What is the ruling on playing music in an internet café, knowing that it is prohibited and that it is possible to block pornographic websites?

It is not permissible to open an internet cafe if its owner knows that its patrons will use it to listen to forbidden music, because this falls under the category of cooperation in sin and aggression, which Allah has prohibited in His statement: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." It also involves condoning evil. A Muslim should fear Allah and strive to earn a lawful livelihood.