Tim W caught a ticket. The PHP system he inherited allowed users to upload files, and then would process those files. It worked… most of the time. It seemed like a Heisenbug. Logging was non-existent, documentation was a fantasy, and to be honest, no one was exactly 100% certain what the processing feature was supposed to do- but whatever it was doing now was the right thing, except the times that it wasn’t right.

Specifically, some files got processed. Some files didn’t. They all were supposed to.

But other than that, it worked.

Tim worried that this was going to be difficult to replicate, especially after he tried it with a few files he had handy. Digging through the code though, made it perfectly clear what was going on. Buried on about line 1,200 in a 3,000 line file, he found this:

while (false !== ($file = readdir($handle))) {
    if ($file != "." && $file != ".." && ( $file == strtolower($file) ) ) {

For some reason, this code required that the name of the file contain no capital letters. Why? Well, again, no documentation, no comments, and the change predated the organization’s use of source control. Someone put in the effort to add the feature, but was it necessary?

Tim took the line out, and now it processes all files. Unfortunately, it’s still only working most of the time, but nobody can exactly agree on what it’s doing wrong.

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