Send single-line UTF8 strings as string when permitted.

Sending as literal requires counting bytes, which is a pain while testing.
And it causes an unnecessary slowdown due to the server roundtrip.

Author: arnt

lib/net/imap.rb

@@ -491,7 +491,7 @@ module Net
   #
   # ==== RFC6855: <tt>UTF8=ACCEPT</tt>, <tt>UTF8=ONLY</tt>
   #
-  # - See #enable for information about support foi UTF-8 string encoding.
+  # - See #enable for information about support for UTF-8 string encoding.
   #
   #--
   # ==== RFC7888: <tt>LITERAL+</tt>, +LITERAL-+
@@ -1974,7 +1974,10 @@ def enable(*capabilities)
         .join(' ')
       synchronize do
         send_command("ENABLE #{capabilities}")
-        return @responses.delete("ENABLED")[-1]
+        result = @responses.delete("ENABLED")[-1]
+        @utf8_strings ||= result.include? "SMTPUTF8"
+        @utf8_strings ||= result.include? "IMAP4REV2"
+        result
       end
     end
 
@@ -2222,6 +2225,7 @@ def initialize(host, port_or_options = {},
       @port = options[:port] || (options[:ssl] ? SSL_PORT : PORT)
       @tag_prefix = "RUBY"
       @tagno = 0
+      @utf8_strings = false
       @open_timeout = options[:open_timeout] || 30
       @idle_response_timeout = options[:idle_response_timeout] || 5
       @parser = ResponseParser.new

lib/net/imap/command_data.rb

@@ -52,13 +52,20 @@ def send_data(data, tag = nil)
     end
 
     def send_string_data(str, tag = nil)
-      case str
-      when ""
+      if str.empty?
         put_string('""')
-      when /[\x80-\xff\r\n]/n
-        # literal
+      elsif str.match?(/[\r\n]/n)
+        # literal, because multiline
         send_literal(str, tag)
-      when /[(){ \x00-\x1f\x7f%*"\\]/n
+      elsif !str.ascii_only?
+        if @utf8_strings
+          # quoted string
+          send_quoted_string(str)
+        else
+          # literal, because of non-ASCII bytes
+          send_literal(str, tag)
+        end
+      elsif str.match?(/[(){ \x00-\x1f\x7f%*"\\]/n)
         # quoted string
         send_quoted_string(str)
       else