Statements making use of user-defined functions are not safe for replication.
For an example, see
sql/udf_example.cc in the source tree. For a collection of existing UDFs go to the UDF Repository on GitHub.
There are alternative ways to add a new function: writing a native function, which requires modifying and compiling the server source code; or writing a stored function.
Creating User-Defined FunctionsHow to create user-defined functions in C/C++.
User-Defined Functions Calling SequencesDeclaring the functions required in a user-defined function.
User-Defined Functions SecurityMariaDB imposes a number of limitations on user-defined functions for security purposes.
CREATE FUNCTION UDFCreate a user-defined function.
DROP FUNCTION UDFDrop a user-defined function.
mysql.func TableUser-defined function information