A man traded blows with a porn-loving patron at the Brooklyn Public Library and was slapped with assault charges — while the sex addict got off easy, police sources said.

The brawl started at 5 p.m. Saturday when Santiago Real, 38, of Brooklyn, was viewing pornography on a library computer while Durail Wright, 25, of Manhattan, was waiting to use it and became irate, the sources said.

The two exchanged blows and Wright was charged with assault, disorderly conduct and harassment. Real, meanwhile, was given a summons for disorderly conduct.