inz's blog

Prompt silliness

While having fun with terminal colors, the old-school 16 colors, the extended 256 colors, and the more extended 24-bit colors, I noticed that the 256 color palette is modifiable with OSC codes (seems to work with st, xterm, rxvt, gnome-terminal; and NOT with at least putty and qterminal).

Palette changing does not sound very exciting when you also have 24-bit colours, but it does have its perks. Namely: changing the palette also affects all blocks already appearing on screen. Hence by side-loading palette control codes, you can change what is shown on the screen without actually touching the contents.

And that led to the incubation of a little utility that puts a clock on your terminal that updates even when the shell is idle, which then extended a bit with a 4-bar cpu meter. The resulting utility outputs a string with the appropriate placeholders (to be put into PS1: PS1="$(prompt)"). The output is escaped in bash style. The utility spawns a background process and periodically feeds palette changes to the tty.

Another utility abusing the same mechanism is nyancat. (Probably should rename, as nyancat is already a thing; but it is cat, and it does nyan, so whatchamacallit...). When fed the -g or -n flags, uses palette tricks in the same manner to make your eyes bleed with rainbows everywhere.

Also while pushing the latter one to git, wrote a small ANSI code "syntax hilighter" for gitea, the resulting snippet works well enough for my purposes.

Exporting tokens from FreeOTP

After using FreeOTP on a single device for a while, I came to the conclusion that it would be safer to store the tokens on multiple devices, in case one is out of battery or out-of-arms-reach.

I didn't find any option from the UI to do it, so I checked the data over adb, and as the tokens were stored as JSON-in-XML, I whipped up a quick perl script to convert the data to a list of otpauth:// URIs.

#!/usr/bin/perl -w

use XML::LibXML;
use JSON;
use MIME::Base32;
use URI::Encode qw/uri_encode/;

my $p = XML::LibXML->new();
my $d = $p->load_xml(string => join '', <<>>);
my $j = JSON->new();

for ($d->findnodes('/map/string')) {
	my $l = $_->findvalue('@name');
	next if $l eq 'tokenOrder';
	my $d = $j->decode($_->findvalue('.'));
	$d->{secret} = encode_base32(join('', map {
		chr(($_ + 256) % 256)
	} @{$d->{'secret'}}));
	print "otpauth://" . lc($d->{'type'}) . "/" .
		uri_encode($l) . "?" .
		join("&", map { $_ . "=" . uri_encode($d->{$_}) } keys %$d) .
		"\n";
}

The output of which can be then be fed to qrencode or similar to get tokens added to another device.

I used:

adb shell su -c 'cat /data/data/org.fedorahosted.freeotp/shared_prefs/tokens.xml'|./otp.pl|while read u; do qrencode -o - $u | display -; done

to view the codes one-by-one. (Note: this method needs rooted device, it may be possible to do it without, but didn't look for one).

nginx, cgit and git-http-backend

Sounds simple, right. Plug in cgit and git-http-backend with nginx to get nice web interface and working clone URL. And pushable too, of course. It turned out not to be quite that easy, but seems doable with some quirks.

There are plenty of instructions for parts of this lying around, but didn't find one that catches 'em all, so needed to some cuttin', pastin' and retryin'. The end result nginx configuration:

cgit also requires configuration, it could be done system wide with /etc/cgitrc, but I opted defining CGIT_CONFIG environment variable to point to a custom path, the .cgitrc ended up like something like this:

The binary and socket paths, and cgit data path, are those used by Debian default configuration, may need adjustment for different installations. Tried to get rid of the virtual-root directive in cgitrc, but that would require setting SCRIPT_PATH, which fcgiwrap eats away.

For more access control, you could grab the repository name from the request paths: "(?/(?.*)/", and integrate the $repo into auth_basic_user_file.

node.js and wordpress sessions

For a leetle project, I needed a way to validate a wordpress session from node.js. WordPress uses a somewhat complicated session system, with HMACs and using part of password salt, and was unable to find a ready puzzle piece for the purpose. So I wrote my own.

The result is a javascript module. Sample usage:

It is way from perfect, but it works well enough for me.

xterm.js + ssh2 + websocket-stream + browserify = webssh

While pondering ideas for a website facelift, there was an idea to have a terminal for easy ssh access. However, none of the readily available options really suited my fancy; wssh came close, but it was actually doing ssh on the server side, and throwing the raw data inside websockets.

Fortunately npm is full of nice bits and pieces to build on, and browserify makes it quite easy to use most of them in a browser too.

Long story short, in the end it only required about a screenful of glue code to tie in the bits, and voilà. Place the code in webssh.js, grab also the test html file.

(You'll need npm and websockify for the above). Then launch the html file in your favorite browser, and login. Tune the addresses to your liking.

There's also a demo version, just enter your websocket endpoint (for example ws://localhost:8022), username and password, and on you go.

CSS / SVG filters for fun and profit

Nowadays the web technologies support nice and fancy things, such as CSS filters. The basic filters are pretty nice for many interactions, like hover effects etc. However there is also support for SVG effects, which can be really complex and produce some really nice results. I wanted to share some little hacks with which I had fun. Unfortunately the browser support is not quite there yet, in my experience these work best in Firefox, but YMMV.

First up, a very simple "bloom" filter

This is very simple, just blur the image and add it up with the original, this makes lighter areas "leak" and makes them look bright.

Next up, slight variation of the previous, unsharp mask:

Here, instead of adding the blurred version, we substract it from the original, giving areas with higher contrast some depth.

Next up an homage to simpler times: