Reporting Squid errors that have been shown to users

Issue

How to collect statistics about errors reported by squid to users, e.g., ERR_ZERO_SIZE_OBJECT, ERR_READ_ERROR, ERR_WRITE_ERROR.

Could you please point out:

1. how to set the debug_options in order to keep logs smaller and get the info we are looking for?
2. the expected layout for error event logs and in which log files we will find them;
3. how is it possible to relate the error events with user clients, e.g., ERR_READ_ERROR with the client IP?