unbound-dhcp-leases-bridge: Replace leases file atomically

When there is a large number of leases, writing the file may
take a long time. When unbound is re-reading its configuration
in that time, the file might syntactically incorrect.

This change writes the file first and then moves it
to the right place in one transaction.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

config/rootfiles/core/130/filelists/files

@@ -18,6 +18,7 @@ usr/local/bin/ipsec-interfaces
 usr/local/bin/suricatactrl
 usr/local/bin/update-ids-ruleset
 usr/sbin/convert-snort
+usr/sbin/unbound-dhcp-leases-bridge
 var/ipfire/backup/bin/backup.pl
 var/ipfire/backup/include
 var/ipfire/general-functions.pl

config/unbound/unbound-dhcp-leases-bridge

@@ -25,9 +25,11 @@ import daemon
 import ipaddress
 import logging
 import logging.handlers
+import os
 import re
 import signal
 import subprocess
+import tempfile
 
 import inotify.adapters
 
@@ -519,11 +521,15 @@ class UnboundConfigWriter(object):
 				self._cached_leases.append(l)
 
 	def write_dhcp_leases(self, leases):
-		with open(self.path, "w") as f:
+		with tempfile.NamedTemporaryFile(mode="w", delete=False) as f:
+			filename = f.name
+
 			for l in leases:
 				for rr in l.rrset:
 					f.write("local-data: \"%s\"\n" % " ".join(rr))
 
+		os.rename(filename, self.path)
+
 	def _control(self, *args):
 		command = ["unbound-control"]
 		command.extend(args)