Picture this: 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, on the other hand, found the typo but also couldn't accurately predict the behavior of the operation. Claude also noticed the mistake but refused to display the execution result Conclusion Always check important function's post-conditions even if you think you will have performance penalties. You can never be too safe. Relation Code Smells Code Smell 15 - Missed Preconditions Disclaimer: Code Smells are my opinion. 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 from Software Engineering Great works. This article is part of the CodeSmell Series: How to Find the Stinky Parts of your Code Photo Credit: Luke Jernejcic on Unsplash Picture this: You copy a file and don't verify it Picture this: You copy a file and don't verify it TL;DR: Don't rely on external solutions without good handlers TL;DR: Don't rely on external solutions without good handlers Problems Silent Modifications Least Surprise Principle violation Fail Fast Principle Violation Silent Modifications Silent Modifications Least Surprise Principle violation Least Surprise Principle violation Fail Fast Principle Violation Fail Fast Principle Violation Solutions Ensure you meet your function's postconditions Use mature languages Ensure you meet your function's postconditions Ensure you meet your function's postconditions Use mature languages Use mature languages Context The copy() function is used to copy files from one location to another. copy() 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 <?

  $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
  } <?

  $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 [x] Semi-Automatic [x] You can check all copy() handlers and wrap them Tags Fail Fast Fail Fast Level [x]Beginner [x] Beginner [x] AI Generation Gemini is the only generator that avoided the problem dealing with ":" on file names AI Detection With this prompt: With this prompt: What happens with this code on windows and what is the value of copyWasSuccessful 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, on the other hand, found the typo but also couldn't accurately predict the behavior of the operation. Claude also noticed the mistake but refused to display the execution result Conclusion Always check important function's post-conditions even if you think you will have performance penalties. You can never be too safe. you think Relation Code Smells Code Smell 15 - Missed Preconditions Code Smell 15 - Missed Preconditions Disclaimer: Code Smells are my opinion. Disclaimer: Code Smells are my opinion . opinion 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. 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 from Software Engineering Great works. - Boris Beizer from Software Engineering Great works. Boris Beizer This article is part of the CodeSmell Series: How to Find the Stinky Parts of your Code This article is part of the CodeSmell Series: How to Find the Stinky Parts of your Code How to Find the Stinky Parts of your Code Photo Credit: Luke Jernejcic on Unsplash Photo Credit: Luke Jernejcic on Unsplash Luke Jernejcic Unsplash

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