The problem#

Java and JavaScript are insufficiently easily confused. I had some code I wanted to run on the user's computer and not the server, and it specifically had to be in Java to reference a library written in Java. I found¹ Doppio, a JVM written in TypeScript, but it had bitrotted enough that I was having trouble getting it to run, despite confirming it did what I wanted using the official demo, which provides an in-browser console-like interface.

The solution#

I was able to piece together a working simple page using Doppio, modified from the official example. It's in a repository on GitHub and should be straightforward to modify for your needs.

The details#

The problem#

Last time, I built a user script that could run on the Folklife 2024 schedule page¹ and reorganize it so it would display the schedule as a grid. But it was brittle and awkward to use because it requiring careful ordering of the interactions with the page and reloading to view a different day's schedule.

The solution#

After failing to come up with an appropriate place to add an event handler, I gave up and took a different approach. I modified the script to work fine if it's run multiple times (and exit quickly if there's no work to do), even if the page is not in a valid state, and then simply set it to rerun every half second. Definitely a hack, but it worked.

Here's the final version of the user script and the Git repo showing the version history.

The details#

The problem#

The Folklife 2024 schedule page¹ is a schedule grid: locations are along the x-axis and time is along the y-axis. Except it's not actually arranged as a grid: each column is just stacked in order with no correspondence to the other columns or the absolute times of the events. Glancing at the code, I noticed the schedule data was available in JSON format, so it should be pretty easy write a user script to display the schedule in a slightly different format.

But when I went to actually make the changes, I found the code is obfuscated React that turned out to be tricky to modify.

The solution#

I was able to write this user script (git repo), which changes the display from the columns of events to a schedule grid. It even works on Firefox mobile, although only if you explicitly request the desktop site.

The details#

The problem#

I had recently done an apt upgrade that included upgrading ZFS and noticed zpool status showed a weird "(non-allocating)" message, which seemed concerning:

$ zpool status
  pool: tank
 state: ONLINE
config:

    NAME         STATE     READ WRITE CKSUM
    tank         ONLINE       0     0     0
      mirror-0   ONLINE       0     0     0
        ata-***  ONLINE       0     0     0  (non-allocating)
        ata-***  ONLINE       0     0     0  (non-allocating)

errors: No known data errors

The solution#

This forum thread suggested the error may be due to a version mismatch between the ZFS tools and the kernel module. I confirmed there was a mismatch:

$ zpool --version
zfs-2.2.3-2
zfs-kmod-2.1.14-1

The easy way to load the new version of a kernel module after an update is to reboot the computer. But if you don't want to do that, here's the general outline of the commands I ran to unload and reload ZFS (run as root):

# Stop using ZFS
$ zfs umount -a
$ zpool export tank
$ service zfs-zed stop
# Remove modules
$ rmmod zfs
$ rmmod spl
# will show error: rmmod: ERROR: Module spl is in use by: ...
# repeatedly rmmod dependencies until spl is removed.

# Reload ZFS
$ modprobe zfs
$ service zfs-zed start
$ zpool import tank

The details#

The problem#

I use KeePassXC as my password manager in Firefox and while sometimes the connection between Firefox and KeePassXC drops and I have to explicitly click reconnect, it recently stopped working entirely.

The solution#

Install the keepassxc-full package instead of the keepassxc package. If you get the browser extension via the webext-keepassxc-browser package, then your package manager will automatically get the right one.

(This only applies to Debian Sid and Trixie or newer.)

The details#

The problem#

I was writing a user script where I wanted to be able to intercept the fetch() calls the web page made so my script could use the contents. I found a suggestion of simply reassigning window.fetch to my own function that internally called the real window.fetch while also doing whatever else I wanted. While it worked fine under Tampermonkey on Chromium, under Greasemonkey on Firefox, the script would just silently fail with no indication of why the code wasn't running.

(The script I was writing was this one for fixing the formatting on the Folklife 2024 schedule to reformat the schedule to display as a grid. I plan to write a devlog post on it in the future, but just writing about the most pernicious issue in this post.)

The solution#

The problem was that Firefox's security model special-cases function calls between web pages and extensions (and user scripts running inside Greasemonkey count as part of an extension for this purpose). And, furthermore, Promises can't pass the boundary, so you need to carefully define functions such that the implicit Promise created by declaring the function async lives on the right side of the boundary.

The following code combines all of that together to intercept fetch() on both Firefox and Chromium such that a userscript function intercept is called with the text of the response to every fetch():

const intercept = responseText => {
  // use responseText somehow ...
};

const w = window.wrappedJSObject;
if (w) {
  exportFunction(intercept, window,
                 { defineAs: "extIntercept" });
  w.eval("window.origFetch = window.fetch");

  w.eval(`window.fetch = ${async (...args) => {
    let [resource, config] = args;
    const response = await window.origFetch(resource,config);
    window.extIntercept(await response.clone().text())
    return response;
  }}`);
} else {
  const { fetch: origFetch } = window;

  window.fetch = async (...args) => {
    let [resource, config] = args;
    const response = await origFetch(resource, config);
    intercept(await response.clone().text());
    return response;
  };
}

The details#

The problem#

My personal desktop runs Debian Unstable ("Sid")¹. The nature of running a bleeding edge distro is that things break sometimes. I use Debian Testing/Stable or Ubuntu on my other machines to make my life easier, but I often want access to the latest version of some piece of software and running Debian Unstable is one way to do that. Admittedly, I also do it partially just because fixing things that break is a good way of learning how things work.

The most common kind of problem I run into is that upgrades are not straightforward. For their unstable distro, Debian doesn't make any promises about package dependencies not changing. This is less of a problem when there's an additional package that needs to be installed, but can be complicated when there's conflicts which require removing packages to get an upgrade to go through.

Recently I ran into an extreme version of this problem: trying to upgrade, it proposed uninstalling nearly everything I had installed. Worse, trying to resolve the issue, I got a scary sounding warning that I had uninstalled libssl3:

dpkg: libssl3:amd64: dependency problems, but removing anyway as you requested:
 [...]
 systemd depends on libssl3 (>= 3.0.0).
 sudo depends on libssl3 (>= 3.0.0).
 [...]

Both of those sound important.

The solution#

Luckily, it wasn't as bad as it sounded. Looking at the message, it turned out I had replaced libssl3 with libssl3t64. The latter of which is actually the exact same thing, although the package manager doesn't know that. The reason for the different package name is part of the Debian project to transition to 64-bit time_t, which is required to fix the Year 2038 problem. While on AMD64 and other 64-bit architectures, everything already uses 64-bit time_t, that's not true of all platforms that Debian supports. The way Debian handles ABI transitions like this is to rename the library packages with a suffix (t64 for this one) to ensure the old and new ABI don't get mixed accidentally. Since all of the architectures share the package names, the rename also happens on AMD64 even though there's actual change to match the rename on other platforms where the ABI did change.

Presumably the upgrade will be smoother when done between stable versions, but it really confused apt (which I usually use via wajig):

$ wajig install libssl-dev
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 libegl1 : Depends: libegl-mesa0 but it is not going to be installed
 libreoffice-core : Depends: libgstreamer-plugins-base1.0-0 (>= 1.0.0) but it is not going to be installed
                    Depends: libgstreamer1.0-0 (>= 1.4.0) but it is not going to be installed
                    Depends: liborcus-0.18-0 (>= 0.19.2) but it is not going to be installed
                    Depends: liborcus-parser-0.18-0 (>= 0.19.2) but it is not going to be installed
 wine-development : Depends: wine64-development (>= 8.21~repack-1) but it is not going to be installed or
                             wine32-development (>= 8.21~repack-1)
                    Depends: wine64-development (< 8.21~repack-1.1~) but it is not going to be installed or
                             wine32-development (< 8.21~repack-1.1~)
E: Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages.

Yeah, no idea what libegl1, libreoffice-core, or wine-development have to do with upgrading libssl-dev, but apt was showing those same packages in the error messages no matter what I tried to upgrade and trying to upgrade those packages didn't work either. Luckily, aptitude was able to handle it somewhat better:

$ sudo aptitude install libssl-dev
The following packages will be upgraded:
  libssl-dev{b}
1 packages upgraded, 0 newly installed, 0 to remove and 1459 not upgraded.
Need to get 2,699 kB of archives. After unpacking 1,122 kB will be used.
The following packages have unmet dependencies:
 libssl-dev : Depends: libssl3t64 (= 3.2.1-3) but it is not going to be installed
The following actions will resolve these dependencies:

     Remove the following packages:
1)     libssl3 [3.1.4-2 (now)]
2)     libssl3:i386 [3.1.4-2 (now)]

     Install the following packages:
3)     libssl3t64 [3.2.1-3 (testing, unstable)]
4)     libssl3t64:i386 [3.2.1-3 (testing, unstable)]



Accept this solution? [Y/n/q/?] y
The following NEW packages will be installed:
  libssl3t64{a} libssl3t64:i386{a}
The following packages will be REMOVED:
  libssl3{a} libssl3:i386{a}
The following packages will be upgraded:
  libssl-dev
1 packages upgraded, 2 newly installed, 2 to remove and 1457 not upgraded.
Need to get 7,177 kB of archives. After unpacking 2,294 kB will be used.
Do you want to continue? [Y/n/?]

Getting the packages to upgrade involved a lot of calls to aptitude that looked like that: removing a list of libraries and a installing a matching list of new libraries whose names were identical to those removed except with t64 at the end.

The details#

The problem#

In an RSS/Atom feed, relative links are a bad idea because it's unclear what they're relative to. There are ways to specify a base for them to be relative to, but since feed readers do not consistently respect those mechanisms, it's safer to just always use absolute URLs in feeds. And Pelican recommends setting RELATIVE_URLS = False to always generate absolute URLs. But that setting does not apply to the anchor links generated by the Markdown toc extension to link to headers.

The solution#

I wrote a Pelican plugin, absolute_anchors which rewrites all link destinations starting with # in every article to add the absolute URL of the article at the beginning of the link.

The details#

The problem#

Every game, no matter how old and simple, I run on my computer constantly uses an entire CPU thread even when idling at a menu. (Except for some newer multi-threaded games that do the same with multiple threads!) To raise this from a curiosity to a problem, this means that my computer's fans are on at full blast whenever I have a game going, so I notice.

The solution#

To be clear, that symptom could be the result of many different possible causes, others of which I may explore in future blog posts.¹ But specifically for systems with Nvidia GPUs using the Nvidia proprietary driver (as opposed to nouveau), setting the environmental variable __GL_YIELD to USLEEP fixed the issue in some games for me. To do so when running a single game, run __GL_YIELD="USLEEP" /path/to/game or to do so permanently, add the line

export __GL_YIELD="USLEEP"

to ~/.profile and restart X.

The details#

The problem#

Compiling the Haskell package language-python (a dependency of xcffib), I got the following warning stating that the typeclass Error is deprecated:

language-python/src/Language/Python/Common/ParseError.hs:25:10: warning: [-Wdeprecations]
    In the use of type constructor or class ‘Error’
    (imported from Control.Monad.Error.Class, but defined in Control.Monad.Trans.Error):
    Deprecated: "Use Control.Monad.Trans.Except instead"
   |                                 
25 | instance Error ParseError where 
   |          ^^^^^                  

I wasn't sure how to "Use Control.Monad.Trans.Except instead", as Except is not a drop-in replacement for Error.

The solution#

As this StackOverflow answer recommended,

Short answer is: Replace Error by nothing at all

The code used throwError, which I replaced with

throwError = lift . Left

Other than that, I just removed the imports of Control.Monad.Error and the typeclass instance of Error. The full diff is in this pull request.

The details#