Exceptions not handled in server thread

We are occasionally getting an ssl.SSLEOFError when using the prometheus client with HTTPS (as of the new version 0.19.0). That error is raised in the server thread and because it is not handled there, the entire process dies:

Traceback (most recent call last):
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 138, in run
    self.finish_response()
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 184, in finish_response
    self.write(data)
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 288, in write
    self.send_headers()
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 346, in send_headers
    self.send_preamble()
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 268, in send_preamble
    self._write(
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 467, in _write
    result = self.stdout.write(data)
  File "/usr/lib/python3.10/socketserver.py", line 826, in write
    self._sock.sendall(b)
  File "/usr/lib/python3.10/ssl.py", line 1237, in sendall
    v = self.send(byte_view[count:])
  File "/usr/lib/python3.10/ssl.py", line 1206, in send
    return self._sslobj.write(data)
ssl.SSLEOFError: EOF occurred in violation of protocol (_ssl.c:2426)
Traceback (most recent call last):
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 138, in run
    self.finish_response()
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 184, in finish_response
    self.write(data)
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 288, in write
    self.send_headers()
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 346, in send_headers
    self.send_preamble()
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 268, in send_preamble
    self._write(
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 467, in _write
    result = self.stdout.write(data)
  File "/usr/lib/python3.10/socketserver.py", line 826, in write
    self._sock.sendall(b)
  File "/usr/lib/python3.10/ssl.py", line 1237, in sendall
    v = self.send(byte_view[count:])
  File "/usr/lib/python3.10/ssl.py", line 1206, in send
    return self._sslobj.write(data)
ssl.SSLEOFError: EOF occurred in violation of protocol (_ssl.c:2426)

I verified that this exception is not raised within start_http_server() so it must be happening in the server thread.

The goal would be that the exception raised in the server thread causes the server thread to terminate and the main thread has some means to get to the exception raised in the server thread. The solution would need to work for both HTTP and HTTPS.

There seem to be different techniques on how that can be achieved:

• https://stackoverflow.com/q/2829329/1424462

This would probably require that the start_http_server() function returns the thread object (see issue #883)

Beginne bei start_http_server() und prüfe Issue #883 auf das vorgeschlagene Rückgabeverhalten des Threads. Verfolge, wie die HTTP- und HTTPS-Server-Threads Ausnahmen behandeln, und bestimme dann, wie die ausgelöste Ausnahme für den Haupt-Thread sichtbar werden soll; abgeschlossen ist die Aufgabe, wenn beide Protokolle den Server-Thread beenden, ohne den Prozess stillschweigend zu beenden.