From 60a00c452bd22714459660f367c3d73e686580a3 Mon Sep 17 00:00:00 2001
From: Markus Hilger <markus.hilger@megware.com>
Date: Sat, 11 Jul 2026 00:24:30 +0200
Subject: [PATCH] Warn on conflicting entries in confluent2hosts and
 confluent2dnsmasq

Neither tool detected when the attribute database produces conflicting
name/IP data, silently emitting the conflicts.

confluent2hosts now warns when the same hostname is generated for
multiple different addresses within one address family (dual-stack
IPv4+IPv6 pairs stay silent), which happens naturally in -a mode when a
node has several networks without distinct per-net hostnames.

confluent2dnsmasq now warns when generated reservations share a
hostname across different IPs, reserve the same IP more than once
(dnsmasq refuses to start on a duplicate dhcp-host IP), or reuse a MAC.
---
 confluent_client/bin/confluent2dnsmasq | 40 +++++++++++++++++++++++++-
 confluent_client/bin/confluent2hosts   |  9 ++++++
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/confluent_client/bin/confluent2dnsmasq b/confluent_client/bin/confluent2dnsmasq
index 488cc1ac..321972c3 100644
--- a/confluent_client/bin/confluent2dnsmasq
+++ b/confluent_client/bin/confluent2dnsmasq
@@ -147,6 +147,41 @@ def existing_regen_args(targetpath):
 
 
 
+def warn_conflicts(hostentries):
+    """Warn about reservations that conflict with one another: the same
+    hostname on different IPs, one IP reserved more than once (dnsmasq
+    refuses to start on a duplicate dhcp-host IP), or one MAC reserved
+    more than once.  Diagnostics only; every entry is still emitted."""
+    byname = {}
+    byip = {}
+    bymac = {}
+    for e in hostentries:
+        if e['hostname']:
+            prev = byname.setdefault(e['hostname'], e)
+            if prev is not e and prev['ip'] != e['ip']:
+                sys.stderr.write(
+                    "WARNING: hostname '{0}' maps to both {1} ({2}) and "
+                    '{3} ({4})\n'.format(
+                        e['hostname'], prev['ip'], prev['node'],
+                        e['ip'], e['node']))
+        prev = byip.setdefault(e['ip'], e)
+        if prev is not e:
+            sys.stderr.write(
+                'WARNING: address {0} is reserved for both {1} ({2}) and '
+                '{3} ({4}); dnsmasq refuses to start on a duplicate '
+                'dhcp-host IP address\n'.format(
+                    e['ip'], ','.join(prev['macs']), prev['node'],
+                    ','.join(e['macs']), e['node']))
+        for mac in e['macs']:
+            prev = bymac.setdefault(mac.lower(), e)
+            if prev is not e:
+                sys.stderr.write(
+                    'WARNING: MAC {0} is reserved for both {1} ({2}) and '
+                    '{3} ({4})\n'.format(
+                        mac, prev['ip'], prev['node'],
+                        e['ip'], e['node']))
+
+
 def main():
     ap = argparse.ArgumentParser(
         description='Create /etc/dnsmasq.d static DHCP reservations for a '
@@ -336,7 +371,10 @@ def main():
 
             hostentries.append({'subnetkey': subnetkey,
                                 'macs': split_list(hwaddr),
-                                'ip': ip, 'hostname': hostname})
+                                'ip': ip, 'hostname': hostname,
+                                'node': node})
+
+    warn_conflicts(hostentries)
 
     # Resolve optional per-subnet options from the aggregated values.
     def resolve(values, what, subnetkey):
diff --git a/confluent_client/bin/confluent2hosts b/confluent_client/bin/confluent2hosts
index d31708bb..66af0f48 100644
--- a/confluent_client/bin/confluent2hosts
+++ b/confluent_client/bin/confluent2hosts
@@ -33,6 +33,8 @@ class HostMerger(object):
         self.byip = {}
         self.byname = {}
         self.byname6 = {}
+        self.ipbyname = {}
+        self.ipbyname6 = {}
         self.sourcelines = []
         self.targlines = []
 
@@ -54,14 +56,21 @@ class HostMerger(object):
 
     def add_entry(self, ip, names):
         targ = self.byname
+        ipbyname = self.ipbyname
         if ':' in ip:
             targ = self.byname6
+            ipbyname = self.ipbyname6
         line = '{:<39} {}'.format(ip, names)
         x = len(self.sourcelines)
         self.sourcelines.append(line)
         for name in names.split():
             if not name:
                 continue
+            if ipbyname.setdefault(name, ip) != ip:
+                sys.stderr.write(
+                    'WARNING: {0} is mapped to both {1} and {2}; all entries '
+                    'will be written to /etc/hosts\n'.format(
+                        name, ipbyname[name], ip))
             targ[name] = x
         self.byip[ip] = x