TSUL Best Log

Self-defined Locations for Desktop, Music, Downloads, Pictures and Videos in Ubuntu

2011-04-30T23:01:00.001+08:00

As Ubuntu release its 11.04 natty narwhal, have you ever wanted to define the default locations for Desktop, Music, Downloads, Pictures and Videos on your own?

All you need is go to $HOME/.config/ folder and modify the user-dirs.dirs with your favorite text editor. The default looks like this:

# This file is written by xdg-user-dirs-update

# If you want to change or add directories, just edit the line you're

# interested in. All local changes will be retained on the next run

# Format is XDG_xxx_DIR="$HOME/yyy", where yyy is a shell-escaped

# homedir-relative path, or XDG_xxx_DIR="/yyy", where /yyy is an

# absolute path. No other format is supported.

#

XDG_DESKTOP_DIR="$HOME/Desktop"

XDG_DOWNLOAD_DIR="$HOME/Downloads"

XDG_TEMPLATES_DIR="$HOME/Templates"

XDG_PUBLICSHARE_DIR="$HOME/Public"

XDG_DOCUMENTS_DIR="$HOME/Documents"

XDG_MUSIC_DIR="$HOME/Music"

XDG_PICTURES_DIR="$HOME/Pictures"

XDG_VIDEOS_DIR="$HOME/Videos"

You might also want to check this configuration file if any of your special folder icon is missing.

Sina opens App Engine (SAE) service like GAE

2010-02-06T15:39:00.001+08:00

Sina opens an App Engine service, named SAE, some while ago, and is now at alpha 2, public for registration in China.

This SAE service is very similar to Google App Engine in that it provides a cloud environment for applications to run on. Unlike GAE, SAE supports the PHP + MySQL combination. This means, potential, more web applications could be migrated to sina app platform. Actually, the famous blogging application, Wordpress, is already migrated. Although flexible, the use of MySQL as a database storage might mean the scalability will not be so good.

Sina App Engine and My SAE App

Trick or Treat, LayoutFocusTraversalPolicy

2010-01-04T14:18:00.000+08:00

Have you ever met such focus traversal issue in Java UI applications? By default, LayoutFocusTraversalPolicy is used to determine the sequence of focus traversal. As stated in Java documents, it sorts components based on their size, position, orientation etc.. However, when two identical components are laid at the same position, there will be a focus traversal issue.

A demo is better than a thousand words. Copy the code to a file FocusTraversal.java and compile and run it.

package tsul.example;

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.Dimension;
import java.lang.reflect.Field;
import java.util.ArrayList;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JButton;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;

public class FocusTraversal extends JPanel {

    JButton b1 = new JButton("Columns");
    JButton b2 = new JButton("Rows");
    JTextArea content = new JTextArea("Textarea");
    /**
     * This is the main pane
     */
    JScrollPane pane = new JScrollPane();

    public FocusTraversal() {
        super(new BorderLayout());

        pane.setColumnHeaderView(b1);
        // Try to add a duplicate component to pane's header. In such a case,
        // the default
        // LayoutFocusTraversalPolicy won't work properly as expected. The
        // result is we
        // cannot move focus from Columns to Rows by tabling.
        try {
            Field f = Container.class.getDeclaredField("component");
            // bypass default security check
            f.setAccessible(true);
            ArrayList comp = (ArrayList) f.get(pane.getColumnHeader());
            comp.add(b1);
        } catch (Exception e) {
            e.printStackTrace();
        }
        pane.setRowHeaderView(b2);
        pane.setViewportView(content);
        setPreferredSize(new Dimension(600, 400));
        add(pane, BorderLayout.CENTER);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                frame = new JFrame("Focus Traversal Example");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                FocusTraversal panel = new FocusTraversal();
                frame.getContentPane().add(panel);
                frame.pack();
                frame.setVisible(true);
            }
        });
    }

    static JFrame frame;

}

Step Back Debugging for Java in Eclipse?

2009-12-24T10:58:00.000+08:00

In debugging, there are "step into", "step over" etc., but what about a "step back" feature? There are chances that when you hit a "step over" twice by mistake, or when you find out it might be just the previous line which is causing trouble, you just want a "roll back" feature.

Debugging is like traversal on a tree or on a graph. Every breakpoint is a state or a node. In theory, if we save these states, we can step back and forth among any of them. Snapshot, versioning or savepoint can be useful in helping save the debugging states.

There are already such support in C/C++ debuggers like gdb. However, it seems that no Java debugger supports "step back" or "roll back". It would be even nicer if such feature could be included in Eclipse IDE.

Apache: Full Long File Names in Index

2009-12-16T11:35:00.000+08:00

There are cases that the default index file in Apache server trimmed your long file name. Instead you'd like to show them in full length. To do this, you can edit the configuration file of your Apache server (httpd.conf). Add "NameWidth=*" to IndexOptions, so that it looks like:

IndexOptions FancyIndexing NameWidth=*

Reference
http://httpd.apache.org/docs/1.3/mod/mod_autoindex.html#indexoptions

SQL: a Cross-Tabular Report with Case, Rollup and Grouping Functions

2009-12-12T18:38:00.000+08:00

A Cross-Tabular Report is widely used in computer software. If you keep a journal of expenses, for instance, and by the end of year, you would like to review how much you have spent on each type of goods in a month-by-month view. Or a website administrator would like to know, for each page or URL of website, how many visitors visited using different browsers. These are cases when you need a cross-tabular report. (Definitions of Cross Tabulation or Contingency table.)

So how to generate a cross tab report in just one line of SQL? The idea is to split columns with "CASE" and group rows with "GROUP BY ROLLUP(name)" and decorate the result with "DECODE(GROUPING(name), 1, 'Total', name)".

Here's an Example:

We have a log table:

SQL> select page "Page", brws_type "Browser" from visit_table;

Page            Browser

--------------- ----------

index.htm       FF

index.htm       IE

index.htm       IE

page1.htm       FF

page2.htm       FF

page3.htm       FF

about.htm       FF

about.htm       SF

index.htm       SF

index.htm       SF

index.htm       FF

Page            Browser

--------------- ----------

page2.htm       IE

page2.htm       IE

contact.htm     IE

contact.htm     SF

page3.htm       SF

And now comes the query for cross-tabular report.

SQL> SELECT DECODE(GROUPING(page), 1, 'All pages', page) "Pages",

            COUNT(CASE WHEN brws_type='FF' THEN 1 ELSE null END) "Firefox",

            COUNT(CASE WHEN brws_type='IE' THEN 1 ELSE null END) "Internet Explorer",

            COUNT(CASE WHEN brws_type='SF' THEN 1 ELSE null END) "Safari",

            COUNT(*) count

      FROM visit_table

      WHERE 1=1

      GROUP BY ROLLUP(page)

      ORDER BY count desc;

Pages              Firefox Internet Explorer     Safari      COUNT

--------------- ---------- ----------------- ---------- ----------

All pages                6                 5          5         16

index.htm                2                 2          2          6

page2.htm                1                 2          0          3

about.htm                1                 0          1          2

contact.htm              0                 1          1          2

page3.htm                1                 0          1          2

page1.htm                1                 0          0          1

SQL is a powerful language.

Recent Risks on Internet

2009-11-25T13:15:00.000+08:00

1. URL shorten service.
Hidden of advertisements or even worse, malicious websites.
Lost of service if the URL shorten service provider is down or hacked.

2. Websites, especially SNS, request user to provide email login and password in order to add friends.
Do they really need your password to just get a list of your friends?
Even the websites requesting your credentials are trustworthy, you are still at risk. For example, some website can add your friends on MSN or Gtak by requesting your logins and passwords, but your credentials are transferred in plain HTML to them. This means sniffers can get your passwords with ease.
There is no reason to request your password while other methods like oauth are available.

Connection Interrupted (TCP RST) has nothing to do with HTTPS aka HTTP over TLS

2009-10-17T11:15:00.001+08:00

A network has layers.

In the TCP/IP model, there are four layers. TCP, UDP belong to the transport layer, while HTTP, SSL/TLS belong to application layer. RST (Reset the connection) is a flag in TCP header as in RFC793. RST vulnerability as well as off-path attacks are disscussed in RFC4953. Basically, if a connection is interrupted, it simply means that there is an accepted TCP package with RST flag set. It could be the server who reset the connection, or it could be an attacker. HTTP over TLS aka HTTPS, RFC 2818, is an application layer protocol. SSL/TLS protocol is used between HTTP and the transport layer. From a transport layer's view, the upper layer applications are served in the same way.

To summarize, TCP RST vulnerability is applicable to HTTP or HTTPS or any other application protocols as long as they rely on TCP connection, but it has nothing to do with application layer protocols.

A link to RFC.

Migrate from Goolge Pages to Appengine

2009-10-14T15:19:00.000+08:00

Migration without losing any data.

When it comes to Google Pages, will you opt-out or do nothing and wait for your pages to be migrated to sites smoothly? We can wait, but at a cost. Google Sites do not provide equal or more features than Pages do. No custom Javascript; no uploaded HTML; limited layouts, themes. It dose not seem possible to migrate without losing any data. Even the appearance will change. So, where else can we migrate to?

Our choice is Appengine.

Pros:

Powerful.
From the same vendor.

Cons:

Technical skills required

Step by step migration:

Download your pages as a zip from Google Pages
Create a new appspot handle
Download appengine SDK from http://code.google.com/appengine/
Create a new project
Configure the project
Unzip pages into static content directory
Test on localhost
Deploy to appspot
Test with http://<your-handle>.appspot.com/
(Optional) Bind your domain

The long waited automatical migration from Pages to Sites is still not done! Is Google waiting for everyone to opt-out? The magic is a rumor.

Option 1 - Do nothing, and your pages will automatically be moved to Google Sites

We'll set up the new site and move your pages for you.

Visits to your googlepages.com URL will redirect to your new site.

Note that Google Sites does not support custom JavaScript or CSS in its pages.

Option 2 - Opt out of the move, and take your pages to a new location

Download your site.

Once you've moved your site to its new location, opt out of migration by setting up a redirect below.

Let's wait and see.

A History of man-made Lunar Impact

2009-10-14T14:27:00.000+08:00

Hit the Moon

An incomplete list of lunar impact by human being.

2009.10.9 7:31 EDT
Nasa LCROSS
http://www.nasa.gov/

2009.03.01 16:13 CST
嫦娥一号 ChangE1
http://baike.baidu.com/view/32160.htm

2008.11.14
The Moon Impact Probe
http://en.wikipedia.org/wiki/Moon_Impact_Probe

2006.9.3 05:42 UT
SMART-1
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=39961

Distinguish the two words in reCAPTCHA

2009-09-29T22:38:00.000+08:00

reCAPTCHA is a great idea, but people can `easily` distinguish the known word from the unknown one.

Moebius Gears

2009-09-26T16:59:00.001+08:00

Here's a picture of Moebius Gears.

Look cool? If you are on a Linux box, you might already have a lively demo installed. For Ubuntu users, it is located at /usr/lib/xscreensaver/moebiusgears.

Press Alt+F2 and type /usr/lib/xscreensaver/moebiusgears and run!

The xscreensaver source code could be downloaded from here.

The Risk of OpenID

2009-09-23T15:30:00.000+08:00

OpenID seems a promising standard for user authentication. If service providers support OpenID, users can login without creating another pair of account and password. Ideally, a user need only remember one pair of account and password. However, such convenience comes at a cost. The only pair of account and password or the OpenID provider becomes a Single Point Of Failure. If you ever forgot your password or the Identity Provider withdrew your account because you didn't login in the past three months, you will have no way to login to any of the services. Here, we assume that the service providers only accept authentication from OpenID providers. This also applies to other forms of third party authentications.

For users, care should be taken on choosing OpenID providers. Users should keep their OpenID account active and secure the password. For service providers, they should allow other ways of authentication besides OpenID. Users should not lose the service if they lose their OpenID.

OpenID is not that open, not even as open as telephone numbers which could be transfered among telephone service providers.

Inventions: Fancy Disk Copier and Fancier Copy Dragger

2009-03-21T23:07:00.004+08:00

Here are our two new inventions: the Fancy Disk Copier and the Fancier Copy Dragger.

The Fancy Disk Copier is a CD/DVD copy machine. It works like a photo copier. You put in a source CD/DVD, and press "COPY"; the copy CD/DVD will come out instantly. Unlike a photo copier, the Fancy Disk Copier will copy with absolutely no loss of quality. The differences between copies and the original CD/DVD is not distinguishable by anyone except the Fancy Disk Copiers. This will, hopefully, prevent copyright abuse.

Our second invention, the Fancier Copy Dragger, is a dragging controller of copy speed. The Fancier Copy Dragger not only supports dragging forward at any pace, but also enables user to drag back in case a user would enjoy the copy process again. What's more, the Fancier Copy Dragger allows users to undo all copies by dragging to the very beginning. Those undo-ed CD/DVDs can be used as if they are new ones. Unlike photo copiers, hundreds of pieces of paper got wasted once any error occurred. The Fancier Copy Dragger will help protecting our environment.

Thanks for your interest in our new inventions. We will send out our "beta" products to selected users starting from next week. Get involved.

Happy New Year 2009

2009-01-01T10:22:00.002+08:00

Today is January 1st, 2009. The sun raises as usual, but there's a leap second added after GMT 23:59:59 Dec. 31, 2008. At that time spot, you might notice something like XX:59:60. XX depends on your timezone. If you are using Beijing time, it should be 07:59:60, and if you locate in central America, it should be 17:59:60.

Talk to foreigners (even aliens) in your language seamlessly

2008-12-21T22:45:00.002+08:00

Proposal

Build an automatic translation mechanism into instance message system (and other Internet communication system), as if a simultaneous interpreter were there.

It would be exciting if you master three languages. However, one could not master all languages. Even if such an interpreter exists, hiring him/her would be expensive. Internet helps people communicate easily from every corner around the world, and if it were an even probability to talk to anyone on earth, the chance a talker speaks foreign language is much higher. If we have such an automatic translation system, as if a simultaneous interpreter is ready, negotiation should be much simpler.

The problem currently is that a machine could not translate as good as an average interpreter. Languages are not one-to-one mapping, and machines are not good at analyzing and choosing which words to use and in what order. And this is why interpret is still a career.

Whenever a computer is not good at something, we could try to train it in hope that it will eventually learns and masters it. The source of training material would be from thousands of millions of people. As in image recognition, tags from Internet users helps classify and recognize pictures a lot. If, in one day, computers could seamlessly translate one language into another, we would be happy that we no longer need to learn a second language, and we would be equally sad that we will never drive to learn other than native language.

Currently, machine translation in instance message system should be more than experimental, but at least it could provide some information which might be helpful to international talkers. And, have fun to laugh at silly computers.

File names you can NOT create on Windows

2008-12-17T22:51:00.003+08:00

Try to create a file named NUL.txt on Windows XP, and you probably get an error message.

Many characters are not allowed for file names on Windows. This includes
< > : " / \ | ? *

Besides, many reserved device names should be avoided. This includes
NUL, CON, PRN, AUX, COM1, COM2, ..., LPT1, LPT2, ...

Also, using the device names unintended might raise security vulnerability.

Dimensional Modeling vs Interval Tree

2008-12-13T00:44:00.002+08:00

The concept Dimensional Modeling is like the Interval Tree (Segment Tree). Both speed up queries by storing information at different levels. The difference is that in Dimensional Modeling, levels are defined by users, while in Interval Tree, levels are usually defined by a complete binary tree. Interval Tree usually solves problems on one dimension, but it could also be applied to 2D problems. One dimension is not a limit.

Quotes

2008-11-23T21:54:00.003+08:00

Quoted

Quotes are widely used in scripting languages, including (but not limited to) Bash, SQL, Python, Tcl, Perl, PHP, JavaScript. However, there is no universal rule for quotes. Most languages support single quote (') or double quote ("), while others have their own quotes like triple quote (''' or """), or braces ({, }). When one should code in a combination of different languages, the quotes would definitely confues programmers, not mentioning variable substitution, regular expression, etc.

Different outputs in Tcl - Stdout vs Return Value

2008-11-13T10:51:00.004+08:00

When both set a {hi} and puts "hi" echo a "hi" in an interactive tcl shell, what is the difference between them?

Clarification on "output"
1. standard output
puts command will output to stdout by default.

% puts "hello"

hello

2. return values
set hi {hello} has a return value hello and will echo back to user

% set hi {hello}

hello

To make things clear, look at this example.

% set ret [puts "hello"]

hello

% puts $ret

(blank)

So that the return value from puts is blank.

Compound statements
Let move on to compound statements.

% set a "hello"; set b "hello2"

hello2

This gives a single line of output from `set b`, and a and b are both set.

% puts $a

hello

% puts $b

hello2

Here's two lines of output from stdout.

% puts "hello"; puts "hello2"

hello

hello2

Importance
Why is this important? What if we would like to store a calculated value into variable a.

% set a [expr 3+3]

6

% puts $a

6

This is what we expected. However, if we wrote another version of expr that output the result into stdout.

% set a [set b [expr 3+3]; puts $b]

6

% puts $a

(blank)
We get nothing.

Generally speaking, it is not a good idea to print to screen from many functions. Because this would make the testing difficult, if not impossible. Usually, assert will compare the return result to expected result, while the output to standard output are ignored. Despite all that, we can still try to test function which output to stdout. The idea is to trap the stdout. This assert for stdout would look like this pseudo code:

procedure assertStdout (expected, command) {
create out for this instance
execute command > out
flush out
return expected == out
}

One trick is that if multiple assertStdout procedures are running, 'out's must be distinct in order to keep thread-safe.

The echo back of tcl might be of use, but it could confuse people with the output from within procedures. However, it is mandatory to distinguish them for a programmer. Other scripting languages like shell does not have such echo back, but that doesn't mean it is OK to output from many functions for them. Especially, for compicated software that requires a thorough test, standard out or output to file everywhere would definitely bring down the testing.

Snapshot in UI Testing

2008-09-29T18:40:00.003+08:00

If you have experience in JUnit or other testing tools, you probably know the importance of setup and teardown methods. These two methods help build a testing environment. However, when it comes to UI testing, it is not the case. UI testing means taking a long time, boring, and random exceptions. What's more, every time an error occurs, which might be caused either by a typo or by the tested codes, the only solution is to start over again from the very beginning. This is boring!

If we could take a snapshot at certain points (which are called save points), we could easily get started from those points. It should be time efficient. It certainly save a lot of time otherwise wasted in setting up the environment again. What's more, you can benefit from reproducing some random errors. If a snapshot were taken just before it occurs, the error would probably show up again, which also helps reduce the number of bugs.

It is not too hard to implement such a system. There are various ways though. It can be implemented as a functionality of the testing tools, or it could be bounded with the help of underlying systems. One good candidate is the virtual machine. Most VMMs, including open source ones, have a similar function. Taking snapshot takes seconds to minutes, depending on the implementations of VMM and the size of the virtual machine. We could take multiple snapshots, and rollback to a certain one, and even make branches. Although making use of VMM might seem easier, it is harder, but necessary, to integrate the snapshot into the testing tools. Taking snapshot should be as simple as setting breakpoints in debug.

Expecting analytical tools for individuals

2008-08-31T10:26:00.002+08:00

Analytical tools for websites are everywhere. However, analytical tools for individuals are rare. Google web history might be one, but has much less functions compared to its analytics.

One may wonder why would we need an analytical tool for individuals. The reason is that tracing one's activities is interesting (as long as it's not privacy related). As it should be helpful to a website, an analytical tool for individual would benefit the user and even provide suggestions on time management. The analytical tool for individual has to be

automatic; users won't log each into a document manually.
complete; a partial result is of mere use.
precise; an imprecise log will lead to fault result.

Of these characters, automatic is the most important. A user is usually not willing to log his/her activities manually. Users are not able to log each activity precisely. However logging is a required step in time management, without which analyzing would be impossible.

It would be difficult to implement such an analytical tool, especially for fine-grained user activities. There are different operating systems, browsers, etc. Besides, there are hundreds of thousands of activities outside computer world.

Seamless mode of virtual machines could be improved.

2008-07-26T18:46:00.004+08:00

Thanks to Windows, we are so used to Ctrl+Tab. (What? You are using a device called mouse?)

Virtual machine has advantages over host machines, though it is usually because of the users rather than the OS itself. Consider the case that you are using Linux as your host OS, but you would also like the the benefits from Windows, besides you get an licensed version. You might be using VirtualBox, or VMware products. They both have a seamless mode which integrates the guest OS into your host OS. This blurs the edge between the host and the guest. You might not notice that the applications are running on different machines. I could watch from Windows Media Player and update my Ubuntu at the same time.

All seems good before you come to a keyboard-only guru. The 'Ctrl+Tab' simply won't work when you want to switch between host and guest. The focus will not be released, when it is captured by the guest, unless the 'host key' is pressed. This is not an idea 'seamless' mode, where even gurus will not notice the switching from guest from host.

There are two possible trends of seamless mode for virtual machines on Linux. One is to make use of workspace on Linux. A workspace is like a separate root window on windows and the number of workspace can be changed by users. A virtual machine could use one entire workspace for the guest OS. This is especially convenient if the guest OS is a single workspace operating system. Another possibility is to make guest applications more like host applications. This is similar to Wine. However, one might still want to keep the original theme from guest OS.

A 'seamless mode' is a very good start point for improved user experience.

A screen shot of seamless mode of VirtualBox.

What next? Cloud computing, mashup, or app engine.

2008-07-24T19:52:00.003+08:00

Cloud computing, Mashup, and App engine.

It might be interesting to build a 'cloud' instead of building an OS. As time goes by, a TV set is no longer an expensive property. Although a computer ( the hardware plus many software bundled) is not as cheap as a TV set, it certainly will in the near future. Will these clouds in the future become OSes which we are now used to? It might be. It was once the era of hardware, and followed by software. It is now Internet and services.

os.system() and its return value

2008-04-17T15:24:00.001+08:00

When os.system('exit 1') returns 256, you might wonder what is going on with python? Why isn't it simply 1 (one)? Let's take a look at this command.

A system() command might be frequently used when you were interacting with the system or other scripts.

Try help(os.system) will only show:
system(command) -> exit_status

Execute the command (a string) in a subshell.

And it talks nothing about the exit status.

This function appears in the tutorial as an example and in library reference:

system(command)

Execute the command (a string) in a subshell. This is implemented by calling the Standard C function system(), and has the same limitations. Changes to posix.environ, sys.stdin, etc. are not reflected in the environment of the executed command.

On Unix, the return value is the exit status of the process encoded in the format specified for wait(). Note that POSIX does not specify the meaning of the return value of the C system() function, so the return value of the Python function is system-dependent.

On Windows, the return value is that returned by the system shell after running command, given by the Windows environment variable COMSPEC: on command.com systems (Windows 95, 98 and ME) this is always 0; on cmd.exe systems (Windows NT, 2000 and XP) this is the exit status of the command run; on systems using a non-native shell, consult your shell documentation.

Availability: Macintosh, Unix, Windows.

wait(command)

Wait for completion of a child process, and return a tuple containing its pid and exit status indication: a 16-bit number, whose low byte is the signal number that killed the process, and whose high byte is the exit status (if the signal number is zero); the high bit of the low byte is set if a core file was produced. Availability: Macintosh, Unix.

So this explains why os.system('exit 1') returns 256 instead of 1. Actually, the signal number killed the process is zero. To get the exit status, just shift the value 8-bit to the right.

Here is a link talking about the return code of os.system(). http://mail.python.org/pipermail/python-list/2001-March/073147.html