Permissions on key directories/files.

[Havoc Pennington]

Hi,

The way dbus works is in my view the best solution for the general case,
though it's not really going to work for X I don't think.

In essence what dbus does is:
 - the listening server creates a file in /tmp with a random name
   mkstmp-style
 - you then have a well-known way or ways to discover the filename

Then you have no problem with collisions. There's a bit of a garbage
collection problem because UNIX is dumb and you get dead sockets around;
the fix is twofold:
 - on Linux, use abstract sockets instead
 - on other UNIX, run a cron job with dbus-cleanup-sockets to mop up 
   dead sockets

The specific way dbus works is to set an environment variable with the
address for the message bus; the address includes the filename in the
UNIX domain socket case. This works fine since the bus is scoped
per-user-session.

In contexts other than dbus, possibilities for locating the filename
include setting a root window property, advertising it on the message
bus, etc. Or just using the message bus in the first place instead of
inventing a new kind of thing that needs a socket.

The problem I'd like to solve even more than this one is to use
dbus-style cookie authentication; i.e. make the cookie file map a random
ID number determined by the server to a cookie, rather than mapping a
hostname to a cookie. Then pass the ID number to clients as a challenge
and the clients have to return the cookie. Then one can change hostname
with impunity.

Havoc