Technitribe

Have you ever had a sub-select where you really needed to reference a value in the outer query? I know I have! The naive way would be to run the outer query and then loop over the results running the inner query on each one. Luckily, there’s a better way. The Correlated subquery. Check it out! The example given is

SELECT employee_number, name
  FROM employees AS Bob
  WHERE salary > (
    SELECT AVG(salary)
      FROM employees
      WHERE department = Bob.department);

See how the sub-select references the outer query? It’s SQL magic.

The “git archive” man page states:

git archive behaves differently when given a tree ID versus when given a commit ID or tag ID. In the first case the current time is used as the modification time of each file in the archive.

By using the current time in this case, git-archive is dooming all of our tarballs to have constantly changing SHA256 hashes. A lot of build systems, including Fedora’s Koji, rely on source tarballs maintaining a consistent fingerprint. What is a person to do?

Fix it of course! Below is a Python 2 program I wrote that addresses the issue. The code is well-commented (I hope) so you should be able to follow along. You give it the Unix timestamp you want the files to have, the git ref you want baked into the tar header, and the initial tarball. The result is printed to stdout so just redirect that to wherever you please (or pipe it into gzip). It also has some code in there to deal with tarballs created by the maven-assembly plugin, but it doesn’t surface that on the primitive CLI. I’m leaving that as an exercise for the reader I guess.

Recently I noticed that in my IRC client, when I right-click a URL and select “Open Link In Browser”, the system would open a new browser window (or tab if appropriate) but not pointed to the link I wanted to visit. It would just open the home page.

What gives? Well, I happen to know from experience that in Linux most programs that need to use a “default” type service of which there are many implementations (such as a web-browser) use the xdg-open command. XDG associates different mime-types to default applications. Step one then is to figure out what’s going on with XDG.

% xdg-mime query default text/html
firefox.desktop firefox.desktop

Here I’m asking XDG what applications are associated with the text/html mime-type. Seeing two firefox.desktop files was a bit of a surprise. Let’s find out more!

% locate firefox.desktop
/usr/share/applications/firefox.desktop
/usr/share/xfce4/helpers/firefox.desktop

So I open up those two files and the first file looks normal and that file actually belongs to the Firefox package according to rpm -qf. In the second file, I see

X-XFCE-Commands=%B -remote "openURL(about:blank,new-window)";%B;
X-XFCE-CommandsWithParameter=%B -remote "openURL(%s,new-window)";%B "%s";

That looks strange to me. If I want to open a URL from the command line, I don’t use openURL. Let’s see what happens if I replace that with

X-XFCE-Commands=%B;
X-XFCE-CommandsWithParameter=%B "%s";

Aha! It works! But why? Well, after a little searching I came across Mozilla Bug 1080319. Looks like the openURL was a legacy thing and got removed in Firefox 36. And a quick rpm -q firefox confirms that I’m running that version. Firefox 36.0.1 add support for openURL back in, but my hack will serve until that version hits Fedora.