If n is smaller than the string length (as in: distance to first null byte) then you're bound to have garbage in your return destination

Wha? N is just maximum length of string to copy. Data after dst+n is unchanged.

In retrospect null-terminated strings were a mistake, but so were many other things, at some point you just have to accept that there's hysterical raisins everywhere.

All hail length-prefixed strings!