[REBOL] Re: open/direct and stream underrun?
From: holger:rebol at: 12-Jun-2001 9:03
On Tue, Jun 05, 2001 at 11:44:55PM +0200, Petr Krenzelok wrote:
> while [data: copy/part http-port buffer-size][append file-port data]
>
> 1) We are faster than server. What happens? Am I correct if I assume, that
> in such case, we end up with not fully downloaded file? We don't wait for
> anything, right? So if there are no data coming from http-port, we quit ...
> Is it better to use cached port then?
This depends on whether you use the /no-wait refinement in 'open:
Without no-wait: 'copy waits until an end-of-file is received, i.e. instead
of copy/part you could just as well use copy.
With no-wait: 'copy returns an empty string if no data is available, i.e.
your while-loop busy-loops until the server returns some data. You should
insert a 'wait call into the condition block of your loop.
> 2) Reverse scenario - our server sends us data "too fast", so in comparison
> our script is "too slow" and before we read out data out of the port, server
> sends us new data. But we are using /direct refinement, so what happens with
> older data? Does OS take care of tcp data caching to some degree?
Yes, of course. No data is lost.
> Does it
> have anything in common with TCP stack "window" size?
Sort of, indirectly. The TCP "window" size is one of the parameters that
determines how much data can be "in transit" in a TCP connection. Regardless
of the window size you never lose data though. The worst case is that the
connection gets stalled (backlogged) at the server, i.e. that the server
cannot send any more data before you read some of the queued data from the
port.
--
Holger Kruse
[holger--rebol--com]
