Might want to read the section on Lingering Close from here:

https://httpd.apache.org/docs/2.4/misc/perf-tuning.html

> Send off the data and close the socket. If there's data still pending to be read, this will cause a RST, I think.

Um, yes? That's how TCP has been universally implemented for more than 30 years. See [0], 2.17 for discussion.

[0] https://www.rfc-editor.org/rfc/rfc2525#page-50