dhcp: only install signal handlers from the server

"Silently" installing signal handlers from a module that may be
imported from another project is not the best idea.

Instead we move them to the server, which is where we want them here
and as an usage example for other PyPXE users.

pypxe/dhcp.py

@@ -8,7 +8,6 @@
 import struct
 import os
 import logging
-import signal
 import json
 from collections import defaultdict
 from time import time
@@ -130,12 +129,7 @@ def __init__(self, **server_settings):
             except ValueError:
                 pass
 
-        signal.signal(signal.SIGINT, self.export_leases)
-        signal.signal(signal.SIGTERM, self.export_leases)
-        signal.signal(signal.SIGALRM, self.export_leases)
-        signal.signal(signal.SIGHUP, self.export_leases)
-
-    def export_leases(self, signum, frame):
+    def export_leases(self):
         if self.save_leases_file:
             export_safe = dict()
             for lease in self.leases:
@@ -145,10 +139,6 @@ def export_leases(self, signum, frame):
             json.dump(export_safe, leases_file)
             self.logger.info('Exported leases to {0}'.format(self.save_leases_file))
 
-        # if keyboard interrupt, propagate upwards
-        if signum == signal.SIGINT:
-            raise KeyboardInterrupt
-
     def get_namespaced_static(self, path, fallback = {}):
         statics = self.static_config
         for child in path.split('.'):

pypxe/server.py

@@ -6,6 +6,7 @@
 import json
 import logging
 import logging.handlers
+import signal
 
 try:
     import argparse
@@ -250,6 +251,13 @@ def main():
         # configure/start DHCP server
         if args.USE_DHCP:
 
+            def dhcp_export_leases(signum, frame):
+                dhcp_server.export_leases()
+
+                # if keyboard interrupt, propagate upwards
+                if signum == signal.SIGINT:
+                    raise KeyboardInterrupt
+
             # setup DHCP logger
             dhcp_logger = helpers.get_child_logger(sys_logger, 'DHCP')
             if args.DHCP_MODE_PROXY:
@@ -278,6 +286,10 @@ def main():
                 static_config = loaded_statics,
                 logger = dhcp_logger,
                 saveleases = args.LEASES_FILE)
+            signal.signal(signal.SIGINT, dhcp_export_leases)
+            signal.signal(signal.SIGTERM, dhcp_export_leases)
+            signal.signal(signal.SIGALRM, dhcp_export_leases)
+            signal.signal(signal.SIGHUP, dhcp_export_leases)
             dhcpd = threading.Thread(target = dhcp_server.listen)
             dhcpd.daemon = True
             dhcpd.start()