DBus binding & direct connections (p2p)?

DBus binding & direct connections (p2p)?

[Nicolas Petton]

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Hi,

I was wondering if the Emacs binding for DBus handles peer to peer
connections between two applications without a bus daemon?

Cheers,
Nico

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Re: DBus binding & direct connections (p2p)?

[Michael Albinus]

Nicolas Petton <nicolas@petton.fr> writes:

> Hi,

Hi Nicolas,

> I was wondering if the Emacs binding for DBus handles peer to peer
> connections between two applications without a bus daemon?

There does not exist such an interface in the D-Bus specification. The
standard interface org.freedesktop.DBus.Peer offers the methods Ping and
GetMachineId, which are something different. See
<https://dbus.freedesktop.org/doc/dbus-specification.html#standard-interfaces-peer>.

The Java D-Bus bindings offer the interface
org.freedesktop.dbus.DirectConnection, which "Handles a peer to peer
connection between two applications withou a bus daemon.". See
<https://dbus.freedesktop.org/doc/dbus-java/api/org/freedesktop/dbus/DirectConnection.html>. Likely
this is what you've asked for; it isn't implemented in the Emacs bindings.

> Cheers,
> Nico

Best regards, Michael.

Re: DBus binding & direct connections (p2p)?

[Nicolas Petton]

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Michael Albinus <michael.albinus@gmx.de> writes:

Hi Michael,

> The Java D-Bus bindings offer the interface
> org.freedesktop.dbus.DirectConnection, which "Handles a peer to peer
> connection between two applications withou a bus daemon.". See
> <https://dbus.freedesktop.org/doc/dbus-java/api/org/freedesktop/dbus/DirectConnection.html>. Likely
> this is what you've asked for; it isn't implemented in the Emacs
> bindings.

That's exactly what I meant.  Some applications communicate through
dbus, using peer-to-peer communications, without using a bus.

The Python binding allows for direct connections to be open like the
following (TCP in this example):

    import dbus;
    conn = dbus.connection.Connection("tcp:host=localhost,port=1234")

I think that calling `dbus_connection_open' with a dbus address would be
enough to support direct connections in the Emacs binding (but I might
be wrong).

Cheers,
Nico

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Re: DBus binding & direct connections (p2p)?

[Michael Albinus]

Nicolas Petton <nicolas@petton.fr> writes:

> Hi Michael,

Hi Nicolas,

> That's exactly what I meant.  Some applications communicate through
> dbus, using peer-to-peer communications, without using a bus.
>
> The Python binding allows for direct connections to be open like the
> following (TCP in this example):
>
>     import dbus;
>     conn = dbus.connection.Connection("tcp:host=localhost,port=1234")
>
> I think that calling `dbus_connection_open' with a dbus address would be
> enough to support direct connections in the Emacs binding (but I might
> be wrong).

I've never tried it peer-to-peer, but there is `dbus-init-bus'. If you
don't use `:system' or `:session' as BUS argument but a string address
as shown by you, it calls `dbus_connection_open' with that address. If
you provide a non-nil PRIVATE argument, it calls
`dbus_connection_open_private' instead. Play with this :-)

> Cheers,
> Nico

Best regards, Michael.

Re: DBus binding & direct connections (p2p)?

[Nicolas Petton]

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Michael Albinus <michael.albinus@gmx.de> writes:

Hi Michael,

> I've never tried it peer-to-peer, but there is `dbus-init-bus'. If you
> don't use `:system' or `:session' as BUS argument but a string address
> as shown by you, it calls `dbus_connection_open' with that address. If
> you provide a non-nil PRIVATE argument, it calls
> `dbus_connection_open_private' instead. Play with this :-)

I tried this already, but I get:

  D-Bus error: "No such interface 'org.freedesktop.DBus' on object at path
  /org/freedesktop/DBus"

Nico

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Re: DBus binding & direct connections (p2p)?

[Nicolas Petton]

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Nicolas Petton <nicolas@petton.fr> writes:

> I tried this already, but I get:
>
>   D-Bus error: "No such interface 'org.freedesktop.DBus' on object at path
>   /org/freedesktop/DBus"

My guess is that dbusbind.c tries to register to a bus, but there is no bus:

  if (STRINGP (bus))
    dbus_bus_register (connection, &derror);

Nico

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Re: DBus binding & direct connections (p2p)?

[Michael Albinus]

Nicolas Petton <nicolas@petton.fr> writes:

> Nicolas Petton <nicolas@petton.fr> writes:
>
>> I tried this already, but I get:
>>
>>   D-Bus error: "No such interface 'org.freedesktop.DBus' on object at path
>>   /org/freedesktop/DBus"
>
> My guess is that dbusbind.c tries to register to a bus, but there is no bus:
>
>   if (STRINGP (bus))
>     dbus_bus_register (connection, &derror);

Yes, `dbus-init-bus' is intended for that purpose ...

Implementing something like Java's org.freedesktop.dbus.DirectConnection
seems to be expensive, so I fear we haven't anything in Emacs which
could be used w/o a bus.

> Nico

Best regards, Michael.

Re: DBus binding & direct connections (p2p)?

[Nicolas Petton]

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Michael Albinus <michael.albinus@gmx.de> writes:

> Yes, `dbus-init-bus' is intended for that purpose ...
>
> Implementing something like Java's org.freedesktop.dbus.DirectConnection
> seems to be expensive, so I fear we haven't anything in Emacs which
> could be used w/o a bus.

I don't understand, why it would be expensive?

Cheers,
Nico

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Re: DBus binding & direct connections (p2p)?

[Michael Albinus]

Nicolas Petton <nicolas@petton.fr> writes:

>> Implementing something like Java's org.freedesktop.dbus.DirectConnection
>> seems to be expensive, so I fear we haven't anything in Emacs which
>> could be used w/o a bus.
>
> I don't understand, why it would be expensive?

It must be in C, I suppose. And while listening, it must implement
something a bus (daemon) is supposed to handle.

Just from roughly reading that Java implementation. But I might be
wrong. You could try to implement yourself, of course.

> Cheers,
> Nico

Best regards, Michael.

Re: DBus binding & direct connections (p2p)?

[Nicolas Petton]

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Michael Albinus <michael.albinus@gmx.de> writes:

> Just from roughly reading that Java implementation. But I might be
> wrong. You could try to implement yourself, of course.

Yes, I'll give it a shot.  I'll start by looking at the existing usages
in C of direct DBus communications.

Cheers,
Nico

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Re: DBus binding & direct connections (p2p)?

[Michael Albinus]

Nicolas Petton <nicolas@petton.fr> writes:

> Yes, I'll give it a shot.  I'll start by looking at the existing usages
> in C of direct DBus communications.

Could you send me a pointer?

> Cheers,
> Nico

Best regards, Michael.

Re: DBus binding & direct connections (p2p)?

[Nicolas Petton]

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Michael Albinus <michael.albinus@gmx.de> writes:

>> Yes, I'll give it a shot.  I'll start by looking at the existing usages
>> in C of direct DBus communications.
>
> Could you send me a pointer?

Sure.  One thing I'm interested in is connecting Indium with
WebKitGTK+.  The remote inspector server starts a p2p dbus connection,
and the client connects to it, see:

https://trac.webkit.org/browser/webkit/trunk/Source/WebKit/UIProcess/glib/RemoteInspectorClient.cpp#L160

Cheers,
Nico

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Re: DBus binding & direct connections (p2p)?

[Michael Albinus]

Nicolas Petton <nicolas@petton.fr> writes:

> Michael Albinus <michael.albinus@gmx.de> writes:
>
>>> Yes, I'll give it a shot.  I'll start by looking at the existing usages
>>> in C of direct DBus communications.
>>
>> Could you send me a pointer?
>
> Sure.  One thing I'm interested in is connecting Indium with
> WebKitGTK+.  The remote inspector server starts a p2p dbus connection,
> and the client connects to it, see:
>
> https://trac.webkit.org/browser/webkit/trunk/Source/WebKit/UIProcess/glib/RemoteInspectorClient.cpp#L160

Well, this is g_dbus_connection_new_for_address, see
<https://developer.gnome.org/gio/stable/GDBusConnection.html#g-dbus-connection-new-for-address>.

The gio implementation of D-Bus offers functions, which are not
available in libdbus-1.so, the reference implementation we use in Emacs.

> Cheers,
> Nico

Best regards, Michael.

Re: DBus binding & direct connections (p2p)?

[Nicolas Petton]

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Michael Albinus <michael.albinus@gmx.de> writes:

>> https://trac.webkit.org/browser/webkit/trunk/Source/WebKit/UIProcess/glib/RemoteInspectorClient.cpp#L160
>
> Well, this is g_dbus_connection_new_for_address, see
> <https://developer.gnome.org/gio/stable/GDBusConnection.html#g-dbus-connection-new-for-address>.

Yes, I saw that.

> The gio implementation of D-Bus offers functions, which are not
> available in libdbus-1.so, the reference implementation we use in
> Emacs.

Ok, thanks.  I wasn't aware that the gio implementation was something
different entirely, I thought it was just wrapping libdbus.

Then I'll have to check what the Python binding is using, because the
following works just fine in Python 3:

  import dbus

  connection = dbus.connection.Connection("tcp:host=localhost,port=1234")
  res = c.call_blocking(None, "/org/webkit/Inspector", "org.webkit.Inspector", "SetupInspectorClient", "ay", [dbus.ByteArray()])
  str = "".join(chr(byte) for byte in res)

Cheers,
Nico

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