It’s good to keep your mind focussed. It’s also good to keep a look on your improvements.

1

$ mvn package -Dmaven.test.skip=true

Have fun with your additionally won spare time ;).

I prepared an IMG tag to display a specified image URL by setting the src attribute using JavaScript. The src attribute of that image has been left empty for that purpose (see code below).

1
2
3

<div id="imgWrapper" style="display: none;">
  <img id="imgEl" src="" alt="Empty src attribute!" />
</div>

1
2
3
4

function showImage(src) {
  $('imgEl').src = src;
  $('imgWrapper').show();
}

Later I discovered by using Firebug that an additional request is being sent to the server. That request used the same path and query string as the original page request used. That way two tickets were added to the shopping cart instead of one. What was keeping me from discovering that issue earlier was that the first response from the server didn’t know yet about the second ticket – so the browser displayed only one ticket in the shopping cart. After reloading the second ticket showed up.

Some JavaScript debugging and HTML commenting later I found out that this behaviour comes from the IMG element with its empty src attribute. Firefox uses the currently called URL for that image to get its content! Even though the wrapping DIV is set to not display it the browser loads that images content.

Happy about figuring out what caused the problem I rewrote the JavaScript mechanism for displaying that specific image. Using the excellent Prototype Library the code snippet would look something like this:

1
2

<div id="imgWrapper" style="display: none;">
</div>

1
2
3
4
5
6
7
8
9

function showImage(src) {
  var wrapper = $('imgWrapper');
  var img = $(document.createElement('img'));
  img.src = src;
  img.alt = 'Don\'t use an empty src attribute!';
  wrapper.update('');
  wrapper.appendChild(img);
  wrapper.show();
}

Creating the Keystore

Creating a keystore to store certificates that JBoss can use.

keytool -genkey -alias $MYDOMAIN -keyalg RSA ↵
-keystore my.keystore

You will be asked for a password to this keystore, just set any password you like. Furthermore you will need to enter some more information, just enter whatever you like – you only need these values to be correct if you are going to sign the certificate at your Certificate Authority.

Creating a Certificate Request

Then we need to create a Certificate Request.

keytool -certreq -keystore my.keystore ↵
-alias $MYDOMAIN -file myserver.csr

Normally you would want to send this Certificate Request to your Certificate Authority to sign it. That way browsers would accept your certificate without complaining. But we only need this certificate for our local development machine, so don’t worry about a security exception. You need to accept this certificate within your browser, though.

Configuring JBoss

You need to change this file to enable SSL with our created certificate: $JBOSS_HOME/server/default/deploy/jbossweb-tomcat50.sar/server.xml. Look for the following lines and uncomment them:

<Connector port="8443" address="${jboss.bind.address}"
  maxThreads="100" strategy="ms" maxHttpHeaderSize="8192"
  emptySessionPath="true"
  scheme="https" secure="true" clientAuth="false" 
  keystoreFile="${jboss.server.home.dir}/conf/ssl/my.keystore"
  keystorePass="KEYSTORE_PASSWORD" sslProtocol = "TLS" />

At last we need to copy your keystore to the proper place:

mkdir $JBOSS_HOME/server/default/conf/ssl
cp my.keystore $JBOSS_HOME/server/default/conf/ssl/

After a JBoss restart you can now use the https connection.

See also

This how-to is a short version of SSL mit JBoss (german).

Problem

A typed language defines types (such as integer, string, boolean, …) to variables – that way the contents of variables are clearly defined. When not having this restriction (as JavaScript doesn’t) one might do the following (JavaScript code):

1
2

var alpha = 'This is some String';
alpha = 5;

Most of the time this is OK, but there are times when you clearly need to know how values are evaluated. You might check for content if you need to do special things for special types. Let us assume you want to assign alpha a default value if it is empty (''). Your code might look like this:

3
4
5

if(alpha == '') {
    alpha = '-';
}

This is perfectly OK if alpha is a string.

Nevertheless, alpha could always be an integer, too. And strangely, when the value of alpha is 0 (zero) the boolean expression alpha == '' evaluates to true! So alpha would become '-' in our case, which is not exactly what we intended to do, right? This could lead to some serious errors in your programme flow.

Solution

What can you do about it? Is there anything you could do? Yes, there is. When operating with values like '' (empty string), true/false (boolean contents of variable) and 0 (zero) you should always use the strict equivalence operators: === (equals to and same type) and !== (not equals to or not same type). The above code would then look something like this:

3
4
5

if(alpha === '') {
    alpha = '-';
}

That small change effects the semantics of the code. It now sets the default value if and only if the value of alpha is equals to '' and the type of alpha is the same as the type of '' (which is string, respectively). In fact, this is what you wanted to do, isn’t it?

If you use strict equivalence operators correctly then you can make sure the code does what you want it to do. Keep this in mind if you like writing correct code using untyped languages.

See also

Here are some useful links for JavaScript and PHP:

• JavaScript – Comparison Operators
• PHP – Expressions

Source

MPlayer knows of those sources (use these in substitution for SOURCE in below examples):

• file: uses a file as input
• URL: uses an URL as input (useful for streams)
• playlist: uses the given playlist as input
• -: uses stdin as input
• [dvd|dvdnav]://[title|[starttitle]-endtitle]: uses a DVD as input
• vcd://track[/device]: uses a VCD as input
• tv://[channel][/input_id]: uses some TV channel
• radio://[channel|frequency][/capture]: uses some radio channel
• pvr://: uses video-in of your TV card
• dvb://[card_number@]channel: uses DVB channel
• mf://[filemask|@listfile]: uses a list of jpg/png files
• [cdda|cddb]://track[-endtrack][:speed][/device]: uses audio CD

If you are unsure which source you want to use consult the man page:

man mplayer

Copying

If you just want to copy some SOURCE without changing its coding then this is what you need:

mencoder SOURCE -oac copy -ovc copy /tmp/MOVIE.avi

Encoding

Here is an example of encoding some SOURCE to DivX with Mp3 sound.

mencoder SOURCE -oac lavc -ovc lavc -lavcopts ↵
vcodec=divx:acodec=mp3:vbitrate=1800:abitrate=128 ↵
/tmp/MOVIE.avi

Languages

To select a specific language you need these parameters:

mencoder SOURCE OPTIONS -alang en -slang de /tmp/MOVIE.avi

Crop and Scale

Cropping cuts off parts of the visible movie screen. Scaling uses the input resolution and scales it to the given resolution. Scaling uses a lot of CPU and negatively effects not only encoding time but also quality.

mencoder SOURCE OPTIONS -vf crop=720:544:0:16,scale=720:576

MPlayer has a neat method to extract those values from the movie. Just run

mplayer SOURCE -vf cropdetect

and MPlayer will generate a lot of output. Let the movie play until these parameters don’t change anymore.

Errors on Encoding

From time to time you encounter a DVD you cannot encode. mencoder stops encoding and your DVD-drive makes a suspicious noice. This happens almost always at the beginning of the encoding process. Then you have two options to choose from:

• leave alone that DVD and don’t copy/rip it
• crop some seconds/minutes from the beginning

If your choise was number two – congratulations and welcome in my world. The first few seconds, eventually minutes, of every movie are the opening credits. If you’re not that much interested in this information then continue as follows.

mencoder -ss 40 SOURCE -ovc copy -oac copy -o /tmp/MOVIE.avi

The switch -ss tells mencoder to seek forward 40 seconds and start encoding at this position.

See also

• HOWTO Mencoder Introduction Guide – Gentoo Linux Wiki
• mkmvsh

Have a look at it and tell me what you think. I like it a lot – and I use it a lot!

Some information about the boat

The boat is about 15 meters long and 8 meters wide. It is a catamaran and has been completely build by my fathers (with some help from family and friends).

I like the idea of building my own boat and I’m proud my father did what he dreamed of.

Tell me what you think about it.

Update: The link at heise.de seems to be down – use this link instead: Lest We Remember: Cold Boot Attacks on Encryption Keys.

If you downloaded the script and executed it then you can easily use the network manager to connect/disconnect OpenVPN. You can put the following lines in a separate file called uni-klu.pcf (put it anywhere you like – just remember the location, you will need it later on):

[openvpn]
description=uni-klu
connection-type=x509
remote=143.205.212.10
port=1194
dev=tun
proto=tcp-client
servercert-insecure=no
ca=/etc/openvpn/ca.crt
cert=/etc/openvpn/USERNAME.ocrt
key=/etc/openvpn/USERNAME.okey
comp-lzo=no
shared-key=
local-ip=
remote-ip=
username=
cipher=
ta=
ta_dir=
routes=

Substitute USERNAME with your uni-klu username. THIS IS IMPORTANT!

OpenVPN plugin for network manager

You will need to install the OpenVPN plugin for network manager:

sudo apt-get install network-manager-openvpn

Setting up the OpenVPN plugin

Then logout and login into Gnome. You will see the network manager icon in the notification area (usually on the top-right of your screen) – click on it and select VPN Connections – Configure VPN…. Choose to Add a new configuration, then Forward and Forward. Then choose Import Saved Configuration… and select the file you created earlier. Check the entered values and then Forward, Apply.

After that you can connect using the network manager icon – goto VPN Connections and select uni-klu. As simple as that.