I don't believe a process reading from a pipe/socketpair/whatever can enforce such constraints on a writing process (except using heavy hackery like ptrace()).

I don't believe a process reading from a pipe/socketpair/whatever can enforce such constraints on a writing process (except using heavy hackery like ptrace()). While it might be possible to adjust the pipe buffer size, I'm not aware of any convention requiring standard C I/O to respect this. In any case, stdbuf doesn't seem to help with this: $ ./a | stdbuf -i0 -- cat #include <stdio.h> #include <unistd.h> int main(void) { for (;;) { printf("n"); usleep(100000); } }