From d56acecb806760776b38077cb69d2ff689adfde6 Mon Sep 17 00:00:00 2001
From: Earlopain <14981592+Earlopain@users.noreply.github.com>
Date: Sat, 16 Dec 2023 13:58:58 +0100
Subject: [PATCH] Consider IPv4-mapped IPv6 addresses link local/loopback if
 IPV4 address is private

Same as #57
---
 lib/ipaddr.rb       | 19 ++++++++++++++-----
 test/test_ipaddr.rb | 15 +++++++++++++++
 2 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/lib/ipaddr.rb b/lib/ipaddr.rb
index 03e1c18..0ec6143 100644
--- a/lib/ipaddr.rb
+++ b/lib/ipaddr.rb
@@ -247,12 +247,17 @@ def ipv6?
   end
 
   # Returns true if the ipaddr is a loopback address.
+  # Loopback IPv4 addresses in the IPv4-mapped IPv6
+  # address range are also considered as loopback addresses.
   def loopback?
     case @family
     when Socket::AF_INET
-      @addr & 0xff000000 == 0x7f000000
+      @addr & 0xff000000 == 0x7f000000 # 127.0.0.1/8
     when Socket::AF_INET6
-      @addr == 1
+      @addr == 1 || # ::1
+        (@addr & 0xffff_0000_0000 == 0xffff_0000_0000 && (
+          @addr & 0xff000000 == 0x7f000000 # ::ffff:127.0.0.1/8
+        ))
     else
       raise AddressFamilyError, "unsupported address family"
     end
@@ -282,15 +287,19 @@ def private?
   end
 
   # Returns true if the ipaddr is a link-local address.  IPv4
-  # addresses in 169.254.0.0/16 reserved by RFC 3927 and Link-Local
+  # addresses in 169.254.0.0/16 reserved by RFC 3927 and link-local
   # IPv6 Unicast Addresses in fe80::/10 reserved by RFC 4291 are
-  # considered link-local.
+  # considered link-local. Link-local IPv4 addresses in the
+  # IPv4-mapped IPv6 address range are also considered link-local.
   def link_local?
     case @family
     when Socket::AF_INET
       @addr & 0xffff0000 == 0xa9fe0000 # 169.254.0.0/16
     when Socket::AF_INET6
-      @addr & 0xffc0_0000_0000_0000_0000_0000_0000_0000 == 0xfe80_0000_0000_0000_0000_0000_0000_0000
+      @addr & 0xffc0_0000_0000_0000_0000_0000_0000_0000 == 0xfe80_0000_0000_0000_0000_0000_0000_0000 || # fe80::/10
+        (@addr & 0xffff_0000_0000 == 0xffff_0000_0000 && (
+          @addr & 0xffff0000 == 0xa9fe0000 # ::ffff:169.254.0.0/16
+        ))
     else
       raise AddressFamilyError, "unsupported address family"
     end
diff --git a/test/test_ipaddr.rb b/test/test_ipaddr.rb
index 90a7fc3..9b5d5a5 100644
--- a/test/test_ipaddr.rb
+++ b/test/test_ipaddr.rb
@@ -396,6 +396,12 @@ def test_loopback?
     assert_equal(true,  IPAddr.new('::1').loopback?)
     assert_equal(false, IPAddr.new('::').loopback?)
     assert_equal(false, IPAddr.new('3ffe:505:2::1').loopback?)
+
+    assert_equal(true,  IPAddr.new('::ffff:127.0.0.1').loopback?)
+    assert_equal(true,  IPAddr.new('::ffff:127.127.1.1').loopback?)
+    assert_equal(false, IPAddr.new('::ffff:0.0.0.0').loopback?)
+    assert_equal(false, IPAddr.new('::ffff:192.168.2.0').loopback?)
+    assert_equal(false, IPAddr.new('::ffff:255.0.0.0').loopback?)
   end
 
   def test_private?
@@ -463,6 +469,15 @@ def test_link_local?
     assert_equal(false, IPAddr.new('fb84:8bf7:e905::1').link_local?)
 
     assert_equal(true,  IPAddr.new('fe80::dead:beef:cafe:1234').link_local?)
+
+    assert_equal(false, IPAddr.new('::ffff:0.0.0.0').link_local?)
+    assert_equal(false, IPAddr.new('::ffff:127.0.0.1').link_local?)
+    assert_equal(false, IPAddr.new('::ffff:10.0.0.0').link_local?)
+    assert_equal(false, IPAddr.new('::ffff:172.16.0.0').link_local?)
+    assert_equal(false, IPAddr.new('::ffff:192.168.0.0').link_local?)
+
+    assert_equal(true,  IPAddr.new('::ffff:169.254.1.1').link_local?)
+    assert_equal(true,  IPAddr.new('::ffff:169.254.254.255').link_local?)
   end
 
   def test_hash