When TCP's send function returns OK, does it return OK only after receiving the other party's ACK, or does it just send it out?

乔海权

When TCP's send function returns OK, does it return OK only after receiving the other party's ACK, or does it just send it out? [Copy link]

Question 1:

The TCP send function returns OK only after receiving the other party's ACK.

Or does it only guarantee that it has been sent, but not whether the other party has received it?

Question 2:

In the lwip send function, after the data is sent, how can I check whether the other party has received it?

lwip_send(int s, const void *data, size_t size, int flags)