From e3a6cbf1b64c1c74d98e19624bf5ea23fe384847 Mon Sep 17 00:00:00 2001
From: Richard Hansen <rhansen@rhansen.org>
Date: Thu, 11 Jun 2020 17:09:46 -0400
Subject: [PATCH] Prefer `ip` command from iproute2 over `ifconfig`

On Linux systems, `ifconfig` is long deprecated in favor of the `ip`
command from iproute2. Some systems don't have iproute2 (BSDs in
particular), so ddclient will still attempt `ifconfig` if `ip` is
missing.

Also: Don't hide STDERR because error messages are important for
troubleshooting problems. To avoid STDERR noise on systems without the
`ip` command, the command's existence is checked before it is run.

Notes:
  * The fetched addresses could be limited to IPv4 or IPv6 depending
    on `opt('ipv6')`, and non-global addresses could be filtered out,
    but any filtering risks breaking a nontrivial number of existing
    configurations.
  * This change runs the risk of breaking existing configs that set
    `if-skip`. Due to the deprecation of `ifconfig`, and the belief
    that only a negligible number of users set `if-skip`, the benefits
    of this change are believed to outweigh the config migration
    burden imposed on users.

Fixes #93.
---
 ChangeLog.md |  3 +++
 ddclient     | 17 ++++++++++++-----
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/ChangeLog.md b/ChangeLog.md
index 6f494ab..ac709a2 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -12,6 +12,9 @@ repository history](https://github.com/ddclient/ddclient/commits/master).
 ### Compatibility changes
 
   * Perl v5.10.1 or later is now required.
+  * When `use=if`, iproute2's `ip` command is now attempted before falling back
+    to `ifconfig` (it used to be the other way around). If you set `if-skip`,
+    please check that your configuration still works as expected.
   * Removed the `concont` protocol. If you still use this protocol, please
     [file a bug report](https://github.com/ddclient/ddclient/issues) and we
     will restore it.
diff --git a/ddclient b/ddclient
index b6b6aa9..414618e 100755
--- a/ddclient
+++ b/ddclient
@@ -754,7 +754,7 @@ my @opt = (
     [ "ip",          "=s", "-ip address           : set the IP address to 'address'" ],
     "",
     [ "if",          "=s", "-if interface         : obtain IP address from 'interface'" ],
-    [ "if-skip",     "=s", "-if-skip pattern      : skip any IP addresses before 'pattern' in the output of ifconfig {if}" ],
+    [ "if-skip",     "=s", "-if-skip pattern      : skip any IP addresses before 'pattern' in the output of 'ip address show dev {if}' (or 'ifconfig {if}')" ],
     "",
     [ "web",         "=s", "-web provider|url     : obtain IP address from provider's IP checking page" ],
     [ "web-skip",    "=s", "-web-skip pattern     : skip any IP addresses before 'pattern' on the web provider|url" ],
@@ -1477,8 +1477,15 @@ sub test_possible_ip {
 
     {
         local $opt{'use'} = 'if';
-        foreach my $if (grep {/^[a-zA-Z]/} `ifconfig -a`) {
-            $if =~ s/:?\s.*//is;
+        # Note: The `ip` command adds a `@eth0` suffix to the names of VLAN
+        # interfaces. That `@eth0` suffix is NOT part of the interface name.
+        my @ifs = map({ /^[^\s:]*:\s*([^\s:@]+)/ ? $1 : () }
+                      `command -v ip >/dev/null && ip -o link show`);
+        @ifs = map({ /^([a-zA-Z].*?)(?::?\s.*)?$/ ? $1 : () }
+                   `command -v ifconfig >/dev/null && ifconfig -a`) if $? || !@ifs;
+        @ifs = () if $?;
+        warning("failed to get list of interfaces") if !@ifs;
+        foreach my $if (@ifs) {
             local $opt{'if'} = $if;
             printf "use=if, if=%s address is %s\n", opt('if'), define(get_ip('if'), 'NOT FOUND');
         }
@@ -2201,8 +2208,8 @@ sub get_ip {
 
     } elsif ($use eq 'if') {
         $skip  = opt('if-skip', $h) || '';
-        $reply = `ifconfig $arg 2> /dev/null`;
-        $reply = `ip addr list dev $arg 2> /dev/null` if $?;
+        $reply = `command -v ip >/dev/null && ip address show dev $arg`;
+        $reply = `command -v ifconfig >/dev/null && ifconfig $arg` if $?;
         $reply = '' if $?;
 
     } elsif ($use eq 'cmd') {