GSoC10 Infosession — numbers and pictures

A little bit delayed there it go some info about the talk we did at Unicamp about GSoC10. There was about 70 attendees and the session lasted 1h30. The first 20-30 min were spend on presenting the GPSL FOSS Seminars Series — since this was the first talk of the series for this semester — and going through the official program slides. The remaining hour or so was spent with an open chat between speakers and  the attendees mixed with each speaker talking about his personal experience with the program. There were 8 speakers in total:

And now, as promised in the title, pictures:

GSoC2010 Info Session on University of Campinas

Me and other several past students and mentors are going to give an informational session about Google Summer of Code at the University of Campinas.

The idea is to do a brief talk about what the program is and tell about our personal experiences on past-years programs, but also answer questions and chat aftwards, so it’s gonna be a kind of pre-meetup. All past and wanna-be GSoCers in the area are welcome!

Universidade Estadual de Campinas – UNICAMP
March 3rd, 16h
Room CB04

Handsfree HF role

Here at ProFUSION we’ve been helping people at BlueZ, oFono, and PulseAudio to add support for the Handsfree-unit role of the bluetooth Handsfree Profile to Linux. We had some nice progress this week that lead us to make a video showing what we have so far. It’s still not merged upstream, and definitely not user friendly. But hey, it works!

Kudos to Gustavo Padovan for implementing most of this support into BlueZ and oFono.

D-Bus 1.3.0 deb packages for ubuntu

In the need to update D-Bus to a version with fd-passing support, I’ve updated the ubuntu packages for D-Bus 1.3.0, since I couldn’t find any. If you also need to update your D-Bus, you can get the packages here. Use them at your own risk, since it has been tested only on my machine.

1, 2, 3, 4, A2DP Stream

After a few people asking me how to use the A2DP Sink with BlueZ, I’ve decided to write this mini-tutorial with a step-by-step on how to establish a A2DP stream from any device to a BlueZ-enabled host.

Before we start the hands-on, let’s see a little bit of nomenclature. In our use-case we have an stream being transmitted between two devices through a pipeline. Our pipeline is constructed of the remote host, BlueZ and PulseAudio. Each element of this pipeline has a Source (SRC) and a Sink (SNK) interface. The stream is handled between different elements by being sent from one element’s source to another element’s sink. So, the big picture of our pipeline is something like this (with the stream being represented by an arrow):

Remote-SRC ----> SNK-BlueZ-SRC ----> SNK-PulseAudioBT-SRC

With the PulseAudio bluetooth source being available for applications to connect to it and serve themselves with fresh, just-decoded PCM frames of pure stereo audio. In our example, we gonna add another element to the pipeline tho. In order to able to hear the audio we’re receiving, we gonna connect the PulseAudio bluetooth source to a PulseAudio ALSA sink which pushes the audio out through our soundcard speakers.

PulseAudioBT-SRC ----> SNK-PulseAudioALSA ----> SoundCard

So after these lines on theory, let’s get out hands dirty. First of all, you need a recent version of BlueZ and PulseAudio. BlueZ 4.46 and PulseAudio 0.9.16 should be enough, but I strongly recommend getting the newest releases available by the time you read this. Right now the most recent releases are BlueZ 4.58 and PulseAudio 0.9.21.

  1. PulseAudio must be running with module-bluetooth-discover loaded;
    • This module is automatically loaded on startup with the default configuration;
    • If it’s not loaded you can use pactl to load it manually or configure PulseAudio to load it on startup in /etc/pulse/default.pa;
  2. Enable the Source interface on BlueZ:
    • edit /etc/bluetooth/audio.conf and add the following line: Enable=Source ;
    • restart bluetoothd;
  3. Pair both devices;
  4. On the object path representing the remote host, on org.bluez D-Bus service, call the org.bluez.AudioSource.Connect() method;
    • For the connection to succeed you’ll probably have to grant access on the remote host;
    • When the connection is established, a new card should show up on PulseAudio with one source available;
  5. Connect PulseAudio bluetooth source to PulseAudio ALSA sink;
    • load-module module-loopback source=<name> sink=<name>
    • You can use the line above to load the module-loopback, using pactl (on the command line) or inside pacmd shell;
    • To find out the name of the source and the sink, you can use the commands list-sources and list-sinks inside pacmd shell;
    • This step is only needed if you want to send the audio coming through A2DP to your speakers.

It’s important to remember that the current implementation is working but could see some improvements, so expect to hear some glitches if you go through signal variation. Happy bluetooth audio streaming!

BlueZ talk at Unicamp

Me and Gustavo Padovan are presenting a talk about BlueZ at a series of seminars about free software hosted at University of Campinas (Unicamp). If you’re nearby come to join us 16h at CB01 today. We gonna give a brief overview of bluetooth and BlueZ, talk about our contributions to the BlueZ project, and show a little about how to use the BlueZ API inside your applications or as an end-user.

If you’re far away from Campinas, you can at least take a look at the slides: BlueZ talk

BlueZ now has A2DP Sink support

Last week was the midterm evaluations for GSoC and also the very same week when my patches were merged upstream into BlueZ. Most of the work was to adapt the existing Source functions to support both Source and Sink and to add Sink logic to the A2DP Server.

There is now a new Source interface on D-Bus, similar to the Sink interface, than can be used to access the Sink functionality. It may sound odd the Sink being accessed through an interface called Source, but in this case it actually acts as a sink on the air interface (receives audio stream from other bluetooth device) and as a source on the application interface (generates audio stream to applications).

Unfortunately, that’s not enough for one to be able to stream audio to a BlueZ device. Right now there is no client able to handle the incoming stream. The good news are that this is part 2 of my SoC project, to implement some clients outside BlueZ to handle this stream. I’m gonna start with PulseAudio, since I’ve implemented the bluetooth sink module on it last year and am more familiar with it’s implementation. After that, I’ll probably implement an ALSA client too.

So what’s the current implementation useful for? From an users perspective, not much. But it shows we are on the way to have it done. Right now it’s possible to connect to the audio sink and put it on STREAMING state, but it doesn’t know how handle the stream and disconnects after a few packets. I’ve tested it with two bluetooth adapter on my laptop and also trying to stream from an Android phone to the laptop.

The Source interface is disabled by default, so if want to test it, make sure to add an “Enable=Source” line to your audio.conf. The code is available on bluez git repo and will be on release 4.46.

FISL10 Programming Arena

This is the third edition FISL organizes a programming contest called Programming Arena. This name came from the original idea that the participants had to stay inside a glass room in the middle of the event area without being allowed to exit (except for bathroom, which they had go accompanied). This year some of this restrictions were relaxed and participants could go in and out as they wish, with the only restriction they had to arrive before 10AM every day of the competition.

The competition consists in two phases: Qualifying, in which participants have to discover a nine letter code that’s needed for the inscription, and Insanifying, when participants spend three days working on a challenge proposed by the organization.

I wasn’t very excited about it at the beginning, since I didn’t want to spend a lot of time working on discovering the code and then spend almost the whole FISL programming (the same thing I usually do every day). But then, some weeks after the qualifying had started, they published a notice telling that no one had found out the right code yet. It was a cold friday night, I had gone to spend the weekend at my parents house, and after having some fondue and wine for dinner, I grabbed the remaining half bottle of wine, sat with my laptop by the fireplace, and decided to give it a try. I already knew that there were some hints for the code as comments in the HTML source of first link in this post, and then discovered one additional hint in the source of the second link on this post. About 4:00 in the morning, I’ve managed to find out that the code was hidden in a pseudo-echo server at arena.softwarelivre.org:1996, that when string “peixe” (a keyword on the Tux profile at the softwarelivre.org social network) is inputed, responds with a cyphered string. During the whole process, I had been chating with Padovan on IM, since he had spent some time working on the problem with his housemate, a few days before, with no success. We both agreed that it should be some simple cypher, some sort of substitution-based cypher, since there was no hints on cypher algorithms so far and that the string was short and had some blank spaces, resembling a phrase of a few words. At that moment Padovan stopped what he was doing before and said: “Let’s break that cypher!”. So I continued working on trying to find a key hidden somewhere else while he wrote a script for a dictionary-based attack using the Firefox portuguese dictionary. Since one of the words had 2 letters that repeated, he aimed at it and no much time latter he could guess that word: inscricao, the ascii-only version of the word inscription in portuguese (“inscrição”). With the mapping of this word and guessing some other letters we could find out almost the whole phrase, missing only one letter, exactly in the middle of the 9-letter code. There were only 12 letters not matched, so we could had tryed the inscription using brute-force, but we decided to have some sleep and try a bit more in the next day. In the next morning, someone had find out the key and posted it on a blog. The key was hidden as the TXT DNS record of arena.softwarelivre.org, and had the matching for the whole alphabet. The whole decyphered phrase was “parabens seu codigo de inscricao eh goosfabra” (congratulations your inscription code is goosfraba).

The second phase, during FISL, was even more interesting. The challenge was to implement DNSCurve, a security extension of the DNS protocol, both in a forwarder (server) and in a cache (client). Before the implementation started we saw a panel discussion about DNSCurve vs DNSSEC with Daniel J. Bernstein, the creator of DNSCurve (and also of djbdns and qmail). DJB was also responsible for judgin the code produced during the arena. There was a draw to group the participants in three groups of three people and one group of two people, and luckily me and Padovan ended in the same group, together with Rodrigo Tjäder, from UFSM. After three days of work, we had the following work done:

(1) DNS Server — pymdscurve.tar.bz2

We based our implementation on pymds, a modular python DNS server licensed under the MIT license. It’s a standalone DNS server, in terms it doesn’t resolve any names it doesn’t know. For the NaCl (crypto) functions, we used the slownacl lib from dnscurve. Despite it doesn’t says on the website, we contacted the authors (both Matthew and Angel) and both of them told us it’s public domain and a note on the project page is missing. Matthew even added a README to the code which says it’s public domain and updated some code on the lib to make it compliant with NaCl newer spec on DJB’s website.

(2) DNS Cache

For the cache we tried two different approaches.

(i) PyDNSCacheCurve.tar.bz2 — First we added the DNSCurve messages to PyDNSCache, which is a very simple DNS cache written in python and intended to be used as a python library. This code didn’t had any license note on the project page either, but we contacted the author and he licensed it under Creative Commons Attribution 3.0 United States License. Since it’s just a cache of DNS information, it used
gethostbyname() from the socket module. We changed it to use a function we implemented, gethostfromDNS(), to send the necessary DNS messages to get the information from a server. For the cryptography part we’ve also used slownacl from dnscurve. We didn’t implemented the ability to resolve names recursively on PyDNSCache, so we hardcoded the server public key inside the code.

(ii) dnspythoncurve.tar.bz2 — Since solution (i) was unable to resolve names recursively, we decided to use dnspython, which provides a lot of helper functions to deal with DNS. We’ve added DNSCurve extensions to it and also added a recursive resolver. dnspython is released under a BSD-style license. Since recursive resolution works we can get the server name to check if it a DNSCurve enabled server and, if so, obtain it’s public key. We’ve tested pymdscurve and dnspythoncurve under a scenery with two servers, one configured as authority for .com and other as authority for example.com, in order to test recursive resolution. Both config files are shipped in pymdscurve package.

So much work worth every line of code. Besides learning a lot and having fun, we also won the contest, getting an Android Dev Phone 1 for each participant of the team as a stipend (thanks google!) and lots of good words about our implementation from DJB. I will son add some photos and a video of the winners announcement.:

Explaining our implementation

The winner team with DJB

 

We gonna send patches back to all projects we’ve added code to. We have also added some code to some dns helper functions on dnscurve, outside of slownacl. The source code of our implementation can be found at http://www.las.ic.unicamp.br/~joaopaulo/dnscurve/ http://www.las.ic.unicamp.br/~jprvita/dnscurve/.

Oda al vino

La atracción empieza a la primera mirada: las curvas de la botella cubierta por la ropa-rótulo intentan llamar a la atención. El color, todavía medio oculto, despierta la curiosidad de aquello que alguna vez ha probado sus sabores. La aproximación debe ser muy suave. El toque a la botella terno, pero firme. El cuidadoso y osado saque del corcho seguido del manso servir a la copa. Será ese el sitio donde él, el vino, irá proporcionar los placeres más indescriptibles a las bocas que sepan apreciar sus encantos y atender sus caprichos.

GSoC09 is up and running!

I’m glad to announce that I was accepted for one more Google Summer of Code program. I’m going to work with BlueZ again, this year to implement the A2DP sink profile. Full proposal following.

Abstract

This project is to implement the Sink role on BlueZ, according to the A2DP specification v1.2. This role provide means to receive an audio stream coming from an audio Source on the same piconet. It’s very important, and can add several use cases for the Linux bluetooth stack, like Linux to Linux streams, bluetooth microphones support or using a Linux device as bluetooth speakers. It’s also a mandatory feature for an implementation to be full compliant with A2DP v1.2.

Content

Have you worked on a Linux system before?

I’ve been working with Linux since 2002, when I’ve started the Computer Engineering undergrad. In the beginning I just did the school projects on Linux, but since the middle of 2002 it’s my main system. By that time I had Conectiva on my home computer, RedHat on the school, and Slackware on my home router. After a few years I got in touch with Gentoo, and I liked so much the idea that it became my main distro. In addition, I’ve also started working on a project at University of Campinas, to make a Linux distribution for Itautec, a brazilian IT company, which was Gentoo based. Nowadays I’m using Ubuntu in my laptop, because of the speedy install and no need of much tweaking, so I have more time to work with other projects, but I’m confortable using and administrating any distribution.

Have you contributed to a open source project? if yes, please provide the details

My first contribution was a little bit frustrating, since I never got any answer (a two lines patch to python-dialog – http://sourceforge.net/projects/pythondialog/ – to support one dialog that was missing). After that I’ve made some performance improvements in ImageMagick and DevIL using OpenMP, both of them being accepted upstream. I was also accepted and successfully completed a GSoC 08 project with BlueZ to make the bluetooth audio client for PulseAudio. All these successful experiences were outstanding and all of them (now including the never answered patch) were very useful to learn about the community and how to work with open source model. Now I’m looking for a job with open source, and also plan to continue contributing to some projects of my personal interest. Right now I’m following the BlueZ and PulseAudio mailing lists.

What is your educational Qualification (grad/under-grad) ?

I’m a Computer Engineer, majored on University of Campinas (Unicamp), Brazil. I’ve started my master degree on Computer Science studies last year, on the same university, working with visualization of concurrent algorithms. I’ve also been working as a teaching assistant of the Operating Systems course in my university, for two semesters. The last time we proposed to the students to make some changes in a memory filesystem that was developed for them to work on. This activity is giving me a bit more of knowledge on the Linux kernel, that maybe can be helpful to complete this project.

Why do you want to do a project involving Bluetooth/BlueZ ?

I’ve already been a GSoC student with BlueZ and was a very good experience. I’ve worked with the same protocol of this project, so I already have some knowledge on it. The initial motivation to choose BlueZ last year was because it’s something that I use on my daily activities (I have a bluetooth mouse on my notebook and a headset that I use to talk with friends and family on VoIP systems) and because I’m very enthusiastic about wireless devices and mobility. Besides that, I always had interest about network-related stuff.

If your application is accepted will it be a part of your graduation process or it will it be just for hobby?

If I get accepted to this project, it will not be part of my graduation process.

Give us an *estimative* of your schedule (exams period, etc.) and how much time you would be able to dedicate to the project.

The project will be divided into 5 activities. I plan to work around 20h per week with this project, during the whole program. The other 20h of a working week are going to be dedicated to my Master degree program, but it’s flexible enough to allow me some extra hours near deadlines, if needed.

1. Re-read the A2DP specification v1.2 from bluetooth.com (and related specs like AVDTP, GAVDP etc) and understand it’s current implementation. The A2DP Sink role is the dual of the A2DP Source role, with the main difference being the implementation of the “Receive Audio Stream” procedure, described in Section 3.2.2 of the spec, instead of the “Send Audio Stream procedure”. Together with this study of the spec, the code under the audio dir on BlueZ source code will be studied, to learn exactly what’s implemented and which files implement each part.

2. Maybe reorganize some code to enable reuse. If there are some already implemented parts for the Source which the Sink is also going to use (likely the AVDTP signaling procedures), the idea is to use the same implementation to minimize bugs and easy the maintenance.

3. Find out which are the missing parts and procedures to full support the Sink role and implement them.

4. Create the API for clients that want to obtain the audio received by BlueZ and export it via D-Bus, as it already done for the Source profile (which acts as a sink for software clients like media players).

Community Bounding Period (April 20th – May 22nd): Activities 1 and 2 are going to be performed on this period.

Coding Phase I (May 23rd – July 12nd): Most of activity 3 is going to be performed on this period.

Coding Phase II (July 13rd – August 17th): Finish of activity 3 and activity 4 are going to be performed on this period.

Future Work: If there is enough time, or as a future project, I would like to implement a client that uses the bluetooth audio somehow, in order to test the Sink implementation. My first idea is to do so on PulseAudio, as I’ve already worked with it before, but other ideas are also welcome.