Gaku.net Uklog

Things to be done before upgrading to iOS5

Thu, 13 Oct 2011 23:19:05 -0400

Google Authenticator stopped working after I upgraded iphone to iOS5. It crushed right after invocations. My co-worker told me about this, so I was at least mentally prepared.

Actually, it is pretty troublesome as you’ll lose access to Google accounts. Before you’re upgrading to iOS5, here’s what you should do:

turn-off 2-factor authenticator
upgrade your iPhone to iOS5
uninstall Authenticator
install Authenticator from App Store.
configure Authenticator

It sounds pretty dumb, but worked.

8/15/2011

Tue, 16 Aug 2011 03:35:12 -0400

Setup a periodic http ping program.

currently runs under screen.
writes timestamp and {0,1} value to STDOUT and it is redirected to ~/src/pinger/data.
writes log every 30 seconds.
It fetches http://www.yahoo.com.

TODO: - flush STDOUT every output.

How iPhone app is initialized with XIB

Mon, 11 Jul 2011 04:08:58 -0400

iPhone application starts with UIApplicationMain() called in main().

It does a couple of things under the hood. It instantiates a UIApplication. It also loads a main nib file specified in .plist file. In my case it is MainWindow in .plist file and it loads MainWindow.xib file.

Each application works differently. In Cocoa, these application specific behaviors are implemented using UIApplicationDelegate instance instead of subclassing UIApplication. In other words, UIApplication and your UIApplicationDelegate protocol-supported class works together to implement your application’s behavior.

Let’s look into MainWindow.xib.

XIB file has two types of objects. They are not quite noticeable in default UI, but by expanding the view by clicking a little triangle below, it is more understandable:

The objects above the line are Placeholders. They are objects that already created somewhere in a program, and XIB connects them to references in XIB.

Other objects are instantiated by XIB. Application Delegate is one of these objects created by XIB. My Application Delegate has two outlets: viewController and window. Outlets are set up by XIB: these objects are instantiated by XIB (because they are Objects in the XIB file) and you can refer them via these member variables.

@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) IBOutlet UINavigationController *viewController;

Application does the final step. It shows window and sets what to be shown on the window.

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // Override point for customization after application launch.
     
    self.window.rootViewController = self.viewController;
    [self.window makeKeyAndVisible];
    return YES;
}

Show branch name in bash command line prompt

Tue, 05 Jul 2011 02:49:22 -0400

I’m getting better with Git and I use git branches more. I often found myself working on a wrong branch especially I worked on a code longer than a day. You can easily forget which branch you were working on. I thought it would be nice to show branch in command line prompt.

I found Jon Maddox’s “Show Your GIT Branch Name In Your Prompt” which does the job for me. As I don’t use his prompt as it is, I needed to understand what it does. I’ve discovered a few things I didn’t know, so I recorded how I got the prompt I wanted.

I put following code in my .bashrc.

function git_branch {
  git branch 2>/dev/null | sed -e '/^[^*]/d' -e 's/* \(.*\)/:\1/'
}
PS1="\u@\h[\w\$(git_branch)]$ "

The code renders a prompt with branch name for git managed directories. It doesn’t show branch information if it is not in a git directory.

gaku@spektr[~]$ cd ~/src/sinatra
gaku@spektr[~/src/sinatra:master]$

`$(<command>)` bash notation.

The first thing to know is $(<command>) in bash. This captures the output of specified command. You can create a dynamic prompt by having this in PS1 variable. Note that you need to escape $(<command>) with ‘\’. Otherwise, the command is executed immediately when the script is executed (i.e. when you log in), and it fixes the prompt content and you get a static prompt.

Capturing the branch name

I uses git_branch bash function. This contains git branch command piped to sed. Jon Maddox’s command line outputs branch name in a clever way.

git branch 2>/dev/null | sed -e '/^[^*]/d' -e 's/* \(.*\)/:\1/'

If git branch command is executed outside of a git managed directory, it shows an error in stderr. However, this command line redirect stderr to /dev/null, so there is no output.

If the current directory is a git managed directory, git branch returns something like this:

  master
* translation

The current branch has * at the beginning of the line. The sed command in the pipeline drops lines not starting with * and trim * and a space. The rest of the line is captured with \1 and a ‘:’ is prepended to it. So, the resulting output from git_branch bash function is :branchname.

Output from git_branch is used in PS1 to form the final command line prompt.

Xcode and git

Fri, 24 Jun 2011 03:49:30 -0400

For existing Xcode project, Xcode doesn’t provide a UI for creating a git repository. You just need to go to the xcode directory and create git repository from a command line.

6/19/2011

Sun, 19 Jun 2011 18:07:46 -0400

Wikipedia’s reference.

<ref>{{Cite web | author = World Organization of the Scout Movement | authorlink = 世界スカウト機構 | date =  | url = http://www.scout.org/en/about_scouting/facts_figures/census | title = Census (Facts & Figures) - World Organization of the Scout Movement | accessdate = 2010-08-31 }}</ref>

{{Cite web requires url=, title= and accessdate=.

User location

Setting showUserLocation doesn’t do anything about scrolling or zooming the map so the user location is visible. To do that, you need to create a CLLocationManager object and request location updates. The LocateMe sample app is a good example of how to check the accuracy of location updates.(04/11/2011).

Another solution is on stackoverflow. What is KVO notification? KVO stands for Key Value Observing. It is an Observer pattern. You get notification (a method call) when your observing key’s value changes. KVO defines a mechanism that allows objects to be notified of changes to the specified properties of other objects.

I used the solution on stackoverflow and it worked.

location accuracy

Now, I’m interested in GPS accuracy. User location is CLLocation class instance and it has holizontalAccuracy property. I could get that with:

CLLocationAccuracy accuracy = myMapView.userLocation.location.holizontalAccuracy;
NSLog(@"accuracy: %f", accuracy);

In a house with Wi-Fi signal, I get 100.0 (meters) as the accuracy.

6/18/2011

Sat, 18 Jun 2011 22:25:11 -0400

MKPolylineView inherits from MKOverlayPathView : MKOverlayView : UIView. MKPolylineView strokes the path.

MKOverlayPathView represents a path drawn on a map.

Read Introduction to Event-Driven XML Programming Guide for Cocoa

NSXMLParser sends messages to its delegate instead of using callbacks.
NSXMLParserDelegate protocol.
NSXMLParser is a stream style parser.
SeismicXML sample code seems worth looking into.

RRD

Thu, 28 Apr 2011 02:13:39 -0400

The behavior of RRD was not straightforward. By just recording a data point doesn’t store anything (it is actually recorded, but not provided for reading), and the value looked like off (actually there’s a legitimate reason behind this).

I’ve started by creating a simple rrd with following command:

$ rrdtool create test.rrd -s 10 -b 1000000000 DS:temp:GAUGE:20:U:U RRA:AVERAGE:0.5:1:10

A span of a data is 10 second(-s 10). DS:temp:GAUGE:20:U:U defines a data source. temp is the identifier or the name of the data source. GAUGE is a data source type, and it means it records absolute value. 20 is heartbeat which I explains it later. U:U is min and max values.

RRA defines a round robin archive. AVERAGE is a consolidation function. RRA samples one data(AVERAGE:0.5:1:10) and keeps last 10 samples(AVERAGE:0.5:1:10) of 10 seconds. Intuitively, it should remember a data point with following command, but it doesn’t.

$ rrdtool update test.rrd 1000000001:10
$ rrdtool dump test.rrd
...
<database>
<!-- 2001-09-08 18:45:10 PDT / 999999910 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:45:20 PDT / 999999920 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:45:30 PDT / 999999930 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:45:40 PDT / 999999940 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:45:50 PDT / 999999950 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:46:00 PDT / 999999960 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:46:10 PDT / 999999970 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:46:20 PDT / 999999980 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:46:30 PDT / 999999990 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:46:40 PDT / 1000000000 --> <row><v> NaN </v></row>
</database>

Actually, only when a period completes, a value is provided by RRD. In other words, while a period hasn’t completed, the value is undetermined. The period for 11,000,000,001-11,000,000,010 completes when data arrives for 11000000010 or newer. The following commands should finalize the value for 1000000010.

(you need to re-create test.rrd)

$ rrdtool update test.rrd 1000000001:10
$ rrdtool update test.rrd 1000000010:20
$ rrdtool dump test.rrd
...
<database>
<!-- 2001-09-08 18:45:20 PDT / 999999920 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:45:30 PDT / 999999930 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:45:40 PDT / 999999940 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:45:50 PDT / 999999950 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:46:00 PDT / 999999960 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:46:10 PDT / 999999970 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:46:20 PDT / 999999980 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:46:30 PDT / 999999990 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:46:40 PDT / 1000000000 --> <row><v> NaN </v></row>
<!-- 2001-09-08 18:46:50 PDT / 1000000010 --> <row><v> 1.9000000000e+01 </v></row>
</database>

However, the value for the bucket ends up with 19, not 10 nor 20 I provided. How does this happen? With a following experiment, I could explain how it works:

$ rrdtool update test.rrd 1000000001:10
$ rrdtool update test.rrd 1000000004:15
$ rrdtool update test.rrd 1000000010:20
$ rrdtool dump test.rrd
...
<!-- 2001-09-08 18:46:50 PDT / 1000000010 --> <row><v> 1.7500000000e+01 </v>
...

Because a period is 10 seconds, there are 10 data slots which affects the outcome. Data can be visualize like this:

1000000001  OOOOOOOOOO (10)
1000000002  no data
1000000003  no data
1000000004  OOOOOOOOOOOOOOO (15)
1000000005  no data
1000000006  no data
1000000007  no data
1000000008  no data
1000000009  no data
1000000010  OOOOOOOOOOOOOOOOOOOO (20)

RRD assumes that the value of no data slot as the immediate next value. For 100000002, the value assumed is 15 of 100000004. For 100000005, the value is 20.

1000000001  OOOOOOOOOO (10)
1000000002  OOOOOOOOOOOOOOO (15)
1000000003  OOOOOOOOOOOOOOO (15)
1000000004  OOOOOOOOOOOOOOO (15)
1000000005  OOOOOOOOOOOOOOOOOOOO (20)
1000000006  OOOOOOOOOOOOOOOOOOOO (20)
1000000007  OOOOOOOOOOOOOOOOOOOO (20)
1000000008  OOOOOOOOOOOOOOOOOOOO (20)
1000000009  OOOOOOOOOOOOOOOOOOOO (20)
1000000010  OOOOOOOOOOOOOOOOOOOO (20)

The final value is computed as the average of all these values. (10+15x3+20x6)/10 = 17.5. Voila!

The number of data points backfilled by RRD is controlled by heartbeat parameter of DS (DS:temp:GAUGE:20:U:U’s heartbeat is 20 seconds). This 20 seconds is the number of slots that RRD is backfilling. If there are 25 seconds of interval between two data, first 5 seconds won’t have any data. If there’s at least one second with unknown data, the value of the slot will be unknown or nan.

launchctl

Mon, 21 Mar 2011 06:16:24 -0400

launchctl is hard to use. XML was a failure and writing a config file in XML is not a good choice. Yet, I had to use this for starting a web server on OS X.

nginx Startup scripts found by searching on Google seems not correct. I encounter the following error:

com.apple.launchd.peruser.502[153] (nginx): Unknown key for boolean: NetworkState

This was due to the way NetworkState key was used. I searched an example from /System/Library/LaunchDaemons/ and nmbd.plist uses it. In fact, NetworkState needs to be in a dictionary.

<key>KeepAlive</key>
<dict>
  <key>NetworkState</key>
  <true/>
</dict>

KeePassX

Sun, 13 Feb 2011 06:42:09 -0500

I’ve been using KeePassX for managing my passwords for years, but I didn’t know much tricks.

By selecting an entry on KeePassX, you can use ⌘-C to copy the password to clipboard. It will stay in clipboard for short period of time (30 seconds by default. You can change it via preference).