emax http://maxsobell.com/wp Hello world! A blog about programming, eating and surviving as a student in the Big Apple. Wed, 04 Aug 2010 16:53:33 +0000 en hourly 1 http://wordpress.org/?v=3.0.1 NYT’s Tricky Images http://maxsobell.com/wp/?p=90 http://maxsobell.com/wp/?p=90#comments Wed, 04 Aug 2010 16:52:32 +0000 Max Sobell http://maxsobell.com/wp/?p=90 Here’s a cute trick the nyt uses for their slideshows to prevent users from saving images locally (Note: I am not encouraging this). If a user right clicks an image and selects “save as…” the image which gets saved is pixel.gif, which is garbage (example here). By viewing the page source, we can figure out why that happens:

<div class="figure module">
<div class="image">
<div class="centeredElement" style="background-image:
     url('http://graphics8.nytimes.com/images/2010/08/04/
     arts/design/04maker-ss-slide-GSQJ/04maker-ss-slide-
     GSQJ-slide.jpg');width:333px; height:500px;">
<img width="333" height="500" src="<a href=
     "view-source:http://graphics8.nytimes.com/images/
     misc/pixel.gif">http://graphics8.nytimes.com/images/
     misc/pixel.gif</a>" />

The image we want is the background, covered by pixel.gif. Tricky.

]]> http://maxsobell.com/wp/?feed=rss2&p=90 0 e-puck Robot Lead/Follow http://maxsobell.com/wp/?p=83 http://maxsobell.com/wp/?p=83#comments Wed, 12 May 2010 04:13:52 +0000 Max Sobell http://maxsobell.com/wp/?p=83 A leader/follower scheme with obstacle avoidance using e-puck educational robots.

YouTube here: Video

Paper here: e-puck Leader/Follower Final Paper

]]> http://maxsobell.com/wp/?feed=rss2&p=83 0 LSB Encoding/Decoding http://maxsobell.com/wp/?p=79 http://maxsobell.com/wp/?p=79#comments Thu, 06 May 2010 02:07:00 +0000 Max Sobell http://maxsobell.com/wp/?p=79 Added a new project: Least Significant Bit (LSB) Encoding and Decoding. By changing the least significant bit of each byte in an image (B&W), its possible to encode an invisible string of text into the image. Check out ways to break it in the code :-P

Code and paper under “Projects” section.

]]> http://maxsobell.com/wp/?feed=rss2&p=79 0 Tanks Game http://maxsobell.com/wp/?p=63 http://maxsobell.com/wp/?p=63#comments Mon, 08 Feb 2010 21:06:00 +0000 Max Sobell http://maxsobell.com/wp/?p=63 Finally got around to putting up my assembly language Tanks game. Here’s the Tanks Source and here are some screenshots:




All files here.

]]> http://maxsobell.com/wp/?feed=rss2&p=63 0 New Sections http://maxsobell.com/wp/?p=57 http://maxsobell.com/wp/?p=57#comments Wed, 06 Jan 2010 20:17:42 +0000 Max Sobell http://maxsobell.com/wp/?p=57 I added a “Restaurants” section from my google doc and a “Projects” section — updates there!

]]> http://maxsobell.com/wp/?feed=rss2&p=57 1 rsync published! http://maxsobell.com/wp/?p=39 http://maxsobell.com/wp/?p=39#comments Mon, 30 Nov 2009 17:42:40 +0000 Max Sobell http://maxsobell.com/wp/?p=39 The rsync material on my wiki is on Amazon in the new version of A Practical Guide to Linux Commands, Editors, and Shell Programming!

]]> http://maxsobell.com/wp/?feed=rss2&p=39 1 MySQL Project http://maxsobell.com/wp/?p=28 http://maxsobell.com/wp/?p=28#comments Sat, 24 Oct 2009 05:44:00 +0000 Max Sobell http://slashmax.com/wp/?p=28 I’ve started a MySQL wiki for a chapter of A Practical Guide to Red Hat Linux. I’m learning as I write it up, so feel free to correct or change anything! Here’s the link.

(Update 11/20/09: This page now contains other utilities, too!)

]]> http://maxsobell.com/wp/?feed=rss2&p=28 1 Karmic Koala! http://maxsobell.com/wp/?p=27 http://maxsobell.com/wp/?p=27#comments Tue, 20 Oct 2009 06:04:00 +0000 Max Sobell http://slashmax.com/wp/?p=27 Ubuntu: For Desktops, Servers, Netbooks and in the cloud

]]> http://maxsobell.com/wp/?feed=rss2&p=27 2 Programming Contest http://maxsobell.com/wp/?p=26 http://maxsobell.com/wp/?p=26#comments Mon, 19 Oct 2009 15:01:00 +0000 Max Sobell http://slashmax.com/wp/?p=26 This year’s problems for the ICPC:
http://www.acmgnyr.org/year2009/problems.shtml

]]> http://maxsobell.com/wp/?feed=rss2&p=26 0 SVN Part 2 http://maxsobell.com/wp/?p=25 http://maxsobell.com/wp/?p=25#comments Thu, 08 Oct 2009 19:43:00 +0000 Max Sobell http://slashmax.com/wp/?p=25 Now that we can log in automatically (SVN Part 1), we can do some cool stuff. This summer I managed a SVN server for a company that has multiple programs, each of which had different developers working on them. Each of these programs is stored as a repository in SVN. For example, developer A needs access to repository 1 and 2 and developer B needs access to repository 1 and 3, etc. To make it even trickier, in repository 1, developer A should have access to the entire repository, while developer B should only have access to the directory devB in repository 1. Also, every time a developer makes a change to a file, the change needs to be logged with their username.

This is where the RSA keys come in. Each repository should be owned by a different user. For example, /usr/bin/svnserver/repository1 is owned by user repo1, /usr/bin/svnserver/repository2 by repo2, etc. Put any developer who needs access to [repo]‘s RSA pubkey in the /home/[repo]/.ssh/authorized_keys file, where [repo] is the name of the repository’s owner (repo1, repo2). Configure authorized_keys like:

command="/usr/bin/svnserve -t -r /var/svn/ --tunnel-user=[developer's username]",no-port-forwarding,no-pty,no-agent-forwarding,no-X11-forwarding ssh-rsa [developer's RSA pubkey]== [developer's username]

This enables developers to check out [repository] using: svn+ssh://[repo]@[server]/[repository]. While we are sending the information over SSH, the developer does not have a SSH account and can do nothing but use SVN to check out (svn co) and update (svn ci) repositories owned by a user (repo1, repo2) whose authorized_keys file contains the developer’s pubkey. The last column in the authorized_keys file is the comment line. SVN automatically uses this line as the comment when a developer commits code to the SVN repository.

The last part, giving only partial access to a repository, coming in Part 3.

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