Delivery-Date: Mon Nov 17 10:56:21 2008
Message-Id: <200811171852.mAHIqr5q027250@bourbon.usc.edu>
To: cs551@merlot.usc.edu
Subject: Re: Store question
Date: Mon, 17 Nov 2008 10:52:53 -0800
From: Bill Cheng <william@bourbon.usc.edu>

Someone wrote:

  > So if i receive a command like:
  > 
  > " store mall.c 1 type="code" " from the user first time, i will store the
  > file mall.c in the files directory.

Well, you need to store the file as "N.data" where N is a
number.

  > Now, if the user enters the same command, no change at all , is this
  > considered as a duplicate file ?

No.  It will be a new version of the same file.

  > or anything from the prompt is always
  > assumed to be unique.  This can happen after n commands after the user gave
  > the first store command too.

Correct.

  > If say we have match in the above scenario i.e. both the files are same,
  > then do we need to inform the user that the file already exists on the node,
  > the second time he tries to save it and stop processing the Store further ?
  > or shud we just process the command normally ??

You do not need to check if the file is already in the node
since every time you initiate a STORE, you will have to
generate a Nonce, and that will make the new file different
from what's already stored.
--
Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>


  On Mon, Nov 17, 2008 at 9:11 AM, Bill Cheng <william@bourbon.usc.edu> wrote:
  > Someone wrote:
  >
  >  >      Upon your comments about STORE message below, I conclude that when
  >  > receiving STORE message, the node doesn't need to check if it already
  >  > has a copy of the file. Because it's impossible since the nonce must be
  >  > different.
  >
  > Correct.
  >
  >  >      What about when forwarding GET message? I think after it flips the
  >  > coin and decides to cache the file, it needs to check if it already has
  >  > a copy of the file, correct?
  >
  > Correct.
  >
  >  >      If it is correct, besides forwarding GET message and receiving GET
  >  > message, is there any other situation we need to check if it already has
  >  > a copy of the file?
  >
  > I cannot think of anything at this point.  If you see a
  > situation where it needs to be done, then you need to write
  > code for it.
  > --
  > Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>
  >
  >
  >
  >
  >
  >   Bill Cheng wrote:
  >  > Someone wrote:
  >  >
  >  >   > Had a few doubts on the store feature ...
  >  >   > Is it possible for the same file to be stored twice on the
  >  >   > network?
  >  >
  >  > Yes.
  >  >
  >  >   > Seems possible so when I get a store response on a node
  >  >   > I need to check if the file already exists on the node before
  >  >   > storing it (in the Cache area).
  >  >
  >  > You don't need to check if you already has a copy of the file
  >  > if you are just caching it.  (Of course, you need check if
  >  > you have seen the *message* by looking at the message UOID
  >  > and discard duplicate messages -- this is what you do for
  >  > messages of all types anyway.)
  >  >
  >  >   > While matching should the
  >  >   > filename and the SHA value be enough or should we match the
  >  >   > keywords also ?
  >  >
  >  > No.  FileName, SHA1, *and* Nonce.
  >  >
  >  >   > Should we consider the files to be different if
  >  >   > they have the same name and content but different keywords ?
  >  >
  >  > Just FileName, SHA1, *and* Nonce.  If the keywords are
  >  > different for the same file, Nonce must also be different!
  >  >
  >  >   > If I already have the file do I still need to probabilistically
  >  >   > flood it ?
  >  >
  >  > Yes.  You should *not* even be checking if you have the
  >  > file already if you are forwarding a file.
  >  > --
  >  > Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>