From 98d77f2552cd02ccd836ce67c72e9868a74b2a2f Mon Sep 17 00:00:00 2001
From: Ry Biesemeyer <ry.biesemeyer@elastic.co>
Date: Thu, 7 Feb 2019 21:55:43 +0000
Subject: [PATCH] backport patch to resolv for underqualified domain names

---
 lib/logstash/filters/dns.rb                   |  2 +-
 .../filters/{ => dns}/resolv_patch.rb         | 34 ++++++++++++++++---
 2 files changed, 30 insertions(+), 6 deletions(-)
 rename lib/logstash/filters/{ => dns}/resolv_patch.rb (51%)

diff --git a/lib/logstash/filters/dns.rb b/lib/logstash/filters/dns.rb
index 5650b72..3a22a09 100644
--- a/lib/logstash/filters/dns.rb
+++ b/lib/logstash/filters/dns.rb
@@ -4,7 +4,7 @@
 require "lru_redux"
 require "resolv"
 require "timeout"
-require "logstash/filters/resolv_patch"
+require "logstash/filters/dns/resolv_patch"
 
 java_import 'java.net.IDN'
 
diff --git a/lib/logstash/filters/resolv_patch.rb b/lib/logstash/filters/dns/resolv_patch.rb
similarity index 51%
rename from lib/logstash/filters/resolv_patch.rb
rename to lib/logstash/filters/dns/resolv_patch.rb
index 61eb109..9d20751 100644
--- a/lib/logstash/filters/resolv_patch.rb
+++ b/lib/logstash/filters/dns/resolv_patch.rb
@@ -1,5 +1,7 @@
 require "resolv"
 
+jruby_gem_version = Gem::Version.new(JRUBY_VERSION)
+
 # ref: https://github.com/logstash-plugins/logstash-filter-dns/issues/40
 #
 # JRuby 9k versions prior to 9.1.16.0 have a bug which crashes IP address
@@ -10,10 +12,7 @@
 #
 # The code below is copied from JRuby 9.1.16.0 resolv.rb:
 # https://github.com/jruby/jruby/blob/9.1.16.0/lib/ruby/stdlib/resolv.rb#L775-L784
-
-JRUBY_GEM_VERSION = Gem::Version.new(JRUBY_VERSION)
-
-if JRUBY_GEM_VERSION >= Gem::Version.new("9.1.13.0") && JRUBY_GEM_VERSION < Gem::Version.new("9.1.16.0")
+if jruby_gem_version >= Gem::Version.new("9.1.13.0") && jruby_gem_version < Gem::Version.new("9.1.16.0")
   class Resolv
     class DNS
       class Requester
@@ -32,4 +31,29 @@ def sender(msg, data, host, port=Port)
       end
     end
   end
-end
\ No newline at end of file
+end
+
+# JRuby 1.x ships with a Ruby stdlib that has a bug in its resolv implementation
+# in which it fails to correctly canonicalise unqualified or underqualified
+# domains (e.g., domain names with fewer than the configured ndots, which defaults
+# to 1).
+#
+# See: https://bugs.ruby-lang.org/issues/10412
+#
+# Conditionally apply the patch to the method definition by wrapping it at runtime.
+if jruby_gem_version < Gem::Version.new("9.0")
+  class Resolv::DNS
+    class Config
+      alias generate_candidates_without_toplevel generate_candidates
+      def generate_candidates_with_toplevel(name)
+        candidates = generate_candidates_without_toplevel(name)
+        fname = Name.create("#{name}.")
+        if !candidates.include?(fname)
+          candidates << fname
+        end
+        candidates
+      end
+      alias generate_candidates generate_candidates_with_toplevel
+    end
+  end
+end