Issue with _dbus_write_socket on windows

[Peter Kümmel]

Havoc Pennington wrote:
> Timothy Vismor wrote:
>>
>> The named mutex is a system-wide object. If you want one for the
>> system bus and one for each session bus, you have to devise a suitable
>> naming convention.
>>
> 
> Found this suggestion on MSDN,
> http://msdn2.microsoft.com/en-us/library/ms682411.aspx

I've tried this:

  CreateMutex( NULL, FALSE, "Global\\UniqueDBusInstanceMutex");
  return GetLastError() != ERROR_ALREADY_EXISTS;

but it doesn't work. Seems I've missed something.

> 
>> If you are using a named mutex to limit your application to a single
>> instance, a malicious user can create this mutex before you do and
>> prevent your application from starting. To prevent this situation,
>> create a randomly named mutex and store the name so that it can only
>> be obtained by an authorized user. Alternatively, you can use a file
>> for this purpose. To limit your application to one instance per user,
>> create a locked file in the user's profile directory.
>>
> 
> I *think* this is saying just use a lockfile and don't use the mutex at
> all if you want per-user, though I guess it could be saying store the
> mutex name in the lockfile.

The Zen of Interpreting MSDN. :)

> File locking docs:
> https://msdn.microsoft.com/library/default.asp?url=/library/en-us/fileio/fs/lockfile.asp
> 
> 
> So autolaunch on Windows could use a locked file in the user's profile
> dir in place of an X selection.
> 
> The bus address could simply be stored in the locked file.
> 
> The next question is what is that bus address. Right now Windows is
> using TCP, but a problem is that it's unclear how to generate a per-user
> TCP address. I guess a random port can be picked, but that's likely to
> be evil (collide with other apps), I would think?
> 
> So it may be necessary to create a named pipe transport in addition to
> the socket transport, generate a random name for the named pipe just as
> we do for unix domain sockets, and then store the bus address (including
> name of the pipe) in the lock file.
> 
> This would mean creating a new "named-pipe:name=blahblah" kind of
> address for use on Windows.
> 
> I guess on Windows we could also use a window with messages instead of a
> named pipe, I have no idea what kind of tradeoffs there might be. The
> named pipe API _looks_ essentially equivalent to unix domain sockets...

I could remember that named pipes on Windows have some drawbacks, there
should be something in the archive.

> 
> Havoc
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-- 
Peter Kümmel