❓ I'm submitting a ...

• 🐞 bug report
• 🐣 feature request
• ❓ question about the decisions made in the repository

🐞 Describe the bug. What is the current behavior?
If a client goes away while a request timeout is being processed, the socket.error exception produced in /cheroot/server.py _conditional_error() bubbles up uncaught all the way to the thread worker. This generates a stack trace regardless of logging config.

❓ What is the motivation / use case for changing the behavior?
This is producing STDERR errors in our container log, preventing us from handling errors properly. I also suspect given enough occurrence it may lead to thread pool starvation although I have not experimented with it.

💡 To Reproduce
This is hard to reproduce, I suspect timing is heavily involved. We are seeing it occur in our environment when requests timeout. These requests are coming from a load balancer.

💡 Expected behavior
The exception should be caught and treated as a simple failure and simply trigger completion and cleanup of the client's request (the client simply has gone away).

📋 Details
Here is the traceback we're seeing:

Traceback (most recent call last):
  File "/usr/local/lib/python2.7/threading.py", line 801, in __bootstrap_inner
    self.run()
  File "/usr/local/lib/python2.7/site-packages/cheroot/workers/threadpool.py", line 114, in run
    conn.communicate()
  File "/usr/local/lib/python2.7/site-packages/cheroot/server.py", line 1286, in communicate
    self._conditional_error(req, '408 Request Timeout')
  File "/usr/local/lib/python2.7/site-packages/cheroot/server.py", line 1334, in _conditional_error
    req.simple_response(response)
  File "/usr/local/lib/python2.7/site-packages/cheroot/server.py", line 1115, in simple_response
    self.conn.wfile.write(EMPTY.join(buf))
  File "/usr/local/lib/python2.7/site-packages/cheroot/makefile.py", line 78, in write
    data_mv[bytes_sent:bytes_sent + SOCK_WRITE_BLOCKSIZE],
  File "/usr/local/lib/python2.7/site-packages/cheroot/ssl/pyopenssl.py", line 144, in send
    *args, **kwargs
  File "/usr/local/lib/python2.7/site-packages/cheroot/ssl/pyopenssl.py", line 91, in _safe_call
    raise socket.error(errnum)
error: -1

📋 Environment

• PyOpenSSL version: 19.0.0
• Cheroot version: 6.5.4
• CherryPy version: 17.4.2
• Python version: 2.7.13
• OS: Linux Alpine

📋 Additional context
I believe a simple try/except/pass for the socket.error in the context of https://github.com/cherrypy/cheroot/blob/v6.5.5/cheroot/server.py#L1276 should fix the issue without any negative side-effects since the server is already dealing with a client that has gone away.