I just realised that I cannot add tags to my API:Gateway-stage using CloudFormation templates. However, it’s possible to tag using the command line. But this requires knowledge of the id of the stage - which you don’t get when you use the !Ref function on the Stage.

But luckily it can be constructed easily:

aws apigateway tag-resource --resource-arn arn:aws:apigateway:<REGION-NAME>::/restapis/<RESTAPI-ID>/stages/<STAGE-NAME> --profile <PROFILE-NAME> --tags sometag=somevalue,anothertag=anothervalue

I hope this save someone time.

Quick post on how to set Alarms in AWS CloudWatch that trigger for certain URLs only. This assumes you use API Gateway.

Bascially, you can set Alarms in 3 ways only: Either on the entire API, on the API and the Stage OR on API, Stage, Resource and Method. For the latter two Enable Detailed CloudWatch Metrics has to be checked in the Logs section of Stage properties.

That’s basically it. You need all four dimensions if you want to filter by URL and you need enable Cloudwatch metrics on the stage.

Here’s a YAML snippet showing the declaration of an alarm.

ApiGateway5xxAlarm:
Type: "AWS::CloudWatch::Alarm"
Properties:
  ActionsEnabled: true
  AlarmActions: [!ImportValue {"Fn::Sub": "SomeNotificationTopicArn"}]
  AlarmDescription: "Some Description"
  AlarmName: "alarm-name"
  ComparisonOperator: GreaterThanThreshold
  Dimensions:
    - Name: ApiName
      Value: "my-api"
    - Name: Stage
      Value: "LATEST"
    - Name: Resource
      Value: "/some_resource/{somePathParameter}/{anotherPathParameter}"
    - Name: Method
      Value: "GET"
  EvaluationPeriods: 1
  MetricName: 5XXError
  Namespace: AWS/ApiGateway
  OKActions: [!ImportValue {"Fn::Sub": "SomeNotificationTopicArn"}]
  Period: 60
  Statistic: Sum
  Threshold: 0
  TreatMissingData: notBreaching

(I didn’t check the YAML but it should be fine.)

If you, like me, started to recently get the error “This item cannot be shared. Please select a different item” when sharing to Whatsapp, then this might help you.

You are probably sharing a text-item. In my case it was a text containing an URL.

Instead, I now share the NSURL-object (or an array of objects, in which one is an NSURL object).

I am relatively sure this is a bug in the latest version of Whatsapp, but as long as it persists, this might be a workable workaround.

It’s Java-time.

I need this from time to time, and each time I have to look it up. A little reminder for myself.

How to create a date:

Date object representing “now”:

Date date = new Date();

Date object representing a specific time using Calendar:

Calendar cal = Calendar.getInstance();
cal.set(2012, Calendar.DECEMBER, 21, 14, 21, 33);
Date date = cal.getTime();

Date object representing a specific time using SimpleDateFormat:

SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy hh:mm:ss");
Date date = sdf.parse("21/12/2012 14:21:33");

How to format a date:

Using SimpleDateFormat:

Date date = new Date();
SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy hh:mm:ss");
String s = sdf.format(date);

There’s many more ways to do this, but these are just common ways.

Here is an overview of the format strings.

It’s taken from here.

Ok, this isn’t very complicated, even though it looks kind of cool.

The aim is to go from this:

to this:

The idea is that the brighter a pixel on the heightmap is, the higher the elevation of the resulting mesh is. So the first step is to get the values for all the pixels in the PNG. This is accomplished by drawing the image onto a canvas, and then getting the pixel data from it. It looks something like this:

canvas.getContext('2d').drawImage(img, 0, 0, img.width, img.height);
var data = canvas.getContext('2d').getImageData(0,0, img.height, img.width).data;

The next step is to create a planar mesh with ThreeJS and go through all the pixel and set their z-value, their elevation, according to the color of the pixel.

for (var i = 0, l = geometry.vertices.length; i < l; i++)
{
  var terrainValue = terrain[i] / 255;
  geometry.vertices[i].z = geometry.vertices[i].z + terrainValue * 200 ;
}

Please keep in mind that in this case the width in pixels is 1 more than the number of segments in the plane. (If there’s one segment, theres 2 vertices, two segments, 3 vertices, and so forth..) If that’s not the case more work is required, because the landscape will be “skewed” if height and width dont correspond correctly.

And that’s it.

I also afterwards call

geometry.computeFaceNormals();
geometry.computeVertexNormals();

so the shading according to the light-source is correct.

You can get the code from Github.

Klaus Trainer has just posted a short article on how to write a short program, that checks usernames and passwords on a Linux machine.

I was at first confused why it works, since there was no salt. But in fact it’s there, inside the entry in /etc/shadow.

Here’s the format:

$<HASHING-METHOD>$<SALT>$<HASHED-PASSWORD (base64)>

So for example if we have a row like this:

$6$qUgyc2fC$hljmJlJU7TV4gm8GDZd51eZnxNgWp3rUJ49kSblRLssLqxux5K.xSIcIn2QjL27jXOREBfXiB1WES3SEIPHk10

Then the 6 means that SHA512 was used, and qUgyc2fC is the salt.

I decided to play around with node.js, specifically with node-webkit.

Node-webkit allows programmers to write desktop-apps with Javascript, and even package them for distribution, for example via the Mac App Store. (Check out this list of apps written with it.)

To play with it, I’ve decided to write a tiny thesaurus-app.

• It should lookup and display synonyms and related words using a (German) thesaurus via the JSON-API at openthesaurus.de.
• To be really useful, it should be possible to bring the app to the foreground using a keyboard shortcut. In my case it’s Shift+Alt+T.
• It should be possible to dismiss the app by tapping ESC

It worked quite nicely. The app doesn’t really feel like a web-app, even though it utilizes web-app technologies. And I could even create a binary for the App Store.

Here’s a short video of the app in action:

And here’s the source on Github.

Here’s a simulation of the Monty Hall Problem.

# this is about http://en.wikipedia.org/wiki/Monty_Hall_problem

num_rounds = 5000
num_correct_guesses_keep = 0
num_correct_guesses_switch = 0

num_rounds.times do

        doors = [false, false, false]
        doors[rand(3)] = true

        # first pick = random

        player_pick = rand(3)
        show_bad_door = doors.index(true)

        # show a bad door that is not the price_door and not player's pick

        while (doors[show_bad_door] || show_bad_door == player_pick)
                show_bad_door = rand(3)
        end

        # second pick, player choses to switch to the other door
        
        remaining_doors = [0, 1, 2]
        remaining_doors.delete(show_bad_door)
        remaining_doors.delete(player_pick)

        player_switch_pick = remaining_doors.first        

        win = if doors[player_pick]
                num_correct_guesses_keep += 1
                "yes"
        else 
                "no"
        end

        win_switch = if doors[player_switch_pick]
                num_correct_guesses_switch += 1
                "yes"
        else 
                "no"
        end

        puts "doors: #{doors}, show_bad_door: #{show_bad_door}, "\
        "player keeps: #{player_pick}, player wins: #{win}, "\
        "player wins if he switches: #{win_switch}"

end

win_ratio = ( num_correct_guesses_keep.to_f / num_rounds.to_f * 100.to_f ).round(2)
win_ratio_pick = ( num_correct_guesses_switch.to_f / num_rounds.to_f * 100.to_f ).round(2)
puts "correct: #{num_correct_guesses_keep}, correct-switch: #{num_correct_guesses_switch}, "\
         "win-ratio: #{win_ratio}%, win-ratio switch: #{win_ratio_pick}%"

Switching really doubles the probability to win. Dang it. ;)

Just a reminder for myself. How to fold and unfold code in XCode:

• ⌘ + ⌥ + ⇧ + ← fold all methods in file.
• ⌘ + ⌥ + ⇧ + → unfold all methods in file.
• ⌘ + ⌥ + ← fold block underneath the cursor.
• ⌘ + ⌥ + → unfold block underneath the cursor.

I’ve just uploaded my new app. It is called “Zones” and it’s one of those desktop helper tools for Mac OS X. You can take a look at Zones here.

It was fun to do and I learned a bunch of stuff about Mac OS X. It was probably also the last side-project ever written in Objective-C for me, since the Apple world is switching to Swift now. (Which is good.)

Sadly, I cannot distribute the app through the AppStore, because it cannot be sandboxed using the APIs it does (Accessibility). Which means I will probably never earn enough money to buy a happy meal with it.