You copy a file and don't verify it
TL;DR: Don't rely on external solutions without good handlers
Problems
Silent Modifications
Least Surprise Principle violation
Fail Fast Principle Violation
Solutions
Ensure you meet your function's postconditions
Use mature languages
Context
The copy() function is used to copy files from one location to another.
However, when used on some systems, it can fail silently or make unexpected conversions.
For example, Windows interprets paths ending with a backslash () as directories.
If the intended destination file has the same name as a directory in the path, copy() will silently create an empty file with the intended filename within that directory.
This can be confusing and lead to data loss.
Sample Code
Wrong
<?
$sourceFile = 'C:\temp\source.txt';
$destination = 'C:\temp\destination.txt';
$copyWasSuccessful = copy($sourceFile, $destination); // true
$destinationFileExists = file_exists($destination); // true
$sourceFile = 'C:\temp\source.txt';
$destination = 'C:\temp\destination :txt';
// The filename is simplified
// and might come from a programmatic construction
$copyWasSuccessful = copy($sourceFile, $destination);
// true - this is a mistake
$destinationFileExists = file_exists($destination);
// false since it was not created
$destinationChangedFileExists = file_exists('C:\temp\destination ');
// true but unexpected
Right
<?
$sourceFile = 'C:\temp\source.txt';
$destination = 'C:\temp\destination :txt';
// The filename is simplified
// and might come from a programmatic construction
$copyWasSuccessful = copy($sourceFile, $destination);
if (!$copyWasSuccessful || !$file_exists($destination)) {
// Don't trust the function result. Handle the postcondition error
}
Detection
[X] Semi-Automatic
You can check all copy() handlers and wrap them
Tags
- Fail Fast
Level
[X] Beginner
AI Generation
Gemini is the only generator that avoided the problem dealing with ":" on file names
AI Detection
With this prompt:
what happens with this code on windows and what is the value of copyWasSuccessful
ChatGPT found the mistake and (wrongly) predicted the operation would fail
Gemini found the typo but also couldn't predict the behavior
Claude also noticed the mistake but refused to tell the execution result
Conclusion
Always check important function's post-conditions even if you think you will have performance penalties.
Relations
Disclaimer
Code Smells are my opinion.
Credits
Photo by Luke Jernejcic on Unsplash
Blaming programmers has been the prevailing approach for a half century of software development: It has not solved the problem yet, so it is time to look in different directions.
Boris Beizer
Software Engineering Great Quotes
Maxi Contieri ・ Dec 28 '20
This article is part of the CodeSmell Series.
Top comments (2)
It looks like your backslash got eaten by the markdown editor.
No. This is an example and the code snipet has another one with dots