9:40 PM PT -- Cardi has declared full-on war, sending a message to Nicki, "I've let a lot of s*** slide! I let you sneak diss me, I let you lie on me ... But when you mention my child, you choose to like comments about me as a mother, make comments about my abilities to take care of my daughter is when all bets are f***in off!!"

Cardi goes on ... "I've worked hard and come too far to let anybody f*** with my success!!!! Bitches talk about all that s**** in they raps but in real life are p***y!!"

9:15 PM PT -- People connected to Cardi tell us, when Cardi approached the table she was not looking for a fight ... they say she wanted "to address the lies Nicki was spreading." They believe security had a plan if Cardi came anywhere near, and one of them elbowed her in her face (check out the lump). They say at that point it was on.

Cardi B showed off her shoes Friday night at a New York Fashion Week party ... by throwing one of them at Nicki Minaj ... TMZ has learned.

Cardi and Nicki both showed up at the Harper's Bazaar's bash. Nicki was with her crew at a table, when Cardi "aggressively approached the table" ... this according to eyewitnesses.

We're told Cardi said, "Let me tell you something" ... as she lunged toward Nicki, but security stopped her inches from contact.

But, Cardi wasn't done ... she pulled off her shoe and threw it at her enemy ... missing her target.

As for Nicki ... we're told cool as a cucumber. She didn't even flinch.

Cardi was escorted out by security, and she left the building with one shoe on her foot.