SystemBusPrivate doesn't return a working conn.

[james-lawrence]

to get a working conn need to invoke:

    conn, err := dbus.SystemBusPrivate()
    if err != nil {
        return err
    }
    if err = conn.Auth(nil); err != nil {
        conn.Close()
        return err
    }
    if err = conn.Hello(); err != nil {
        conn.Close()
        return  err
    }

[philips]

The problem is that you don't want to have to do the Auth and Hello?

[james-lawrence]

The problem is shouldn't have to. expected it to return a working connection. instead I got a broken one without any documentation as to why on the method.

[purpleidea]

I just figured out there were private/shared buses for both session and system. This explains why different parts of the code are receiving each other's messages! In any case, I couldn't get the PrivateBus to work, until I dug through the code and found this:

func SystemBus() (conn *Conn, err error) {
    systemBusLck.Lock()
    defer systemBusLck.Unlock()
    if systemBus != nil {
        return systemBus, nil
    }
    defer func() {
        if conn != nil {
            systemBus = conn
        }
    }()
    conn, err = SystemBusPrivate()
    if err != nil {
        return
    }
    if err = conn.Auth(nil); err != nil {
        conn.Close()
        conn = nil
        return
    }
    if err = conn.Hello(); err != nil {
        conn.Close()
        conn = nil
    }
    return
}

Which is approximately what @james-lawrence is saying.

So I do agree some doc/api fixes are in order... Will test this all tomorrow!

[purpleidea]

Incidentally, if you're not using private buses, then if you close the connection, everyone who is on the shared bus will see it closed!

[kyrofa]

@purpleidea indeed, the docs for Close() say to not call it on shared connections.

[purpleidea]

@philips would you accept a patch to either:

1. Change the API so that SystemBusPrivate returns something usable, and creates a SystemBusBase which does what SystemBusPrivate does?

or
2) Add a SystemBusPrivateReady method that returns the usable thing we expect, similar to SystemBus.

I'd prefer the first choice, because it fixes the API to make it most logical.

LMK

[purpleidea]

I have this snippet in my code in the meantime now:

func SystemBusPrivateUsable() (conn *dbus.Conn, err error) {
    conn, err = dbus.SystemBusPrivate()
    if err != nil {
        return nil, err
    }
    if err = conn.Auth(nil); err != nil {
        conn.Close()
        conn = nil
        return
    }
    if err = conn.Hello(); err != nil {
        conn.Close()
        conn = nil
    }
    return conn, nil // success
}

Happy to merge it upstream if someone is interested.

[philips]

@purpleidea Is there another dbus API that we can compare this Private/Base solution to?

[purpleidea]

@purpleidea Is there another dbus API that we can compare this Private/Base solution to?

@philips I'm sorry, I'm not sure if I understand what you're asking. The point is to make using the "Private" version of the bus a drop in replacement for the regular dbus.SystemBus() call.

[philips]

@purpleidea I am asking how does a C or python or Java library handle this?

[purpleidea]

On Mon, Feb 22, 2016 at 5:34 PM, Brandon Philips notifications@github.com
wrote:

@purpleidea https://github.com/purpleidea I am asking how does a C or
python or Java library handle this?

Oh, typically AFAIK there is a private (true/false) keyword on the main
initializer... This would also break API. I'm actually file with the two
bus objects, but as I said, the naming is confusing, and we lack the easy
private option. Python:

https://dbus.freedesktop.org/doc/dbus-python/api/dbus._dbus.Bus-class.html#__new__

[tomkcook]

Just to say, I have also been burned by this. At least an update to the API docs to say, "This doesn't return a working connection in the same way SystemBus() does, you need to call Auth() and Hello() on it before you use it" would be nice.

[james-lawrence]

I agree, that is the minimum that should be done.

[ozmy]

I ask if it is possible to put in example a working sample code for dbus.SystemBusPrivate. Thank you.

[jsouthworth]

Are the changes in #140 sufficient?

[james-lawrence]

believe so

[ozmy]

managed to figure it out
ip address must be passed as a separate argument.
Thank.

[jsouthworth]

The request was to add documentation on how to use SystemBusPrivate. See the example here: https://godoc.org/github.com/godbus/dbus#SystemBusPrivate

[tomkcook]

Stumbled across the changes in the godoc today. Looks good, thank you.

[guelfey]

Adressed in #140.