Fail graciously when there's no more file descriptors available.

[lvets]

Hello,

I forgot to increase the max. amount of file descriptors and instead of exiting ElectrumX filled approx. 64GB (Yes, GB) of log files with error messages. I believe at some point the original electrum-server checked the max. open files at startup.

Can we have some sort of check in place for ElectrumX?

[bauerj]

What message filled your logs?

[lvets]

Lines and lines of:

ERROR:asyncio:Exception in callback BaseSelectorEventLoop._start_serving(functools.par...4f9b0>, 'TCP'), <socket.socke..
.2049, proto=6>, None, <Server sockets=None>, 100)
handle: <TimerHandle when=8402620.28011113 BaseSelectorEventLoop._start_serving(functools.par...4f9b0>, 'TCP'), <socket.
socke...2049, proto=6>, None, <Server sockets=None>, 100)>
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/asyncio/events.py", line 126, in _run
    self._callback(*self._args)
  File "/usr/local/lib/python3.6/asyncio/selector_events.py", line 169, in _start_serving
    protocol_factory, sock, sslcontext, server, backlog)
  File "/usr/local/lib/python3.6/asyncio/selector_events.py", line 264, in _add_reader
    key = self._selector.get_key(fd)
  File "/usr/local/lib/python3.6/selectors.py", line 189, in get_key
    return mapping[fileobj]
  File "/usr/local/lib/python3.6/selectors.py", line 70, in __getitem__
    fd = self._selector._fileobj_lookup(fileobj)
  File "/usr/local/lib/python3.6/selectors.py", line 224, in _fileobj_lookup
    return _fileobj_to_fd(fileobj)
  File "/usr/local/lib/python3.6/selectors.py", line 41, in _fileobj_to_fd
    raise ValueError("Invalid file descriptor: {}".format(fd))
ValueError: Invalid file descriptor: -1

Grepping a 64GB file isn't easy :)