i2devlabs Blog

Supporting CORS and OPTIONS in ServiceStack

pcarvalho — Tue, 09 Apr 2013 11:39:00 -0400

To enable CORS headers and HTTP OPTIONS method in ServiceStack, add the following code to Configure()

 this.Plugins.Add(new CorsFeature());

 this.RequestFilters.Add((httpReq, httpResp, requestDto) =&gt; {
       if(httpReq.HttpMethod == "OPTIONS"){
               httpResp.EndServiceStackRequest();
   }
});

Working hardThat’s Real Racing HD on the iPad :-)

pcarvalho — Tue, 08 Jan 2013 09:47:59 -0500

Working hard

That’s Real Racing HD on the iPad :-)

Friday Talk: AngularJS

pcarvalho — Thu, 20 Dec 2012 06:28:58 -0500

Cátia is more and more into frontend development and she talked about AngularJS.

AngularJS basics from i2devlabs

Friday Talk: Isolation Levels in SQL Server 2012

pcarvalho — Tue, 18 Dec 2012 07:36:00 -0500

Luís reformated the talk he gave past October about Sql Server isolation levels and concurrency and here is the result.

ISOLATION LEVELS?

Isolation Levels exist so that users can control various concurrency problems when creating reading, updating and deleting data from a database. The concurrency problems are the following:

Note: The examples will run assuming that there is only one row in the TestTable, that is {id = 1, Value = 1}, the isolation level will be READ UNCOMMITED, that is the lowest level and allows us to test all the following problems.

Dirty Read

Dirty read happens when selected data is being changed by a transaction, but it was not committed.

Example:

Transaction 1:

SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
BEGIN TRAN
Select Value from TestTable where id = 1
COMMIT

Transaction 2:

BEGIN TRAN
UPDATE TesteTble SET Value = 2 where id = 1
--Simulate having some intensive processing here with a wait
WAITFOR DELAY '00:00:10'
ROLLBACK

If we run the transaction simultaneous, Transaction 1 will tell us that Value is 2, but Transaction 1 is not yet committed, the data we are reading is only valid for 10 seconds.

Non-Repeatable Read

Non-Repeatable Read is when two selects to the same data under the same transaction return different data.

Example

Transaction 1:

SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
BEGIN TRAN
Select Value from TestTable where id = 1
WAITFOR DELAY '00:00:10'
Select Value from TestTable where id = 1
COMMIT

Transaction 2:

BEGIN TRAN
UPDATE TestTable SET Value = 2 where id = 1
--Simulate having some intensive processing here with a wait
WAITFOR DELAY '00:00:05'
ROLLBACK

If we run the transaction simultaneous, Transaction 1 will tell us that Value is 2 in the first select and in the second we will have that the Value is 1.

Phantom Reads

Phantom Reads is when 2 selects to the same data under the same transaction return different number of rows.

Example

Transaction 1:

SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
BEGIN TRAN
Select * from TestTable
WAITFOR DELAY '00:00:10'
Select * from TestTable
COMMIT

Transaction 2:

BEGIN TRAN
Insert Into TestTable (Value) Values (2)
--Simulate having some intensive processing here with a wait
WAITFOR DELAY '00:00:05'
ROLLBACK

If we run the transaction simultaneous, Transaction 1 will tell us TestTable has 2 rows {id = 1, Value = 1} and {id = 2, Value = 2}, but the second select will only return 1 row {id = 1, Value = 1}.

SQL SERVER ISOLATION LEVELS

Read Uncommitted

Read Uncommitted is the lowest Level (Optimistic) and is when reading operations do not respect locks and don’t lock data, has we said before all concurrency problems can occur with this isolation level.

Dirty Read – Yes
Non-Repeatable Read – Yes
Phantom Reads – Yes

Read Committed

Read Committed is when reading operation can’t read data that is being changed by another transaction a Dead Lock will occur.

Dirty Read – No
Non-Repeatable Read – Yes
Phantom Reads – Yes

Snapshot

Snapshot is only available in SQL Server. In this level, a reading operation will return data that is being changed by another transaction, but without the changes made by it.

Dirty Read – No
Non-Repeatable Read – Yes
Phantom Reads – Yes

Serializable

Serializable is the highest Level (Pessimistic) and is when rows and tables being read by a transaction will be locked, Dead Lock will occur in update, insert and delete operations.

Dirty Read – No
Non-Repeatable Read – No
Phantom Reads – NO

Repeatable Read

Repeatable Read is when rows being read by a transaction will be locked, a deadlock will occur in update operations.

Dirty Read – No
Non-Repeatable Read – No
Phantom Reads – Yes

Carpenter programmerThat’s Luis Torres right there!

pcarvalho — Tue, 04 Dec 2012 12:35:19 -0500

Carpenter programmer

That’s Luis Torres right there!

Friday Talk: Command Line Interface basics in Linux

pcarvalho — Fri, 16 Nov 2012 12:05:00 -0500

Last Monday, it was y turn to present the Friday Talk (I know, it’s never on Friday). Lately we have been working on Windows and .NET, and both Luís and Cátia are a tad green on a Linux shell, so I decided to refresh the basics of using the shell on Linux (Ubuntu). The support for this talk wasn’t a slidedeck, it was the following plain text.

Bash CLI (Command Line Interface) basics in Linux (Ubuntu)

Getting help

Use man to show the manual for a command

Try man man

File & directory

~ (tilde) is your home directory, tipically /home/user
pwd (stands for print working directory) returns the directory you are in
ls (list) lists the files in a directory
cd (change directory)
cp (copy) copy a file. For directories, use the -r flag cp -r directory foo (copy recursively)
mv (move) move a file to a different location or rename a file
rm remove a file
rmdir delete empty directory. To delete a directory and it’s contents rmdir -r
mkdir to create a new directory
sudo execute a command as root (dangerous stuff)

Running a file

./filename

System information

df displays filesystem disk space usage for all mounted partitions. df -h is more useful, being -h the flag for “human-readable”
top (table of processes) displays running processes and system resources
free displays the amount of free and used memory. free -h (human-readable) shows values in megabytes, and is probably more useful
uname -a prints all system information, inclunding machine name, kernel name & version and more details.
lsb_release -a prints version information for the Linux release

User management

adduser newuser creates a new user called “newuser”
passwd someuser changes the password for “someuser”
addgroup newgroup creates a new group called “newgroup”
useradd -G groupname username creates a new user called “username” and adds it to group “groupname”
usermod -a -G sftp pedro adds the existing user “pedro” to the group “sftp”
-G for secondary groups, -g for primary groups
id user shows the id for the user
groups user prints the groups to which the user belongs
su username The su command is used to become another user during a login session. Invoked without a username, su defaults to becoming the superuser.

File permissions

In Linux and Unix, eveything is a file. Directories are files, files are files and devices are files.

types of access:
- read (r or 4)
- write (w or 2)
- execute (x or 1)
user restrictions
- owner
- group
- other
chmod change permissions
chown change file owner
apt-get install acl for more granular permissions

Text

cat concatenate files and print on the standard output.
grep find a string in a file or stream. It can be used with Regular expression to be more flexible at finding strings.
awk pattern scanning and processing language. It’s a beast and I’m not going to discuss it here. More details http://www.grymoire.com/Unix/Awk.html)
sed stream editor. Simple example: sed s/day/night/ old.txt > new.txt. A powerful tool as seen here http://www.grymoire.com/Unix/Sed.html

Networking

ifconfig (interface configuration) configure, control, and query TCP/IP network interface parameters
ping
traceroute
nslookup

Piping

The pipe makes the output of a command the input for another program. Piping is achieved using the | character.

ls -l | grep 'init' | less

xargs

cat files.txt | cp but this does cat files.txt | xargs cp because cp doesn’t read input, only arguments.

backticks

cp `cat files.txt`

Shell runs the command ct files.txt, intercepts the standard output and uses the result as parameters to cp

Directing output

Consider this example ls -l > temp.txt where the output of ls -l is redirected from the screen to a text file. With the > character, it the file exists, it will be replaced. To append to a text use >>

ls -l >> temp.txt

Reversing also works_

grep 'init' < temp.txt

grep 'init' < temp.txt > temp2.txt

Shell scripting

#!/bin/bash
echo "The simplest of the scripts"
exit 0

Every shell script starts with #!, frequently called Sha-bang
#! is the magic number. When the kernel goes to run a program, it looks at the first 16 bits of the file. Simply put, it tells the kernel to execute the file contents with the tool specified after the sha-bang

Some other sha-bang lines you can use:

#!/bin/sh
 #!/bin/bash
 #!/usr/bin/perl
 #!/usr/bin/tcl
 #!/bin/sed -f
 #!/bin/awk -f
 #!/bin/python

Note: the file containing the shell script must be executable chmod +x in order to be run like this ./script

Processes

ps aux lists all running processes
kill -signal pid send the signal “signal” to process with id “pid”. Omit “signal” to just terminate the process
kill -9 pid send signal number 9 (SIGKILL) to process with id “pid”. This is a last-resort method to terminate a process.
command & runs command in the background

Useful things

touch change file timestamp, creating file if it doesn’t exist

Sources

https://help.ubuntu.com/community/UsingTheTerminal

http://en.wikipedia.org/wiki/Ifconfig

https://help.ubuntu.com/community/FilePermissions

https://help.ubuntu.com/10.04/serverguide/network-configuration.html

http://www.faqs.org/faqs/unix-faq/faq/part3/section-16.html

http://en.wikipedia.org/wiki/Xargs

http://help.lockergnome.com/linux/help-understand-pipe-xargs—ftopict549399.html

http://www.ece.ucy.ac.cy/courses/ece306/Linux%20primers/LinuxBasics.pdf

Friday Talk: Python generators

pcarvalho — Mon, 29 Oct 2012 18:52:00 -0400

Today isn’t Friday, but last Friday the team was working at full speed closing features and client requests, so the talk was postponed for today, Monday. It was Catia turn to present, and she chose to talk about Python generators.

Python Generators from i2devlabs

Friday Talk: Concurrency in SQL Server

pcarvalho — Fri, 19 Oct 2012 18:00:00 -0400

Luís, our in-house Microsoft evangelist, talked about concurrency in SQL Server. His slides were in portuguese, so as soon as he rewrites them in english, this post will be updated with the slidedeck.

Edit: Luís talk is available in this post http://blog.i2devlabs.com/friday-talk-isolation-levels-in-sql-server-20

Friday Talk: JavaScript inheritance

pcarvalho — Fri, 12 Oct 2012 11:05:00 -0400

Today we started a new initiative called Friday Talks. Every Friday a team member does a presentation to other team members on a topic he or she chooses. These talks are meant to be small, no more than one hour, and no topic is too small. The whole idea is to share with others that little bits of investigation and reading we (at least I) do on the couch, in the evening.

I was the first one to present and I talked about JavaScript inheritance. Check out the slides.

2012 oct-12 - java script inheritance from i2devlabs

Apresentação de proposta de estágio no Instituto Politécnico de Leiria

pcarvalho — Mon, 02 Jul 2012 07:43:00 -0400

No passado dia 26 de Junho estive no Instituto Politécnico de Leiria a apresentar a i2devlabs e a nossa proposta de estágio aos alunos do Mestrado em Engenharia Informática - Computação Móvel.

Podem ver o vídeo aqui:

Se não quiserem ver o vídeo, podem ver só os slides:

Whiteboarding

pcarvalho — Fri, 09 Mar 2012 06:54:05 -0500

Whiteboarding

When all you have is a hammer…Our specially made, custom...

pcarvalho — Mon, 30 Jan 2012 08:03:33 -0500

When all you have is a hammer…

Our specially made, custom built, branded hammer!

StickersWe’ve just received the stickers we ordered from...

pcarvalho — Fri, 16 Sep 2011 09:33:54 -0400

Stickers

We’ve just received the stickers we ordered from uk.moo.com and they look awesome!

New website is live!

pcarvalho — Tue, 06 Sep 2011 10:58:45 -0400

Our new website is up and running. Can you guess what CMS we used to build it? Can you? Did you say Mobilastic? You are absolutely right!

New website design

pcarvalho — Mon, 30 May 2011 19:32:38 -0400

Take a look at the final design for the i2DevLabs website.

An excellent work, as usual, by magaworks.com

Now we just need to find the time to build the website. Guess what tool we are going to use to build the new website? hint: getmobilastic.com Yup, that’s true, we are going to use Mobilastic to build it, not only for mobile, but also for desktop browsers.

iPad2 has arrived

pcarvalho — Tue, 19 Apr 2011 17:01:45 -0400

Last week we received a brand new iPad2.

It’s the WiFi and 16GB model. The engraving in the back looks really cool!

Now, on to develop some apps!

i2DevLabs new logo Take a look at i2devlabs new logo. The...

pcarvalho — Sat, 16 Apr 2011 18:53:00 -0400

i2DevLabs new logo

Take a look at i2devlabs new logo.

The “i2” refers back to the old i2Mobile logo and the logic behind the “devlabs” part is of a marker writing on a whiteboard. We do love our whiteboards to discuss and sketch ideas!

The new website is coming soon :)

New books in our bookshelfNew books just arrived. Everyone loves...

pcarvalho — Wed, 30 Mar 2011 05:25:14 -0400

New books in our bookshelf

New books just arrived.

Everyone loves the smell of a new book, right?

i2Mobile is now i2DevLabs

pcarvalho — Tue, 08 Mar 2011 08:50:00 -0500

The time has arrived to change our name. For some time we have been talking in changing the name of the company formerly know as i2Mobile. Back in 2005, when Miguel and I founded the company, i2Mobile sounded right because our ideas where all about mobile. As our work evolved, we found ourselves, by request of our clients, doing full blown software development projects where mobile was only a tiny part and sometimes not a part at all.

By this time, your should have some questions:

If not mobile only, what does your company do?
We team up with our clients to create great software, the agile way. That’s it!Great! So, what’s the new name?
i2DevLabs. We like it, it’s new but doesn’t do a complete cut with the past. Apart from that, the .com was available!

What kind of projects are you used to do?
Consumed focused web, enterprise software, mobile web, Android and iPhone apps.

So, you’re another Rails shop, is it?
No, we don’t even know Ruby or Rails. We believe in using the best tool to do the job. Of course, we don’t know how to do stuff on every single platform or programming language, but we try to identify and use the tool set that will bring the best results and will make our clients happy. That said, we do have our favorites: Python and Django for consumer based web apps and Microsoft stack (ASP .NET, SQL Server, C#) for enterprise apps. Maybe one of these days, we will add Rails to our tool belt, who knows? We do have an internal rule: “religious” discussions regarding programming languages are not welcome.

Ok, that’s a lot of talk. I want to know what’s i2DevLabs score on The Joel Test.

(For those who don’t know the Joel test, here is the link http://www.joelonsoftware.com/articles/fog0000000043.html)

The Joel Test

1. Do you use source control? Sure. Git+GitHub for some projects; Subversion for others
2. Can you make a build in one step? Most of the times, yes.
3. Do you make daily builds? Yes.
4. Do you have a bug database? Yes, we use Pivotal Tracker for that.
5. Do you fix bugs before writing new code? We sure do.
6. Do you have an up-to-date schedule? Yes. Basecamp helps us with that.
7. Do you have a spec? Yes.
8. Do programmers have quiet working conditions? The best we can afford.
9. Do you use the best tools money can buy? Yes.
10. Do you have testers? No. We are working on that.
11. Do new candidates write code during their interview? Yes.
12. Do you do hallway usability testing? Yes

Why does your website i2devlabs.com look so bad?
It really sucks right now! We are working on it. It will look a lot better any time soon.