DeltaQ.RTB - Update 25

Filtering – better path filtering was needed. I had implemented two schemes independently: exclude paths starting with a given prefix, and exclude paths containing a given component. Each was a separate list of strings in the configuration, and two separate bits of code handled them. It wasn't flexible enough, though. I wanted the ability to say, "Ignore paths that start with this subpath inside any home directory", or, more generally, "Ignore paths that match this regular expression."

So, I did it :-)

First, I wrote some code to enumerate users on the system. On POSIX systems, this consists of parsing a text file called /etc/passwd. I wanted to be able to unit test this, though, and a unit test that includes a read of the external file /etc/passwd isn't a unit test, it's (to some degree at least) an integration test. So, I abstracted accessing the file behind an interface that tests can mock out.

Then, I created a new concept of a PathFilter. At its core, the PathFilter uses a regular expression, but it can build those for you in several modes. You can create a Prefix-type PathFilter, which creates a regular expression that does the same filtering as the old ExcludePaths collection. You can create a Component-type PathFilter, which creates a regular expression that does the same filtering as the old ExcludePathsWithComponent collection. Or, you can create a Regex-type PathFilter and just write your own expression. This last one has an extension to the base regular expression syntax: if the string starts with ~, then it automatically enumerates all real users on the system and replaces the ~ with an expression that matches any home directory. On my system, ~ gets turned into ^(/root|/home/logiclrd)/.

Then to polish up that initial implementation, because freshly-written code is always full of bugs. I created a suite of unit tests that cover the intended functionality through all code paths, and used that to drive debugging until all the tests passed. Two minor complications:

• With DeltaQ.RTB running out of the code directory, sometimes (though for some reason not always) I can't build because the build output files are in use by the running process.
• For some reason, the C# Dev Kit extension for Visual Studio Code has stopped working on my system. I've tried reinstalling it, to no avail thus far. So, I don't get any of the fancy helper introspection right now. Good thing I have a mind like a steel thingamajig for all the framework details. :-)

With these changes, DeltaQ.RTB is running right now in realtime mode right now, ignoring Firefox's incessant modification of cache files and Visual Studio Code's state files and the GPUCache and DawnCache of, I believe, all the Electron-based apps running on the system, in addition to the baseline of path prefixes I previously determined.

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