7

I am writing some code in NodeJs, and want to check to see if the file is in use by another process, if it is then do nothing, if it isn't in use do something.

fs.stats is kind of a, at this instant what is the file size. And doesn't tell me me if its currently in use from another process.

Not sure what else to try.

What is the best way to tell if a file is currently locked for editing by another process, before trying to access the file using nodejs?

shaun
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  • I don't think `fs` really locks the file down while editing, it does the edit if it can, and then calls the callback, and if it wasn't successful the callbacks first argument would be an error. – adeneo Jun 07 '16 at 22:28
  • You are right, node doesn't lock the file, but if a file is currently being uploaded by FTP, then the FTP Server has it locked for editing. At that point in time I would like to ignore the file. If it is no longer locked for editing by an outside process, then and only then do I want to interact with the file. – shaun Jun 07 '16 at 22:31
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    If the file is truly locked, trying to access it with `fs` should generate an error in the callback that you can handle. The other option would be to set some sort of flag in a map when a file is uploaded, and then clear the flag when the FTP upload is done, and then use the map to see if the file is finished or not. – adeneo Jun 07 '16 at 22:33

2 Answers2

15

Code I ended up using after some instruction from the comments left.

var delInterval = setInterval(del(), 1000);

function del(){
    fs.open(filePath, 'r+', function(err, fd){
        if (err && err.code === 'EBUSY'){
            //do nothing till next loop
        } else if (err && err.code === 'ENOENT'){
            console.log(filePath, 'deleted');
            clearInterval(delInterval);
        } else {
            fs.close(fd, function(){
                fs.unlink(filePath, function(err){
                    if(err){
                    } else {
                    console.log(filePath, 'deleted');
                    clearInterval(delInterval);
                    }
                });
            });
        }
    });
}
shaun
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0

I came up with a smaller approach, so I'd like to share it:

function isWritable(filePath) {
  let fileAccess = false
  try {
      fs.closeSync(fs.openSync(filePath, 'r+'))
      fileAccess = true
  } catch (err) {
      console.log('can not open file!')
  }
  return fileAccess
}
Alex Rintt
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Resk
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