[Aglets-users] Fwd: Urgent need help! Problem with file access permissions-Aglets

[Thomas H. <max...@us...>]

(Forgot to send this to the list)


---------- Forwarded message ----------
From: Thomas Herlea <max...@us...>
Date: Sat, Mar 31, 2012 at 19:23
Subject: Re: Urgent need help! Problem with file access permissions-Aglets
To: shruti nagani <shr...@gm...>


Dear Shruti,

The security exception you got does not mean the aglet is prevented
from accessing the file, but that it is prevented from finding out
what the current directory is. That is what the 'user.dir' property
stores. See http://docs.oracle.com/javase/tutorial/essential/environment/sysprop.html
for a list of system properties. Perhaps you are using a relative path
to your file in your code and therefore at some point the method for
accessing the file has to first look up the current directory, at
which point it throws the exception.

You can use the AccessControlException messages to guide you in adding
the required permission to the 'aglets.policy' file. It mentions the
missing permission type, 'java.util.PropertyPermission', so you should
look it up to see how it is granted
(http://docs.oracle.com/javase/7/docs/technotes/guides/security/permissions.html#PropertyPermission).
 You will discover the parameters available when granting it. These
parameters are specific to the permission type, so you really need to
look in yhe documentation. For PropertyPermission you specify a
pattern to match one or more properties, in your case 'user.dir' or
something with wildcards which covers 'user.dir', too. Then you
provide in the grant of a PropertyPermission an action about the
property or properties matching the first parameter. In your case
'read' is needed, but you also can grant a 'write' permission or both,
using the list syntax specified in the documentation.

I think it is an interesting problem to determine during development
which permissions an aglet may need. Does anyone know a more automated
method than looking up in the API documentation which
AccessControlExceptions every method call might throw? The guide
linked to above does have a section "Methods and the Permissions They
Require", but if the method listed there is called internally by
another standard library method which you call, I don't know if it is
easy to determine what exceptions may be thrown indirectly like that.

Good luck!

Thomas



On Sat, Mar 31, 2012 at 16:28, shruti nagani <shr...@gm...> wrote:
>
> Hi,
>
> I am accessing a file on my system from an aglet whose code is also on my system
> I am getting the following exception:
>
> java.security.AccessControlException:access denied ("java.util.PropertyPermission" "user.dir" "read")
>
> at java.security...etc etc
>
>
> I edited the aglets.policy in $HOME/.aglets/security and appended the following line
>
> permission java.io.FilePermission  "C:\\Users\\new\\Documents\\arffs\\bayes_labeled.arff", "read";
>
> to all 3 sections, (atp, http and file)
>
> bayes_labeled.arff is the file I need to read
>
> I am still getting the same exception. Please someone tell what am I doing wrong here?
>
> I'll be very grateful! Have been stuck on this for the past week.
>
> Thanks a tonne in advance!!
>
> Shruti