The Boston Diaries

The ongoing saga of a programmer who doesn't live in Boston, nor does he even like Boston, but yet named his weblog/journal “The Boston Diaries.”

Go figure.

Thursday, August 26, 2021

The case of the regression test regression, part IV

Like all bugs, it was a simple fix once identified—it was just identifying the bug that was difficult. The bug was due to a semantic change in an API. Lua has a file interface that includes a read() function, and the parameter it's given dictates how much to read. One of the parameters is “a” (or “*a” if you are using Lua 5.1) that indicates you want to read all possible data until the end-of-file is reached.

I ended up writing my own read() function to deal with network activity. I couldn't just open up a normal Lua file object with a network connection because that doesn't work nicely with event driven programs. An earlier version of my read() function had a different semantic meaning with “a”—it just returned any buffered data. It was in a later change where I aligned the semantics to match Lua's semantics, but forgot to change that bit of code in the one component. And those semantic changes explain the behavior I was seeing yesterday. It only took what? A week? To find the culprit.

Now the regression test with the updated code runs as fast as the previous version.

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