Why does Sharp lock the original image file after thumbnail creation in Node.js?

It turns out that sharp may be keeping a file lock on the input image when you pass the file path directly. This can prevent deletion later on. One effective solution is to read the file as a Buffer and then pass that Buffer to sharp. This way, the file is read and closed (releasing the file handle) before sharp processes it.

Below is an example of how you could modify your endpoint:

JAVASCRIPTCopied
const fs = require('fs').promises;

// inside your endpoint:
app.post('/upload-submission', upload.any(), async (req, res) => {
  const folderPath = req.body.folderPath;
  const targetDir = path.join(__dirname, folderPath);
  console.log('Resolved path:', targetDir);
  
  try {
    // Assume mainFile is obtained earlier from req.files
    const mainFileName = path.basename(mainFile.path);
    const mainFilePath = path.join(targetDir, mainFileName);
    
    // Read the file into a buffer first
    const imageBuffer = await fs.readFile(mainFilePath);

    // Create a thumbnail filename and path
    const thumbnailName = `thumb-${mainFileName}`;
    const thumbnailPath = path.join(targetDir, thumbnailName);

    try {
      // Pass the buffer to sharp instead of the file path directly
      await sharp(imageBuffer)
        .resize(150, 150)
        .toFile(thumbnailPath);
      console.log("Thumbnail created successfully.");
    } catch (err) {
      console.error('Error creating thumbnail:', err);
      throw new Error('Error creating thumbnail');
    }

    // Continue with your response logic here...
    
  } catch (err) {
    console.error('Error in file processing:', err);
    res.status(500).send('Error processing the file');
  }
});

Explanation

• Read as Buffer: By using fs.readFile, the file is fully read into memory and closed immediately, removing any locks on the file.
• Pass Buffer to sharp: When you call sharp(imageBuffer), it processes the image from memory. This means the original file no longer remains open or locked by sharp.
• File Deletion: Once the thumbnail is created and sharp is done processing, you should be able to delete the original image without encountering file lock issues.

This change should resolve the EPERM unlink error you're observing when trying to delete the main image.