protect against mutating frozen strings

Author: mwrock

Diff for: lib/net/ntlm/encode_util.rb

@@ -27,7 +27,7 @@ def self.swap16(str)
       # Decode a UTF16 string to a ASCII string
       # @param [String] str The string to convert
       def self.decode_utf16le(str)
-        str.force_encoding(Encoding::UTF_16LE)
+        str = str.dup.force_encoding(Encoding::UTF_16LE)
         str.encode(Encoding::UTF_8, Encoding::UTF_16LE).force_encoding('UTF-8')
       end
 
@@ -39,7 +39,6 @@ def self.decode_utf16le(str)
       #   the function will convert the string bytes to UTF-16LE and note the encoding as UTF-8 so that byte
       #   concatination works seamlessly.
       def self.encode_utf16le(str)
-        str = str.force_encoding('UTF-8') if [::Encoding::ASCII_8BIT,::Encoding::US_ASCII].include?(str.encoding)
         str.dup.force_encoding('UTF-8').encode(Encoding::UTF_16LE, Encoding::UTF_8).force_encoding('UTF-8')
       end
     end

Diff for: spec/lib/net/ntlm/encode_util_spec.rb

@@ -4,13 +4,13 @@
 
   context '#encode_utf16le' do
     it 'should convert an ASCII string to UTF' do
-      expect(Net::NTLM::EncodeUtil.encode_utf16le('Test')).to eq("T\x00e\x00s\x00t\x00")
+      expect(Net::NTLM::EncodeUtil.encode_utf16le('Test'.encode(::Encoding::ASCII_8BIT).freeze)).to eq("T\x00e\x00s\x00t\x00")
     end
   end
 
   context '#decode_utf16le' do
     it 'should convert a UTF string to ASCII' do
-      expect(Net::NTLM::EncodeUtil.decode_utf16le("T\x00e\x00s\x00t\x00")).to eq('Test')
+      expect(Net::NTLM::EncodeUtil.decode_utf16le("T\x00e\x00s\x00t\x00".freeze)).to eq('Test')
     end
   end
 end