Upstream: pipe length and input_filter_init in buffered mode. As long as ngx_event_pipe() has more data read from upstream than specified in p->length it's passed to input filter even if buffer isn't yet full. This allows to process data with known length without relying on connection close to signal data end. By default p->length is set to -1 in upstream module, i.e. end of data is indicated by connection close. To set it from per-protocol handlers upstream input_filter_init() now called in buffered mode (as well as in unbuffered mode).