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Articles indexed Monday May 26 2014

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• Simple monitoring of a Raspberry Pi powered screen - Part 2

  - by Chris Houston

  If you have read my previous blog post Raspberry Pi entrance signed backed by Umbraco - Part 1 which describes how we used a Raspberry Pi to drive an Entrance sign for QV Offices you will have seen I mentioned a follow up post about monitoring the sign.As the sign is mounted in the entrance of the building on the ground floor and the reception is on the 1st floor, this meant that if there was a fault of any kind showing on the screen, the first person to see this was inevitably one of QV Offices' clients as they walked into the building.Although the QV Offices' team were able to check the Umbraco website address that the sign uses, this did not always mean that everything was working as expected. We noticed a couple of times that the sign had Wifi issues (it is now hard wired) and this caused the Chromium browser to render a 404 error when it tried to refresh the screen.The simple monitoring solutionWe added the following line to our refresh script, so that after the sign had been refreshed a screen shot of the Raspberry Pi would be taken:import -display :0 -window root ~/screenshot.jpgFinally we wrote a small Crontab task that ran on a QV Offices Mac that grabs this screen shot and saved it on the desktop, admittedly we have used a package that it not mega secure, but in reality this is an internal system that only runs an office sign, so we are not to concerned about it being hacked.*/5 * * * * /usr/local/bin/sshpass -p 'password' /usr/bin/scp [email protected]:screenshot.jpg Desktop/QVScreenShot.jpgAs the file icon updates, if the image changes, this gives a quick visual indication of the status of the sign, if for some reason the icon does not look correct the QV Offices administrator can just click on the file to see the exact image currently displayed on the sign.Sometimes a quick and easy solution is better than a more complex and expensive one.

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• Raspberry Pi entrance signed backed by Umbraco - Part 1

  - by Chris Houston

  Being experts on all things Umbraco, we jumped at the chance to help our client, QV Offices, with their pressing signage predicament. They needed to display a sign in the entrance to their building and approached us for our advice. Of course it had to be electronic: displaying multiple names of their serviced office clients, meeting room bookings and on-the-pulse promotions. But with a winding Victorian staircase and minimal storage space how could the monitor be run, updated and managed? That’s where we came in…Raspberry PiUmbraco CMSAutomatic updatesAutomated monitor of the signPower saving when the screen is not in useMounting the screenThe screen that has been used is a standard LED low energy Full HD screen and has been mounted on the wall using it's VESA mounting points, as the wall is a stud wall we were able to add an access panel behind the screen to feed through the mains, HDMI and sensor cables.The Raspberry Pi is then tucked away out of sight in the main electrical cupboard which just happens to be next to the sign, we had an electrician add a power point inside this cupboard to allow us to power the screen and the Raspberry Pi.Designing the interface and editing the contentAlthough a room sign was the initial requirement from QV Offices, their medium term goal has always been to add online meeting booking to their website and hence we suggested adding information about the current and next day's meetings to the sign that would be pulled directly from their online booking system.We produced the design and built the web page to fit exactly on a 1920 x 1080 screen (Full HD in Portrait)As you would expect all the information can be edited via an Umbraco CMS, they are able to add floors, rooms, clients and virtual clients as well as add meeting bookings to their meeting diary.How we configured the Raspberry PiAfter receiving a new Raspberry Pi we downloaded the latest release of Raspbian operating system and followed the official guide which shows how to copy the OS onto an SD card from a Mac, we then followed the majority of steps on this useful guide: 10 Things to Do After Buying a Raspberry Pi.Installing ChromiumWe chose to use the Chromium web browser which for those who do not know is the open sourced version of Google Chrome. You can install this from the terminal with the following command:sudo apt-get install chromium-browserInstalling UnclutterWe found this little application which automatically hides the mouse pointer, it is used in the script below and is installed using the following command:sudo apt-get install unclutterAuto start Chromium and disabling the screen saver, power saving and mouseWhen the Raspberry Pi has been installed it will not have a keyboard or mouse and hence if their was a power cut we needed it to always boot and re-loaded Chromium with the correct URL.Our preferred command line text editor is Nano and I have assumed you know how to use this editor or will be able to work it out pretty quickly.So using the following command:sudo nano /etc/xdg/lxsession/LXDE/autostartWe then changed the autostart file content to:@lxpanel --profile LXDE@pcmanfm --desktop --profile LXDE@xscreensaver -no-splash@xset s off@xset -dpms@xset s noblank@chromium --kiosk --incognito http://www.qvoffices.com/someURL@unclutter -idle 0The first few commands turn off the screen saver and power saving, we then open Cromium in Kiosk Mode (full screen with no menu etc) and pass in the URL to use (I have changed the URL in this example) We found a useful blog post with the Cromium command line switches.Finally we also open an application called Unclutter which auto hides the mouse after 0 seconds, so you will never see a mouse on the sign.We also had to edit the following file:sudo nano /etc/lightdm/lightdm.confAnd added the following line under the [SeatDefault] section:xserver-command=X -s 0 dpmsRefreshing the screenWe decided to try and add a scheduled task that would trigger Chromium to reload the page, at some point in the future we might well change this to using Javascript to update the content, but for now this works fine.First we installed the XDOTool which enables you to script Keyboard commands:sudo apt-get install xdotoolWe used the Refreshing Chromium Browser by Shell Script post as a reference and created the following shell script (which we called refreshing.sh):export DISPLAY=":0"WID=$(xdotool search --onlyvisible --class chromium|head -1)xdotool windowactivate ${WID}xdotool key ctrl+F5This selects the correct display and then sends a CTRL + F5 to refresh Chromium.You will need to give this file execute permissions:chmod a=rwx refreshing.shNow we have the script file setup we just need to schedule it to call this script periodically which is done by using Crontab, to edit this you use the following command:crontab -eAnd we added the following:*/5 * * * * DISPLAY=":.0" /home/pi/scripts/refreshing.sh >/home/pi/cronlog.log 2>&1This calls our script every 5 minutes to refresh the display and it logs any errors to the cronlog.log file.SummaryQV Offices now have a richer and more manageable booking system than they did before we started, and a great new sign to boot.How could we make sure that the sign was running smoothly downstairs in a busy office centre? A second post will follow outlining exactly how Vizioz enabled QV Offices to monitor their sign simply and remotely, from the comfort of their desks.

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• MSCC: Career & IT Fair 2014

  Already a couple of weeks ago, I've been addressed by Ibraahim and Yunus to see whether it would be interesting to participate in the 1st Career & IT Fair organised by the UoM Computer Club. Well, luckily we met at the Global Windows Azure Bootcamp and I wasn't too sure whether it would be possible for me to attend after all. The main reason is given because of work demand and furthermore due to the fact that the Mauritius Software Craftsmanship Community currently has no advertising material at all. Here's the brief statement of the event: "The UOM Students' Computer Club in collaboration with the UOM Students' Union and UOM CSE Department is organising a 'Career & IT Fair' on the 23rd and 24th April 2014. This event has for objective to provide a platform to tertiary students, secondary students as well as vocational students, the opportunity to meet job recruiters." Luckily, I was reminded that the 23rd is a Wednesday, and therefore I decided that it might be interesting to move our weekly Code & Coffee session to the university and hence be able to attend the career fair. As it turned out it was a great choice and thankfully Pritvi, Nadim as well as Ishwon volunteered to be around at the "community booth". Thankfully, the computer club gave us - the MSCC and the LUGM - one of their spaces in the lobby area of the Paul Octave Wiéhé Auditorium. My impression about the event Very well and professionally organised. Seriously, the lads over at the UoM Computer Club did a great job in organising their 2 days event, and felt very comfortable at any time. Actually, it was kind of amusing to some of the members constantly running around and checking everything. Even though that the whole process went smooth and easy off the hand. There were a couple of interesting pieces of information and announcements during the opening ceremony. For example, the Computer Science faculty is a very young one and has been initiated back in 1988 only - just by 4 staff members at that time. Now, after 25 years they have achieved quite a lot and there are currently 1.000+ active students attending the numerous lectures and courses. But there is no room to rest on previous achievements, and I was kind of surprised to hear that there are plans to extend the campus, and offer new lectures in the fields of nanotechnology, big data handling, and - crossing fingers - the introduction and establishment of a space control centre. Mauritius is already part of the Square Kilometre Array (SKA) and hopefully there will be more activities into that direction in the near future. Community - Awareness and collaboration As stated earlier, I could only spent one morning but luckily other members of the MSCC and the LUGM stayed during the whole two days and provided answers to any interested person. As for me, I took the opportunity to get in touch with the other companies in the lobby. Mainly, to create some awareness about our IT communities but also to see whether there might be options for future engagement in common activities, too. So far, I was able to speak to representatives of the following companies: ACCA Mauritius Business at Work Infomil LinkByNet Microsoft Indian Ocean Islands & French Pacific Spherinity Training Institute Spoon Consulting Ltd. State Informatics Ltd. Unfortunately, I only had a quick chat with an HR representative of LinkByNet but I fully count on our MSCC members like Nitin or LUGM member Ronny to spread our intentions over there.  So far, all of the representatives were really interested in our concepts and activities and I'm currently catching up with an introduction flyer for the MSCC that I'm going to send out to all those contacts via mail. It would be great to have more craftsmen as well as professional support on board. Some pictures from the event MSCC: Fantastic outlook for the near future. Announcements were made on Big data, nanotechnology, and space control centre in Mauritius. Interesting! MSCC: The lobby area was cramped with students. Great way to exchange and network. Good luck to all candidates! Passing the relay staff to... I recommend you to continue to read about the first Career & IT Fair on Ish's blog. He has a great summary and more details on those two days of IT activities than I have. Thanks and feel free to leave a comment (or two)... 

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• Game Review: God of Light

  Luckily I came across this title at a very early stage. If I remember correctly, I took notice of God of Light on Twitter right on the weekend it has been published on the Play Store. "Sit back and become immersed into the world of God of Light, the game that rethinks the physics puzzle genre with its unique environment exploration gameplay, amazing graphics and exclusive soundtrack created by electronic music icon UNKLE. Join cute game mascot, Shiny, on his way to saving the universe from the impending darkness. Play through a variety of exciting game worlds and dozens of levels with mind-blowing puzzles. Your goal is to explore game levels, seek for game objects that reflect, split, combine, paint, bend and teleport rays of light energy to activate the Sources of Life and bring light back to the universe." Mastering the various reflection items in God of Light is very easy to learn and new elements are introduced during the game. Amazing puzzle game Here's the initial review I posted on the Play Store: "Great change in puzzles Fantastic and refreshing concept of puzzle solving. The effects and the music match very well, putting the player in the right mood to game. Get enlightened and grow your skills until you are a true God of Light." And it remains true, even after completing the first realm completely. Similar to Quell it took me only a couple of hours during the evening to complete all levels in the available three realms, unfortunately. God of Light currently consists of 75 levels, well it's 25 in each realm to be precise, and the challenges are increasing. Compared to the iOS version from the AppStore, God of Light is available for free on Android - at least the first realm (25 levels). Unlocking the other two remaining realms is done through an in-app purchase. The visual appearance, the sound effects and the background music provided by UNKLE makes God of Light a superb package for any puzzle gamer. Whether it is simply reflecting light over multiple mirrors, or later on bending the rays of light with black holes, or using prisms to either split, enforce, or colourise your beam, God of Light is great fun and offers a good amount of joy. Check out the following screenshots for some impressions. God of Light: Astonishing graphics and visual appeal throughout the game God of Light - Introduction to the game during the first levels. New light items are introduced at each stage during the game play God of Light: Increasing complexity and puzzle fun Hopefully, Playmous is going to provide more astonishing looking realms and interesting gimmicks in future versions. Play Store: God of Light Also, check out the latest game updates on the official web site of Playmous

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• MSCC: Global Windows Azure Bootcamp

  Mauritius participated and contributed to the Global Windows Azure Bootcamp 2014 (GWAB). Again! And this time stronger than ever, and together with 137 other locations in 56 countries world-wide. We had 62 named registrations, 7 guest additions and approximately 10 offline participants prior to the event day. Most interestingly the organisation of the GWAB through the MSCC helped to increased the number of craftsmen. The Mauritius Software Craftsmanship Community has currently 138 registered members - in less than one year! Only with those numbers we can proudly say that all the preparations and hard work towards this event already paid off. Personally, I'm really grateful that we had this kind of response and the feedback from some attendees confirmed that the MSCC is on the right track here on Cyber Island Mauritius. Inspired and motivated by the success of this event, rest assured that there will be more public events like the GWAB. This time it took some time to reflect on our meetup, following my first impression right on spot: "Wow, what an experience to organise and participate in this global event. Overall, I've been very pleased with the preparations and the event itself. Surely, there have been some nicks that we have to address and to improve for future activities like this. Quite frankly, we are not professional event organisers (not yet) but we learned a lot over the past couple of days. A big Thank You to our event sponsors, namely Microsoft Indian Ocean Islands & French Pacific, Ceridian Mauritius and Emtel. Without them this event wouldn't have happened - Thank You! And to the cool team members of Microsoft Student Partners (MSPs). You geeks did a great job! Thanks!" So, how many attendees did we actually have? 61! - Awesome - 61 cloud computing instances to help on the research of diabetes. During Saturday afternoon there was even an online publication on L'Express: Les développeurs mauriciens se joignent au combat contre le diabète Reactions of other attendees Don't take my word for granted... Here are some impressions and feedback from our participants: "Awesome event, really appreciated the presentations :-)" -- Kevin on event comments "very interesting and enriching." -- Diana on event comments "#gwab #gwabmru 2014 great success. Looking forward for gwab 2015" -- Wasiim on Twitter "Was there till the end. Awesome Event. I'll surely join upcoming meetup sessions :)" -- Luchmun on event comments "#gwabmru was not that cool. left early" -- Mohammad on Twitter The overall feedback is positive but we are absolutely aware that there quite a number of problems we had to face. We are already looking into that and ideas / action plans on how we will be able to improve it for future events. The sessions We started the day with welcoming speeches by Thierry Coret, Sr. Marketing Manager of Microsoft Indian Ocean Islands & French Pacific and Vidia Mooneegan, Managing Director and Sr. Vice President of Ceridian Mauritius. The clear emphasis was on the endless possibilities of cloud computing and how it can enable any kind of sectors here in the country. Then it was about time to set up the cloud computing services in order to contribute each attendees cloud computing resources to the global research of diabetes, a step by step guide presented by Arnaud Meslier, Technical Evangelist at Microsoft. Given a rendering package and a configuration file it was very interesting to follow the single steps in Windows Azure. Also, during the day we were not sure whether the set up had been correctly, as Mauritius didn't show up on the results board - which should have been the case after approximately 20 to 30 minutes. Anyways, let the minions work... Next, Arnaud gave a brief overview of the variety of services Windows Azure has to offer. Whether you need a development environment for your websites or mobiles app, running a virtual machine with your existing applications or simply putting a SQL database online. No worries, Windows Azure has the right packages available and the online management portal is really easy t handle. After this, we got a little bit more business oriented while Wasiim Hosenbocus, employee at Ceridian, took the attendees through the inerts of a real-life application, and demoed a couple of the existing features. He did a great job by showing how the different services of Windows Azure can be created and pulled together. After the lunch break it is always tough to keep the audience awake... And it was my turn. I gave a brief overview on operating and managing a SQL database on Windows Azure. Well, there are actually two options available and depending on your individual requirements you should be aware of both. The simpler version is called SQL Database and while provisioning only takes a couple of seconds, you should take into consideration that SQL Database has a number of constraints, like limitations on the actual database size - up to 5 GB as web edition and up to 150 GB maximum as business edition -, among others. Next, it was Chervine Bhiwoo's session on Windows Azure Mobile Services. It was absolutely amazing to see that the mobiles services directly offers you various project templates, like Windows 8 Store App, Android app, iOS app, and even Xamarin cross-platform app development. So, within a couple of minutes you can have your first mobile app active and running on Windows Azure. Furthermore, Chervine showed the attendees that adding another user interface, like Web Sites running on ASP.NET MVC 4 only takes a couple of minutes, too. And last but not least, we rounded up the day with Windows Azure Websites and hosting of Virtual Machines presented by some members of the local Microsoft Students Partners programme. Surely, one of the big advantages using Windows Azure is the availability of pre-defined installation packages of known web applications, like WordPress, Joomla!, or Ghost. Compared to running your own web site with a traditional web hoster it is surely en par, and depending on your personal level of expertise, Windows Azure provides you more liberty in terms of configuration than maybe a shared hosting environment. Running a pre-defined web application is one thing but in case that you would like to have more control over your hosting environment it is highly advised to opt for a virtual machine. Provisioning of an Ubuntu 12.04 LTS system was very simple to do but it takes some more minutes than you might expect. So, please be patient and take your time while Windows Azure gets everything in place for you. Afterwards, you can use a SecureShell (ssh) client like Putty in case of a Linux-based machine, or Remote Desktop Services when operating a Windows Server system to log in into your virtual machine. At the end of the day we had a great Q&A session and we finalised the event with our raffle of goodies. Participation in the raffle was bound to submission of the session survey and most gratefully we had a give-away for everyone. What a nice coincidence to finish of the day. Note: All session slides (and demo codes) will be made available on the MSCC event page. Please, check the Files section over there. (Some) Visual impressions from the event Just to give you an idea about what has happened during the GWAB 2014 at Ebene... Speakers and Microsoft Student Partners are getting ready for the Global Windows Azure Bootcamp 2014 GWAB 2014 attendees are fully integrated into the hands-on-labs and setting up their individuals cloud computing services 60 attendees at the GWAB 2014. Despite some technical difficulties we had a great time running the event GWAB 2014: Using the lunch break for networking and exchange of ideas - Great conversations and topics amongst attendees There are more pictures on the original event page: Questions & Answers Following are a couple of questions which have been asked and didn't get an answer during the event: Q: Is it possible to upload static pages via FTP? A: Yes, you can. Have a look at the right side column on the dashboard of your website. There you'll find information about the FTP and SFTP host names. You can use any FTP client, like ie. FileZilla to log in. FTP also gives you access to your log files. Q: What are the size limitations on SQL Database? A: 5 GB on the Web Edition, and 150 GB on the business edition. A maximum 150 databases (inclusing 'master') per SQL Database server. More details here: General Guidelines and Limitations (Azure SQL Database) Q: What's the maximum size of a SQL Server running in a Virtual Machine? A: The maximum Windows Azure VM has currently 8 CPU cores, 14 or 56 GB of RAM and 16x 1 TB hard drives. More details here: Virtual Machine and Cloud Service Sizes for Azure Q: How can we register for Windows Azure? A: Mauritius is currently not listed for phone verification. Please get in touch with Arnaud Meslier at Microsoft IOI & FP Q: Can I use my own domain name for Windows Azure websites? A: Yes, you can. But this might require to upscale your account to Standard. In case that I missed a question and answer, please use the comment section at the end of the article. Thanks! Final results Every participant was instructed during the hands-on-lab session on how to set up a cloud computing service in their account. Of course, I won't keep the results from you... Global Azure Lab GWAB 2014: Our cloud computing contribution to the research of diabetes And I would say Mauritius did a good job! Upcoming Events What are the upcoming events here in Mauritius? So far, we have the following ones (incomplete list as usual) in chronological order: Launch of Microsoft SQL Server 2014 (15.4.2014) Corsair Hackers Reboot (19.4.2014) WebCup (TBA ~ June 2014) Developers Conference (TBA ~ July 2014) Linuxfest 2014 (TBA ~ November 2014) Hopefully, there will be more announcements during the next couple of weeks and months. If you know about any other event, like a bootcamp, a code challenge or hackathon here in Mauritius, please drop me a note in the comment section below this article. Thanks! Networking and job/project opportunities Despite having technical presentations on Windows Azure an event like this always offers a great bunch of possibilities and opportunities to get in touch with new people in IT, have an exchange of experience with other like-minded people. As I already wrote about Communities - The importance of exchange and discussion - I had a great conversation with representatives of the University des Mascareignes which are currently embracing cloud infrastructure and cloud computing for their various campuses in the Indian Ocean. As for the MSCC it would be a great experience to stay in touch with them, and to work on upcoming, common activities. Furthermore, I had a very good conversation with Thierry and Ludovic of Microsoft IOI & FP on the necessity of user groups and IT communities here on the island. It's great to see that the MSCC is currently on a run and that local companies are sharing our thoughts on promoting IT careers and exchange of IT knowledge in such an open way. I'm also looking forward to be able to participate and to contribute on more events in the near future. My resume of the day We learned a lot today and there is always room for improvement! It was an awesome event and quite frankly it was a pleasure to spend the day with so many enthuastic IT people in the same room. It was a great experience to organise such event locally and participate on a global scale to support the GlyQ-IQ Technology in their research on diabetes. I was so pleased to see the involvement of new MSCC members in taking the opportunity to share and learn about the power of cloud computing. The Mauritius Software Craftsmanship Community is on the right way and this year's bootcamp on Windows Azure only marked the beginning of our journey. Thank you to our sponsors and my kudos to the MSPs! Update: Media coverage The event has been reported in local media, too. Following are some resources: Orange - Local - Business: Le cloud, pour des recherches approfondies sur le diabète Maurice Info.mu: Le cloud, pour des recherches approfondies sur le diabète Le Quotidien Pg 2: Global Windows Azure Bootcamp 2014 - Le cloud pour des recherches approfondies sur le diabète The Observer Pg 12: Le cloud, pour des recherches approfondies sur le diabète

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• MSCC: Global Windows Azure Bootcamp - 29th March 2014

  The Mauritius Software Craftsmanship Community proudly presents you the Global Windows Azure Bootcamp 2014 in Mauritius. Global Windows Azure Bootcamp 2014 in Mauritius - MSCC together with Microsoft, Ceridian and Emtel We are very happy and excited about our participation in this global event and would like to draw your attention to the official invitation letter below. Please sign up and RSVP on the official website of the MSCC. Participation is for free! Call for action Please create more awareness of this event in Mauritius and use the hash tag #gwabmru as well as the shortened link: http://aka.ms/gwabmru And remember: Sharing is Caring! Official invitation letter to the GWAB 2014 in Mauritius With over 130 confirmed locations around the globe, the Global Windows Azure Bootcamp is going to be a truly memorable event - and now here's your chance to take part! In April of 2013 we held the first Global Windows Azure Bootcamp at more than 90 locations around the globe! This year we want to again offer up a one day deep dive class to help thousands of people get up to speed on discovering Cloud Computing Applications for Windows Azure. In addition to this great learning opportunity the hands on labs will feature pooling a huge global compute farm to perform diabetes research! In Mauritius, the event will be organised by Microsoft Indian Ocean Islands & French Pacific in partnership with The Mauritius Software Craftsmanship Community (MSCC) and sponsored by Microsoft, Ceridian and Emtel. What do I need to bring?  You will need to bring your own computer which can run Visual Studio 2012 or 2013 (i.e. Windows, OSX, Ubuntu with virtualization, etc.) and have it preloaded with the following: Visual Studio 2012 or 2013 The Windows Azure SDK - http://www.windowsazure.com/en-us/develop/net/ Optionally (or if you will not be doing just .NET labs), the following can also be installed: Node.js SDK - http://www.windowsazure.com/en-us/develop/nodejs/ JAVA SDK - http://www.windowsazure.com/en-us/develop/java/ Doing mobile? Android? iOS? Windows Phone or Windows 8? - http://www.windowsazure.com/en-us/develop/mobile/ PHP - http://www.windowsazure.com/en-us/develop/php/ More info here: http://www.windowsazure.com/en-us/documentation Important: Please do the installation upfront as there will be very little time to troubleshoot installations during the day.  

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• Accessing your web server via IPv6

  Being able to run your systems on IPv6, have automatic address assignment and the ability to resolve host names are the necessary building blocks in your IPv6 network infrastructure. Now, that everything is in place it is about time that we are going to enable another service to respond to IPv6 requests. The following article will guide through the steps on how to enable Apache2 httpd to listen and respond to incoming IPv6 requests. This is the fourth article in a series on IPv6 configuration: Configure IPv6 on your Linux system DHCPv6: Provide IPv6 information in your local network Enabling DNS for IPv6 infrastructure Accessing your web server via IPv6 Piece of advice: This is based on my findings on the internet while reading other people's helpful articles and going through a couple of man-pages on my local system. Surfing the web - IPv6 style Enabling IPv6 connections in Apache 2 is fairly simply. But first let's check whether your system has a running instance of Apache2 or not. You can check this like so: $ service apache2 status Apache2 is running (pid 2680). In case that you got a 'service unknown' you have to install Apache to proceed with the following steps: $ sudo apt-get install apache2 Out of the box, Apache binds to all your available network interfaces and listens to TCP port 80. To check this, run the following command: $ sudo netstat -lnptu | grep "apache2\W*$"tcp6       0      0 :::80                   :::*                    LISTEN      28306/apache2 In this case Apache2 is already binding to IPv6 (and implicitly to IPv4). If you only got a tcp output, then your HTTPd is not yet IPv6 enabled. Check your Listen directive, depending on your system this might be in a different location than the default in Ubuntu. $ sudo nano /etc/apache2/ports.conf # If you just change the port or add more ports here, you will likely also# have to change the VirtualHost statement in# /etc/apache2/sites-enabled/000-default# This is also true if you have upgraded from before 2.2.9-3 (i.e. from# Debian etch). See /usr/share/doc/apache2.2-common/NEWS.Debian.gz and# README.Debian.gzNameVirtualHost *:80Listen 80<IfModule mod_ssl.c>    # If you add NameVirtualHost *:443 here, you will also have to change    # the VirtualHost statement in /etc/apache2/sites-available/default-ssl    # to <VirtualHost *:443>    # Server Name Indication for SSL named virtual hosts is currently not    # supported by MSIE on Windows XP.    Listen 443</IfModule><IfModule mod_gnutls.c>    Listen 443</IfModule> Just in case that you don't have a ports.conf file, look for it like so: $ cd /etc/apache2/$ fgrep -r -i 'listen' ./* And modify the related file instead of the ports.conf. Which most probably might be either apache2.conf or httpd.conf anyways. Okay, please bear in mind that Apache can only bind once on the same interface and port. So, eventually, you might be interested to add another port which explicitly listens to IPv6 only. In that case, you would add the following in your configuration file: Listen 80Listen [2001:db8:bad:a55::2]:8080 But this is completely optional... Anyways, just to complete all steps, you save the file, and then check the syntax like so: $ sudo apache2ctl configtestSyntax OK Ok, now let's apply the modifications to our running Apache2 instances: $ sudo service apache2 reload * Reloading web server config apache2   ...done. $ sudo netstat -lnptu | grep "apache2\W*$"                                                                                               tcp6       0      0 2001:db8:bad:a55:::8080 :::*                    LISTEN      5922/apache2    tcp6       0      0 :::80                   :::*                    LISTEN      5922/apache2 There we have two daemons running and listening to different TCP ports. Now, that the basics are in place, it's time to prepare any website to respond to incoming requests on the IPv6 address. Open up any configuration file you have below your sites-enabled folder. $ ls -al /etc/apache2/sites-enabled/... $ sudo nano /etc/apache2/sites-enabled/000-default <VirtualHost *:80 [2001:db8:bad:a55::2]:8080>        ServerAdmin [email protected]        ServerName server.ios.mu        ServerAlias server Here, we have to check and modify the VirtualHost directive and enable it to respond to the IPv6 address and port our web server is listening to. Save your changes, run the configuration test and reload Apache2 in order to apply your modifications. After successful steps you can launch your favourite browser and navigate to your IPv6 enabled web server. Accessing an IPv6 address in the browser That looks like a successful surgery to me... Note: In case that you received a timeout, check whether your client is operating on IPv6, too.

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• Enabling DNS for IPv6 infrastructure

  After successful automatic distribution of IPv6 address information via DHCPv6 in your local network it might be time to start offering some more services. Usually, we would use host names in order to communicate with other machines instead of their bare IPv6 addresses. During the following paragraphs we are going to enable our own DNS name server with IPv6 address resolving. This is the third article in a series on IPv6 configuration: Configure IPv6 on your Linux system DHCPv6: Provide IPv6 information in your local network Enabling DNS for IPv6 infrastructure Accessing your web server via IPv6 Piece of advice: This is based on my findings on the internet while reading other people's helpful articles and going through a couple of man-pages on my local system. What's your name and your IPv6 address? $ sudo service bind9 status * bind9 is running If the service is not recognised, you have to install it first on your system. This is done very easy and quickly like so: $ sudo apt-get install bind9 Once again, there is no specialised package for IPv6. Just the regular application is good to go. But of course, it is necessary to enable IPv6 binding in the options. Let's fire up a text editor and modify the configuration file. $ sudo nano /etc/bind/named.conf.optionsacl iosnet {        127.0.0.1;        192.168.1.0/24;        ::1/128;        2001:db8:bad:a55::/64;};listen-on { iosnet; };listen-on-v6 { any; };allow-query { iosnet; };allow-transfer { iosnet; }; Most important directive is the listen-on-v6. This will enable your named to bind to your IPv6 addresses specified on your system. Easiest is to specify any as value, and named will bind to all available IPv6 addresses during start. More details and explanations are found in the man-pages of named.conf. Save the file and restart the named service. As usual, check your log files and correct your configuration in case of any logged error messages. Using the netstat command you can validate whether the service is running and to which IP and IPv6 addresses it is bound to, like so: $ sudo service bind9 restart $ sudo netstat -lnptu | grep "named\W*$"tcp        0      0 192.168.1.2:53        0.0.0.0:*               LISTEN      1734/named      tcp        0      0 127.0.0.1:53          0.0.0.0:*               LISTEN      1734/named      tcp6       0      0 :::53                 :::*                    LISTEN      1734/named      udp        0      0 192.168.1.2:53        0.0.0.0:*                           1734/named      udp        0      0 127.0.0.1:53          0.0.0.0:*                           1734/named      udp6       0      0 :::53                 :::*                                1734/named   Sweet! Okay, now it's about time to resolve host names and their assigned IPv6 addresses using our own DNS name server. $ host -t aaaa www.6bone.net 2001:db8:bad:a55::2Using domain server:Name: 2001:db8:bad:a55::2Address: 2001:db8:bad:a55::2#53Aliases: www.6bone.net is an alias for 6bone.net.6bone.net has IPv6 address 2001:5c0:1000:10::2 Alright, our newly configured BIND named is fully operational. Eventually, you might be more familiar with the dig command. Here is the same kind of IPv6 host name resolve but it will provide more details about that particular host as well as the domain in general. $ dig @2001:db8:bad:a55::2 www.6bone.net. AAAA More details on the Berkeley Internet Name Domain (bind) daemon and IPv6 are available in Chapter 22.1 of Peter Bieringer's HOWTO on IPv6. Setting up your own DNS zone Now, that we have an operational named in place, it's about time to implement and configure our own host names and IPv6 address resolving. The general approach is to create your own zone database below the bind folder and to add AAAA records for your hosts. In order to achieve this, we have to define the zone first in the configuration file named.conf.local. $ sudo nano /etc/bind/named.conf.local //// Do any local configuration here//zone "ios.mu" {        type master;        file "/etc/bind/zones/db.ios.mu";}; Here we specify the location of our zone database file. Next, we are going to create it and add our host names, our IP and our IPv6 addresses. $ sudo nano /etc/bind/zones/db.ios.mu $ORIGIN .$TTL 259200     ; 3 daysios.mu                  IN SOA  ios.mu. hostmaster.ios.mu. (                                2014031101 ; serial                                28800      ; refresh (8 hours)                                7200       ; retry (2 hours)                                604800     ; expire (1 week)                                86400      ; minimum (1 day)                                )                        NS      server.ios.mu.$ORIGIN ios.mu.server                  A       192.168.1.2server                  AAAA    2001:db8:bad:a55::2client1                 A       192.168.1.3client1                 AAAA    2001:db8:bad:a55::3client2                 A       192.168.1.4client2                 AAAA    2001:db8:bad:a55::4 With a couple of machines in place, it's time to reload that new configuration. Note: Each time you are going to change your zone databases you have to modify the serial information, too. Named loads the plain text zone definitions and converts them into an internal, indexed binary format to improve lookup performance. If you forget to change your serial then named will not use the new records from the text file but the indexed ones. Or you have to flush the index and force a reload of the zone. This can be done easily by either restarting the named: $ sudo service bind9 restart or by reloading the configuration file using the name server control utility - rndc: $ sudo rndc reconfig Check your log files for any error messages and whether the new zone database has been accepted. Next, we are going to resolve a host name trying to get its IPv6 address like so: $ host -t aaaa server.ios.mu. 2001:db8:bad:a55::2Using domain server:Name: 2001:db8:bad:a55::2Address: 2001:db8:bad:a55::2#53Aliases: server.ios.mu has IPv6 address 2001:db8:bad:a55::2 Looks good. Alternatively, you could have just ping'd the system as well using the ping6 command instead of the regular ping: $ ping6 serverPING server(2001:db8:bad:a55::2) 56 data bytes64 bytes from 2001:db8:bad:a55::2: icmp_seq=1 ttl=64 time=0.615 ms64 bytes from 2001:db8:bad:a55::2: icmp_seq=2 ttl=64 time=0.407 ms^C--- ios1 ping statistics ---2 packets transmitted, 2 received, 0% packet loss, time 1001msrtt min/avg/max/mdev = 0.407/0.511/0.615/0.104 ms That also looks promising to me. How about your configuration? Next, it might be interesting to extend the range of available services on the network. One essential service would be to have web sites at hand.

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• DHCPv6: Provide IPv6 information in your local network

  Even though IPv6 might not be that important within your local network it might be good to get yourself into shape, and be able to provide some details of your infrastructure automatically to your network clients. This is the second article in a series on IPv6 configuration: Configure IPv6 on your Linux system DHCPv6: Provide IPv6 information in your local network Enabling DNS for IPv6 infrastructure Accessing your web server via IPv6 Piece of advice: This is based on my findings on the internet while reading other people's helpful articles and going through a couple of man-pages on my local system. IPv6 addresses for everyone (in your network) Okay, after setting up the configuration of your local system, it might be interesting to enable all your machines in your network to use IPv6. There are two options to solve this kind of requirement... Either you're busy like a bee and you go around to configure each and every system manually, or you're more the lazy and effective type of network administrator and you prefer to work with Dynamic Host Configuration Protocol (DHCP). Obviously, I'm of the second type. Enabling dynamic IPv6 address assignments can be done with a new or an existing instance of a DHCPd. In case of Ubuntu-based installation this might be isc-dhcp-server. The isc-dhcp-server allows address pooling for IP and IPv6 within the same package, you just have to run to independent daemons for each protocol version. First, check whether isc-dhcp-server is already installed and maybe running your machine like so: $ service isc-dhcp-server6 status In case, that the service is unknown, you have to install it like so: $ sudo apt-get install isc-dhcp-server Please bear in mind that there is no designated installation package for IPv6. Okay, next you have to create a separate configuration file for IPv6 address pooling and network parameters called /etc/dhcp/dhcpd6.conf. This file is not automatically provided by the package, compared to IPv4. Again, use your favourite editor and put the following lines: $ sudo nano /etc/dhcp/dhcpd6.conf authoritative;default-lease-time 14400; max-lease-time 86400;log-facility local7;subnet6 2001:db8:bad:a55::/64 {    option dhcp6.name-servers 2001:4860:4860::8888, 2001:4860:4860::8844;    option dhcp6.domain-search "ios.mu";    range6 2001:db8:bad:a55::100 2001:db8:bad:a55::199;    range6 2001:db8:bad:a55::/64 temporary;} Next, save the file and start the daemon as a foreground process to see whether it is going to listen to requests or not, like so: $ sudo /usr/sbin/dhcpd -6 -d -cf /etc/dhcp/dhcpd6.conf eth0 The parameters are explained quickly as -6 we want to run as a DHCPv6 server, -d we are sending log messages to the standard error descriptor (so you should monitor your /var/log/syslog file, too), and we explicitely want to use our newly created configuration file (-cf). You might also use the command switch -t to test the configuration file prior to running the server. In my case, I ended up with a couple of complaints by the server, especially reporting that the necessary lease file wouldn't exist. So, ensure that the lease file for your IPv6 address assignments is present: $ sudo touch /var/lib/dhcp/dhcpd6.leases$ sudo chown dhcpd:dhcpd /var/lib/dhcp/dhcpd6.leases Now, you should be good to go. Stop your foreground process and try to run the DHCPv6 server as a service on your system: $ sudo service isc-dhcp-server6 startisc-dhcp-server6 start/running, process 15883 Check your log file /var/log/syslog for any kind of problems. Refer to the man-pages of isc-dhcp-server and you might check out Chapter 22.6 of Peter Bieringer's IPv6 Howto. The instructions regarding DHCPv6 on the Ubuntu Wiki are not as complete as expected and it might not be as helpful as this article or Peter's HOWTO. But see for yourself. Does the client get an IPv6 address? Running a DHCPv6 server on your local network surely comes in handy but it has to work properly. The following paragraphs describe briefly how to check the IPv6 configuration of your clients, Linux - ifconfig or ip command First, you have enable IPv6 on your Linux by specifying the necessary directives in the /etc/network/interfaces file, like so: $ sudo nano /etc/network/interfaces iface eth1 inet6 dhcp Note: Your network device might be eth0 - please don't just copy my configuration lines. Then, either restart your network subsystem, or enable the device manually using the dhclient command with IPv6 switch, like so: $ sudo dhclient -6 You would either use the ifconfig or (if installed) the ip command to check the configuration of your network device like so: $ sudo ifconfig eth1eth1      Link encap:Ethernet  HWaddr 00:1d:09:5d:8d:98            inet addr:192.168.160.147  Bcast:192.168.160.255  Mask:255.255.255.0          inet6 addr: 2001:db8:bad:a55::193/64 Scope:Global          inet6 addr: fe80::21d:9ff:fe5d:8d98/64 Scope:Link          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1 Looks good, the client has an IPv6 assignment. Now, let's see whether DNS information has been provided, too. $ less /etc/resolv.conf # Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTENnameserver 2001:4860:4860::8888nameserver 2001:4860:4860::8844nameserver 192.168.1.2nameserver 127.0.1.1search ios.mu Nicely done. Windows - netsh Per description on TechNet the netsh is defined as following: "Netsh is a command-line scripting utility that allows you to, either locally or remotely, display or modify the network configuration of a computer that is currently running. Netsh also provides a scripting feature that allows you to run a group of commands in batch mode against a specified computer. Netsh can also save a configuration script in a text file for archival purposes or to help you configure other servers." And even though TechNet states that it applies to Windows Server (only), it is also available on Windows client operating systems, like Vista, Windows 7 and Windows 8. In order to get or even set information related to IPv6 protocol, we have to switch the netsh interface context prior to our queries. Open a command prompt in Windows and run the following statements: C:\Users\joki>netshnetsh>interface ipv6netsh interface ipv6>show interfaces Select the device index from the Idx column to get more details about the IPv6 address and DNS server information (here: I'm going to use my WiFi device with device index 11), like so: netsh interface ipv6>show address 11 Okay, address information has been provided. Now, let's check the details about DNS and resolving host names: netsh interface ipv6> show dnsservers 11 Okay, that looks good already. Our Windows client has a valid IPv6 address lease with lifetime information and details about the configured DNS servers. Talking about DNS server... Your clients should be able to connect to your network servers via IPv6 using hostnames instead of IPv6 addresses. Please read on about how to enable a local named with IPv6.

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• Configure IPv6 on your Linux system (Ubuntu)

  After the presentation on IPv6 at the first event of the Emtel Knowledge Series and some recent discussion on social media networks with other geeks and Linux interested IT people here in Mauritius, I thought that I should give it a try (finally) and tweak my local network infrastructure. Honestly, I have been to busy with contractual project work and it never really occurred to me to set up IPv6 in my LAN. Well, the following paragraphs are going to shed some light on those aspects of modern computer and network technology. This is the first article in a series on IPv6 configuration: Configure IPv6 on your Linux system DHCPv6: Provide IPv6 information in your local network Enabling DNS for IPv6 infrastructure Accessing your web server via IPv6 Piece of advice: This is based on my findings on the internet while reading other people's helpful articles and going through a couple of man-pages on my local system. Let's embrace IPv6 The basic configuration on Linux is actually very simple as the kernel, operating system, and user-space programs support that protocol natively. If your system is ready to go for IP (aka: IPv4), then you are good to go for anything else. At least, I didn't have to install any additional packages on my system(s). We are going to assign a static IPv6 address to the system. Hence, we have to modify the definition of interfaces and check whether we have an inet6 entry specified. Open your favourite text editor and check the following entries (it should be at least similar to this): $ sudo nano /etc/network/interfaces auto eth0# IPv4 configurationiface eth0 inet static  address 192.168.1.2  network 192.168.1.0  netmask 255.255.255.0  broadcast 192.168.1.255# IPv6 configurationiface eth0 inet6 static  pre-up modprobe ipv6  address 2001:db8:bad:a55::2  netmask 64 Of course, you might have to adjust your interface device (eth0) or you might be interested to have multiple directives for additional devices (eth1, eth2, etc.). The auto instruction takes care that your device is enabled and configured during the booting phase. The use of the pre-up directive depends on your kernel configuration but in most scenarios this might be an optional line. Anyways, it doesn't hurt to have it enabled after all - just to be on the safe side. Next, either restart your network subsystem like so: $ sudo service networking restart Or you might prefer to do it manually with identical parameters, like so: $ sudo ifconfig eth0 inet6 add 2001:db8:bad:a55::2/64 In case that you're logged in remotely into your PC (ie. via ssh), it is highly advised to opt for the second choice and add the device manually. You can check your configuration afterwards with one of the following commands (depends on whether it is installed): $ sudo ifconfig eth0eth0      Link encap:Ethernet  HWaddr 00:21:5a:50:d7:94            inet addr:192.168.160.2  Bcast:192.168.160.255  Mask:255.255.255.0          inet6 addr: fe80::221:5aff:fe50:d794/64 Scope:Link          inet6 addr: 2001:db8:bad:a55::2/64 Scope:Global          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1 $ sudo ip -6 address show eth03: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qlen 1000    inet6 2001:db8:bad:a55::2/64 scope global        valid_lft forever preferred_lft forever    inet6 fe80::221:5aff:fe50:d794/64 scope link        valid_lft forever preferred_lft forever In both cases, it confirms that our network device has been assigned a valid IPv6 address. That's it in general for your setup on one system. But of course, you might be interested to enable more services for IPv6, especially if you're already running a couple of them in your IP network. More details are available on the official Ubuntu Wiki. Continue to configure your network to provide IPv6 address information automatically in your local infrastructure.

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• Question about casting a class in Java with generics

  - by Florian F

  In Java 6 Class<? extends ArrayList<?>> a = ArrayList.class; gives and error, but Class<? extends ArrayList<?>> b = (Class<? extends ArrayList<?>>)ArrayList.class; gives a warning. Why is (a) an error? What is it, that Java needs to do in the assignment, if not the cast shown in (b)? And why isn't ArrayList compatible with ArrayList? I know one is "raw" and the other is "generic", but what is it you can do with an ArrayList and not with an ArrayList, or the other way around?

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• Restful Java based web services in json + html5 and javascript no templates (jsp/jsf/freemarker) aka fat/thick client

  - by Ismail Marmoush

  I have this idea of building a website which service JSON data through restful services framework. And will not use any template engines like jsp/jsf/freemarker. Just pure html5 and Javascript libs. What do you think of the pros and cons of such design ? Just for elaboration and brain storming a friend of mine argued with the following concerns: sounds like gwt this way you won't have any control over you service api for example say you wanna charge the user per request how will you handle it? how will you control your design and themes? what about the 1st request the browser make? not easy with this all of the user's requests will come with "Accept" header "application/json" how will you separate browser from abuser? this way all of your public apis will be used by third party apps abusively and you won't be able to lock it since you won't be able to block the normal user browser We won't use compiled html anyway but may be something like freemarker and in that case you won't expose any of your json resources to the unauthorized user but you will expose all the html since any browser can access them all the well known 1st class services do this can you send me links to what you've read? keep in mind the DOM based XSS it will be a nightmare ofc, if what you say is applicable.

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• Is this method pure?

  - by Thomas Levesque

  I have the following extension method: public static IEnumerable<T> Apply<T>( [NotNull] this IEnumerable<T> source, [NotNull] Action<T> action) where T : class { source.CheckArgumentNull("source"); action.CheckArgumentNull("action"); return source.ApplyIterator(action); } private static IEnumerable<T> ApplyIterator<T>(this IEnumerable<T> source, Action<T> action) where T : class { foreach (var item in source) { action(item); yield return item; } } It just applies an action to each item of the sequence before returning it. I was wondering if I should apply the Pure attribute (from Resharper annotations) to this method, and I can see arguments for and against it. Pros: strictly speaking, it is pure; just calling it on a sequence doesn't alter the sequence (it returns a new sequence) or make any observable state change calling it without using the result is clearly a mistake, since it has no effect unless the sequence is enumerated, so I'd like Resharper to warn me if I do that. Cons: even though the Apply method itself is pure, enumerating the resulting sequence will make observable state changes (which is the point of the method). For instance, items.Apply(i => i.Count++) will change the values of the items every time it's enumerated. So applying the Pure attribute is probably misleading... What do you think? Should I apply the attribute or not?

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• End user query syntax?

  - by weberc2

  I'm making a command line tool that allows end users to query a statically-schemed database; however, I want users to be able to specify boolean matchers in their query (effectively things like "get rows where (field1=abcd && field2=efgh) || field3=1234"). I did Googling a solution, but I couldn't find anything suitable for end users--still, this seems like it would be a very common problem so I suspect there is a standard solution. So: What (if any) standard query "languages" are there that might be appropriate for end users? What (if any) de facto standards are there (for example, Unix tools that solve similar problems). Failing the previous two options, can you suggest a syntax that would be simple, concise, and easy to validate?

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• What technique to use when trying to drag elements around on a canvas

  - by choise

  I want to achieve two things in my java swing application: First, i need a canvas zone where i can drag elements (a rectangle or a circle) from the outside of a pane inside the canvas and place it at the position where they where dropped. also it should be possible to select an element on the canvas and move it around and drop it on another location on the canvas. what techniques would fit best to do such a job? Please leave a comment if something is unclear.

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• Understanding UML composition better

  - by Prog

  The technical difference between Composition and Aggregation in UML (and sometimes in programming too) is that with Composition, the lifetime of the objects composing the composite (e.g. an engine and a steering wheel in a car) is dependent on the composite object. While with Aggregation, the lifetime of the objects making up the composite is independent of the composite. However I'm not sure about something related to composition in UML. Say ClassA is composed of an object of ClassB: class ClassA{ ClassB bInstance; public ClassA(){ bInstance = new ClassB(); } } This is an example of composition, because bInstance is dependent on the lifetime of it's enclosing object. However, regarding UML notation - I'm not sure if I would notate the relationship between ClassA and ClassB with a filled diamond (composition) or a white diamond (aggregation). This is because while the lifetime of some ClassB instances is dependent of ClassA instances - there could be ClassB instances anywhere else in the program - not only within ClassA instances. The question is: if ClassA objects are composed of ClassB objects - but other ClassB objects are free to be used anywhere else in the program: Should the relationship between ClassA and ClassB be notated as aggregation or as composition?

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• Use unnamed object to invoke method or not?

  - by Chen OT

  If I have a class with only only public method. When I use this class, is it good to use unnamed object to invoke its method? normal: TaxFileParser tax_parser(tax_file_name); auto content = tax_parser.get_content(); or unnamed object version: auto content = TaxFileParser(tax_file_name).get_content(); Because I've told that we should avoid temporary as possible. If tax_parser object is used only once, can I call it a temporary and try to eliminate it? Any suggestion will be helpful.

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• One method with many behaviours or many methods

  - by Krowar

  This question is quite general and not related to a specific language, but more to coding best practices. Recently, I've been developing a feature for my app that is requested in many cases with slightly different behaviours. This function send emails , but to different receivers, or with different texts according to the parameters. The method signature is something like public static sendMail (t_message message = null , t_user receiver = null , stream attachedPiece = null) And then there are many condition inside the method, like if(attachedPiece != null) { } I've made the choice to do it this way (with a single method) because it prevents me to rewrite the (nearly) same method 10 times, but I'm not sure that it's a good practice. What should I have done? Write 10 sendMail method with different parameters? Are there obvious pros and cons for these different ways of programming? Thanks a lot.

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• How do you handle domain logic that spans multiple model objects in an ORM?

  - by duality_

  So I know that business logic should be placed in the model. But using an ORM it is not as clear where I should place code that handles multiple objects. E.g. let's say we have a Customer model which has a type of either sporty or posh and we wanted to customer.add_bonus() to every posh customer. Where would we do this? Do we create a new class to handle all this? If yes, where do we put it (alongside all the other model classes, but not subclass it from the ORM?)? I'm currently using django framework in python, so specific suggestions are even more wanted.

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• Scenario to illustrate how unit testing leads to better design

  - by Cocowalla

  For an internal training session, I'm trying to come up with a simple scenario that illustrates how unit testing leads to better design, by forcing you to think about things like coupling before you start coding. The idea is that I get the participants to code something first, without considering unit testing, then we do it again, but considering unit testing. Hopefully the code produced second time round should be more decoupled and maintainable. I'm struggling to come up with a scenario that can be coded quickly, yet can still demonstrate how unit testing can lead to better overall design.

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• Is backing up a MySQL database in GIT a good idea?

  - by wobbily_col

  I am trying to improve the backup situation for my application. I have a Django application and MySQL database. I read an article suggesting backing up the database in Git. On the one hand I like it, as it will keep a copy of the data and the code in synch. But GIT is a designed for code, not for data. As such it will be doing a lot of extra work diffing the mysql dump every commit, which is not really necessary. If I compress the file before storing it, will git diff the files? (The dump file is currently 100MB uncompressed, 5.7Mb when bzipped). Edit: the code and database schema definitions are already in GIT, it is really the data I am concerned about backing up now.

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• Wrong encoding in DataReceivedEventArgs

  - by user2102508

  I start cmd.exe process and redirect stdin to pass script to it and redirect stdout and stderr to read cmd's output. Here is the code of my DataReceivedEventHandler: (o, a) => { if(!String.IsNullOrEmpty(a.Data)) { bw.Write(a.Data.ToUTF8()); bw.Write((byte)'\n'); } } In the code bw is instance of BinaryWriter, ToUTF8 is string extension method, that converts a string to UTF8 encoded byte array. When I use this code in a separate process it works well, however when I use this code as a shared library inside some other process a.Data doesn't contain valid localized characters (like russian characters for example). So how should I convert characters? How to get cmd's OEM encoding? Why does the code works well in a separate process and doesn't work as a shared library inside some other process?

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• Inheritance vs containment while extending a large legacy project

  - by Flot2011

  I have got a legacy Java project with a lot of code. The code uses MVC pattern and is well structured and well written. It also has a lot of unit tests and it is still actively maintained (bug fixing, minor features adding). Therefore I want to preserve the original structure and code style as much as possible. The new feature I am going to add is a conceptual one, so I have to make my changes all over the code. In order to minimize changes I decided not to extend existing classes but to use containment: class ExistingClass { // .... existing code // my code adding new functionality private ExistingClassExtension extension = new ExistingClassExtension(); public ExistingClassExtension getExtension() {return extension;} } ... // somewhere in code ExistingClass instance = new ExistingClass(); ... // when I need a new functionality instance.getExtension().newMethod1(); All functionality that I am adding is inside a new ExistingClassExtension class. Actually I am adding only these 2 lines to each class that needs to be extended. By doing so I also do not need to instantiate new, extended classes all over the code and I may use existing tests to make sure there is no regression. However my colleagues argue that in this situation doing so isn't a proper OOP approach, and I need to inherit from ExistingClass in order to add a new functionality. What do you think? I am aware of numerous inheritance/containment questions here, but I think my question is different.

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• What is Atomicity?

  - by James Jeffery

  I'm really struggling to find a concrete, easy to grasp, explanation of Atomicity. My understanding thus far is that to ensure an operation is atomic you wrap the critical code in a locker. But that's about as much as I actually understand. Definitions such as the one below make no sense to me at all. An operation during which a processor can simultaneously read a location and write it in the same bus operation. This prevents any other processor or I/O device from writing or reading memory until the operation is complete. Atomic implies indivisibility and irreducibility, so an atomic operation must be performed entirely or not performed at all. What does the last sentence mean? Is the term indivisibility relating to mathematics or something else? Sometimes the jargon with these topics confuse more than they teach.

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• How to represent a tree structure in NoSQL

  - by Vlad Nicula

  I'm new to NoSQL and have been playing around with a personal project on the MEAN stack (Mongo ExpressJs AngularJs NodeJs). I'm building a document editor of sorts that manages nodes of data. Each document is actually a tree. I have a CRUD api for documents, to create new trees and a CRUD api for nodes in a given document. Right now the documents are represented as a collection that holds everything, including nodes. The children parent relationship is done by ids. So the nodes are an map by id, and each node has references to what nodes are their children. I chose this "flat" approach because it is easier to get a node by id from a document. Being used to having a relation table between nodes and documents, a relation table between nodes and children nodes I find it a bit weird that I have to save the entire "nodes" map each time I update a node. Is there a better way to represent such a data type in NoSQL?

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