mongoose/docs/c-api/util.h/mg_avprintf.md

title	decl_name	symbol_kind	signature
mg_avprintf()	mg_avprintf	func	int mg_avprintf(char **buf, size_t size, const char *fmt, va_list ap);

Print message to buffer. If buffer is large enough to hold the message, return buffer. If buffer is to small, allocate large enough buffer on heap, and return allocated buffer. This is a supposed use case:

char buf[5], *p = buf; p = mg_avprintf(&p, sizeof(buf), "%s", "hi there"); use_p_somehow(p); if (p != buf) { free(p); }

The purpose of this is to avoid malloc-ing if generated strings are small.