I spent the last weeks work on my Google Summer of Code project. Code for items 1, 2 and 3 of the roadmap that I posted here[1] 3 week ago is almost done and in process to be merged into bluetooth-testing. Now I’m starting to work on item 4. First I’ll will look to support REJ S-frames and implement retransmission of L2CAP packets.
[1] http://padovan.org/blog/2009/07/bluez-first-patch-was-merged/
I was looking for a pastebin plugin for vim. I’ve found one[1], but it was not working, then I fixed it. The plugin is here[2]. And if is useful to you there is a git repo[3] too.
How to use:
Put it into ~/.vim/plugin to autoload the plugin every time you open VIM. You can also source it manually:
:source /path/to/pastebin.vim
You can set your favorite pastebin site and your name editing the pastebin.vim
From [1]: “To use the script is very simple. Just visually block (Shift-v) the lines of code you want to send to the Pastebin and enter the command :PasteCode. The blocked text will be sent to the Pastebin and the new URL will be shown on the Vim statusline.”
[1] http://djcraven5.blogspot.com/2006/10/vimpastebin-post-to-pastebin-from.html
[2] http://www.las.ic.unicamp.br/~gustavo/pub/vim/vim-pastebin/plugin/pastebin.vim
[3] http://github.com/pao/vim-pastebin/tree/master
I spent the last days studying how Enhanced Retransmission Mode(ERTM) should be implemented on L2CAP. Marcel recommended me to look at TCP[0] code. ERTM on L2CAP is very similar to TCP. Both have retransmission support, recovery error, acknowledgment of packets and timers.
That means that ERTM implementation will look like TCP implementation[1] on Linux. So, there is no need to write ERTM from scratch, I’ve already started to code and I’m basing my code on TCP code to get started with ERTM.
[0] http://en.wikipedia.org/wiki/Transmission_Control_Protocol
[1] http://vger.kernel.org/~davem/tcp_output.html
The first patch, that add support to L2CAP Enhanced Retransmission, was merged into bluetooth-testing yesterday. The patch adds support to configure L2CAP connections in Enhanced Retransmission(ERTM) and Streaming Modes besides the Basic Mode. Streaming Mode will not be implemented now, but it’s better make all configuration code for the 3 modes instead only ERTM and Basic Mode. This way we don’t need to touch twice into configuration code. The commit is here and that is the commit message:
Bluetooth: Add configuration support for ERTM and Streaming mode
Add support to config_req and config_rsp to configure ERTM and Streaming
mode. If the remote device specifies ERTM or Streaming mode, then the
same mode is proposed. Otherwise ERTM or Basic mode is used. And in case
of a state 2 device, the remote device should propose the same mode. If
not, then the channel gets disconnected.Signed-off-by: Gustavo F. Padovan <gustavo@las.ic.unicamp.br>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Now I’m going to implement support to send and receive I-frames and S-frames. Some part of the code for that . First I’m going to add support to transmissions with txWindow = 1 (i.e., only one packet can be sent per time without acknowledgment from the other side) and no retransmission support and I intend to finish it during this week.
Here is a quick roadmap for my work:
I expect that until end of August finish all this topics. So, let’s hack. =)
Durante a décima edição do Fórum Internacional do Software Livre [0] em Porto Alegre – RS, Brasil participei da Arena de Programação do evento. O desafio desse ano foi implementar um servidor e um cache DNS que suportasse o DNSCurve[1], protocolo de criptografia para DNS criado por Daniel J. Bernstein[2], também criador do djbdns[3]. O desafio foi proposto e julgado pelo djb.
A arena durou 3 dias. Às 22 horas do terceiro dia deveríamos entregar o servidor e o cache com DNSCurve para o Daniel. Meu grupo era formado por mim, pelo João Paulo Rechi Vita[4], que também é aluno aqui da Unicamp e assim como eu, está no Google Summer of Code pelo projeto BlueZ. E por Rodrigo Exterckötter Tjäder, aluno de Ciência da Computação da UFSM – Universidade Federal de Santa Maria.
Ficamos sabendo o que teríamos que fazer apenas no início do primeiro dia, então passamos as primeiras horas descobrindo do que se tratava o DNSCurve (principalmente eu, que não estudei Redes formalmente na Unicamp ainda). Após entendermos o DNSCurve fomos atrás de implementações de DNS para tomarmos como ponto de partida para nossa implementação. Partimos preferencialmente para implementações em python, pois seria bem mais rápido e tranquilo desenvolver.
Rechi Vita encontrou uma implementação de servidor DNS em python, chamada pymds[5] e uma implementação de cache chamada PyDNSCache[6]. Ambas as implementações são extremamente pequenas, o que facilitou o nosso entendimento e a expansão desses códigos para suportar o DNSCurve.
Para a parte cripotográfica do DNSCurve usamos a slownacl[7] biblioteca que implementa a todo calculo criptográfico do DNSCurve. Acompanhavam a slowsalt pequenas bibliotecas para manipulação pacotes DNS, isto é, funções prontas pra descriptografar e criptografar pacotes DNS que são enviados e recebidos pelos servidor e cache.
Passamos os dois primeiros dias integrando esses 3 códigos: pymds, PyDNSCache e slownacl. No final do segundo dia tinhamos um servidor e um cache funcionando para o envio e recebimento de pacotes. Mas esse cache nao resolvia nomes recursivamente e como ia dar muito trabalho implementar isso no nosso cache, resolvemos abandoná-lo e partir para uma nova implementação de cache usando a biblioteca dnspython[8]. Com esse novo código foi possível fazer o cache resolver nomes recursivamente e consequentemente conseguir pegar a chave pública do servidor DNS.
O Resultado desses três dias de maratona foi recompesado com a vitória. Nossa solução foi eleita a melhor e recebemos um celular G1 rodando Android cada e muitos elogios do djb sobre o nosso código. =)
Nosso código está aqui[9] e abaixo coloco a descrição sobre a implementação que enviamos ao Daniel junto com nosso código:
We implemented the two proposed parts separately.
(1) DNS Server — pymdscurve.tar.bz2
We based our implementation on pymds [5], 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 functions,
we used the slownacl lib from dnscurve [1]. Despite it doesn’t says on
the website, we contacted the authors (both Matthew and Angel) and
both of them told us the is 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 spec (article on your website).
(2) DNS Cache
For the cache we tried two different approaches.
(i) PyDNSCacheCurve.tar.bz2 — First we added the DNSCurve messages to
PyDNSCache [6], 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 [1]. 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 [8], 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 [4] 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.
We plan to send patches back to all projects we’ve added code to. We
have also added some code to some dns helper functions on dnscurve
[1], outside of slownacl
[0] http://fisl.softwarelivre.org
[1] http://dnscurve.org
[2] http://cr.yp.to/djb.html
[3] http://cr.yp.to/djbdns.html
[4] http://jprvita.wordpress.com
[5] http://sourceforge.net/projects/pymds/
[6] http://www.rbgrn.net/projects
[7] http://github.com/mrd/dnscurve/tree/master
[8] http://www.dnspython.org/
[9] http://www.las.ic.unicamp.br/~joaopaulo/arena/