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From "Mark H. Wood" <mw...@IUPUI.Edu>
Subject Re: Copying large files around
Date Mon, 15 Oct 2007 14:00:15 GMT
On Sat, Oct 13, 2007 at 12:41:45PM +0200, Johnny Kewl wrote:
> OK... now if you on a LAN... thats cool, but for the internet this is not 
> good enough...
>
> If you have a look at something like the Opera browser's file transfer it 
> does some cool things, like if you shut down the machine, next time you 
> start up again, it will pick up where you stopped it, it doesnt start with 
> the whole 1 gb file again....
> In fact if I built a servlet to do this... I would run the Opera browser 
> download against it and stop and start and see it my servlet is to spec...
>
> I think the way to do it is to to modify the code in that link for RANDOM 
> file access... ie the client knows its got 800 MB already and only asks for 
> 800MB onwards.... so how do they do that.
>
> Look at this link..... 
> http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html
> and look at the byte range header spec..... I would build the servlet to 
> that.
>
> With such large files.... I think the biggest problem to solve is 
> interruptions.... ie give the user the ability to close the client and go 
> home... tomorrow it starts where it left off..... I think file change 
> headers (almost RSS) type stuff comes into this as well, in case the file 
> is modified before it all downloaded, in which case it MUST start again....
>
> Nice question.... I'm surprized I cant find code like this on the web 
> already.... have a good look around.... it must be there.

Perhaps not the *fastest*, but there *is* code to deal with
transferring files across flaky paths.  You just didn't look far
enough back in history.  UUCP over TCP works well, remembers how far
it got, and will keep trying on a schedule you specify until the job
is done.  I still use it to throw huge files across WAN paths, even
dialup links.

-- 
Mark H. Wood, Lead System Programmer   mwood@IUPUI.Edu
"Don't throw the past away. / You might need it some rainy day."

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