Shekhar

JSON-RPC protocol has got much less attention than it deserves. It is so elegant and simple. Our experience of working on JSON-RPC was plesant.

For uninitiated JSON-RPC is lightweight remote procedure call protocol similar to XML-RPC. I find it incredibly useful in building easy to maintain applications.

We effectively used JSONRPC in our project Cowoop to make it easy to debug application.

It is often seen that unless it is an open source application, in the design phase very little attention is paid towards maintainablity of the application. With many no so clearly seperated layers it makes it increasingly difficult to debug. This makes bug fixing painful and no fun process for those who are working on it. And further these in most cases are not the architects who designed the application. Architect is either moved on to design some other project or is working on next release.

Lets directly jump to example code. So here is my python function.

>>> def add(a, b):
        return a + b

>>> add(1, 2)
3

Project exposes above function add using JSON-RPC. We use Flask + jsonrpc2 to serve JSONRPC over http.

Let us see how does jquery JSONRPC plugin calls this API.

Result

jsonrpc function that you see in above screenshot is part of our js client library. Really it is a a few lines wrapper on top of jquery jsonrpc plugin function jsonRPC.request()

Do you think JSONRPC2 is fairly successful in helping create a maintainable application?

add(1, 2, _session='somesessionid')

--> { "method": "login", "params": {"username": "me", "password": "secret"}, "id": 1}
<-- { "result": "somesessionid", "error": null, "id": 1}
--> { "method": "echo", "params": ["Hello protected JSON-RPC"], "id": 1, "session": "somesessionid"}
<-- { "result": "Hello protected JSON-RPC", "error": null, "id": 1}

In the initial phase of this open source project cowspa developed by Cowoop, we had chosen knockout.js as important client side component. However during the implementation team bowed to the delivery pressure and couldn’t get a chance to learn, explore and use knockout or any other MVC library. Certainly a mistake! Ultimately we have to paid the price of having to maintain really complex pure jquery based bug-prone codebase. However at this stage, I decided to rectify this and started looking for different client side templating and MVC libraries. Essentially the library that binds the templates to data and can auto-update as the data changes. I was stunned by choice of libraries/frameworks available. There are just too many of them. Ones I liked are

• knockout.js
• angular.js
• Ember.js
• Agility
• knockback

Ember is perhaps the best one even according to this post. Angular is very capable and is sheer magic. And well there are many more like excellent backbone.js. We finally narrowed down two options: Knockout and Agility. Agility, I liked most, mainly because of it’s clear syntax and looked like producing very maintainable code. So it was really tempting to go for it. But for us at this point of time knockout scored better at mainly with it’s project maturity (age). Agility is at 0.1.2 at this moment and knockout 2.0.0 and hence knockout enjoys much bigger community.

So while we go ahead now with knockout I will certainly keep an eye on agility’s development would love to find an excuse to use it.

While there is a lot already written here my quick howto

$ sudo bash
# apt-get install dnsmasq squid
# echo "listen-address=127.0.0.1" >> /etc/dnsmasq.conf
# echo "no-dhcp-interface=" >> /etc/dnsmasq.conf
# vi /etc/dhcp3/dhclient.conf
# # ^ uncomment line #prepend domain-name-servers 127.0.0.1;
# vi /etc/resolv.conf  # Add nameserver 127.0.0.1
# /etc/init.d/dnsmasq restart
# vi /etc/squid/squid.conf

http_port 3128
visible_hostname localhost

acl all src 0.0.0.0/0.0.0.0

cache_effective_user proxy
cache_effective_group proxy

http_access allow all
icp_access allow all

positive_dns_ttl 1 month
negative_dns_ttl 1 minute
httpd_accel_port 80
httpd_accel_with_proxy on
httpd_accel_uses_host_header on

cache_dir ufs /cache 400 16 256
cache_store_log none


# mkdir /cache # I have this dir on reizerfs partition
# chown proxy.proxy /cache

# /etc/init.d/squid restart

Configure your browser to use 127.0.0.1:8080. Also read detailed dnsmasq setup article http://ubuntu.wordpress.com/2006/08/02/local-dns-cache-for-faster-browsing/

Surely one of the most over-hyped film. What was good? Aamir, Music and the first half laughs. Post interval it becomes a predictable, boring, idiot bollywood movie.

Munnabhai s were certainly better. I would say watch it on TV or atleast don’t pay 3 times higher than usual for tickets like we did. 4 and half stars by critic hmmmm..

• It works. Make sure while purchasing you inform them that you use Linux
• It’s fast and reliable in Pashan, Pune area
• Below config worked for me on Ubuntu 9.10 AND 10.04
• There are Linux drivers on the CD but I could not get it working on Ubuntu 9.10.
• For activation, I had to use Windows :(

sudo apt-get install usb-modeswitch wvdial

vi /etc/wvdial

[Dialer Defaults]
Phone = #777
Password =
Username =
Baud = 460800
Stupid Mode = 1
New PPPD = 1
Tonline = 0
Init1 = ATZ
Init2 = ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
Modem Type = Analog Modem
Baud = 460800
Modem = /dev/ttyUSB0
ISDN = 0

I do like Ubuntu Netbook Remix’s UI. However with 10.04 it’s just gone so unstable for me.

• After login when system prompts for keyring secret, UNR environment crashes and drops to gnome. I have to relogin if I need UNR env.
• After I removed a few packages it could not just start gnome panel causing a great inconvenience. I guess this is due to Evolution integration with latest Ubuntu. Mail client I like and use is Thunderbird. I cant switch to Evolution.
• Initially after 10.04 release it was damn slow to respond, so had to do some work around to get it to acceptable speed.

Considering all that I decided to switch to Xfce. It just worked like charm. But now I also use (and like :) ) UbuntuOne service for my backup. UbuntuOne is not integrated for XFCE. Also you cant do everything from UbuntuOne’s cli.

u1sdtool -q; killall ubuntuone-login; u1sdtool -c # configuration
u1sdtool --create-folder ~/my_data # add folders you want to be synced
u1sdtool --list-folders
u1sdtool --current-transfers

For more details you might want to check Ubuntu One wiki .

Pulling your hairs over some i18n bug or you fix it but are not able to explain what. This is little help in getting fair idea about unicode/codecs/encoding/decoding etc.

Quick tips:

1. It does not make sense to have a string without knowing what encoding it uses.
2. Utf-8 is a way of storing string of Unicode code points.
3. Encoding: Transforming a unicode object into a sequence of bytes
4. Decoding: Recreating the unicode object from the sequence of bytes is known as decoding. There are many different methods for how this transformation can be done (these methods are also called encodings).

Now

Must Read

1. http://www.joelonsoftware.com/articles/Unicode.html
2. http://stackoverflow.com/questions/447107/whats-the-difference-between-encode-decode-python-2-x

Continue reading

1. http://farmdev.com/talks/unicode/
2. http://diveintopython.org/xml_processing/unicode.html
3. http://stackoverflow.com/questions/440320/unicode-vs-str-decode-for-a-utf8-encoded-byte-string-python-2-x

This how I convert flash I usually use Firefox VideoHelper Addon to download youtube videos. To play them on my Philips DVP5986K DVD player from USB drive, I need to convert it to DivX.

mencoder /home/shon/Desktop/file-864260998.flv -ovc lavc -oac mp3lame -ffourcc DX50 -o out.avi

Linkedin is one of the few sites that has certainly impressed me with it’s clever design. I would rate it very highly for professional networking. It has one very popular feature “recommendations”. Well while I am not against recommending or get recommended by, as I have done both in past. But I see people who think that more and more people they have in their list (no matter how they know well each other professionally) and more recommendations they have received (mostly by requesting others) would make their prospects better. Umm oh, I wonder why are they are madly behind this. I receive a quite a few requests often. Some morning you check your emails and you see that some colleague in your company 2 years ago sends you a mail with subject “can you endorse me?”. And the email says something similar.

Dear ,

I’m sending this to ask you for a brief recommendation of my work that I can include in my LinkedIn profile. If you have any questions, let me know.

Thanks in advance for helping me out. -

Now this above guy could be someone I don’t know that well how well he/she is skilled. But now I can’t deny the request so in a day or two I would look at some other recommendations available for my other LinkedIn friends, copy some matter and send what is requested for. He happily accepts and send me a nice Thank you email. I see people who worked completely unrelated departments and has probably no ability to judge other’s work, go praising out of good relationships. May be what should happen on Orkut testimonials or somewhere similar. Does these people who have tens and hundreds of people in network and so many recommendations have no work other than hopping the jobs and sending such requests.

Next time I interview a guy with many endorsements , I would probably more cautious hiring him.

cat /etc/wvdial.conf:

[Dialer Defaults]
Init1 = ATZ
Init2 = ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
Modem Type = USB Modem
Baud = 460800
New PPPD = yes
Modem = /dev/ttyACM0
ISDN = 0
Stupid mode = 1
Phone = #777
Password = internet
Username = internet

Don’t understand above. Um ok but I am too lazy to explain.

better than struggling with the graphical tools.

$ cat test.dot

digraph FlowChart {

 node [
         fontname = "Bitstream Vera Sans"
         fontsize = 8
         shape = "record"
     ]

 edge [
         fontname = "Bitstream Vera Sans"
         fontsize = 8
         fontcolor = "Red"
     ]

// all blocks
greet [label="Hello, techie", shape="oval"]
which_os [label="What OS do you use?" shape="diamond"]
like_me [label="Great, me too!", shape="oval"]
which_browser [label="You must be using firefox", shape="diamond"]
ff [label="Cool", shape="oval"]
bye [label="Bye", shape="oval"]

// relations
greet -> which_os
which_os -> like_me [label="I use Linux"]
which_os -> which_browser [label="I use Windows"]
which_browser -> ff [label="Right"]
which_browser -> bye [label="what firefox?"]
}

$ dot test.dot -Tpng -o test.png && eog test.png

Python programming is joy. I was stuck on python 2.3 at my work for long and could not really get chance to explore later versions. Now that I got the opportunity doing re-architecture of the product I started exploring these. I am more than excited looking at deque, groupby, defaultdict and much more … Also on top of it there exist excellent python softwares like twisted, sqlalchemy, turbogears makes it even more cool.

It’s little pity that the language is stll somewhat less recognized than others. Or there are more hyped languages exist.