fs.writeFile fails without error when writing to a specific (not full) partition

Question

I'm implementing an image cache for favicons found on the web. At one point I have the favicon's URL, and I'm sending it to my page, everything is fine.

Now alongside this, I write the icon to disk, using a pseudo-unique filename that I construct using the URL components.

And this works too, but only if I write to /tmp/!?

Here is my code:

router.get('/favicon', function(req, res) {
  favicon(req.query.url, function(err, iconUrl) {
    if (iconUrl) {
      var u = Url.parse(iconUrl);
      request.get({url: iconUrl}, function (err, response, body) {
        if (!err && typeof body !== 'undefined') {
          var h = u.host.replace(/\//g, ''),
              p = u.path.replace(/\//g, ''),
              fileName;

          fileName = path.join('/tmp', h + '.' + p);
          // fileName = path.join(__dirname, '..', 'cache', h + '.' + p);

          fs.writeFile(fileName, body, function(err) {
            if(err)
              console.log(err);
            else
              console.log("SAVED! (%s)", fileName);
          });
        } else {
          console.log('### ERROR iconUrl: (%s) err: (%s)', iconUrl, err);
        }
      });
      res.send(iconUrl);
    } else {
      res.status(500).send('No icon found');
    }
  });
});

This is called on the client (web browser) side like this:

$.get("/favicon", {
  url: decodeURI(feedHost),
  dataType: "json",
  timeout: 2000
}, function(iconURL) {
  console.info('OK (icon: %s)', iconURL);
}).done(function(iconURL) {
  console.info('OK (icon: %s)', iconURL);
}).fail(function() {
  console.error('ERROR');
});

I though it was a "disk full" problem but no, here is the partition table on this machine, the project directory (where my image cache directory resides) in inside the /home partition, and /tmp/ is, well, on /:

# df -h   
Filesystem      Size  Used Avail Use% Mounted on
udev            1.9G     0  1.9G   0% /dev
tmpfs           388M  6.3M  382M   2% /run
/dev/sda6        19G   14G  3.8G  79% /
tmpfs           1.9G   23M  1.9G   2% /dev/shm
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs           1.9G     0  1.9G   0% /sys/fs/cgroup
/dev/loop0       82M   82M     0 100% /snap/core/4206
/dev/loop1      128M  128M     0 100% /snap/shotcut/20
/dev/loop2       82M   82M     0 100% /snap/core/4110
/dev/loop3       82M   82M     0 100% /snap/core/4017
/dev/loop4      298M  298M     0 100% /snap/shotcut/17
/dev/loop5      128M  128M     0 100% /snap/shotcut/21
/dev/sda5       121G  102G   14G  89% /home
tmpfs           388M   12K  388M   1% /run/user/1000

So when I use the code above, everything works fine, and /tmp/ fills with images, asynchronously, perfect.

As soon as I remove the leading / of the file path - pointing to a valid path, of course - then one, two, maximum 3 favicons are copied and then the process fails somehow, triggering the .fail() method one the client side, but without any error on the server.

Help!

Questions:

• What could be causing this weird "write 2 or 3 files then stop" problem? NB: The server is launched with PM2.
• Is my ajax call (JQuery $.get()) correct? Why does it make the other ajax calls in the page fail, instead of gently erroring and then move on?

UPDATE

It turns out that I was not saving a correct image file in /tmp/ ; I am now using this code:

router.get('/favicon', function(req, res) {

  favicon(req.query.url, function(err, iconUrl) {
    if (iconUrl) {

      if (!iconUrl.startsWith('..') && Url.parse(iconUrl)) {

        var u = Url.parse(iconUrl),
            h = u.host.replace(/\//g, ''),
            p = u.path.replace(/\//g, ''),
            fileName;

        fileName = path.join('/tmp/cache', h + '.' + p);
        // fileName = path.join(__dirname, '..', 'cache', h + '.' + p);

        let stream = fs.createWriteStream(fileName);
        stream.on('finish', function () {
          console.log("SAVED %s (%s)", fileName, iconUrl);
        }).on('error', function (err) {
          console.log("NOT SAVED %s (%s)", fileName, err);
        });
        request(iconUrl).pipe(stream);

      } else {
        console.log('iconUrl NOT OK: (%s)', iconUrl);
      }

      res.send(iconUrl);
    } else {
      res.status(500).send('No icon found');
    }
  });
});

And now the files saved are proper image files ; However the problem persists, and I have now tested this code on several other (Linux) machines including a production web server, same thing! No way to save (more than a handful of) files within the project repo, and yet if I use /tmp/* as the file path, everything is fine!

This is rendering me crazy, please put me out of this misery :|

Update 2

I managed to write to my home partition. The only place I cannot write to is any directory inside (and including) the project directory.

Answer 1

OK, I found out. The culprit is the pm2 watcher, that restarts the server when something is written within the whole scope of the project.

That's the (hard to find, if it's written somewhere I don't know where) reason why I could write my image files everywhere on the disk but in the project directory without any error, just a slow and chaotic collapsing of the server ; Thank you for your patience.

So I created the following pm2 process management file (by running pm2 ecosystem simple thanks to this answer)

{
  "apps" : [{
    "name"            : "petrolette",
    "script"          : "./bin/www",
    "watch"           : true,
    "ignore_watch"    : ["favicons-cache"],
    "log_date_format" : "YYYY-MM-DD HH:mm",
    "env": {
      "PORT": 8666,
      "FAVICONS_CACHE_DIR": "favicons-cache"
    },
    "env_production" : {
      "NODE_ENV": "production"
    }
  }]
}

So now my favicons-cache dir is protected from the watch process, and as a bonus its name is now an ENV var so I can access it with process.env.FAVICONS_CACHE_DIR :)