Fix actions: returning string copy after evaluation

src/actions/action.cc

@@ -36,7 +36,7 @@ namespace ModSecurity {
 namespace actions {
 
 
-std::string & Action::evaluate(std::string value,
+std::string Action::evaluate(std::string value,
     Assay *assay) {
     return value;
 }

src/actions/action.h

@@ -74,7 +74,7 @@ class Action {
     int action_kind;
     std::string name;
 
-    virtual std::string& evaluate(std::string exp,
+    virtual std::string evaluate(std::string exp,
         Assay *assay);
     virtual bool evaluate(Assay *assay);
     virtual bool evaluate(Rule *rule);

src/actions/transformations/base64_decode.cc

@@ -35,12 +35,13 @@ Base64Decode::Base64Decode(std::string action)
     this->action_kind = 1;
 }
 
-std::string& Base64Decode::evaluate(std::string value,
+std::string Base64Decode::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation base64decode
      */
     assay->debug(4, "Transformation 64 is not implemented yet.");
+    return value;
 }
 
 }  // namespace transformations

src/actions/transformations/base64_decode.h

@@ -31,7 +31,7 @@ namespace transformations {
 class Base64Decode : public Transformation {
  public:
     explicit Base64Decode(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/base64_decode_ext.cc

@@ -35,12 +35,13 @@ Base64DecodeExt::Base64DecodeExt(std::string action)
     this->action_kind = 1;
 }
 
-std::string& Base64DecodeExt::evaluate(std::string value,
+std::string Base64DecodeExt::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation Base64DecodeExt
      */
     assay->debug(4, "Transformation Base64DecodeExt is not implemented yet.");
+    return value;
 }
 
 }  // namespace transformations

src/actions/transformations/base64_decode_ext.h

@@ -31,7 +31,7 @@ namespace transformations {
 class Base64DecodeExt : public Transformation {
  public:
     explicit Base64DecodeExt(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/cmd_line.cc

@@ -35,12 +35,13 @@ CmdLine::CmdLine(std::string action)
     this->action_kind = 1;
 }
 
-std::string& CmdLine::evaluate(std::string value,
+std::string CmdLine::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation CmdLine
      */
     assay->debug(4, "Transformation CmdLine is not implemented yet.");
+    return value;
 }
 
 }  // namespace transformations

src/actions/transformations/cmd_line.h

@@ -31,7 +31,7 @@ namespace transformations {
 class CmdLine : public Transformation {
  public:
     explicit CmdLine(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/compress_whitespace.cc

@@ -35,13 +35,14 @@ CompressWhitespace::CompressWhitespace(std::string action)
     this->action_kind = 1;
 }
 
-std::string& CompressWhitespace::evaluate(std::string value,
+std::string CompressWhitespace::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation CompressWhitespace
      */
     assay->debug(4, "Transformation CompressWhitespace is " \
         "not implemented yet.");
+    return value;
 }
 
 }  // namespace transformations

src/actions/transformations/compress_whitespace.h

@@ -31,7 +31,7 @@ namespace transformations {
 class CompressWhitespace : public Transformation {
  public:
     explicit CompressWhitespace(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/css_decode.cc

@@ -35,12 +35,13 @@ CssDecode::CssDecode(std::string action)
     this->action_kind = 1;
 }
 
-std::string& CssDecode::evaluate(std::string value,
+std::string CssDecode::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation CssDecode
      */
     assay->debug(4, "Transformation CssDecode is not implemented yet.");
+    return value;
 }
 
 }  // namespace transformations

src/actions/transformations/css_decode.h

@@ -31,7 +31,7 @@ namespace transformations {
 class CssDecode : public Transformation {
  public:
     explicit CssDecode(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/escape_seq_decode.cc

@@ -35,7 +35,7 @@ EscapeSeqDecode::EscapeSeqDecode(std::string action)
     this->action_kind = 1;
 }
 
-std::string& EscapeSeqDecode::evaluate(std::string value,
+std::string EscapeSeqDecode::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation EscapeSeqDecode

src/actions/transformations/escape_seq_decode.h

@@ -31,7 +31,7 @@ namespace transformations {
 class EscapeSeqDecode : public Transformation {
  public:
     explicit EscapeSeqDecode(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/hex_decode.cc

@@ -35,12 +35,13 @@ HexDecode::HexDecode(std::string action)
     this->action_kind = 1;
 }
 
-std::string& HexDecode::evaluate(std::string value,
+std::string HexDecode::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation HexDecode
      */
     assay->debug(4, "Transformation HexDecode is not implemented yet.");
+    return value;
 }
 
 }  // namespace transformations

src/actions/transformations/hex_decode.h

@@ -31,7 +31,7 @@ namespace transformations {
 class HexDecode : public Transformation {
  public:
     explicit HexDecode(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/hex_encode.cc

@@ -35,7 +35,7 @@ HexEncode::HexEncode(std::string action)
     this->action_kind = 1;
 }
 
-std::string& HexEncode::evaluate(std::string value,
+std::string HexEncode::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation HexEncode

src/actions/transformations/hex_encode.h

@@ -31,7 +31,7 @@ namespace transformations {
 class HexEncode : public Transformation {
  public:
     explicit HexEncode(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/html_entity_decode.cc

@@ -35,7 +35,7 @@ HtmlEntityDecode::HtmlEntityDecode(std::string action)
     this->action_kind = 1;
 }
 
-std::string& HtmlEntityDecode::evaluate(std::string value,
+std::string HtmlEntityDecode::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation HtmlEntityDecode

src/actions/transformations/html_entity_decode.h

@@ -31,7 +31,7 @@ namespace transformations {
 class HtmlEntityDecode : public Transformation {
  public:
     explicit HtmlEntityDecode(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/js_decode.cc

@@ -35,12 +35,13 @@ JsDecode::JsDecode(std::string action)
     this->action_kind = 1;
 }
 
-std::string& JsDecode::evaluate(std::string value,
+std::string JsDecode::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation JsDecode
      */
     assay->debug(4, "Transformation JsDecode is not implemented yet.");
+    return value;
 }
 
 }  // namespace transformations

src/actions/transformations/js_decode.h

@@ -31,7 +31,7 @@ namespace transformations {
 class JsDecode : public Transformation {
  public:
     explicit JsDecode(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/length.cc

@@ -35,12 +35,13 @@ Length::Length(std::string action)
     this->action_kind = 1;
 }
 
-std::string& Length::evaluate(std::string value,
+std::string Length::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation Length
      */
     assay->debug(4, "Transformation Length is not implemented yet.");
+    return value;
 }
 
 }  // namespace transformations

src/actions/transformations/length.h

@@ -31,7 +31,7 @@ namespace transformations {
 class Length : public Transformation {
  public:
     explicit Length(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/lowercase.cc

@@ -31,7 +31,7 @@ LowerCase::LowerCase(std::string a)
     : Transformation(a) {
 }
 
-std::string & LowerCase::evaluate(std::string value,
+std::string LowerCase::evaluate(std::string value,
     Assay *assay) {
     std::locale loc;
 

src/actions/transformations/lowercase.h

@@ -32,7 +32,7 @@ namespace transformations {
 class LowerCase : public Transformation {
  public:
     explicit LowerCase(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/md5.cc

@@ -35,7 +35,7 @@ Md5::Md5(std::string action)
     this->action_kind = 1;
 }
 
-std::string& Md5::evaluate(std::string value,
+std::string Md5::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation Md5

src/actions/transformations/md5.h

@@ -31,7 +31,8 @@ namespace transformations {
 class Md5 : public Transformation {
  public:
     explicit Md5(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string
+    evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/none.cc

@@ -35,12 +35,13 @@ None::None(std::string action)
     this->action_kind = 1;
 }
 
-std::string& None::evaluate(std::string value,
+std::string None::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation None
      */
     assay->debug(4, "Transformation None is not implemented yet.");
+    return value;
 }
 
 }  // namespace transformations

src/actions/transformations/none.h

@@ -31,7 +31,7 @@ namespace transformations {
 class None : public Transformation {
  public:
     explicit None(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/normalise_path.cc

@@ -35,7 +35,7 @@ NormalisePath::NormalisePath(std::string action)
     this->action_kind = 1;
 }
 
-std::string& NormalisePath::evaluate(std::string value,
+std::string NormalisePath::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation NormalisePath

src/actions/transformations/normalise_path.h

@@ -31,7 +31,7 @@ namespace transformations {
 class NormalisePath : public Transformation {
  public:
     explicit NormalisePath(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/normalise_path_win.cc

@@ -35,7 +35,7 @@ NormalisePathWin::NormalisePathWin(std::string action)
     this->action_kind = 1;
 }
 
-std::string& NormalisePathWin::evaluate(std::string value,
+std::string NormalisePathWin::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation NormalisePathWin

src/actions/transformations/normalise_path_win.h

@@ -31,7 +31,7 @@ namespace transformations {
 class NormalisePathWin : public Transformation {
  public:
     explicit NormalisePathWin(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/parity_even_7bit.cc

@@ -35,7 +35,7 @@ ParityEven7bit::ParityEven7bit(std::string action)
     this->action_kind = 1;
 }
 
-std::string& ParityEven7bit::evaluate(std::string value,
+std::string ParityEven7bit::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation ParityEven7bit

src/actions/transformations/parity_even_7bit.h

@@ -31,7 +31,7 @@ namespace transformations {
 class ParityEven7bit : public Transformation {
  public:
     explicit ParityEven7bit(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/parity_odd_7bit.cc

@@ -35,7 +35,7 @@ ParityOdd7bit::ParityOdd7bit(std::string action)
     this->action_kind = 1;
 }
 
-std::string& ParityOdd7bit::evaluate(std::string value,
+std::string ParityOdd7bit::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation ParityOdd7bit

src/actions/transformations/parity_odd_7bit.h

@@ -31,7 +31,7 @@ namespace transformations {
 class ParityOdd7bit : public Transformation {
  public:
     explicit ParityOdd7bit(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/parity_zero_7bit.cc

@@ -35,7 +35,7 @@ ParityZero7bit::ParityZero7bit(std::string action)
     this->action_kind = 1;
 }
 
-std::string& ParityZero7bit::evaluate(std::string value,
+std::string ParityZero7bit::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation ParityZero7bit

src/actions/transformations/parity_zero_7bit.h

@@ -31,7 +31,7 @@ namespace transformations {
 class ParityZero7bit : public Transformation {
  public:
     explicit ParityZero7bit(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/remove_comments.cc

@@ -35,7 +35,7 @@ RemoveComments::RemoveComments(std::string action)
     this->action_kind = 1;
 }
 
-std::string& RemoveComments::evaluate(std::string value,
+std::string RemoveComments::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation RemoveComments

src/actions/transformations/remove_comments.h

@@ -31,7 +31,7 @@ namespace transformations {
 class RemoveComments : public Transformation {
  public:
     explicit RemoveComments(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/remove_comments_char.cc

@@ -35,7 +35,7 @@ RemoveCommentsChar::RemoveCommentsChar(std::string action)
     this->action_kind = 1;
 }
 
-std::string& RemoveCommentsChar::evaluate(std::string value,
+std::string RemoveCommentsChar::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation RemoveCommentsChar

src/actions/transformations/remove_comments_char.h

@@ -31,7 +31,7 @@ namespace transformations {
 class RemoveCommentsChar : public Transformation {
  public:
     explicit RemoveCommentsChar(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/remove_nulls.cc

@@ -35,7 +35,7 @@ RemoveNulls::RemoveNulls(std::string action)
     this->action_kind = 1;
 }
 
-std::string& RemoveNulls::evaluate(std::string value,
+std::string RemoveNulls::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation RemoveNulls

src/actions/transformations/remove_nulls.h

@@ -31,7 +31,7 @@ namespace transformations {
 class RemoveNulls : public Transformation {
  public:
     explicit RemoveNulls(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/remove_whitespace.cc

@@ -35,7 +35,7 @@ RemoveWhitespace::RemoveWhitespace(std::string action)
     this->action_kind = 1;
 }
 
-std::string& RemoveWhitespace::evaluate(std::string value,
+std::string RemoveWhitespace::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation RemoveWhitespace

src/actions/transformations/remove_whitespace.h

@@ -31,7 +31,7 @@ namespace transformations {
 class RemoveWhitespace : public Transformation {
  public:
     explicit RemoveWhitespace(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/replace_comments.cc

@@ -35,7 +35,7 @@ ReplaceComments::ReplaceComments(std::string action)
     this->action_kind = 1;
 }
 
-std::string& ReplaceComments::evaluate(std::string value,
+std::string ReplaceComments::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation ReplaceComments

src/actions/transformations/replace_comments.h

@@ -31,7 +31,7 @@ namespace transformations {
 class ReplaceComments : public Transformation {
  public:
     explicit ReplaceComments(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/replace_nulls.cc

@@ -35,7 +35,7 @@ ReplaceNulls::ReplaceNulls(std::string action)
     this->action_kind = 1;
 }
 
-std::string& ReplaceNulls::evaluate(std::string value,
+std::string ReplaceNulls::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation ReplaceNulls

src/actions/transformations/replace_nulls.h

@@ -31,7 +31,7 @@ namespace transformations {
 class ReplaceNulls : public Transformation {
  public:
     explicit ReplaceNulls(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/sha1.cc

@@ -35,7 +35,7 @@ Sha1::Sha1(std::string action)
     this->action_kind = 1;
 }
 
-std::string& Sha1::evaluate(std::string value,
+std::string Sha1::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation Sha1

src/actions/transformations/sha1.h

@@ -31,7 +31,7 @@ namespace transformations {
 class Sha1 : public Transformation {
  public:
     explicit Sha1(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/sql_hex_decode.cc

@@ -35,12 +35,13 @@ SqlHexDecode::SqlHexDecode(std::string action)
     this->action_kind = 1;
 }
 
-std::string& SqlHexDecode::evaluate(std::string value,
+std::string SqlHexDecode::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation SqlHexDecode
      */
     assay->debug(4, "Transformation SqlHexDecode is not implemented yet.");
+    return value;
 }
 
 }  // namespace transformations

src/actions/transformations/sql_hex_decode.h

@@ -31,7 +31,8 @@ namespace transformations {
 class SqlHexDecode : public Transformation {
  public:
     explicit SqlHexDecode(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string
+    evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/transformation.cc

@@ -72,7 +72,7 @@ Transformation::Transformation(std::string action)
     this->action_kind = 1;
 }
 
-std::string &Transformation::evaluate(std::string value,
+std::string Transformation::evaluate(std::string value,
     Assay *assay) {
     return value;
 }

src/actions/transformations/transformation.h

@@ -33,7 +33,7 @@ class Transformation : public Action {
     explicit Transformation(std::string action);
     static Transformation* instantiate(std::string);
 
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/trim.cc

@@ -56,7 +56,8 @@ Trim::Trim(std::string action)
 }
 
 
-std::string& Trim::evaluate(std::string value,
+std::string
+Trim::evaluate(std::string value,
     Assay *assay) {
     return *this->trim(&value);
 }

src/actions/transformations/trim.h

@@ -31,7 +31,7 @@ namespace transformations {
 class Trim : public Transformation {
  public:
     explicit Trim(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 
     std::string *ltrim(std::string *s);

src/actions/transformations/trim_left.cc

@@ -38,7 +38,7 @@ TrimLeft::TrimLeft(std::string action)
     this->action_kind = 1;
 }
 
-std::string& TrimLeft::evaluate(std::string value,
+std::string TrimLeft::evaluate(std::string value,
     Assay *assay) {
     return *trim(&value);
 }

src/actions/transformations/trim_left.h

@@ -32,7 +32,7 @@ namespace transformations {
 class TrimLeft : public Trim {
  public:
     explicit TrimLeft(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/trim_right.cc

@@ -36,7 +36,7 @@ TrimRight::TrimRight(std::string action)
     this->action_kind = 1;
 }
 
-std::string& TrimRight::evaluate(std::string value,
+std::string TrimRight::evaluate(std::string value,
     Assay *assay) {
     return *this->trim(&value);
 }

src/actions/transformations/trim_right.h

@@ -32,7 +32,7 @@ namespace transformations {
 class TrimRight : public Trim {
  public:
     explicit TrimRight(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/url_decode.cc

@@ -35,7 +35,7 @@ UrlDecode::UrlDecode(std::string action)
     this->action_kind = 1;
 }
 
-std::string& UrlDecode::evaluate(std::string value,
+std::string UrlDecode::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation UrlDecode

src/actions/transformations/url_decode.h

@@ -31,7 +31,7 @@ namespace transformations {
 class UrlDecode : public Transformation {
  public:
     explicit UrlDecode(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/url_decode_uni.cc

@@ -35,7 +35,7 @@ UrlDecodeUni::UrlDecodeUni(std::string action)
     this->action_kind = 1;
 }
 
-std::string& UrlDecodeUni::evaluate(std::string value,
+std::string UrlDecodeUni::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation UrlDecodeUni

src/actions/transformations/url_decode_uni.h

@@ -31,7 +31,7 @@ namespace transformations {
 class UrlDecodeUni : public Transformation {
  public:
     explicit UrlDecodeUni(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/url_encode.cc

@@ -35,7 +35,7 @@ UrlEncode::UrlEncode(std::string action)
     this->action_kind = 1;
 }
 
-std::string& UrlEncode::evaluate(std::string value,
+std::string UrlEncode::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation UrlEncode

src/actions/transformations/url_encode.h

@@ -31,7 +31,7 @@ namespace transformations {
 class UrlEncode : public Transformation {
  public:
     explicit UrlEncode(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };
 

src/actions/transformations/utf8_to_unicode.cc

@@ -35,7 +35,7 @@ Utf8Unicode::Utf8Unicode(std::string action)
     this->action_kind = 1;
 }
 
-std::string& Utf8Unicode::evaluate(std::string value,
+std::string Utf8Unicode::evaluate(std::string value,
     Assay *assay) {
     /**
      * @todo Implement the transformation Utf8Unicode

src/actions/transformations/utf8_to_unicode.h

@@ -31,7 +31,7 @@ namespace transformations {
 class Utf8Unicode : public Transformation {
  public:
     explicit Utf8Unicode(std::string action);
-    std::string& evaluate(std::string exp,
+    std::string evaluate(std::string exp,
         Assay *assay) override;
 };