Split long text in TXT/SPF records into chunks (for dump)

lib/dns/zone/rr/txt.rb

@@ -7,7 +7,7 @@ class DNS::Zone::RR::TXT < DNS::Zone::RR::Record
 
   def dump
     parts = general_prefix
-    parts << %Q{"#{text}"}
+    parts << quote_text(text)
     parts.join(' ')
   end
 
@@ -19,4 +19,17 @@ def load(string, options = {})
     self
   end
 
+  protected
+
+  # Quotes the given text, e.g. the content of a TXT or SPF record.
+  # Respects the rule that a single string may contain at most 255 chars, but
+  # multiple strings can be used to produce longer content. See also RFC 4408,
+  # section 3.1.3.
+  #
+  # @param text [String] the (potentially long) text
+  # @return [String] the quoted string or, if needed, several quoted strings
+  def quote_text(text)
+    text.chars.each_slice(200).map(&:join).map { |chunk| %Q{"#{chunk}"} }.join(' ')
+  end
+
 end

test/rr/txt_test.rb

@@ -18,6 +18,19 @@ def test_build_rr__txt
     assert_equal 'labelname 2w IN TXT "test text"', rr.dump
   end
 
+  def test_build_multiple_quoted_strings
+    rr = DNS::Zone::RR::TXT.new
+
+    # set a long text with 300 characters
+    rr.text = '(10 chars)' * 30
+
+    # we expect chunks of at most 200 characters
+    # (but actually implementations leading to at most 255 chars would also be fine)
+    chunk1 = %Q{"#{'(10 chars)' * 20}"}
+    chunk2 = %Q{"#{'(10 chars)' * 10}"}
+    assert_equal "@ IN TXT #{chunk1} #{chunk2}", rr.dump
+  end
+
   def test_load_rr__txt
     rr = DNS::Zone::RR::TXT.new.load('txtrecord IN TXT "test text"')
     assert_equal 'txtrecord', rr.label