Listen crashes on inaccessable directories (Errno::EACCES)

[kansaichris]

Given the following very basic program (let's call it test.rb):

require 'listen'

listener = Listen.to('.', :ignore => [/test/]) do |modified, added, removed|
  puts "Something changed!"
end

listener.start
sleep

Also given the following output from ls -l:

total 8
drwx------  2 root   staff   68 Sep  5 16:02 test
-rw-r--r--  1 chris  staff  149 Sep  5 16:10 test.rb

The program will crash with the following error when run:

E, [2014-09-05T16:11:49.509781 #86974] ERROR -- : Actor crashed!
Errno::EACCES: Permission denied @ dir_initialize

This is despite the fact that [/test/] was given as the :ignore parameter to Listen.to!

The culprit appears to be a call to Dir.entries in the _fast_build method:

def _fast_build(root)
  @paths[root] = _auto_hash
  left = Queue.new
  left << '.'

  while !left.empty?
    dirname = left.pop
    add_dir(root, dirname)

    path = ::File.join(root, dirname)
    current = Dir.entries(path.to_s) - %w(. ..)

    current.each do |entry|
      full_path = ::File.join(path, entry)

      if Dir.exist?(full_path)
        left << (dirname == '.' ? entry : ::File.join(dirname, entry))
      else
        begin
          lstat = ::File.lstat(full_path)
          data = { mtime: lstat.mtime.to_f, mode: lstat.mode }
          _fast_update_file(root, dirname, entry, data)
        rescue SystemCallError
          _fast_unset_path(root, dirname, entry)
        end
      end
    end
  end
end

Why does Listen have to call Dir.entries on ignored directories? Shouldn't those be excluded?

[kansaichris]

@parkr @gjtorikian Just putting this on your radar...

[e2]

"ignore" in listen doesn't mean "skip scanning this folder", it means only "don't report" (Honestly, it depends on the adapter, e.g. polling actually should skip the folder).

The problem here is that I didn't consider someone would have an inaccessible folder being watched.

It's probably enough to add a test case for this and wrap the Dir.entries within a SystemCallError rescue block.

The best solution - if you're e.g. testing permissions - is to not watch those folders (since you don't have access, there's no point anyway). Again, ignoring has nothing to do with this.

I might get to this, but it's not a top priority right now - but don't hesitate to take a stab at a PR and ask for review/info.

[e2]

2 different issues here:

1. optimized backends in Listen don't ignore directories (feature request: Feature request: Listen could *really ignore* ignored directories (optimization) #274)
2. almost every tool out there crashes/errors out/exits by design on permission errors

Listen doesn't crash any more (fixed on master), but to prevent rb-inotify from crashing for the same reason, #274 has to be implemented

So I'm closing this (no bug to fix in Listen itself).

Workarounds

1. avoid watching directories which have permission problems (very reasonable)
2. use polling - it's the only backend that really ignores directories (fix on master is needed, though - soon to be released)

Best solution

Getting #274 implemented of course - since everyone benefits
(PRs are more than welcome - I'll be glad to help, answer questions, etc.).