Anand Nalya

A lot of web applications provides you the ability to receive or post updates using SMS (text messages). Twitter is the posterboy of such applications.

But the feature that distinguishes Facebook SMS updates from any other service is that you can actually reply to individual messages and your message then becomes a part of the aforementioned thread. You don’t have to specify any special command to do so. Just hit the reply  button and you are done.

How do they know which message belongs to which thread? Its simple, each message comes from a different number. For example, say A writes something on your wall, then you will receive a message from +91922305501. Also B sends a message to you, a message comes from +91922305502 and when C comments on your note, you get a message from +91922305503. How many numbers do facebook own? Probably 100 in India, from +91922305500 to +9192230599.  A per user mapping of the number from which the message is sent and the object/thread id for that message is kept on the backend. So when the user replies to a particular number, say +91922305502 , it knows that is was a reply to the message sent by B and hence treats as a reply to that message. A rotation policy is used to decide from which number the message is to be sent. So after recieving a message from +9192230599, the next message will be from +91922305500  and now you cannot reply to the thread represented by the earlier message from the same number.

Discalimer: This is just a guess of how this functionality might have been implemented (or at least how I would implement it) and based strictly on SMSes received in India. Actual implementation might (probaly is) be entierly different from what is explained here.

Rule 10 of Steve Souders High Performance Web Sites: Minify Javascript

The most common problem faced while implemnting this is how you handle the full and minified version and how to change there reference in referencing documents. One of the easier ways to do this is to make it part of the deployment process.

Here are the relevent steps involved.

I’m using YUI Compressor.

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#!/bin/bash
 
#Execute this script after checking out the latest source from repository.
 
#Minify all javascript files
cd /path/to/javascript
for x in `ls *.js`
do
        java -jar /path/to/compressor/yuicompressor-2.4.2.jar -o ${x%%.*}-min.js --preserve-semi  $x
done
 
#Minfiy all css files
cd /path/to/css
for x in `ls *.css`
do
        java -jar /path/to/compressor/yuicompressor-2.4.2.jar -o ${x%%.*}-min.css  $x
done

Now you don’t want to replace all references to x.css or x.js in your development code with references to x-min.css and x-min.js respectively. So what you can do is rewrite all those filenames at the web server level.

For apache the following rewrite rules work fine:

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#enable rewriting
RewriteEngine on
RewriteRule /(.*)\.js /$1-min.js
RewriteRule /(.*)\.css /$1-min.css

Caution: Remember to delete existing minified css/js file before running the minifying script or you will end up with file names like x-min-min-min.js and so on. One way to do this is to clear the js/css folder before checking out files from your source repository.

Here is how you run glassfish as a service on CentOS:

1. Create a user glassfish (you can call it anything you want) under which Glassfish will run.

   #useradd glassfish

2. Install glassfish in /home/glassfish.
3. Create the startup script /etc/init.d/glassifsh for glassfish.

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   #!/bin/bash # # glassfish: Startup script for Glassfish Application Server. # # chkconfig: 3 80 05 # description: Startup script for domain1 of Glassfish Application Server.   GLASSFISH_HOME=/home/glassfish/glassfish; export GLASSFISH_HOME   GLASSFISH_OWNER=glassfish; export GLASSFISH_OWNER   start() { echo -n "Starting Glassfish: " echo "Starting Glassfish at `date`" >> $GLASSFISH_HOME/domains/domain1/logs/startup.log su $GLASSFISH_OWNER -c "$GLASSFISH_HOME/bin/asadmin start-domain domain1" >> $GLASSFISH_HOME/domains/domain1/logs/startup.log sleep 2 echo "done" }   stop() { echo -n "Stopping Glassfish: " echo "Stopping Glassfish at `date`" >> $GLASSFISH_HOME/domains/domain1/logs/startup.log su $GLASSFISH_OWNER -c "$GLASSFISH_HOME/bin/asadmin stop-domain domain1" >> $GLASSFISH_HOME/domains/domain1/logs/startup.log echo "done" }   # See how we were called. case "$1" in start) start ;; stop) stop ;; restart) stop start ;; *) echo $"Usage: glassfish {start|stop|restart}" exit esac

4. Install the service

   #chmod +x /etc/init.d/glassfish
   #chkconfig --add glassfish
   #chkconfig --level 3 glassfish on

5. Start glassfish.

   #/etc/init.d/glassfish start