Accessing WebDAV calendar from commandline

March 11, 2011 in open source, programming, projects, python, software

Have you tried to access Zimbra or Google Calendar from command line? I have. And I couldn’t find any normal command line client that would be able to read and write these calendars, display alerts etc. Well there is a googlecl project, but it’s specific for Google Calendar and is not using standard WebDav iCal access methods.

Thus I set out to create console application that would fulfil my needs. What are my requirements?:

  • Read/write access to Google Calendar and Zimbra (at least)
  • Multiple remote calendars
  • Working alerts
  • Nice ncurses UI (but also ability to just display some info and quit)
  • Correct handling of timezones
  • Integration with mail client (open ics files received by email)
  • I guess a lot more :-)

I had a look at existing python modules that work on iCalendar, WebDAV and combination of both. There are quite a few of them, but I just didn’t like their APIs. They were usually complex and required knowledge of iCal specification. So I decided to create simplified module that would be easy to understand (even if not so powerful).

I named the project pywebcal (yes, unimaginative) and it’s now on github. I would LOVE some input. I know it’s far from perfect (or complete), but let’s see. For now it offers read-only support for Zimbra (Google should work too but I haven’t tested in a while).

You can have a look at the example directory that contains one simple example you can run in-place and see if it works :-) I did my best to create proper test cases covering problems with timezones and whatnot, and this helped me quite a lot with recent refactoring. I am now using vobject library as my backend and it is rather nice to use. Plan is to allow access to vobject components so that my simplified API is not preventing some advanced modifications.

Next step is obviously to start working on ncurses application itself. Anyone wants to help?

Automatic squashing of last git commits

December 10, 2010 in git, howto, open source, software

I have written before about my workflow in Fedora. This workflow includes a relatively high number of rebasing where I squash last two commits into one. I use it to quickly refine and test patches. My history then usually looks something like this:

$ git log --format=oneline --decorate=no | head -3
2db8eacd7f7c20be88824caae5f5af16b9520d34 temp
443bb0f019c87f0090bb9da295a019c0eee23729 Add conditional BRs to enable ff merge between f14
b4c602f9f044598544cff3d68710f68b9447ea0f Fix installation of pom files for artifact jars

Where 443bb0f is my first attempt at the fix and 2db8eac is a fixed fix :-). Before pushing this into upstream repository I usually squash last two commits to look like this:

$ git log --format=oneline --decorate=no | head -2
f852c3e260d21bbc642f861e6fa6ea62caa7b69b Add conditional BRs to enable ff merge between f14
b4c602f9f044598544cff3d68710f68b9447ea0f Fix installation of pom files for artifact jars

I used to do it manually, but I do it often enough it made sense to automate this. So without further ado:


export EDITOR="sed -i '2s/pick/squash/;/# This is the 2nd commit message:/,$ {d}'"

git rebase -i HEAD~2

Save this somewhere inside your $PATH and chmod +x (or set up shell alias). Then just running this will automatically squash last two commits, using HEAD~1 commit message and discarding last commit message. No warranties though :-)

Edit: Benjamin suggested to use “fixup” instead of “squash”. This is new thing in git 1.7+. For more information on this see this blogpost.

Local DNS caching – just do it already!

November 11, 2010 in en, network, open source, problem, software

I recently encountered weird problems with my network connection at home. Everything worked, but was unbelievably slooooow. Ping showed times of ~30 ms, but I could easily see it took more time for those packets to go there and back.

I took me some time to figure out what was happening. Looking back, checking DNS server should have been one of the first things to do. Seems like first DNS server provided by my provider has been down. That meant that every DNS query timed out and then went to the second DNS which got me my response. For some reason ping did DNS query before every new package being sent. That explains its weird behaviour.

This problem got me to finally install local caching dns. I was thinking about doing it before, but I never got around to do it until now. I always thought it’s gonna be a few-hour nightmare. Now I blame my previous experience with bind ūüėÄ For simple local caching bind would be overkill, so I chose dnsmasq. Using it was as simple as installing, running dnsmasq and executing

$ echo 'nameserver' > /etc/resolv.conf.head

From that point on every resolv.conf file generated by dhcpcd will have my local DNS as first DNS server to try. For this time you can add it there manually. Then you can verify your setup works by running following command twice in a row:

$ dig

First execution should have Query time: XX msec with XX being few tens of miliseconds. Query time for second run should be zero or very close to zero.

Congratulations. You have your very own caching server. Who knows…maybe you’ll even notice some improvements in your network connection :-)

PyQTrailer revisited

November 10, 2010 in en, fedora, open source, projects, pyqt, python, software

Some time ago, I wrote about my little project: trailer downloader. Apple is still not very open-source friendly as far as its trailer website is concerned. So all points I made in my original post still stand. To my surprise this little project is still alive and kicking, with new ideas for improvements coming and coming :-). What is even more important: it seems that so far no breakage happened due to apple changing something on the web.

Since the first version I released almost 6 months ago several new features appeared. Some of them include:

  • Parallel downloading of trailers
  • Ability to run movie player (mplayer, vlc, etc) without downloading file to HDD
  • Lot of customisation/performance options added
  • Working support for trailer search
  • Localisation support
  • Python 3 support

Latest version (0.5.2) is available in Gentoo repositories already, and should hit Fedora updates in next day or so (this will be delayed due to new package acceptance criteria though). Enjoy.

Python3, PyQt4 and missing QString

October 20, 2010 in howto, open source, programming, pyqt, python, qt

As I was recently adding support for Python 3 to my little trailer downloader application that I mentioned before (PyQTrailer) I encountered a strange problem with PyQt4 that only occurred in Python 3.

Let’s take this simple python example:

$ python
>>> from PyQt4.QtCore import QString

That same code snippet doesn’t work in python3 interpreter though:

$ python3
>>> from PyQt4.QtCore import QString
Traceback (most recent call last):
File "", line 1, in
ImportError: cannot import name QString

My first instinct was: Bug! Gentoo PyQt4 ebuild was doing something terrible and somehow made PyQt4 unusable in python3 interpreter. Turns out my gut instinct was wrong (once again :-) ).

PyQt4 since version 4.6 changed API of QString and QVariant for python 3.x. For QString this is due to fact that from Python 3.0, string literals are unicode objects (no need for u’unicode’ magic anymore). This means that you can use ordinary Python strings in place for QString. But I wanted my QString for something like this:

downloadClicked = pyqtSignal((QString, ))

This snippet creates Qt signals that you can then emit. Question is… How can we update this for Python 3.x? We could probably just replace QString with type(“”), but for a change that wouldn’t work with Python 2.x. So? Python dynamic nature to the rescue!
Edit: simplified QString definition (thanks Arfrever)

from PyQt4.QtCore import QString
except ImportError:
# we are using Python3 so QString is not defined
QString = str

If we put previous code sample to the beginning of our Python file we can use QString in our code and it will keep working both in Python 3.x and Python 2.x. Case closed dear Watson.

Fedora RPG – Three level badge system?

October 20, 2010 in fedora, game, open source, rant

I stumbled upon one great idea on Fedora Planet. It is nothing other than Fedora RPG!

In short, it’s a system to create characters similar as they are in Role-playing games (RPGs) with levels, skill points and more.

You might think it doesn’t make sense to give contributors “points” for non-gaming activities but you would be wrong. Most communities have created ways to reward their members this way. Look no further than my favourite It also uses badge and skill point system for various actions on the website. In one of earliest blog posts about how stackoverflow will work, Jeff Atwood shared his vision: three levels of badges (bronze, silver, gold). Each level with unique badges tailored to the purpose of stackoverflow.

I guess Fedora RPG will go a bit further in this regard. I would love to know how it will all turn out and how the levels will work. Let the games begin!

Uploading original photos from Digikam to Flickr

August 28, 2010 in en, kde, open source, photography, programming, projects, qt, software

I have been using Digikam for managing my photos for some time. It’s pretty neat software and development is progressing quite fast. You can think of it as Lightroom, just without the neat non-destructive editing. But that is coming too, thanks to Google and another round of Summer of Code participants. But I wouldn’t be writing this blog post if Digikam was flawless would I? :-)

First I’ll describe my work-flow in few short bullet-points :-)

  • Shoot a LOT of photos
  • Delete almost as many photos
  • Geotag, tag/keyword and rate remaining photos
  • If it was party or something similar upload to Facebook right away
  • Pick few photos and improve them a bit with Gimp (nothing fancy, just crop/levels)
  • Upload all photos to Flickr as a backup/sharing place

Digikam enables me to work like this, except the last point. Why? Because apparently Digikam developers don’t think anyone would update their photos to Flickr without first resizing/recompressing them. This¬† how flickr export dialog looks like this:

See the problem? Even if I don’t chose “Resize photos before uploading” Digikam will still re-compress them which is a Really-Bad-Thing(tm) to do with jpeg files. I had some previous experience with Qt3 and even Qt4. so I though it might be a good idea to look into fixing this small annoyance. I will not bore you with the details how I checked out svn repository with git and rest of the stuff. Here is the result:

If you un-check “Send original file (no resizing)” original settings will appear and you can resize/recompress as much as you want (Blasphemy! Madness!). The patch is not flawless, because it won’t prevent you from trying to upload RAW files to Flickr, but it’s good enough for me :-) It’s not even that big, stats are like this:

¬†flickrexport/flickrtalker.cpp |¬†¬† 18 ++++++++++++——
 flickrexport/flickrtalker.h   |    2 +-
¬†flickrexport/flickrwidget.cpp |¬†¬† 34 ++++++++++++++++++++++++++——–
 flickrexport/flickrwidget.h   |    5 +++++
 flickrexport/flickrwindow.cpp |    4 ++++
 flickrexport/flickrwindow.h   |    1 +
 6 files changed, 49 insertions(+), 15 deletions(-)

You can download the patch from my Dropbox for now until the bugreport I created some time ago will get sorted out (don’t hold your breath too much though). The patch applies cleanly across all versions of kipi-plugins I tried (from 0.8.something to 1.4.0). Happy uploading.

Downloading trailers on Linux – final solution

May 10, 2010 in en, linux, open source, projects, python, software

I love films. All of them to be exact. I believe you just have to be in the right mood and you would enjoy even few of the worst movies ever made. Even though I am a proponent of open source philosophy, we as a society are obviously not ready to embrace it in entertainment industry just yet.

This is where comes into play. Apple made great deals with movie studios and you can watch/download newest movie trailers. Well…sort of. Apple employs variety of restrictions which makes this site next to useless on a Linux desktop. It hides links to trailers themselves behind reference files so that when you download with your favorite browser, you will only get small reference file not the trailer itself. And that is after you circumvent user-agent protection. Because apple believes nothing but iTunes/iPad/iOtherAppleStuff should access these trailers. There are scripts around that can make downloading possible for Linux users. I have been using Apple Trailer Download script for Greasemonkey for quite some time, but it always stopped working after some time.

Another opportunity for me I guess. I have been trying to improve my Python-fu for some time so what better way then a small project like this? I started last weekend after I found out Apple actually publishes JSON data of trailers on its site. This made access quite easy from python and is quite error-prone to changes of website itself (as long as Apple doesn’t pull whole JSON thingy…but they are actively using it too). Long story short…there are two outputs from this endeavor:

  • pytrailer – python module to simplify access to movies on
  • pyqtrailer – Qt4 interface that displays poster, movie information and enables downloading of trailers

You can report bugs on respective websites (there are quite a few now, but basic downloading for hd trailers works). If you want to try it out just running:

# easy_install pyqtrailer
should work as long as you have PyQt4 installed. You can just run pyqtrailer now and you should see something like this:

That’s it. I will improve/fix it a bit but don’t expect too much :-)

And he’s back! (from hibernating)

March 27, 2010 in bug, en, kernel, linux, open source, problem, software

What better way to celebrate summer solstice, than by making my computer able to hibernate? Since my last post a lot has happened with me. I got a new phone (HTC Hero FTW!), I finished university, went traveling a bit and I also got a new notebook (because the old one died on me). R.I.P. Thinkpad R51, welcome Thinkpad T500. There are several things I could start writing about now. Starting with how great Hero and Android is to use all the way to today’s blog post: How to make my computer hibernate?

Linux has had support for hibernating for quite a few years now and although it’s not perfect, it usually works out of the box. What it needs however is swap device big enough so that it can store image of memory for hibernating. Now I hit a problem. When I got my new Thinkpad I thought “Hey, I have 4GB of RAM…why would I need a swap?”. And even if I REALLY needed more than 4GB RAM I can still create temporary swap by using swapfile. Unfortunately I couldn’t make swapfile on LVM work with TuxOnIce. TuxOnIce also has another alternative to swap or swapfile for hibernating: Using filewriter, which is quite similar to swapfile support, I managed to get it to work (after some work, kernel debugging and one small patch to TuxOnIce).

I set FilewriterLocation in hibernate.conf to point to a place where I wanted to store hibernation file and I set the size to 4GB. As instructed in TuxOnIce HOWTO, I then ran

hibernate --no-suspend

to create this image. It created the file as expected, but when it was supposed to tell me settings for bootloader (resume argument) it silently failed. When I tried again, whole computer froze. I was puzzled. How could this happen? I am using Linux so things like this don’t happen! But hey, I should be able to figure out what’s wrong with it right? I set up my kernel to include netconsole, and ran hibernate again. This time I caught where the bug happened. The output was something like this:

TuxOnIce: No image found.
BUG: unable to handle kernel paging request at 6539207a
IP: [] toi_attr_store+0x186/0x2a0
*pdpt = 0000000032732001 *pde = 0000000000000000
Oops: 0000 [#1] PREEMPT SMP
last sysfs file: /sys/power/tuxonice/file/target
Modules linked in: netconsole aes_i586 aes_generic radeon ttm drm_kms_helper drm
i2c_algo_bit sco bnep ipt_MASQUERADE iptable_nat nf_nat ipt_LOG nf_conntrack_ip
v4 nf_defrag_ipv4 xt_state nf_conntrack ipt_REJECT xt_tcpudp iptable_filter ip_t
ables x_tables rfcomm l2cap vboxnetadp vboxnetflt vboxdrv arc4 iwlagn iwlcore ma
c80211 sdhci_pci snd_hda_codec_conexant sdhci pcmcia e1000e uvcvideo mmc_core cf
g80211 snd_hda_intel yenta_socket btusb rsrc_nonstatic tpm_tis pcspkr pcmcia_cor
e videodev v4l1_compat intel_agp wmi agpgart tpm snd_hda_codec tpm_bios video fu
se xfs raid10 raid1 raid0 md_mod scsi_wait_scan sbp2 ohci1394 ieee1394 usbhid uh
ci_hcd usb_storage ehci_hcd usbcore sr_mod sg uvesafb cfbfillrect cfbimgblt cn c
fbcopyarea [last unloaded: microcode]

Pid: 12870, comm: hibernate Not tainted #16 2082BRG/2082BRG
EIP: 0060:[] EFLAGS: 00010202 CPU: 0
EIP is at toi_attr_store+0x186/0x2a0
EAX: 00000000 EBX: 36203430 ECX: 00000000 EDX: f231f200
ESI: 65392066 EDI: 00f60062 EBP: f6006331 ESP: f62a7f14
DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
Process hibernate (pid: 12870, ti=f62a6000 task=f20a0270 task.ti=f62a6000)
00000000 fffffff4 00000001 c1790ca0 00000000 f6e8ab64 c16c75a4 f6d1c380
<0> f62a7f64 c114298d 00000015 00000015 b7709000 f21385c0 f6d1c394 c16c75a4
<0> f6ec7ac0 f21385c0 b7709000 00000015 f62a7f8c c10f207c f62a7f98 00000000
Call Trace:
[] ? sysfs_write_file+0x9d/0x100
[] ? vfs_write+0x9c/0x180
[] ? sysfs_write_file+0x0/0x100
[] ? sys_write+0x3d/0x70
[] ? sysenter_do_call+0x12/0x22
Code: c7 45 e0 00 00 00 00 3b 5d 08 0f 85 e9 fe ff ff 8b 46 20 85 c0 0f 84 de fe
ff ff ff d0 8b 7d e0 85 ff 8d 76 00 0f 84 d9 fe ff ff <8b> 46 14 31 d2 e8 60 03
05 00 8b 46 10 c7 46 14 00 00 00 00 a8
EIP: [] toi_attr_store+0x186/0x2a0 SS:ESP 0068:f62a7f14
CR2: 000000006539207a
---[ end trace 124a5ee29ef71277 ]---

So what can we deduce from this bug output? Let’s go from the top. Bug name (unable to handle kernel paging request) means that it is likely a memory corruption issue. Someone accessed memory that he was not supposed to. IP tells us that function where the error occurred was toi_attr_store in unknown file, unknown line (I don’t have debug information included in kernel). There are other information we can get from that output, but I didn’t really need them. Quick search through kernel sources told me that toi_attr_store is a function inside kernel/power/tuxonice_sysfs.c. I scanned the code, learning what approximately it did. Then I placed printk statements thorough the function so that I could approximate where inside the function the code fails. After some time I narrowed it down to following snippet:

if (!result)
result = count;

/* Side effect routine? */
if (result == count && sysfs_data->write_side_effect)

/* Free temporary buffers */
if (assigned_temp_buffer) {
(unsigned long) sysfs_data->data.string.variable);
sysfs_data->data.string.variable = NULL;

Kernel crashed when it tried to call toi_free_page. After a few reboots and printks later I found out that this was just a coincidence, and sysfs_data variable itself became corrupt even before the call to the toi_free_page. Good candidate? Of course: write_side_effect. But what exactly was write_side_effect? This function was passed as an argument, and therefore I wasn’t able to easily find out what was real code executed at this point. Time to find out! From my previous debugging attempts I knew code failed while it tried to write location of my resume file into /sys/power/tuxonince/file/target. TuxOnIce code defined handling for string sysfs arguments as such:

#define SYSFS_STRING(_name, _mode, _string, _max_len, _flags, _wse) { \
.attr = {.name = _name , .mode = _mode }, \
.flags = _flags, \
.data = { .string = { .variable = _string, .max_length = _max_len } }, \
.write_side_effect = _wse }

I found this macro used inside tuxonice_file.c source code like this:

SYSFS_STRING("target", SYSFS_RW, toi_file_target, 256,
SYSFS_NEEDS_SM_FOR_WRITE, test_toi_file_target)

So we found our write_side_effect code inside test_toi_file_target function. In one part this function was calling hex_dump_to_buffer to convert device UUID into hexadecimal string. The call looked like this:

hex_dump_to_buffer(fs_info->uuid, 16, 32, 1, buf, 50, 0);

This should convert input (fs_info->uuid) into hexadecimal string and store it inside buf. Author of the original code correctly thought about function adding spaces between bytes and therefore need to have more space in the buffer (argument 50 is telling hex_dump_to_buffer how big is output buffer). Unfortunately that same author declared buf as 33 char array. hex_dump_to_buffer therefore stepped outside the buffer and corrupted memory, causing all the problems. I fixed this bug, and sent a patch to the tuxonice-devel mailing list. As of now, it is already in the git repository ready to be released with next bugfix release of TuxOnIce.

That is everything for today, but as I already noted I am using LVM on my system (except root partition) and also use fbsplash for nice animations while rebooting. I am using initrd for this, and I will have another post on that topic.

Final thoughts on GSoC

August 24, 2009 in en, google, gsoc, linux, open source, projects, software engineering

So this year’s Google Summer of Code is officially over. Today 19:00 UTC was deadline for sending in evaluations for both mentors and students. Therefore I think some kind of summary what was happening and what I was doing is in order.

I was working on implementing neat idea that would allow previously impossible things for Gentoo users. Original name for the idea was “Tree-wide collision checking and provided files database”. You can find it on Gentoo wiki still. I later named the project collagen (as in collision generator). Of course implemented system is quite a bit different from original wiki idea. Some things were added, some were removed. If you want to relive how I worked on my project, you can read my weekly reports at gentoo-soc mailing list (I will not repeat them here). Some information was aggregated also on As final “pencils down” date approached I created final bugreports of features not present in delivered release (and bugs there were present for that matter). Neither missing features, nor present bugs are a real show-stopper, they mostly affect performance. And more importantly I plan to continue my work on this project and perhaps other Gentoo projects. I guess some research what those projects are is in order :-)

Before GSoC I kind of had an idea how open-source projects work since I’ve participated with some to a degree. However I underestimated a lot of things, and now I would do them differently. But that’s a good thing. I kind of like the idea that no project is a failed one as long as you learn something from it. It reminds me of recent Jeff Atwood’s post about Microsoft Bob and other disasters of software engineering. To quote him:

The only truly failed project is the one where you didn’t learn anything along the way.

I believe I have learned a lot. I believe that if I started collagen now, it would be much better in the end. And the best thing is that I can still do that. I get to continue my project and learn some more. If I learned anything during my work on collagen it’s this:

If you develop something in language without strong type checking CREATE THE DAMN UNIT TESTS! It will make you life later on much easier.

In next episode: Why I think Gmail is corrupting minds of people and why I hate mobile phones