Ajnasz Blog

An utility tool I created for i3wm to visualize the the tree of windows in the current i3 session.

i3tree

Some help how to define arguments for a zsh completion

#compdef the_command
#autoload

# basic subcommands, like docker run
local -a _1st_arguments
_1st_arguments=(
    'run'
    'exec'
    'rm'
)

# function to parse the subcommands
_the_command_subcommand() {

    case "$words[1]" in
        'run')
            _alternative "the_command_run:the_command run:"
            return
            ;;
        'exec')
            _arguments "(-t)-t[some description]"
            return
            ;;
    esac
}

_arguments -C '*:: :->subcmds'
if (( CURRENT == 1 ));then
    _describe -t commands "the_command command" _1st_arguments
    return
fi

_the_command_subcommand

A simple option with an alternative short name and with description. It also expects a value after the option.

_arguments \
       '(-o --option-name)'{-o,--option-name}'[Describe what the option is good for]:option name:' \
       && return 0

Example:

the_command -o foobar
# or
the_command --option-name freetext

A simple option with an alternative short name and with description, and provide a fix list as the value of the options

_arguments \
       '(-o --option-name)'{-o,--option-name}'[Describe what the option is good for]:option name:(foo bar baz)' \
       && return 0

Example:

the_command -o foo
# or
the_command --option-name bar

A simple option with an alternative short name and with description, and a shell script which generates the possible values

_arguments \
       '(-o --option-name)'{-o,--option-name}'[Describe what the option is good for]:option name:($(the-shell-script))' \
       && return 0

A simple option with an alternative short name and with description, and provide a function which can generate the available options

_command_option_values() {
       compadd $(shell script where every word is an completion string)
}

_arguments \
       '(-o --option-name)'{-o,--option-name}'[Describe what the option is good for]:option name:_command_option_values' \
       && return 0

$ man grep

 --exclude=GLOB
        Skip any command-line file with a name suffix that matches the
        pattern GLOB, using wildcard matching; a name suffix is either
        the whole name, or a trailing part that starts with a non-slash
        character immediately after a slash (/) in the name.  When
        searching recursively, skip any subfile whose base name matches
        GLOB; the base name is the part after the last slash.  A pattern
        can use *, ?, and [...] as wildcards, and \ to quote a wildcard
        or backslash character literally.

 --exclude-from=FILE
        Skip files whose base name matches any of the file-name globs
        read from FILE (using wildcard matching as described under
        --exclude).

 --exclude-dir=GLOB
        Skip any command-line directory with a name suffix that matches
        the pattern GLOB.  When searching recursively, skip any
        subdirectory whose base name matches GLOB.  Ignore any redundant
        trailing slashes in GLOB.

So to exclude a directory with the name test for example:

grep -r --exclude-dir=test something

I expected that ripgrep has similar options, but in that case it doesn't.

rg --help

-g, --glob <GLOB>... Include or exclude files and directories for searching that match the given glob. This always overrides any other ignore logic. Multiple glob flags may be used. Globbing rules match .gitignore globs. Precede a glob with a ! to exclude it.

So use the --glob option for that:

rg --glob='^test/' something

Take the number and take the number - 1, perform a binary and (&) operation on the two numbers. If the result is 0 then the number is the power of 2.

number != 0 && (number & (number - 1)) == 0

Let's see some numbers which are power of 2 and their binary representation (padded with 0 for easer reading):

2  00010
4  00100
8  01000
16 10000

Let's see the numbers - 1 and their binary representation (padded with 0 for easer reading):

1  00001
3  00011
7  00111
15 01111

An & (and) operation will give 1 for a digit if both of digits are 1.

For example

4: 00100
3: 00011
--------
&: 00000

Which will end up in 0, because a number which is the power of 2 only the first digit will be 1 and when we substitute 1 from the same number, we will get a number where all digits are 1 (except the first of the original number). So in the and we will &-ing 0 to 1 in every digit.

But on the other hand, if we substitute 1 from a non-power of 2, at least the first digit will always be 1 for both numbers, so &-ing them will always return a non 0 number:

3: 00011
2: 00010
--------
&: 00010

Which is 2

6: 00110
5: 00101
--------
&: 00100

Which is 4, so it's definetly not 0. So they are not power of 2.

Originally I found it in the Plan9 source code

Today I learned how to query if an address is on an rbl list.

Reverse the octets of the IP address: 1.2.3.4 becomes 4.3.2.1 Then append the domain name given by the DNSBL service (dnsbl.example.com) Then look up of this domain's A record.

host 4.3.2.1.dnsbl.example.com

If the IP is listed, it will return an address, or it will return an NXDOMAIN if the IP is not listed. The exact meaning of the address can be different at each provider.

Based on the knowledge I created a small program to check if a address is listed on a blacklist: DNSBL Check

From Wikipedia

I built a simple program to share sensitive data securely

In the last few months I've been working on a service, which helps to share data securely. The service called sekret.link.

I wanted to practice Golang and Angular and it was a good candidate for that.

Imagine that a new colleague joined to the company, there are bunch of things she will need to have access, like WiFi, database, internal site or whatever. You know the password or you generate the password and you will need to send it to her on Slack or e-mail. You can send it as a simple message, but that will mean that Slack or her e-mail provider can read the information. What is worse that then this information won't be deleted automatically. If someone breaks into her account now can discover these secret informations and the company will be in a pretty bad situation.

The service what I created tries to help on these issues. You send the sensitive information to the service and it will store it encrypted. It returns an URL which can be used to decrypt the information. After the secret has been read it also destroyed and there is no way to restore it.

No one else will have access to the decryption key. It isn't saved, it isn't logged can not be guessed. The web client (which is visible at https://sekret.link) is even encrypting the data before sending it, so the unencrypted data never left your browser.

As the main purpose of the application is to protect privacy and keep secret hidden from unauthorized third parties I made it as secure as possible:

• The decryption key is random and long enough to be secure
• The decryption key is only known by the user who created the secret
• No external scripts included to the site
• No tracking scripts included to the site, it's not tracking even internally
• It doesn't use any cookies
• Both the frontend application and the server code are Open Source
• It has an API, so if you don't trust in the frontend application you can create your own

There were (are) several challenges I needed to solve. I wanted to make it secure as possible, as usable as possible and as developer friendly as possible.

The very first version had no UI, and I only wanted to be able to use it with curl. For example curl -d 'secret message' https://sekret.link/api/ will return the link what you can send to your friend right away. However, it's simple and good, already has one issue: many applications, like Slack and other services fetches the pasted URLs to create some kind of preview. It means two very bad things: this application will read the secret will also be destroyed, so the real recipient will not be able to read it. That's why I needed to create the frontend application.

I plan to write some more about the challenges, like how I utilized the go interfaces, how I got some hard time with the Angular routing. How I made it work when JavaScript is turned off in the browser and I have some other stories.

Footnote: the idea is not new, there are several other services like that, for example Privnote, what I used before I created this service.

FiiO K1 became very silent recently when you plug it in on Ubuntu for some reason.

To fix it add an UDEV rule:

/etc/udev/rules.d/71-fiio-k1.rules

SUBSYSTEMS=="usb", ACTION=="add|change", ATTRS{manufacturer}=="FiiO", ATTRS{product}=="FiiO USB DAC K1", RUN+="/home/ajnasz/bin/init-fiio-k1.sh"

And create the shelscript which set the volume whenever you plug the DAC:

/home/ajnasz/bin/init-fiio-k1.sh

#!/bin/sh

CARD_ID="$(aplay -l | grep "FiiO.*K1" | cut -d ' ' -f 2 | tr -d ':')"

if [ -z "$CARD_ID" ];then
    return
fi

amixer -c "$CARD_ID" sset PCM 90%

To enable screen backlight brightness adjustment, create the following file and restart the X server

I tried to use Spotify dbus interface to play/pause tracks, found a nice shell script but it did not work, but instead I got this error message:

Error org.freedesktop.DBus.Error.ServiceUnknown: The name org.mpris.MediaPlayer2.spotify was not provided by any .service files

Turned out that the issue is probably with my X11 session initialization.

Note: At the very least, ensure that the last if block in /etc/X11/xinit/xinitrc is present in your ~/.xinitrc file to ensure that the scripts in /etc/X11/xinit/xinitrc.d are sourced.

So, I tried to source the /etc/X11/Xsession before I start the window manager:

. /etc/X11/Xsession
exec i3

(i3 is my window manager)

Called startx but no luck, X did not start. The following error was in the ~/.xsession-errors:

dbus-update-activation-environment: warning: error sending to systemd: org.freedesktop.DBus.Error.InvalidArgs: Invalid environment assignments

I had no clue what would that mean, however after some echo based debugging in /etc/X11/Xsession I could confirm that the files from /etc/X11/Xsession.d were sourced and the last file which was sourced is /etc/X11/Xsession.d/99x11-common_start. That file is a one liner:

exec $STARTUP

I guessed that $STARTUP is undefined. Checked where it would be defined and I found /etc/X11/Xsession.d/50x11-common_determine-startup

If no X session startup program was passed to the Xsession script as an argument (e.g., by the display manager), or if that program was not executable, fall back to looking for a user's custom X session script, if allowed by the options file.

That means I can define it somehow, so I tried by setting it in my:

export STARTUP=i3
. /etc/X11/Xsession

Then everything looks good. Some magic happens in those files (probably in /etc/X11/Xsession.d/20dbus_xdg-runtime) what I didn't tried to figure out yet.

Legutóbb írtam, hogy RAM-ot vettem a 8 éves notebookba, ami nem pont olyan, mint amilyet szerettem volna, de azért végül megtartottam. Abban a cikkben írtam azt is, hogy némi FAN ERROR-ral üzenetet is kaptam a csere után, ami végül elmúlt. Sajnos nem múlt el, hanem állandóvá vált. Így használhatatlan lett szegény gép. Az interneten írták, hogy nem egyedi a gond és a legjobb megoldás a csere. Szétnéztem ebay-en, majd rendeltem is egy vadonatújnak mondottat. Ez volt 2019. március 3-án, a érkezése március 19 és április 17 között várható. Másnap útnak indult Kínából, egy héttel később pedig elégedetten láttam, hogy már Magyarországon volt a csomag. Nagyjából fél nappal később, március 13-án pedig le is szállt vele repülő Ferihegyen. Abban is bíztam, hogy a Magyar Posta a nagy nemzeti ünnep előtt kiszállítja. Ez sajnos nem sikerült. Viszont legalább a megadott legkésőbbi érkezéshez képest csupán egy nap késéssel, április 18-án csütörtökön már itt is volt a postai értesítő, hogy csomagom jött külföldről. Remélem nem túl költséges a csomagok tárolása.

Így, hogy már meg is jött a hűtő (réz borda és ventilátor), ma már időm is volt rá, hogy megpróbáljam beszerelni. Két youtube videó támogatásával nekiálltam kicsavarozni az összes csavart a laptop aljáról, és nagy nehezen a régi ventit is sikerült kivenni. Itt jegyezném meg, hogy a WD-40 nagyon jó csavarlazító és emellett remélem a gépben kárt nem tesz. Letisztítottam a korábbi hővezető pasztákat, aztán kicsi feszegetéssel betettem az új hútőt, ami csak minimálisan különbözik a régitől. Egy leszorító rögzítés van másképp megoldva meg a hátsó borda szélesebb egy fél centivel, de volt neki hely amit most rendesen kitölt. Összeszereltem félig, és bekapcsoltam, nem is sípolt, csak nem tudott bootolni, mivel az SSD-t kifelejtettem. Azt is bepattintottam, és láttam a még nem visszaszerelt billentyűzet helyén, hogy milyen szépen forog az a darab műanyag, ami ventilátor néven kerül forgalmazásba. Pár perc után minden megmaradt csavarnak megtaláltam a helyét, összepattintottam a műanyagokat és immáron az új hűtő halk surrogása felett írom ezt a rövid cikket. Tudom, hogy nagyon régi gép ez már, de 0.1-es load és 1.8G használt memória mellett szerintem elciripel még egy darabig.