It’s not portable but Linux has a TCP_CORK socket option that does this.

olvy0 · on Dec 30, 2022

Here's how to emulate TCP_CORK using TCP_NODELAY, from [0]:

- unset the TCP_NODELAY flag on the socket

- Call send() zero or more times to add your outgoing data into the Nagle-queue

- set the TCP_NODELAY flag on the socket

- call send() with the number-of-bytes argument set to zero, to force an immediate send of the Nagle-queued data

jandrese · on Dec 30, 2022

Wow, that's not awkward at all.