(CWallet * const pwallet)

test/functional/multiwallet.py

@@ -21,8 +21,11 @@ class MultiWalletTest(BitcoinTestFramework):
         w1 = self.nodes[0] / "wallet/w1"
         w1.generate(1)
 
+        # accessing invalid wallet fails
+        assert_raises_jsonrpc(-18, "Requested wallet does not exist or is not loaded", (self.nodes[0] / "wallet/bad").getwalletinfo)
+
         # accessing wallet RPC without using wallet endpoint fails
-        assert_raises_jsonrpc(-32601, "Method not found", self.nodes[0].getwalletinfo)
+        assert_raises_jsonrpc(-19, "Wallet file not specified", self.nodes[0].getwalletinfo)
 
         # check w1 wallet balance
         w1_info = w1.getwalletinfo()