fix: fall back to lease file when DHCPLeases API is empty

lib/fog/libvirt/models/compute/server.rb

@@ -259,11 +259,14 @@
           user_data_path = File.join(dir_path, 'user-data')
           File.write(user_data_path, user_data)
 
-          isofile = Tempfile.new(['init', '.iso']).path
+          iso_tempfile = Tempfile.new(['init', '.iso'])
+          isofile = iso_tempfile.path
           unless system('xorrisofs', '-output', isofile, '-volid', 'cidata', '-joliet', '-rock', user_data_path, meta_data_path)
             raise Fog::Errors::Error.new("Couldn't generate cloud-init iso disk with xorrisofs.")
           end
           blk.call(isofile)
+        ensure
+          iso_tempfile&.close!
         end
 
         def create_user_data_iso
@@ -470,6 +473,44 @@
           args
         end
 
+        DNSMASQ_LEASE_DIR = '/var/lib/libvirt/dnsmasq'.freeze
+
+        # Read IP from a dnsmasq lease file when the libvirt DHCPLeases API
+        # returns nothing.  This happens when DHCP is provided by an external
+        # dnsmasq (not started by libvirt) -- for example, a dnsmasq running
+        # inside a network namespace to work around port conflicts on WSL2.
+        #
+        # dnsmasq lease file format (space-separated):
+        #   <expiry> <mac> <ip> <hostname> [<client-id>]
+        def ip_address_from_leasefile(net, mac)
+          net_name = net.name
+          return nil unless net_name
+
+          lease_file = File.join(DNSMASQ_LEASE_DIR, "#{net_name}.leases")
+          return nil unless File.exist?(lease_file)
+
+          target_mac = mac.to_s.downcase
+          best_expiry = 0
+          best_ip = nil
+
+          begin
+            File.foreach(lease_file) do |line|
+              parts = line.strip.split
+              next unless parts.length >= 4
+
+              expiry, lease_mac, ip = parts[0].to_i, parts[1].downcase, parts[2]
+              if lease_mac == target_mac && expiry > best_expiry
+                best_expiry = expiry
+                best_ip = ip
+              end
+            end
+          rescue Errno::EACCES, Errno::ENOENT
+            return nil
+          end
+
+          best_ip
+        end
+
         # This retrieves the ip address of the mac address using dhcp_leases
         # It returns an array of public and private ip addresses
         # Currently only one ip address is returned, but in the future this could be multiple
@@ -480,14 +521,23 @@
             net = service.networks.all(:name => nic.network).first
             # Assume the lease expiring last is the current IP address
             ip_address = net&.dhcp_leases(nic.mac)&.max_by { |lse| lse["expirytime"] }&.dig("ipaddr")
+
+            # Fallback: when the network has no libvirt-managed DHCP (e.g. an
+            # external dnsmasq running in a network namespace on WSL2), the
+            # DHCPLeases API returns empty.  Read the dnsmasq lease file directly.
+            if ip_address.nil? && net
+              @@leasefile_fallback_warned ||= {}
+              unless @@leasefile_fallback_warned[nic.mac]
+                Fog::Logger.warning("DHCPLeases API returned no address for #{nic.mac}; falling back to dnsmasq lease file.")
+                @@leasefile_fallback_warned[nic.mac] = true
+              end
+              ip_address = ip_address_from_leasefile(net, nic.mac)
+            end
           end
 
           return { :public => [ip_address], :private => [ip_address] }
         end
 
-        # Locale-friendly removal of non-alpha nums
-        DOMAIN_CLEANUP_REGEXP = Regexp.compile('[\W_-]')
-
         def ip_address(key)
           addresses[key]&.first
         end

minitests/server/leasefile_fallback_test.rb

@@ -0,0 +1,86 @@
+require 'test_helper'
+require 'tmpdir'
+
+class LeasefileFallbackTest < Minitest::Test
+  def setup
+    @compute = Fog::Compute[:libvirt]
+    @server = @compute.servers.new(:name => "test")
+    @mac = "52:54:00:01:02:03"
+    @net = stub(:name => "default")
+    @tmpdir = Dir.mktmpdir("fog-leasefile-test")
+    @original_dir = Fog::Libvirt::Compute::Server::DNSMASQ_LEASE_DIR
+    Fog::Libvirt::Compute::Server.send(:remove_const, :DNSMASQ_LEASE_DIR)
+    Fog::Libvirt::Compute::Server.const_set(:DNSMASQ_LEASE_DIR, @tmpdir)
+  end
+
+  def teardown
+    FileUtils.remove_entry(@tmpdir)
+    Fog::Libvirt::Compute::Server.send(:remove_const, :DNSMASQ_LEASE_DIR)
+    Fog::Libvirt::Compute::Server.const_set(:DNSMASQ_LEASE_DIR, @original_dir)
+  end
+
+  def test_returns_ip_for_matching_mac
+    write_lease_file("default", "1000 52:54:00:01:02:03 192.168.122.10 host1 *\n")
+    result = @server.send(:ip_address_from_leasefile, @net, @mac)
+    assert_equal "192.168.122.10", result
+  end
+
+  def test_returns_ip_with_highest_expiry
+    content = <<~LEASES
+      1000 52:54:00:01:02:03 192.168.122.10 host1 *
+      2000 52:54:00:01:02:03 192.168.122.20 host1 *
+      1500 52:54:00:01:02:03 192.168.122.15 host1 *
+    LEASES
+    write_lease_file("default", content)
+    result = @server.send(:ip_address_from_leasefile, @net, @mac)
+    assert_equal "192.168.122.20", result
+  end
+
+  def test_mac_matching_is_case_insensitive
+    write_lease_file("default", "1000 52:54:00:01:02:03 192.168.122.10 host1 *\n")
+    result = @server.send(:ip_address_from_leasefile, @net, "52:54:00:01:02:03".upcase)
+    assert_equal "192.168.122.10", result
+  end
+
+  def test_returns_nil_when_lease_file_missing
+    result = @server.send(:ip_address_from_leasefile, @net, @mac)
+    assert_nil result
+  end
+
+  def test_skips_malformed_lines
+    content = <<~LEASES
+      short line
+      1000 52:54:00:01:02:03 192.168.122.10 host1 *
+      incomplete
+    LEASES
+    write_lease_file("default", content)
+    result = @server.send(:ip_address_from_leasefile, @net, @mac)
+    assert_equal "192.168.122.10", result
+  end
+
+  def test_returns_nil_when_no_mac_matches
+    write_lease_file("default", "1000 52:54:00:ff:ff:ff 192.168.122.99 other *\n")
+    result = @server.send(:ip_address_from_leasefile, @net, @mac)
+    assert_nil result
+  end
+
+  def test_returns_nil_on_permission_error
+    skip("Cannot test permission denial as root") if Process.uid == 0
+    write_lease_file("default", "1000 52:54:00:01:02:03 192.168.122.10 host1 *\n")
+    File.chmod(0o000, File.join(@tmpdir, "default.leases"))
+    result = @server.send(:ip_address_from_leasefile, @net, @mac)
+    assert_nil result
+  end
+
+  def test_returns_nil_when_net_name_is_nil
+    net_nil_name = stub(:name => nil)
+    result = @server.send(:ip_address_from_leasefile, net_nil_name, @mac)
+    assert_nil result
+  end
+
+  private
+
+  def write_lease_file(net_name, content)
+    File.write(File.join(@tmpdir, "#{net_name}.leases"), content)
+  end
+end