In RPC console, attempt to format errors

Try to display a nicer message instead of dumping raw JSON object when possible. If the error
somehow doesn't have the required 'code' and 'message' fields, fall back to printing raw JSON object.

src/qt/rpcconsole.cpp

@@ -153,7 +153,8 @@ void RPCExecutor::request(const QString &command)
     }
     if(args.empty())
         return; // Nothing to do
-    try {
+    try
+    {
         std::string strPrint;
         // Convert argument list to JSON objects in method-dependent way,
         // and pass it along with the method name to the dispatcher.
@@ -173,8 +174,18 @@ void RPCExecutor::request(const QString &command)
     }
     catch (json_spirit::Object& objError)
     {
+        try // Nice formatting for standard-format error
+        {
+            int code = find_value(objError, "code").get_int();
+            std::string message = find_value(objError, "message").get_str();
+            emit reply(RPCConsole::CMD_ERROR, QString::fromStdString(message) + " (code " + QString::number(code) + ")");
+        }
+        catch(std::runtime_error &) // raised when converting to invalid type, i.e. missing code or message
+        {
+            // Show raw JSON object
             emit reply(RPCConsole::CMD_ERROR, QString::fromStdString(write_string(json_spirit::Value(objError), false)));
         }
+    }
     catch (std::exception& e)
     {
         emit reply(RPCConsole::CMD_ERROR, QString("Error: ") + QString::fromStdString(e.what()));