Re: Internet Config from a daemon
Re: Internet Config from a daemon
- Subject: Re: Internet Config from a daemon
- From: Quinn <email@hidden>
- Date: Wed, 20 Aug 2003 08:53:22 +0100
At 16:00 -0400 19/8/03, Mike Cohen wrote:
If I run the agent manually from the terminal, it's able to return
all of the correct information, but none of the user-related info is
available when actually run as a daemon.
Is there any way I can have internet config obtain the settings
either for the currently logged in user or the machine owner?
Given that IC preferences are stored per-user and Mac OS X supports
multiple users, there's a question of whose preferences you want to
get back. IC decides this based on the process's effective user ID
(EUID). A daemon typically runs as root (effective user ID 0), and
thus you'll get back root's preferences (not very helpful). What you
should do is change your effective user ID before making the IC
calls. You can do this using seteuid.
Be warned that the EUID is a per-process property, so if you're
multi-threaded you have to coordinate it between your threads.
Also, changing UID like this does not always work as expected. If
the framework you're calling caches preferences, you can end up with
incorrect values. I have not heard of this sort of problem with IC
on Mac OS X, but it's a general concern.
A better solution might be for your daemon never to call IC directly,
but rather to fork every time it wants to get a user's preferences,
and have the child process call setuid to the UID in question and
then call IC. That way IC won't get chance to cache incorrect
values. It has the added advantage that it limits your security
exposure (as a rule, it's best if root processes don't call
high-level frameworks).
A much better solution is to factor your product into two components.
Have a daemon that runs in the background and responds to network
events and a faceless login item that's run each time a user logs in.
When the login item runs, it connects to the daemon (through whatever
IPC you like, maybe as Mach IPC or a UNIX domain socket), and tells
the daemon that particular user's settings. When the daemon gets a
network request, it just looks at the table of information given to
it by the various login items.
This approach has a number of key advantages.
1. Calling high-level frameworks from low-level processes (like
daemons) is always problematic in terms of compatibility. This
avoids the problem because the login item is running in the user's
context.
2. There are no security concerns because your daemon is not calling
high-level frameworks. Better yet, if your daemon only needs root in
order to bind its low-numbered port, its startup code can do the bind
and then it can drop its UID to minimise the damage of potential
security exploits.
3. It's fully compatible with Fast User Switching (where multiple
users can be logged in at the same time).
4. You get automatic notification of when a user logs in and logs out
via your IPC mechanism.
I don't see any way to obtain that information with SCF rather than IC.
Well, let's look at each in turn.
<CT:setting name="Name" value="Mike Cohen" />
You can the user's real name from getpwname.
<CT:setting name="SMTPHost" value="mail.bellsouth.net" />
<CT:setting name="HomePage" value="http://my.excite.com/"; />
<CT:setting name="Email" value="email@hidden" />
These are pretty much unique to IC.
<CT:setting name="Browser" value="Camino" />
<CT:setting name="Mailer" value="Mail" />
You can get these from Launch Services. Of course, Launch Services
is a high-level framework, just like IC, so it doesn't buy you much.
<CT:setting name="Proxy" value="blueg3.homeip.net:81" />
<CT:setting name="UseProxy" value="false" />
These are available in System Configuration framework via
SCDynamicStoreCopyProxies.
S+E
--
Quinn "The Eskimo!" <
http://www.apple.com/developer/>
Apple Developer Technical Support * Networking, Communications, Hardware
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