static char* ensure(printbuffer *p,int needed)
{
	char *newbuffer;int newsize;
	if (!p || !p->buffer) return 0;
	needed+=p->offset;
	if (needed<=p->length) return p->buffer+p->offset;

	newsize=pow2gt(needed);
	newbuffer=(char*)cJSON_malloc(newsize);
	if (!newbuffer) {cJSON_free(p->buffer);p->length=0,p->buffer=0;return 0;}
	if (newbuffer) memcpy(newbuffer,p->buffer,p->length);
	cJSON_free(p->buffer);
	p->length=newsize;
	p->buffer=newbuffer;
	return newbuffer+p->offset;
}

The product reads data past the end, or before the beginning, of the intended buffer.