Monthly Archives: October 2006

Building obex-method

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I published a Bazaar branch of the Nautilus obex method here:

http://bazaar.launchpad.net/~jamesh/+junk/gnome-vfs-obexftp

This version works with the hcid daemon included with Ubuntu Edgy, rather than requiring the btcond daemon from Maemo.

Some simple instructions on building it:

  1. Download and build the osso-gwobex library:

    svn checkout https://stage.maemo.org/svn/maemo/projects/connectivity/osso-gwobex/trunk osso-gwobex

    The debian/ directory should work fine to build a package using debuild.

  2. Download and build the obex module:

    bzr branch http://bazaar.launchpad.net/~jamesh/+junk/gnome-vfs-obexftp

    There is no debian packaging for this — just an autogen.sh script.

It should work on other distributions, but I haven’t tried it. The main requirement is bluez-utils 3.7, and that -x is passed to hcid to enable the org.bluez.RFCOMM interface.

Still to do is cleaning up the obex:/// listing of bonded devices, so that it serves desktop entries rather than symlinks, so that it is usable in Nautilus. This would also make it easier to show the device names to the user and get nice icons.

Playing Around With the Bluez D-BUS Interface

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In my previous entry about using the Maemo obex-module on the desktop, Johan Hedberg mentioned that bluez-utils 3.7 included equivalent interfaces to the osso-gwconnect daemon used by the method. Since then, the copy of bluez-utils in Edgy has been updated to 3.7, and the necessary interfaces are enabled in hcid by default.

Before trying to modify the VFS code, I thought I’d experiment a bit with the D-BUS interfaces via the D-BUS python bindings. Most of the interesting method calls exist on the org.bluez.Adapter interface. We can easily get the default adapter with the following code:

import dbus

bus = dbus.SystemBus()
manager = dbus.Interface(
    bus.get_object('org.bluez', '/org/bluez'),
    'org.bluez.Manager')

adapter = dbus.Interface(
    bus.get_object('org.bluez', manager.DefaultAdapter()),
    'org.bluez.Adapter')

At this point, it is possible to perform discovery:

import dbus.glib
import gtk

def remote_device_found(addr, class_, rssi):
    print 'Found:', addr
def discovery_complete():
    gtk.main_quit()

adapter.connect_to_signal('RemoteDeviceFound', remote_device_found)
adapter.connect_to_signal('DiscoveryCompleted', discovery_completed)

adapter.DiscoverDevices()
gtk.main()

It is also possible to configure periodic discovery, which will send signals about devices that get found, disappear, or change name, so we could easily implement the obex: directory listing that shows all the devices found that support OBEX-FTP. One thing that isn’t clear from the API documentation is what happens if multiple programs try to start or stop discovery at the same time. It looks like the second program will get a org.bluez.Error.InProgress error when it tries to begin discovery. Ideally discovery would stay active til the last program interested in the results closed. Maybe I am misunderstanding it a bit and you can actually use the interface in this mode.

When we want to actually do OBEX-FTP with the device, we can establish the rfcomm connection:

rfcomm = dbus.Interface(
    bus.get_object('org.bluez', manager.DefaultAdapter()),
    'org.bluez.RFCOMM')

# will return e.g. /dev/rfcomm0
devname = rfcomm.Connect(bluetooth_address, 'ftp')

# communicate with the phone via the new rfcomm device

rfcomm.Disconnect(devname)

So it should be possible to modify obex-method to function with only the daemons included in Ubuntu Edgy. All that’s left is to do the actual work 🙂.

bzr branch https://launchpad.net/products/foo

One of the things we’ve been working on for Launchpad is good integration with Bazaar. Launchpad provides a way to register or host Bazaar branches, and nominate a Bazaar branch as representing a particular product series.

For each registered branch, there is a branch information page. This leads to a bit of confusion since Bazaar uses URLs to identify branches, so people try running bzr branch on a branch information page. We also get people trying to branch the product or product series pages.

There were two ways we could address this problem: (1) do more to encourage people not to do this, or (2) make bzr branch do what the user meant it to do. The second option is the more user friendly, so that’s what we chose. This just left the problem of how to implement it efficiently.

The obvious way to get this to work is with a simple HTTP redirect for files under the .bzr/ directory. Unfortunately this would result in Bazaar hitting the Launchpad webapp for every file in the branch which is not desirable (each request results in a number of database accesses, which would add unnecessary load to the system). There is a Bazaar bug about improving this so that it would use the new location after the first redirect. This bug was the main reason for not implementing the feature previously.

While playing around with things a bit, I realised that Bazaar already had the features needed to implement the redirects and they have been there since 0.8.

In Bazaar 0.8, the concept of a lightweight checkout was introduced. This is just a working tree plus a reference to a branch stored elsewhere. You can perform most operations on the branch from the checkout directory that you can do from the real branch directory. So what happens if you publish the “branch reference” part of a lightweight checkout on the web? It turns out that they work fine, so that’s what I used for launchpad.net.

So with the change in place, the following commands will all give you a copy of the Bazaar webserve plugin:

bzr branch http://bazaar.launchpad.net/~bzr/bzr-webserve/webserve-dev
bzr branch https://launchpad.net/people/bzr/+branch/bzr-webserve/webserve-dev
bzr branch https://launchpad.net/products/bzr-webserve/trunk
bzr branch https://launchpad.net/products/bzr-webserve

Furthermore, they will all record the http://bazaar.launchpad.net/ URL as the parent branch, so future bzr pull commands will go directly to the branch.

OBEX in Nautilus

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When I got my new laptop, one of the features it had that my previous one didn’t was Bluetooth support. There are a few Bluetooth related utilities for Gnome that let you send and receive SMS messages and a few other things, but a big missing feature is the ability to transfer files to and from the phone easily.

Ideally, I’d be able to browse the phone’s file system using Nautilus. Luckily, the Maemo guys have already done the hard work of writing a gnome-vfs module that speaks the OBEX FTP protocol. I had a go at compiling it on my laptop (running Ubuntu Edgy), and you can see the result below:


Browsing files and viewing images stored on my phone

There are a few rough edges:

  • While I can get a list of discovered devices at the location obex:///, it displays the raw bluetooth addresses rather than device names. Furthermore, the files displayed here are symlinks to the appropriate obex://[$ADDRESS]/ URLs, which aren’t that useful given that gnome-vfs does not support symlinks pointing to other schemes or authorities. This could be fixed by generating .desktop files instead, which would make it possible to provide nice icons too.
  • Can’t rename files. This might be a limitation of the OBEX FTP protocol though: the man page for the command line obexftp client says moves only work with Siemens phones.
  • Doesn’t seem to handle devices disappearing very well — when I tried turning off Bluetooth on my phone and told Nautilus to reload the window, Nautilus hung and stopped redrawing til I turned Bluetooth on again.

I don’t have any ready made binaries for others to try at this point. Below are some notes for anyone else who wants to try building it:

  • You’ll need the osso-gwconnect, osso-gwobex and osso-gnomevfs-extra modules. I grabbed them from Maemo Subversion.
  • When trying to build a debian package for osso-gwconnect, I removed the libosso-dev and mce-dev build dependencies, and made an equivalent change to the configure arguments in debian/rules. The configure script also asks for BlueZ 3.2, while Edgy only has 3.1. The package built fine when I decreased the minimum version requirement.
  • You’ll need to build osso-gwconnect and osso-gwobex before osso-gnomevfs-extra. There are a few build problems with this last module:
    1. The autogen.sh script asks for automake 1.8.x specifically, but works fine with the current 1.9.x releases.
    2. I had to change a dbus_connection_disconnect() call to dbus_connection_close() in obex-module/src/om-dbus.c.
    3. You only need to build the obex-utils and obex-module directories. There are other bits in this module that you probably don’t want, and some bits like the replacement GTK filesystem backend didn’t build for me.

With a little bit of work, this would fit into the main Gnome desktop quite well. When talking to Bastien a while back, he said that the extra dbus daemons shouldn’t really be necessary, so it might be worth trying to bypass them.