[Gambas-user] how to start a file?

[Doriano Blengino]

Robert JUHASZ ha scritto:
> Hello,
>
> I'm very happy with this solution and was perfect as long as I used my
> program myself.
> Now I wanna put it in a common folder on the server and for storing the
> files I'll use a folder. To avoid the direct access of this folder, I'll
> make it protected.
>
> The question now is how can I handle this kind of folder from Gambas. I
> don't wish to deal with the rights of teh folder. The idea is to give a read
> and write password to the folder and use the password from Gambas according
> to the user rights in Gambas.
>
> - the files will be displayed by a file view control. Is there any place of
> this control to enter (from code) the reading / writing password of the
> folder used by the control?
>
> - or, when using the Desktop.Open function, can I specify if I open the file
> for read only?
>   
Complicated matter... I don't understand well, but I will try to add 
some information you may miss.

First of all, at the file system level there could be everything you 
need. A file can be made not accessible, or readonly, or fully writable, 
to every single user of the computer. This is not so simple, however, 
because when two different users must share some privileges, you must 
use groups and things get messy. Even so, protecting a folder has 
different effects than proteting files. For example, if you 
write-protect a folder, you only assure that in that folder no files 
will be added or deleted, but single files will remain writeable. I bet 
this is not what you intended. On the other hand, if a file (not its 
folder) is write protected to a user, then that user will have no way to 
modify the file - every program will open that file in read-only mode. 
To prevent the file from being deleted, its folder must be protected, 
not the file itself.

Finally, to use such system, every user must login in the system using 
its own identifier; if you have only one copy of your program running, 
with different users alternating if front of it, then you should have 
your gambas program change user ID (there is a system call for this, but 
gambas don't seem to implement it). However, you can take advantage of 
/bin/sudo, which lets you impersonate other users. The system is 
configurable and not difficult to understand (see the manual page).

About FileView control, it has no property for specifying a username, 
but you can use a textbox aside and ask the user to write its username.

Desktop.Open, or any other "high level" shell function, can not "open a 
file read-only"; it is the final program that must be instructed to work 
in read-only, be it openoffice, or a CAD, or anything else. Perhaps not 
all the program can be instructed to do so. It is possible, however, to 
protect the file before launching the application, and remove the 
protection afterward, Or the file can be copied elsewhere and then 
opened, alerting the user that modifications will be lost.

I don't know what you are trying to do, and what your final system 
should look (one computer? many? Several system-level users? Just one?) 
but the final solutions could be to manage the access rights inside the 
program - your program asks for credentials, and then decides what to 
show, what to open read-only and what to permit to be modified or deleted.

There are add-ons for Linux which permit, at the filesystem level, to 
use ACLs (access control list). This way you can more easily grant 
permissions to single users without getting crazy with users and groups. 
Or you can make several folders with different permissions (one 
writeable to anyone, another only readeable to everyone, and so on).

Hope I pointed out some useful idea,
regards,

-- 
Doriano Blengino

"Listen twice before you speak.
This is why we have two ears, but only one mouth."