Mosaic of thoughts

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  Urban 22:51 on 8 Feb. 2023 Permalink | Log in to leave a Comment  

  Cisco AnyConnect with TouchID on MacOS 

  Quite annoying that AnyConnect doesn’t support TouchID on MacOS, so you need to type in your password every time. But there’s a fix:

  • AnyConnect also has a command-line version, the util is located in /opt/cisco/anyconnect/bin/vpn
  • It is interactive, so upon invoking you must enter your username and password
  • This can be done by piping the username and password to the vpn utility
  • To prevent having your password in plaintext, you can use the command-line password manager pass that saves secrets in encrypted GPG files: https://www.passwordstore.org/
  • However this means you now need to enter the GPG secret on every connect
  • To solve this, install and configure the pinentry-touchid utility that replaces the built-in CLI dialog and saves the secret in the Keychain https://jorgelbg.me/2021/08/introducing-pinentry-touchid/
  • Voila, now you can connect using TouchID

  The following helper script from Superuser¹ is useful to easily control the vpn status:

  #!/bin/bash
  
  # Easily connect to Cisco AnyConnect VPN
  
  # Get first parameter
  COMMAND="$1"
  
  case $COMMAND in
      connect | CONNECT | c | C)
          printf "2\n${username}\n$(pass show my_password_entry)\n" | \
              /opt/cisco/anyconnect/bin/vpn -s connect remote_host_url
          ;;
  
      disconnect | DISCONNECT | d | D)
          /opt/cisco/anyconnect/bin/vpn disconnect
          ;;
  
      *)
          cat <<EOF
  Usage: vpnctl COMMAND
         connect | CONNECT | c | C    Connect to the VPN
         disconnect | DISCONNECT | d | D    Disconnect from the VPN
  EOF
          ;;
  esac

  1. https://superuser.com/a/1723439 [↩]
   

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  Urban 21:48 on 28 Apr. 2020 Permalink | Log in to leave a Comment  

  Cassandra auto-expiring data 

  Just found a beautiful feature of Cassandra — a single update that:

  • performs an upsert (insert or update), so there’s no need to check for existing data
  • ensures items are unique — because we’re using a set { … }
  • and takes care of individual item expiration: each item is valid only 2 weeks, after that it is removed, and when there are no more items left,  the row is removed as well

  UPDATE covid_contact_tracing USING TTL 1209600 
  SET people_met = people_met + {'alice','charlie'}
  WHERE user = 'bob';

  Seems to behave exactly as expected:

  • If Bob meets Alice multiple times, each time Alice’s the TTL is reset to 2 weeks
  • After 2 weeks Alice indeed expires and is removed from the set
  • When all contacts expire, Bob is also removed

  There are drawbacks, however:

  • There’s no way to query a TTL of a collection (set/list/map) item — so you can never know how long it has to live. Or if it has a TTL set at all.
  • If you have existing items without TTL, they have to be reinserted with TTL; this means tons of writes, but at least the whole set can be reinserted at once.
  • This breaks idempotence of writes: you cannot have a job to replay writes (for example, from multiple sources to decrease probability of missing items), since this would reset the TTL
   
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  Urban 22:33 on 29 May. 2017 Permalink | Log in to leave a Comment  

  A tour of Menger sponge 

  Done as a WebGL shader. Runs much smoother than a comparable implementation in three.js

  Direct link to Shadertoy, in case the embed doesn’t work.

   

   

   
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  Urban 20:14 on 11 Jan. 2017 Permalink | Log in to leave a Comment  

  A glimpse of Sri Lanka 

  To my great surprise (and delight), one of my shots from Sri Lanka was published in the December 2016 issue of the National Geographic Slovenija magazine 🙂

  

  

  Below are some of my other favorite shots.

    

  This was a serious photo tour (and an awesome group of enthusiasts), which means we were snapping like crazy. But I still have a long way to go 🙂 More photos.

   
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  Urban 15:41 on 11 Jul. 2015 Permalink | Log in to leave a Comment  

  Torpedo marmorata 

  During vacation snorkeling I stumbled upon an electric ray. I was perplexed by its odd looks, and the fact that it seemed eerily undisturbed by my pursuit. Which is why I left it alone.

  Here’s a pic, and a short clip, taken with a modded GoPro Hero2¹.

  

  I had some trouble looking it up afterwards, but this nice guide helped me — it seems to be a marbled electric ray². If I knew they were that common in Croatia, I wouldn’t have gone so close; supposedly they can produce a 200V discharge³, and on youtube you can find clips of fishermen getting shocked 🙂

   

  1. fitted with a mock underwater flat lens, made from a wide (Cedevita) bottle cap and a cheap kids’ diving mask; the aged Hero2, which I bought for the sole purpose of underwater photography, was completely unfit for it, despite having the housing rated for 200m–the original curved lens produced blurry images.

     Here’s a pic of the mod:

     

     [↩]

  2. also, Torpedo marmorata. It must be really common, since it has 8 names in Croatian: drhtulja šarulja, mramorna drhtulja, trn, trnjevača, tresnavka, banjača, pjegava drhtulja, renjok; see here https://hr.wikipedia.org/wiki/Drhtulja_%C5%A1arulja [↩]
  3. see here https://en.wikipedia.org/wiki/Marbled_electric_ray  [↩]