The native IDNA implementation freaks out about two adjacent dots.

lib/addressable/idna/native.rb

@@ -21,23 +21,35 @@
 module Addressable
   module IDNA
     def self.punycode_encode(value)
-      IDN::Punycode.encode(value)
+      IDN::Punycode.encode(value.to_s)
     end
 
      def self.punycode_decode(value)
-       IDN::Punycode.decode(value)
+       IDN::Punycode.decode(value.to_s)
      end
 
     def self.unicode_normalize_kc(value)
-      IDN::Stringprep.nfkc_normalize(value)
+      IDN::Stringprep.nfkc_normalize(value.to_s)
     end
 
     def self.to_ascii(value)
-      IDN::Idna.toASCII(value)
+      value.to_s.split('.', -1).map do |segment|
+        if segment.size > 0
+          IDN::Idna.toASCII(segment)
+        else
+          ''
+        end
+      end.join('.')
     end
 
     def self.to_unicode(value)
-      IDN::Idna.toUnicode(value)
+      value.to_s.split('.', -1).map do |segment|
+        if segment.size > 0
+          IDN::Idna.toUnicode(segment)
+        else
+          ''
+        end
+      end.join('.')
     end
   end
 end

lib/addressable/idna/pure.rb

@@ -64,6 +64,7 @@ module IDNA
     # Converts from a Unicode internationalized domain name to an ASCII
     # domain name as described in RFC 3490.
     def self.to_ascii(input)
+      input = input.to_s unless input.is_a?(String)
       input = input.dup
       if input.respond_to?(:force_encoding)
         input.force_encoding(Encoding::ASCII_8BIT)
@@ -89,6 +90,7 @@ def self.to_ascii(input)
     # Converts from an ASCII domain name to a Unicode internationalized
     # domain name as described in RFC 3490.
     def self.to_unicode(input)
+      input = input.to_s unless input.is_a?(String)
       parts = input.split('.')
       parts.map! do |part|
         if part =~ /^#{ACE_PREFIX}/
@@ -121,6 +123,7 @@ def self.unicode_normalize_kc(input)
     #   The input string.
     # @return [String] The downcased result.
     def self.unicode_downcase(input)
+      input = input.to_s unless input.is_a?(String)
       unpacked = input.unpack("U*")
       unpacked.map! { |codepoint| lookup_unicode_lowercase(codepoint) }
       return unpacked.pack("U*")
@@ -376,6 +379,7 @@ class PunycodeBigOutput < StandardError; end
     class PunycodeOverflow < StandardError; end
 
     def self.punycode_encode(unicode)
+      unicode = unicode.to_s unless unicode.is_a?(String)
       input = unicode.unpack("U*")
       output = [0] * (ACE_MAX_LENGTH + 1)
       input_length = input.size

spec/addressable/idna_spec.rb

@@ -126,6 +126,12 @@
       "\357\276\257"
     ).should == "xn--4ud"
   end
+
+  it "should handle two adjacent '.'s correctly" do
+    Addressable::IDNA.to_ascii(
+      "example..host"
+    ).should == "example..host"
+  end
 end
 
 shared_examples_for "converting from ASCII to unicode" do
@@ -189,6 +195,12 @@
     ).should == "\341\206\265"
   end
 
+  it "should handle two adjacent '.'s correctly" do
+    Addressable::IDNA.to_unicode(
+      "example..host"
+    ).should == "example..host"
+  end
+
   it "should normalize 'string' correctly" do
     Addressable::IDNA.unicode_normalize_kc(:'string').should == "string"
     Addressable::IDNA.unicode_normalize_kc("string").should == "string"