net/pop: make modified strings mutable

Thanks to Michael Zimmerman for the bug report

* lib/net/pop.rb: make modified strings mutable
  [ruby-core:85210] [Bug #14416]
* test/net/pop/test_pop.rb: new test

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62099 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/net/pop.rb

@@ -467,7 +467,7 @@ module Net
 
     # Provide human-readable stringification of class state.
     def inspect
-      "#<#{self.class} #{@address}:#{@port} open=#{@started}>"
+      +"#<#{self.class} #{@address}:#{@port} open=#{@started}>"
     end
 
     # *WARNING*: This method causes a serious security hole.
@@ -758,7 +758,7 @@ module Net
 
     # Provide human-readable stringification of class state.
     def inspect
-      "#<#{self.class} #{@number}#{@deleted ? ' deleted' : ''}>"
+      +"#<#{self.class} #{@number}#{@deleted ? ' deleted' : ''}>"
     end
 
     #
@@ -799,7 +799,7 @@ module Net
     #
     # This method raises a POPError if an error occurs.
     #
-    def pop( dest = '', &block ) # :yield: message_chunk
+    def pop( dest = +'', &block ) # :yield: message_chunk
       if block_given?
         @command.retr(@number, &block)
         nil
@@ -819,7 +819,7 @@ module Net
     # The optional +dest+ argument is obsolete.
     #
     # This method raises a POPError if an error occurs.
-    def top(lines, dest = '')
+    def top(lines, dest = +'')
       @command.top(@number, lines) do |chunk|
         dest << chunk
       end
@@ -831,7 +831,7 @@ module Net
     # The optional +dest+ argument is obsolete.
     #
     # This method raises a POPError if an error occurs.
-    def header(dest = '')
+    def header(dest = +'')
       top(0, dest)
     end
 
@@ -898,7 +898,7 @@ module Net
     attr_reader :socket
 
     def inspect
-      "#<#{self.class} socket=#{@socket}>"
+      +"#<#{self.class} socket=#{@socket}>"
     end
 
     def auth(account, password)

test/net/pop/test_pop.rb

@@ -64,6 +64,35 @@ class TestPOP < Test::Unit::TestCase
     end
   end
 
+  def test_popmail
+    # totally not representative of real messages, but
+    # enough to test frozen bugs
+    lines = [ "[ruby-core:85210]" , "[Bug #14416]" ].freeze
+    command = Object.new
+    command.instance_variable_set(:@lines, lines)
+
+    def command.retr(n)
+      @lines.each { |l| yield "#{l}\r\n" }
+    end
+
+    def command.top(number, nl)
+      @lines.each do |l|
+        yield "#{l}\r\n"
+        break if (nl -= 1) <= 0
+      end
+    end
+
+    net_pop = :unused
+    popmail = Net::POPMail.new(1, 123, net_pop, command)
+    res = popmail.pop
+    assert_equal "[ruby-core:85210]\r\n[Bug #14416]\r\n", res
+    assert_not_predicate res, :frozen?
+
+    res = popmail.top(1)
+    assert_equal "[ruby-core:85210]\r\n", res
+    assert_not_predicate res, :frozen?
+  end
+
   def pop_test(apop=false)
     host = 'localhost'
     server = TCPServer.new(host, 0)