diff --git a/headers/modsecurity/anchored_set_variable.h b/headers/modsecurity/anchored_set_variable.h
index 0584cb7d..dc0f5fb7 100644
--- a/headers/modsecurity/anchored_set_variable.h
+++ b/headers/modsecurity/anchored_set_variable.h
@@ -88,21 +88,21 @@ class AnchoredSetVariable : public std::unordered_multimap<std::string,
     void set(const std::string &key, const bpstd::string_view &value,
         size_t offset);
 
-    void resolve(VariableValues *l);
+    void resolve(VariableValues *l) const noexcept;
     void resolve(VariableValues *l,
-        variables::KeyExclusions &ke);
+        const variables::KeyExclusions &ke) const noexcept;
 
     void resolve(const std::string &key,
-        VariableValues *l);
+        VariableValues *l) const noexcept;
 
-    void resolveRegularExpression(Utils::Regex *r,
-        VariableValues *l);
+    void resolveRegularExpression(const Utils::Regex *r,
+        VariableValues *l) const noexcept;
 
-    void resolveRegularExpression(Utils::Regex *r,
+    void resolveRegularExpression(const Utils::Regex *r,
         VariableValues *l,
-        variables::KeyExclusions &ke);
+        const variables::KeyExclusions &ke) const noexcept;
 
-    std::unique_ptr<std::string> resolveFirst(const std::string &key);
+    std::unique_ptr<std::string> resolveFirst(const std::string &key) const noexcept;
 
     Transaction *m_transaction;
     std::string m_name;
diff --git a/headers/modsecurity/anchored_variable.h b/headers/modsecurity/anchored_variable.h
index a2f1d51b..6a06abfe 100644
--- a/headers/modsecurity/anchored_variable.h
+++ b/headers/modsecurity/anchored_variable.h
@@ -51,14 +51,6 @@ class AnchoredVariable {
     AnchoredVariable(const AnchoredVariable &a) = delete;
     AnchoredVariable &operator= (const AnchoredVariable &a) = delete;
 
-    /*
-        : m_transaction(a.m_transaction),
-        m_offset(a.m_offset),
-        m_name(a.m_name),
-        m_value(a.m_value),
-        m_var(a.m_var) { }
-    */
-
     void unset();
     void set(const std::string &a, size_t offset);
     void set(const bpstd::string_view &a, size_t offset);
@@ -69,9 +61,9 @@ class AnchoredVariable {
     void append(const std::string &a, size_t offset,
         bool spaceSeparator, int size);
 
-    void evaluate(VariableValues *l);
-    std::string *  evaluate();
-    std::unique_ptr<std::string> resolveFirst();
+    void evaluate(VariableValues *l) const noexcept;
+    const std::string *evaluate() const noexcept;
+    std::unique_ptr<std::string> resolveFirst() const noexcept;
 
     Transaction *m_transaction;
     int m_offset;
@@ -88,4 +80,3 @@ class AnchoredVariable {
 
 
 #endif  // HEADERS_MODSECURITY_ANCHORED_VARIABLE_H_
-
diff --git a/headers/modsecurity/collection/collection.h b/headers/modsecurity/collection/collection.h
index a8bab804..0511a05f 100644
--- a/headers/modsecurity/collection/collection.h
+++ b/headers/modsecurity/collection/collection.h
@@ -57,16 +57,16 @@ class Collection {
     virtual void del(const std::string& key) = 0;
 
     virtual std::unique_ptr<std::string> resolveFirst(
-        const std::string& var) = 0;
+        const std::string& var) const = 0;
 
     virtual void resolveSingleMatch(const std::string& var,
-        VariableValues *l) = 0;
+        VariableValues *l) const noexcept = 0;
     virtual void resolveMultiMatches(const std::string& var,
         VariableValues *l,
-        variables::KeyExclusions &ke) = 0;
+        const variables::KeyExclusions &ke) const noexcept = 0;
     virtual void resolveRegularExpression(const std::string& var,
         VariableValues *l,
-        variables::KeyExclusions &ke) = 0;
+        const variables::KeyExclusions &ke) const noexcept = 0;
 
 
     /* store */
@@ -131,14 +131,14 @@ class Collection {
 
     /* resolveFirst */
     virtual std::unique_ptr<std::string> resolveFirst(const std::string& var,
-        std::string compartment) {
+        const std::string &compartment) const noexcept {
         std::string nkey = compartment + "::" + var;
         return resolveFirst(nkey);
     }
 
 
     virtual std::unique_ptr<std::string> resolveFirst(const std::string& var,
-        std::string compartment, std::string compartment2) {
+        const std::string &compartment, const std::string &compartment2) const noexcept {
         std::string nkey = compartment + "::" + compartment2 + "::" + var;
         return resolveFirst(nkey);
     }
@@ -146,15 +146,15 @@ class Collection {
 
     /* resolveSingleMatch */
     virtual void resolveSingleMatch(const std::string& var,
-        std::string compartment, VariableValues *l) {
+        const std::string &compartment, VariableValues *l) const noexcept {
         std::string nkey = compartment + "::" + var;
         resolveSingleMatch(nkey, l);
     }
 
 
     virtual void resolveSingleMatch(const std::string& var,
-        std::string compartment, std::string compartment2,
-        VariableValues *l) {
+        const std::string &compartment, const std::string &compartment2,
+        VariableValues *l) const noexcept {
         std::string nkey = compartment + "::" + compartment2 + "::" + var;
         resolveSingleMatch(nkey, l);
     }
@@ -162,17 +162,17 @@ class Collection {
 
     /* resolveMultiMatches */
     virtual void resolveMultiMatches(const std::string& var,
-        std::string compartment, VariableValues *l,
-        variables::KeyExclusions &ke) {
+        const std::string &compartment, VariableValues *l,
+        const variables::KeyExclusions &ke) const noexcept {
         std::string nkey = compartment + "::" + var;
         resolveMultiMatches(nkey, l, ke);
     }
 
 
     virtual void resolveMultiMatches(const std::string& var,
-        std::string compartment, std::string compartment2,
+        const std::string &compartment, const std::string &compartment2,
         VariableValues *l,
-        variables::KeyExclusions &ke) {
+        const variables::KeyExclusions &ke) const noexcept {
         std::string nkey = compartment + "::" + compartment2 + "::" + var;
         resolveMultiMatches(nkey, l, ke);
     }
@@ -180,16 +180,16 @@ class Collection {
 
     /* resolveRegularExpression */
     virtual void resolveRegularExpression(const std::string& var,
-        std::string compartment, VariableValues *l,
-        variables::KeyExclusions &ke) {
+        const std::string &compartment, VariableValues *l,
+        const variables::KeyExclusions &ke) const noexcept {
         std::string nkey = compartment + "::" + var;
         resolveRegularExpression(nkey, l, ke);
     }
 
 
     virtual void resolveRegularExpression(const std::string& var,
-        std::string compartment, std::string compartment2,
-        VariableValues *l, variables::KeyExclusions &ke) {
+        const std::string &compartment, const std::string &compartment2,
+        VariableValues *l, const variables::KeyExclusions &ke) const noexcept {
         std::string nkey = compartment + "::" + compartment2 + "::" + var;
         resolveRegularExpression(nkey, l, ke);
     }
diff --git a/src/Makefile.am b/src/Makefile.am
index dd9c6b24..553fc819 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -314,6 +314,7 @@ libmodsecurity_la_CPPFLAGS = \
 	-fPIC \
 	-O3 \
 	-I../headers \
+	$(CURL_CFLAGS) \
 	$(GEOIP_CFLAGS) \
 	$(GLOBAL_CPPFLAGS) \
 	$(MODSEC_NO_LOGS) \
diff --git a/src/actions/action_with_run_time_string.h b/src/actions/action_with_run_time_string.h
index 7b87bb85..76e12d3e 100644
--- a/src/actions/action_with_run_time_string.h
+++ b/src/actions/action_with_run_time_string.h
@@ -49,7 +49,7 @@ class ActionWithRunTimeString : public virtual Action {
         }
     }
 
-    std::string getEvaluatedRunTimeString(Transaction *transaction) const noexcept {
+    std::string getEvaluatedRunTimeString(const Transaction *transaction) const noexcept {
         return (m_string == nullptr)?"":m_string->evaluate(transaction);
     }
 
diff --git a/src/anchored_set_variable.cc b/src/anchored_set_variable.cc
index 367ca668..43a95621 100644
--- a/src/anchored_set_variable.cc
+++ b/src/anchored_set_variable.cc
@@ -71,7 +71,7 @@ void AnchoredSetVariable::set(const std::string &key,
 
 
 void AnchoredSetVariable::resolve(
-    VariableValues *l) {
+    VariableValues *l) const noexcept {
     for (const auto& x : *this) {
         l->insert(l->begin(), x.second);
     }
@@ -80,7 +80,7 @@ void AnchoredSetVariable::resolve(
 
 void AnchoredSetVariable::resolve(
     VariableValues *l,
-    variables::KeyExclusions &ke) {
+    const variables::KeyExclusions &ke) const noexcept {
     for (const auto& x : *this) {
         if (!ke.toOmit(x.first)) {
             l->insert(l->begin(), x.second);
@@ -93,7 +93,7 @@ void AnchoredSetVariable::resolve(
 
 
 void AnchoredSetVariable::resolve(const std::string &key,
-    VariableValues *l) {
+    VariableValues *l) const noexcept {
     auto range = this->equal_range(key);
     for (auto it = range.first; it != range.second; ++it) {
         l->push_back(it->second);
@@ -102,7 +102,7 @@ void AnchoredSetVariable::resolve(const std::string &key,
 
 
 std::unique_ptr<std::string> AnchoredSetVariable::resolveFirst(
-    const std::string &key) {
+    const std::string &key) const noexcept {
     auto range = equal_range(key);
     for (auto it = range.first; it != range.second; ++it) {
         std::unique_ptr<std::string> b(new std::string());
@@ -113,8 +113,8 @@ std::unique_ptr<std::string> AnchoredSetVariable::resolveFirst(
 }
 
 
-void AnchoredSetVariable::resolveRegularExpression(Utils::Regex *r,
-    VariableValues *l) {
+void AnchoredSetVariable::resolveRegularExpression(const Utils::Regex *r,
+    VariableValues *l) const noexcept {
     for (const auto& x : *this) {
         int ret = Utils::regex_search(x.first, *r);
         if (ret <= 0) {
@@ -125,9 +125,9 @@ void AnchoredSetVariable::resolveRegularExpression(Utils::Regex *r,
 }
 
 
-void AnchoredSetVariable::resolveRegularExpression(Utils::Regex *r,
+void AnchoredSetVariable::resolveRegularExpression(const Utils::Regex *r,
     VariableValues *l,
-    variables::KeyExclusions &ke) {
+    const variables::KeyExclusions &ke) const noexcept {
     for (const auto& x : *this) {
         int ret = Utils::regex_search(x.first, *r);
         if (ret <= 0) {
diff --git a/src/anchored_variable.cc b/src/anchored_variable.cc
index c700c8e0..8c7ef86c 100644
--- a/src/anchored_variable.cc
+++ b/src/anchored_variable.cc
@@ -118,7 +118,7 @@ void AnchoredVariable::append(const std::string &a, size_t offset,
 }
 
 
-void AnchoredVariable::evaluate(VariableValues *l) {
+void AnchoredVariable::evaluate(VariableValues *l) const noexcept {
     if (m_name.empty()) {
         return;
     }
@@ -128,12 +128,12 @@ void AnchoredVariable::evaluate(VariableValues *l) {
 }
 
 
-std::string * AnchoredVariable::evaluate() {
+const std::string *AnchoredVariable::evaluate() const noexcept {
     return &m_value;
 }
 
 
-std::unique_ptr<std::string> AnchoredVariable::resolveFirst() {
+std::unique_ptr<std::string> AnchoredVariable::resolveFirst() const noexcept {
     if (m_value.empty()) {
         return nullptr;
     }
diff --git a/src/collection/backend/in_memory-per_process.cc b/src/collection/backend/in_memory-per_process.cc
index 9ff9278d..0d143d68 100644
--- a/src/collection/backend/in_memory-per_process.cc
+++ b/src/collection/backend/in_memory-per_process.cc
@@ -86,7 +86,7 @@ void InMemoryPerProcess::del(const std::string& key) {
 
 
 void InMemoryPerProcess::resolveSingleMatch(const std::string& var,
-    VariableValues *l) {
+    VariableValues *l) const noexcept {
     auto range = this->equal_range(var);
 
     for (auto it = range.first; it != range.second; ++it) {
@@ -96,7 +96,7 @@ void InMemoryPerProcess::resolveSingleMatch(const std::string& var,
 
 
 void InMemoryPerProcess::resolveMultiMatches(const std::string& var,
-    VariableValues *l, variables::KeyExclusions &ke) {
+    VariableValues *l, const variables::KeyExclusions &ke) const noexcept {
     size_t keySize = var.size();
     l->reserve(15);
 
@@ -121,7 +121,7 @@ void InMemoryPerProcess::resolveMultiMatches(const std::string& var,
 
 
 void InMemoryPerProcess::resolveRegularExpression(const std::string& var,
-    VariableValues *l, variables::KeyExclusions &ke) {
+    VariableValues *l, const variables::KeyExclusions &ke) const noexcept {
 
     //if (var.find(":") == std::string::npos) {
     //    return;
@@ -160,7 +160,7 @@ void InMemoryPerProcess::resolveRegularExpression(const std::string& var,
 
 
 std::unique_ptr<std::string> InMemoryPerProcess::resolveFirst(
-    const std::string& var) {
+    const std::string& var) const noexcept {
     auto range = equal_range(var);
     for (auto it = range.first; it != range.second; ++it) {
         return std::unique_ptr<std::string>(new std::string(it->second));
diff --git a/src/collection/backend/in_memory-per_process.h b/src/collection/backend/in_memory-per_process.h
index 81abe0bb..4390c93b 100644
--- a/src/collection/backend/in_memory-per_process.h
+++ b/src/collection/backend/in_memory-per_process.h
@@ -84,16 +84,16 @@ class InMemoryPerProcess :
 
     void del(const std::string& key) override;
 
-    std::unique_ptr<std::string> resolveFirst(const std::string& var) override;
+    std::unique_ptr<std::string> resolveFirst(const std::string& var) const noexcept override;
 
     void resolveSingleMatch(const std::string& var,
-        VariableValues *l) override;
+        VariableValues *l) const noexcept override;
     void resolveMultiMatches(const std::string& var,
         VariableValues *l,
-        variables::KeyExclusions &ke) override;
+        const variables::KeyExclusions &ke) const noexcept override;
     void resolveRegularExpression(const std::string& var,
         VariableValues *l,
-        variables::KeyExclusions &ke) override;
+        const variables::KeyExclusions &ke) const noexcept override;
 
  private:
     pthread_mutex_t m_lock;
diff --git a/src/collection/backend/lmdb.cc b/src/collection/backend/lmdb.cc
index 0836c1b8..3f866d73 100644
--- a/src/collection/backend/lmdb.cc
+++ b/src/collection/backend/lmdb.cc
@@ -48,13 +48,13 @@ LMDB::~LMDB() {
 }
 
 
-void LMDB::string2val(const std::string& str, MDB_val *val) {
+void LMDB::string2val(const std::string& str, MDB_val *val) const {
     val->mv_size = sizeof(char)*(str.size());
     val->mv_data = const_cast<char *>(str.c_str());
 }
 
 
-void LMDB::lmdb_debug(int rc, std::string op, std::string scope) {
+void LMDB::lmdb_debug(int rc, std::string op, std::string scope) const {
 #ifndef LMDB_STDOUT_COUT
     return;
 #else
@@ -162,7 +162,7 @@ void LMDB::lmdb_debug(int rc, std::string op, std::string scope) {
 }
 
 
-std::unique_ptr<std::string> LMDB::resolveFirst(const std::string& var) {
+std::unique_ptr<std::string> LMDB::resolveFirst(const std::string& var) const noexcept {
     int rc;
     MDB_val mdb_key;
     MDB_val mdb_value;
@@ -262,7 +262,7 @@ end_txn:
 
 
 void LMDB::resolveSingleMatch(const std::string& var,
-    VariableValues *l) {
+    VariableValues *l) const noexcept {
     int rc;
     MDB_txn *txn;
     MDB_dbi dbi;
@@ -287,10 +287,11 @@ void LMDB::resolveSingleMatch(const std::string& var,
     mdb_cursor_open(txn, dbi, &cursor);
     while ((rc = mdb_cursor_get(cursor, &mdb_key,
             &mdb_value_ret, MDB_NEXT_DUP)) == 0) {
-        std::string a(
-            reinterpret_cast<char *>(mdb_value_ret.mv_data),
-            mdb_value_ret.mv_size);
-        l->emplace_back(&var, &a);
+        l->insert(l->begin(), std::make_shared<VariableValue>(
+            &m_name,
+            new std::string(var),
+            new std::string(reinterpret_cast<char *>(mdb_value_ret.mv_data),
+            mdb_value_ret.mv_size)));
     }
 
     mdb_cursor_close(cursor);
@@ -466,7 +467,7 @@ end_txn:
 
 void LMDB::resolveMultiMatches(const std::string& var,
     VariableValues *l,
-    variables::KeyExclusions &ke) {
+    const variables::KeyExclusions &ke) const noexcept {
     MDB_val key, data;
     MDB_txn *txn = NULL;
     MDB_dbi dbi;
@@ -528,7 +529,7 @@ end_txn:
 
 void LMDB::resolveRegularExpression(const std::string& var,
     VariableValues *l,
-    variables::KeyExclusions &ke) {
+    const variables::KeyExclusions &ke) const noexcept {
     MDB_val key, data;
     MDB_txn *txn = NULL;
     MDB_dbi dbi;
@@ -567,12 +568,16 @@ void LMDB::resolveRegularExpression(const std::string& var,
             continue;
         }
 
-        VariableValue *v = new VariableValue(
+        l->insert(l->begin(), std::make_shared<VariableValue>(
+            &m_name,
             new std::string(reinterpret_cast<char *>(key.mv_data),
-                key.mv_size),
+            key.mv_size),
             new std::string(reinterpret_cast<char *>(data.mv_data),
-                data.mv_size));
-        l->insert(l->begin(), v);
+            data.mv_size)));
+        //l->insert(l->begin(), std::make_shared<VariableValue>(&m_name,
+        //    new std::string(reinterpret_cast<char *>(key.mv_data), key.mv_size),
+        //    new std::string(reinterpret_cast<char *>(data.mv_data), data.mv_size))
+        //);
     }
 
     mdb_cursor_close(cursor);
diff --git a/src/collection/backend/lmdb.h b/src/collection/backend/lmdb.h
index 9e9c8e08..2fbd404f 100644
--- a/src/collection/backend/lmdb.h
+++ b/src/collection/backend/lmdb.h
@@ -63,20 +63,20 @@ class LMDB :
 
     void del(const std::string& key) override;
 
-    std::unique_ptr<std::string> resolveFirst(const std::string& var) override;
+    std::unique_ptr<std::string> resolveFirst(const std::string& var) const noexcept override;
 
     void resolveSingleMatch(const std::string& var,
-        VariableValues *l) override;
+        VariableValues *l)  const noexcept override;
     void resolveMultiMatches(const std::string& var,
         VariableValues *l,
-        variables::KeyExclusions &ke) override;
+        const variables::KeyExclusions &ke)  const noexcept override;
     void resolveRegularExpression(const std::string& var,
         VariableValues *l,
-        variables::KeyExclusions &ke) override;
+        const variables::KeyExclusions &ke)  const noexcept override;
 
  private:
-    void string2val(const std::string& str, MDB_val *val);
-    void inline lmdb_debug(int rc, std::string op, std::string scope);
+    void string2val(const std::string& str, MDB_val *val) const;
+    void inline lmdb_debug(int rc, std::string op, std::string scope) const;
 
     MDB_env *m_env;
 };
diff --git a/src/rule_with_actions.cc b/src/rule_with_actions.cc
index 994d8ed3..29489b54 100644
--- a/src/rule_with_actions.cc
+++ b/src/rule_with_actions.cc
@@ -396,8 +396,8 @@ bool RuleWithActions::containsMsg(const std::string& name, Transaction *t) const
 }
 
 
-std::string RuleWithActions::getLogData(Transaction *t) const { return m_logData->getEvaluatedRunTimeString(t); }
-std::string RuleWithActions::getMessage(Transaction *t) const { return m_msg->getEvaluatedRunTimeString(t); }
+std::string RuleWithActions::getLogData(const Transaction *t) const { return m_logData->getEvaluatedRunTimeString(t); }
+std::string RuleWithActions::getMessage(const Transaction *t) const { return m_msg->getEvaluatedRunTimeString(t); }
 
 
 }  // namespace modsecurity
diff --git a/src/rule_with_actions.h b/src/rule_with_actions.h
index 0674f64d..cc184349 100644
--- a/src/rule_with_actions.h
+++ b/src/rule_with_actions.h
@@ -420,13 +420,13 @@ class RuleWithActions : public Rule {
 
     inline bool hasLogDataAction() const { return m_logData != nullptr || m_defaultActionLogData != nullptr; }
     inline std::shared_ptr<actions::LogData> getLogDataAction() const { return m_logData; }
-    std::string getLogData(/*const */Transaction *t) const;
+    std::string getLogData(const Transaction *t) const;
     inline void setLogDataAction(const std::shared_ptr<actions::LogData> &data) { m_logData = data; }
 
     inline bool hasMessageAction() const { return m_msg != nullptr || m_defaultActionMsg != nullptr; }
     inline std::shared_ptr<actions::Msg> getMessageAction() const { return m_msg; }
     inline void setMessageAction(const std::shared_ptr<actions::Msg> &msg) { m_msg = msg; }
-    std::string getMessage(/*const */Transaction *t) const;
+    std::string getMessage(const Transaction *t) const;
 
 
     inline bool hasSeverityAction() const { return m_severity != SEVERITY_NOT_SET || m_defaultSeverity != SEVERITY_NOT_SET; }
diff --git a/src/run_time_string.cc b/src/run_time_string.cc
index 08408209..ad16dec7 100644
--- a/src/run_time_string.cc
+++ b/src/run_time_string.cc
@@ -42,7 +42,7 @@ void RunTimeString::append(std::unique_ptr<Variable> var) {
 }
 
 
-std::string RunTimeString::evaluate(/* const */ Transaction *transaction) const noexcept {
+std::string RunTimeString::evaluate(const Transaction *transaction) const noexcept {
     std::string retString;
     // FIXME: Educated guess the size of retString based on the size of the elements.
     for (auto &element : m_elements) {
diff --git a/src/run_time_string.h b/src/run_time_string.h
index 6904dceb..f6426179 100644
--- a/src/run_time_string.h
+++ b/src/run_time_string.h
@@ -67,13 +67,7 @@ class RunTimeString {
     void append(std::unique_ptr<Variable> var);
 
 
-    /*
-     *
-     * FIXME: Transaction should be const here. Variables resolution does
-     *        not change anything on transaction instance.
-     *
-     */
-    std::string evaluate(/* const */ Transaction *t = nullptr) const noexcept;
+    std::string evaluate(const Transaction *t = nullptr) const noexcept;
 
 
     inline bool containsMacro() const noexcept {
@@ -122,7 +116,7 @@ class RunTimeString {
             };
 
 
-        void appendValueTo(/* const */ Transaction *transaction, std::string &v) const noexcept {
+        void appendValueTo(const Transaction *transaction, std::string &v) const noexcept {
             if (m_variable && transaction) {
                 VariableValues l;
                 m_variable->evaluate(transaction, &l);
diff --git a/src/variables/duration.cc b/src/variables/duration.cc
index 2dd9e1bf..bba03f36 100644
--- a/src/variables/duration.cc
+++ b/src/variables/duration.cc
@@ -27,8 +27,8 @@
 namespace modsecurity {
 namespace variables {
 
-void Duration::evaluate(Transaction *transaction,
-    VariableValues *l) {
+void Duration::evaluate(const Transaction *transaction,
+    VariableValues *l) const noexcept {
     double e = utils::cpu_seconds() - transaction->m_creationTimeStamp;
 
     l->push_back(std::make_shared<VariableValue>(
diff --git a/src/variables/duration.h b/src/variables/duration.h
index 7a34f180..eb3700dd 100644
--- a/src/variables/duration.h
+++ b/src/variables/duration.h
@@ -34,8 +34,8 @@ class Duration : public Variable {
         : Variable(_name),
         m_retName("DURATION") { }
 
-    void evaluate(Transaction *transaction,
-        VariableValues *l) override;
+    void evaluate(const Transaction *transaction,
+        VariableValues *l) const noexcept override;
     std::string m_retName;
 };
 
diff --git a/src/variables/env.cc b/src/variables/env.cc
index 6ee885c9..60371958 100644
--- a/src/variables/env.cc
+++ b/src/variables/env.cc
@@ -32,7 +32,7 @@ extern char **environ;
 namespace modsecurity {
 namespace variables {
 
-void Env::evaluate(Transaction *transaction, VariableValues *l) {
+void Env::evaluate(const Transaction *transaction, VariableValues *l) const noexcept {
     bool checkForKey = getVariableKey()->length() > 0;
 
     for (char **current = environ; *current; current++) {
@@ -57,6 +57,7 @@ void Env::evaluate(Transaction *transaction, VariableValues *l) {
             getVariableKeyWithCollection()
         ));
     }
+
 }
 
 
diff --git a/src/variables/env.h b/src/variables/env.h
index dc16517a..78bfe704 100644
--- a/src/variables/env.h
+++ b/src/variables/env.h
@@ -33,7 +33,7 @@ class Env : public Variable {
     explicit Env(const std::string &name)
         : Variable(name) { }
 
-    void evaluate(Transaction *transaction, VariableValues *l) override;
+    void evaluate(const Transaction *transaction, VariableValues *l) const noexcept override;
 };
 
 }  // namespace variables
diff --git a/src/variables/global.h b/src/variables/global.h
index c0506c20..324df19c 100644
--- a/src/variables/global.h
+++ b/src/variables/global.h
@@ -39,8 +39,8 @@ class Global_DictElement : public Variable {
         : Variable("GLOBAL:" + dictElement),
         m_dictElement("GLOBAL:" + dictElement) { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_global_collection->resolveMultiMatches(
             *getVariableKey(), t->m_collections.m_global_collection_key,
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
@@ -55,8 +55,8 @@ class Global_NoDictElement : public Variable {
     Global_NoDictElement()
         : Variable("GLOBAL") { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_global_collection->resolveMultiMatches("",
             t->m_collections.m_global_collection_key,
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
@@ -70,8 +70,8 @@ class Global_DictElementRegexp : public VariableRegex {
         : VariableRegex("GLOBAL", dictElement),
         m_dictElement(dictElement) { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_global_collection->resolveRegularExpression(
             m_dictElement,
             t->m_collections.m_global_collection_key,
@@ -91,8 +91,8 @@ class Global_DynamicElement : public VariableWithRunTimeString {
         )
     { };
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         std::string string = m_string->evaluate(t);
         t->m_collections.m_global_collection->resolveMultiMatches(
             string,
diff --git a/src/variables/highest_severity.cc b/src/variables/highest_severity.cc
index d1b1c1bd..82104c59 100644
--- a/src/variables/highest_severity.cc
+++ b/src/variables/highest_severity.cc
@@ -26,8 +26,8 @@
 namespace modsecurity {
 namespace variables {
 
-void HighestSeverity::evaluate(Transaction *transaction,
-    VariableValues *l) {
+void HighestSeverity::evaluate(const Transaction *transaction,
+    VariableValues *l) const noexcept {
     l->push_back(std::make_shared<VariableValue>(
         std::unique_ptr<std::string>(new std::string(std::to_string(transaction->m_highestSeverityAction))),
         getVariableKeyWithCollection().get()));
diff --git a/src/variables/highest_severity.h b/src/variables/highest_severity.h
index babc01c8..4c0cbd9a 100644
--- a/src/variables/highest_severity.h
+++ b/src/variables/highest_severity.h
@@ -34,8 +34,8 @@ class HighestSeverity : public Variable {
         : Variable(_name)
     { }
 
-    void evaluate(Transaction *transaction,
-        VariableValues *l) override;
+    void evaluate(const Transaction *transaction,
+        VariableValues *l) const noexcept override;
 };
 
 
diff --git a/src/variables/ip.h b/src/variables/ip.h
index 8d6f95c6..09442928 100644
--- a/src/variables/ip.h
+++ b/src/variables/ip.h
@@ -39,8 +39,8 @@ class Ip_DictElement : public Variable {
         : Variable("IP:" + dictElement),
         m_dictElement("IP:" + dictElement) { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_ip_collection->resolveMultiMatches(
             *getVariableKey(), t->m_collections.m_ip_collection_key,
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
@@ -55,8 +55,8 @@ class Ip_NoDictElement : public Variable {
     Ip_NoDictElement()
         : Variable("IP") { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_ip_collection->resolveMultiMatches("",
             t->m_collections.m_ip_collection_key,
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
@@ -70,8 +70,8 @@ class Ip_DictElementRegexp : public VariableRegex {
         : VariableRegex("IP", dictElement),
         m_dictElement(dictElement) { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_ip_collection->resolveRegularExpression(
             m_dictElement, t->m_collections.m_ip_collection_key,
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
@@ -90,8 +90,8 @@ class Ip_DynamicElement : public VariableWithRunTimeString {
         )
     { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         std::string string = m_string->evaluate(t);
         t->m_collections.m_ip_collection->resolveMultiMatches(
             string,
diff --git a/src/variables/modsec_build.cc b/src/variables/modsec_build.cc
index 9a4f1a73..cba253b0 100644
--- a/src/variables/modsec_build.cc
+++ b/src/variables/modsec_build.cc
@@ -24,8 +24,8 @@
 namespace modsecurity {
 namespace variables {
 
-void ModsecBuild::evaluate(Transaction *transaction,
-    VariableValues *l) {
+void ModsecBuild::evaluate(const Transaction *transaction,
+    VariableValues *l) const noexcept {
 
     l->push_back(std::make_shared<VariableValue>(&m_retName, &m_build));
 }
diff --git a/src/variables/modsec_build.h b/src/variables/modsec_build.h
index 319f0a72..78fdc949 100644
--- a/src/variables/modsec_build.h
+++ b/src/variables/modsec_build.h
@@ -43,8 +43,8 @@ class ModsecBuild : public Variable {
         m_build = ss.str();
     }
 
-    void evaluate(Transaction *transaction,
-        VariableValues *l) override;
+    void evaluate(const Transaction *transaction,
+        VariableValues *l) const noexcept override;
 
     std::string m_build;
     std::string m_retName;
diff --git a/src/variables/remote_user.cc b/src/variables/remote_user.cc
index 1c08cc6a..37036e60 100644
--- a/src/variables/remote_user.cc
+++ b/src/variables/remote_user.cc
@@ -37,8 +37,8 @@ namespace variables {
 
 
 
-void RemoteUser::evaluate(Transaction *transaction,
-    VariableValues *l) {
+void RemoteUser::evaluate(const Transaction *transaction,
+    VariableValues *l) const noexcept {
     auto userName = parserRemoteUser(transaction);
     auto var = std::make_shared<VariableValue>(
         std::unique_ptr<std::string>(new std::string(userName.first)),
diff --git a/src/variables/remote_user.h b/src/variables/remote_user.h
index b96c61a7..2809bf02 100644
--- a/src/variables/remote_user.h
+++ b/src/variables/remote_user.h
@@ -37,10 +37,10 @@ class RemoteUser : public Variable {
         : Variable(_name),
         m_retName("REMOTE_USER") { }
 
-    void evaluate(Transaction *transaction,
-        VariableValues *l) override;
+    void evaluate(const Transaction *transaction,
+        VariableValues *l) const noexcept override;
 
-    static std::pair<std::string, VariableOrigin> parserRemoteUser(Transaction *transaction) {
+    static std::pair<std::string, VariableOrigin> parserRemoteUser(const Transaction *transaction) {
         size_t pos;
         std::string base64;
         std::string header;
diff --git a/src/variables/resource.h b/src/variables/resource.h
index 7c262abd..d837ef93 100644
--- a/src/variables/resource.h
+++ b/src/variables/resource.h
@@ -39,8 +39,8 @@ class Resource_DictElement : public Variable {
         : Variable("RESOURCE:" + dictElement),
         m_dictElement("RESOURCE:" + dictElement) { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_resource_collection->resolveMultiMatches(
             *getVariableKey(), t->m_collections.m_resource_collection_key,
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
@@ -55,8 +55,8 @@ class Resource_NoDictElement : public Variable {
     Resource_NoDictElement()
         : Variable("RESOURCE") { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_resource_collection->resolveMultiMatches(*getVariableKey(),
             t->m_collections.m_resource_collection_key,
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
@@ -70,8 +70,8 @@ class Resource_DictElementRegexp : public VariableRegex {
         : VariableRegex("RESOURCE", dictElement),
         m_dictElement(dictElement) { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_resource_collection->resolveRegularExpression(
             m_dictElement, t->m_collections.m_resource_collection_key,
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
@@ -90,8 +90,8 @@ class Resource_DynamicElement : public VariableWithRunTimeString {
         )
     { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         std::string string = m_string->evaluate(t);
         t->m_collections.m_resource_collection->resolveMultiMatches(
             string,
diff --git a/src/variables/rule.h b/src/variables/rule.h
index d0384df3..32acdfaa 100644
--- a/src/variables/rule.h
+++ b/src/variables/rule.h
@@ -54,7 +54,7 @@ class Rule_DictElement : public RuleVariable, public VariableDictElement {
         return new Rule_DictElement(*this);
     };
 
-    static void id(Transaction *t,
+    static void id(const Transaction *t,
         const RuleWithActions *rule,
         VariableValues *l) {
         auto var = std::make_shared<VariableValue>(&m_rule, &m_rule_id, std::unique_ptr<std::string>(new std::string(std::to_string(rule->getId()))));
@@ -67,7 +67,7 @@ class Rule_DictElement : public RuleVariable, public VariableDictElement {
 
 
 
-    static void rev(Transaction *t,
+    static void rev(const Transaction *t,
         const RuleWithActions *rule,
         VariableValues *l) {
 
@@ -83,7 +83,7 @@ class Rule_DictElement : public RuleVariable, public VariableDictElement {
     }
 
 
-    static void severity(Transaction *t,
+    static void severity(const Transaction *t,
         const RuleWithActions *rule,
         VariableValues *l) {
 
@@ -98,7 +98,7 @@ class Rule_DictElement : public RuleVariable, public VariableDictElement {
 
     }
 
-    static void logData(Transaction *t,
+    static void logData(const Transaction *t,
         const RuleWithActions *rule,
         VariableValues *l) {
 
@@ -112,7 +112,7 @@ class Rule_DictElement : public RuleVariable, public VariableDictElement {
         }
     }
 
-    static void msg(Transaction *t,
+    static void msg(const Transaction *t,
         const RuleWithActions *rule,
         VariableValues *l) {
 
@@ -126,8 +126,8 @@ class Rule_DictElement : public RuleVariable, public VariableDictElement {
         }
     }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
 
         if (m_dictElement == "id") {
             id(t, getRule(), l);
@@ -174,8 +174,8 @@ class Rule_DictElementRegexp : public RuleVariable, public VariableRegex {
     { };
 
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
 
         if (Utils::regex_search("id", m_r) > 0) {
             Rule_DictElement::id(t, getRule(), l);
@@ -219,8 +219,8 @@ class Rule_NoDictElement : public RuleVariable, public Variable  {
     { };
 
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         Rule_DictElement::id(t, getRule(), l);
         Rule_DictElement::rev(t, getRule(), l);
         Rule_DictElement::severity(t, getRule(), l);
diff --git a/src/variables/session.h b/src/variables/session.h
index 8f581b74..8206a72e 100644
--- a/src/variables/session.h
+++ b/src/variables/session.h
@@ -38,8 +38,8 @@ class Session_DictElement : public Variable {
         : Variable("SESSION:" + dictElement),
         m_dictElement("SESSION:" + dictElement) { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_session_collection->resolveMultiMatches(
             *getVariableKey(), t->m_collections.m_session_collection_key,
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
@@ -54,8 +54,8 @@ class Session_NoDictElement : public Variable {
     Session_NoDictElement()
         : Variable("SESSION") { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_session_collection->resolveMultiMatches("",
             t->m_collections.m_session_collection_key,
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
@@ -69,8 +69,8 @@ class Session_DictElementRegexp : public VariableRegex {
         : VariableRegex("SESSION", dictElement),
         m_dictElement(dictElement) { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_session_collection->resolveRegularExpression(
             m_dictElement, t->m_collections.m_session_collection_key,
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
@@ -89,8 +89,8 @@ class Session_DynamicElement : public VariableWithRunTimeString {
         )
     { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         std::string string = m_string->evaluate(t);
         t->m_collections.m_session_collection->resolveMultiMatches(
             string,
diff --git a/src/variables/time.cc b/src/variables/time.cc
index 97a75f6d..e7478635 100644
--- a/src/variables/time.cc
+++ b/src/variables/time.cc
@@ -33,8 +33,8 @@
 namespace modsecurity {
 namespace variables {
 
-void Time::evaluate(Transaction *transaction,
-    VariableValues *l) {
+void Time::evaluate(const Transaction *transaction,
+    VariableValues *l) const noexcept {
 
     char tstr[200];
     struct tm timeinfo;
diff --git a/src/variables/time.h b/src/variables/time.h
index e069747f..f51ae33d 100644
--- a/src/variables/time.h
+++ b/src/variables/time.h
@@ -35,8 +35,8 @@ class Time : public Variable {
         : Variable(_name),
         m_retName("TIME") { }
 
-    void evaluate(Transaction *transaction,
-        VariableValues *l) override;
+    void evaluate(const Transaction *transaction,
+        VariableValues *l) const noexcept override;
     std::string m_retName;
 };
 
diff --git a/src/variables/time_day.cc b/src/variables/time_day.cc
index 83271d0c..2085ec81 100644
--- a/src/variables/time_day.cc
+++ b/src/variables/time_day.cc
@@ -33,8 +33,8 @@
 namespace modsecurity {
 namespace variables {
 
-void TimeDay::evaluate(Transaction *transaction,
-    VariableValues *l) {
+void TimeDay::evaluate(const Transaction *transaction,
+    VariableValues *l) const noexcept {
     char tstr[200];
     struct tm timeinfo;
     time_t timer;
diff --git a/src/variables/time_day.h b/src/variables/time_day.h
index 66141821..950e5f75 100644
--- a/src/variables/time_day.h
+++ b/src/variables/time_day.h
@@ -34,8 +34,8 @@ class TimeDay : public Variable {
         : Variable(_name),
         m_retName("TIME_DAY") { }
 
-    void evaluate(Transaction *transaction,
-        VariableValues *l) override;
+    void evaluate(const Transaction *transaction,
+        VariableValues *l) const noexcept override;
     std::string m_retName;
 };
 
diff --git a/src/variables/time_epoch.cc b/src/variables/time_epoch.cc
index f8715b9b..dea7e143 100644
--- a/src/variables/time_epoch.cc
+++ b/src/variables/time_epoch.cc
@@ -33,8 +33,8 @@
 namespace modsecurity {
 namespace variables {
 
-void TimeEpoch::evaluate(Transaction *transaction,
-    VariableValues *l) {
+void TimeEpoch::evaluate(const Transaction *transaction,
+    VariableValues *l) const noexcept {
 
     l->push_back(std::make_shared<VariableValue>(
         std::unique_ptr<std::string>(new std::string(std::to_string(std::time(nullptr)))),
diff --git a/src/variables/time_epoch.h b/src/variables/time_epoch.h
index 994288aa..c34aaf04 100644
--- a/src/variables/time_epoch.h
+++ b/src/variables/time_epoch.h
@@ -34,8 +34,8 @@ class TimeEpoch : public Variable {
         : Variable(_name),
         m_retName("TIME_EPOCH") { }
 
-    void evaluate(Transaction *transaction,
-        VariableValues *l) override;
+    void evaluate(const Transaction *transaction,
+        VariableValues *l) const noexcept override;
     std::string m_retName;
 };
 
diff --git a/src/variables/time_hour.cc b/src/variables/time_hour.cc
index 61b718cc..4a279fcf 100644
--- a/src/variables/time_hour.cc
+++ b/src/variables/time_hour.cc
@@ -33,8 +33,8 @@
 namespace modsecurity {
 namespace variables {
 
-void TimeHour::evaluate(Transaction *transaction,
-    VariableValues *l) {
+void TimeHour::evaluate(const Transaction *transaction,
+    VariableValues *l) const noexcept {
     char tstr[200];
     struct tm timeinfo;
     time_t timer;
diff --git a/src/variables/time_hour.h b/src/variables/time_hour.h
index 497317d1..9e432be0 100644
--- a/src/variables/time_hour.h
+++ b/src/variables/time_hour.h
@@ -34,8 +34,8 @@ class TimeHour : public Variable {
         : Variable(_name),
         m_retName("TIME_HOUR") { }
 
-    void evaluate(Transaction *transaction,
-        VariableValues *l) override;
+    void evaluate(const Transaction *transaction,
+        VariableValues *l) const noexcept override;
     std::string m_retName;
 };
 
diff --git a/src/variables/time_min.cc b/src/variables/time_min.cc
index c6dc12e8..7c499c69 100644
--- a/src/variables/time_min.cc
+++ b/src/variables/time_min.cc
@@ -33,8 +33,8 @@
 namespace modsecurity {
 namespace variables {
 
-void TimeMin::evaluate(Transaction *transaction,
-    VariableValues *l) {
+void TimeMin::evaluate(const Transaction *transaction,
+    VariableValues *l) const noexcept {
     char tstr[200];
     struct tm timeinfo;
     time_t timer;
diff --git a/src/variables/time_min.h b/src/variables/time_min.h
index cde00d58..688ec0c4 100644
--- a/src/variables/time_min.h
+++ b/src/variables/time_min.h
@@ -34,8 +34,8 @@ class TimeMin : public Variable {
         : Variable(_name),
         m_retName("TIME_MIN") { }
 
-    void evaluate(Transaction *transaction,
-        VariableValues *l) override;
+    void evaluate(const Transaction *transaction,
+        VariableValues *l) const noexcept override;
     std::string m_retName;
 };
 
diff --git a/src/variables/time_mon.cc b/src/variables/time_mon.cc
index ad222578..f99a8932 100644
--- a/src/variables/time_mon.cc
+++ b/src/variables/time_mon.cc
@@ -33,8 +33,8 @@
 namespace modsecurity {
 namespace variables {
 
-void TimeMon::evaluate(Transaction *transaction,
-    VariableValues *l) {
+void TimeMon::evaluate(const Transaction *transaction,
+    VariableValues *l) const noexcept {
     char tstr[200];
     struct tm timeinfo;
     time_t timer;
diff --git a/src/variables/time_mon.h b/src/variables/time_mon.h
index 2f96b885..e150b591 100644
--- a/src/variables/time_mon.h
+++ b/src/variables/time_mon.h
@@ -34,8 +34,8 @@ class TimeMon : public Variable {
         : Variable(_name),
         m_retName("TIME_MON") { }
 
-    void evaluate(Transaction *transaction,
-        VariableValues *l) override;
+    void evaluate(const Transaction *transaction,
+        VariableValues *l) const noexcept override;
     std::string m_retName;
 };
 
diff --git a/src/variables/time_sec.cc b/src/variables/time_sec.cc
index b944ab94..f066bbe7 100644
--- a/src/variables/time_sec.cc
+++ b/src/variables/time_sec.cc
@@ -33,8 +33,8 @@
 namespace modsecurity {
 namespace variables {
 
-void TimeSec::evaluate(Transaction *transaction,
-    VariableValues *l) {
+void TimeSec::evaluate(const Transaction *transaction,
+    VariableValues *l) const noexcept {
     char tstr[200];
     struct tm timeinfo;
     time_t timer;
diff --git a/src/variables/time_sec.h b/src/variables/time_sec.h
index 3c460f48..d83b385d 100644
--- a/src/variables/time_sec.h
+++ b/src/variables/time_sec.h
@@ -34,8 +34,8 @@ class TimeSec : public Variable {
         : Variable(_name),
         m_retName("TIME_SEC") { }
 
-    void evaluate(Transaction *transaction,
-        VariableValues *l) override;
+    void evaluate(const Transaction *transaction,
+        VariableValues *l) const noexcept override;
     std::string m_retName;
 };
 
diff --git a/src/variables/time_wday.cc b/src/variables/time_wday.cc
index 8ee36a20..24d30b07 100644
--- a/src/variables/time_wday.cc
+++ b/src/variables/time_wday.cc
@@ -33,8 +33,8 @@
 namespace modsecurity {
 namespace variables {
 
-void TimeWDay::evaluate(Transaction *transaction,
-    VariableValues *l) {
+void TimeWDay::evaluate(const Transaction *transaction,
+    VariableValues *l) const noexcept {
     char tstr[200];
     struct tm timeinfo;
     time_t timer;
diff --git a/src/variables/time_wday.h b/src/variables/time_wday.h
index f9bc3946..9bc1bf9a 100644
--- a/src/variables/time_wday.h
+++ b/src/variables/time_wday.h
@@ -34,8 +34,8 @@ class TimeWDay : public Variable {
         : Variable(_name),
         m_retName("TIME_WDAY") { }
 
-    void evaluate(Transaction *transaction,
-        VariableValues *l) override;
+    void evaluate(const Transaction *transaction,
+        VariableValues *l) const noexcept override;
     std::string m_retName;
 };
 
diff --git a/src/variables/time_year.cc b/src/variables/time_year.cc
index ed918ba8..23850bfe 100644
--- a/src/variables/time_year.cc
+++ b/src/variables/time_year.cc
@@ -33,8 +33,8 @@
 namespace modsecurity {
 namespace variables {
 
-void TimeYear::evaluate(Transaction *transaction,
-    VariableValues *l) {
+void TimeYear::evaluate(const Transaction *transaction,
+    VariableValues *l) const noexcept {
     char tstr[200];
     struct tm timeinfo;
     time_t timer;
diff --git a/src/variables/time_year.h b/src/variables/time_year.h
index 4b5882d2..56c1c034 100644
--- a/src/variables/time_year.h
+++ b/src/variables/time_year.h
@@ -34,8 +34,8 @@ class TimeYear : public Variable {
         : Variable(_name),
         m_retName("TIME_YEAR") { }
 
-    void evaluate(Transaction *transaction,
-        VariableValues *l) override;
+    void evaluate(const Transaction *transaction,
+        VariableValues *l) const noexcept override;
     std::string m_retName;
 };
 
diff --git a/src/variables/tx.h b/src/variables/tx.h
index 1b432d10..b6e73151 100644
--- a/src/variables/tx.h
+++ b/src/variables/tx.h
@@ -39,8 +39,8 @@ class Tx_DictElement : public Variable {
         : Variable("TX:" + dictElement),
         m_dictElement("TX:" + dictElement) { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_tx_collection->resolveMultiMatches(
             *getVariableKey(), l, m_keyExclusion);
     }
@@ -54,8 +54,8 @@ class Tx_NoDictElement : public Variable {
     Tx_NoDictElement()
         : Variable("TX") { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_tx_collection->resolveMultiMatches("", l,
             m_keyExclusion);
     }
@@ -68,8 +68,8 @@ class Tx_DictElementRegexp : public VariableRegex {
         : VariableRegex("TX", dictElement),
         m_dictElement(dictElement) { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_tx_collection->resolveRegularExpression(
             m_dictElement, l, m_keyExclusion);
     }
@@ -87,8 +87,8 @@ class Tx_DynamicElement : public VariableWithRunTimeString {
         )
     { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         std::string string = m_string->evaluate(t);
         t->m_collections.m_tx_collection->resolveMultiMatches(string, l,
             m_keyExclusion);
diff --git a/src/variables/user.h b/src/variables/user.h
index 4f5223de..78040d87 100644
--- a/src/variables/user.h
+++ b/src/variables/user.h
@@ -39,8 +39,8 @@ class User_DictElement : public Variable {
         : Variable("USER:" + dictElement),
         m_dictElement("USER:" + dictElement) { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_user_collection->resolveMultiMatches(
             *getVariableKey(), t->m_collections.m_user_collection_key,
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
@@ -55,8 +55,8 @@ class User_NoDictElement : public Variable {
     User_NoDictElement()
         : Variable("USER") { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_user_collection->resolveMultiMatches(*getVariableKey(),
             t->m_collections.m_user_collection_key,
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
@@ -70,8 +70,8 @@ class User_DictElementRegexp : public VariableRegex {
         : VariableRegex("USER", dictElement),
         m_dictElement(dictElement) { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         t->m_collections.m_user_collection->resolveRegularExpression(
             m_dictElement, t->m_collections.m_user_collection_key,
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
@@ -90,8 +90,8 @@ class User_DynamicElement : public VariableWithRunTimeString {
         )
     { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         std::string string = m_string->evaluate(t);
         t->m_collections.m_user_collection->resolveMultiMatches(
             string,
diff --git a/src/variables/variable.cc b/src/variables/variable.cc
index 161320b9..345a9e78 100644
--- a/src/variables/variable.cc
+++ b/src/variables/variable.cc
@@ -29,10 +29,10 @@ namespace variables {
 
 
 Variable::Variable(const std::string &name)
-    : m_keyWithCollection(new std::string("")),
-    m_keyExclusion(),
-    m_collectionName(new std::string("")),
-    m_key(new std::string("")) {
+    : m_keyExclusion(),
+    m_keyWithCollection(new std::string("")),
+    m_key(new std::string("")),
+    m_collectionName(new std::string("")) {
     size_t a = name.find(":");
     if (a == std::string::npos) {
         a = name.find(".");
diff --git a/src/variables/variable.h b/src/variables/variable.h
index d4eddc60..c1c9b56c 100644
--- a/src/variables/variable.h
+++ b/src/variables/variable.h
@@ -47,8 +47,8 @@ class n ## _DictElementRegexp : public VariableRegex { \
     explicit n ## _DictElementRegexp(const std::string &regex) \
         : VariableRegex(#N, regex) { } \
 \
-    void evaluate(Transaction *transaction, \
-        VariableValues *l) override { \
+    void evaluate(const Transaction *transaction, \
+        VariableValues *l) const noexcept override { \
         transaction-> e .resolveRegularExpression(&m_r, l, \
             m_keyExclusion); \
     } \
@@ -61,8 +61,8 @@ class n ## _DictElement : public VariableDictElement { \
     explicit n ## _DictElement(const std::string &dictElement) \
         : VariableDictElement(#N, dictElement) { } \
 \
-    void evaluate(Transaction *transaction, \
-        VariableValues *l) override { \
+    void evaluate(const Transaction *transaction, \
+        VariableValues *l) const noexcept override { \
         transaction-> e .resolve(m_dictElement, l); \
     } \
 };
@@ -74,8 +74,8 @@ class n ## _NoDictElement : public Variable { \
     explicit n ## _NoDictElement() \
         : Variable(#N) { } \
 \
-    void evaluate(Transaction *transaction, \
-        VariableValues *l) override { \
+    void evaluate(const Transaction *transaction, \
+        VariableValues *l) const noexcept override { \
         transaction-> e .resolve(l, m_keyExclusion); \
     } \
 };
@@ -87,8 +87,8 @@ class n : public Variable { \
     n() \
         : Variable(#N) { } \
     \
-    void evaluate(Transaction *transaction, \
-        VariableValues *l) override { \
+    void evaluate(const Transaction *transaction, \
+        VariableValues *l) const noexcept override { \
         transaction-> e .evaluate(l); \
     } \
 };
@@ -104,8 +104,8 @@ namespace variables {
 class KeyExclusion {
  public:
     KeyExclusion() { }
-    virtual bool match(const std::string &a) = 0;
-    virtual bool match(const bpstd::string_view &a) = 0;
+    virtual bool match(const std::string &a) const = 0;
+    virtual bool match(const bpstd::string_view &a) const = 0;
     virtual ~KeyExclusion() { }
 };
 
@@ -120,10 +120,10 @@ class KeyExclusionRegex : public KeyExclusion {
 
     ~KeyExclusionRegex() override { }
 
-    bool match(const std::string &a) override {
+    bool match(const std::string &a) const override {
         return m_re.searchAll(a).size() > 0;
     }
-    bool match(const bpstd::string_view &a) override {
+    bool match(const bpstd::string_view &a) const override {
         // FIXME: string_view will be a good thing in searchAll.
         return m_re.searchAll(std::string(a)).size() > 0;
     }
@@ -139,14 +139,14 @@ class KeyExclusionString : public KeyExclusion {
 
     ~KeyExclusionString() override { }
 
-    bool match(const std::string &a) override {
+    bool match(const std::string &a) const override {
         return a.size() == m_key.size() && std::equal(a.begin(), a.end(),
             m_key.begin(),
             [](char aa, char bb) {
                 return static_cast<char>(toupper(aa)) == static_cast<char>(bb);
             });
     }
-    bool match(const bpstd::string_view &a) override {
+    bool match(const bpstd::string_view &a) const override {
         return a.size() == m_key.size() && std::equal(a.begin(), a.end(),
             m_key.begin(),
             [](char aa, char bb) {
@@ -174,7 +174,7 @@ class KeyExclusions : public std::deque<std::unique_ptr<KeyExclusion>> {
         //}
     };
 
-    bool toOmit(const std::string &a) {
+    bool toOmit(const std::string &a) const {
         for (auto &z : *this) {
             if (z->match(a)) {
                 return true;
@@ -183,7 +183,7 @@ class KeyExclusions : public std::deque<std::unique_ptr<KeyExclusion>> {
         return false;
     }
 
-    bool toOmit(const bpstd::string_view &a) {
+    bool toOmit(const bpstd::string_view &a) const {
         for (auto &z : *this) {
             if (z->match(a)) {
                 return true;
@@ -206,7 +206,7 @@ class VariableMonkeyResolution {
         });
     }
 
-    static void stringMatchResolveMulti(Transaction *t,
+    static void stringMatchResolveMulti(const Transaction *t,
         const std::string &variable,
         VariableValues *l) {
         size_t collection = variable.find(".");
@@ -369,7 +369,7 @@ class VariableMonkeyResolution {
         }
     }
 
-    static std::string stringMatchResolve(Transaction *t,
+    static std::string stringMatchResolve(const Transaction *t,
         const std::string &variable) {
         std::unique_ptr<std::string> vv = nullptr;
         size_t collection = variable.find(".");
@@ -578,18 +578,18 @@ class Variable : public VariableMonkeyResolution {
 
 
     explicit Variable(Variable *var)
-        : m_keyWithCollection(var->m_keyWithCollection),
-        m_keyExclusion(var->m_keyExclusion),
-        m_collectionName(var->m_collectionName),
-        m_key(var->m_key)
+        : m_keyExclusion(var->m_keyExclusion),
+        m_keyWithCollection(var->m_keyWithCollection),
+        m_key(var->m_key),
+        m_collectionName(var->m_collectionName)
     { };
 
 
     Variable(const Variable &v)
-        : m_keyWithCollection(v.m_keyWithCollection),
-        m_keyExclusion(v.m_keyExclusion),
-        m_collectionName(v.m_collectionName),
-        m_key(v.m_key)
+        : m_keyExclusion(v.m_keyExclusion),
+        m_keyWithCollection(v.m_keyWithCollection),
+        m_key(v.m_key),
+        m_collectionName(v.m_collectionName)
     { };
 
 
@@ -597,8 +597,8 @@ class Variable : public VariableMonkeyResolution {
     { };
 
 
-    virtual void evaluate(Transaction *t,
-        VariableValues *l) = 0;
+    virtual void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept = 0;
 
 
     bool inline belongsToCollection(Variable *var) const noexcept {
@@ -748,8 +748,8 @@ class VariableModificatorExclusion : public Variable {
         : Variable(var.get()),
         m_base(std::move(var)) { }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
         m_base->evaluate(t, l);
     }
 
@@ -765,8 +765,8 @@ class VariableModificatorCount : public Variable {
             m_base.reset(var.release());
         }
 
-    void evaluate(Transaction *t,
-        VariableValues *l) override {
+    void evaluate(const Transaction *t,
+        VariableValues *l) const noexcept override {
 
         VariableValues reslIn;
         m_base->evaluate(t, &reslIn);
diff --git a/src/variables/web_app_id.h b/src/variables/web_app_id.h
index 2c60afd9..8b79c9b6 100644
--- a/src/variables/web_app_id.h
+++ b/src/variables/web_app_id.h
@@ -35,8 +35,8 @@ class WebAppId : public Variable {
     WebAppId()
         : Variable("WEBAPPID") { }
 
-    void evaluate(Transaction *transaction,
-        VariableValues *l) override {
+    void evaluate(const Transaction *transaction,
+        VariableValues *l) const noexcept override {
         const std::string rname = transaction->m_rules->m_secWebAppId.m_value;
         l->push_back(std::make_shared<VariableValue>(getVariableKeyWithCollection().get(), &rname));
     }
diff --git a/src/variables/xml.cc b/src/variables/xml.cc
index 534d2d30..b2c1de76 100644
--- a/src/variables/xml.cc
+++ b/src/variables/xml.cc
@@ -49,12 +49,12 @@ namespace modsecurity {
 namespace variables {
 
 #ifndef WITH_LIBXML2
-void XML_WithNSPath::evaluate(Transaction *t,
-    VariableValues *l) { }
+void XML_WithNSPath::evaluate(const Transaction *t,
+    VariableValues *l) const noexcept { }
 #else
 
-void XML_WithNSPath::evaluate(Transaction *t,
-    VariableValues *l) {
+void XML_WithNSPath::evaluate(const Transaction *t,
+    VariableValues *l) const noexcept {
     xmlXPathContextPtr xpathCtx;
     xmlXPathObjectPtr xpathObj;
     xmlNodeSetPtr nodes;
diff --git a/src/variables/xml.h b/src/variables/xml.h
index c081e5d4..fb23acac 100644
--- a/src/variables/xml.h
+++ b/src/variables/xml.h
@@ -50,8 +50,8 @@ class XML_WithoutNSPath : public RuleVariable, public Variable {
         m_var(r.m_var)
     { };
 
-    void evaluate(Transaction *transaction,
-        VariableValues *l) override {
+    void evaluate(const Transaction *transaction,
+        VariableValues *l) const noexcept override {
         l->push_back(m_var);
     }
 
@@ -75,8 +75,8 @@ class XML_WithNSPath : public RuleVariable, public VariableDictElement {
         VariableDictElement(r)
     { };
 
-    void evaluate(Transaction *transaction,
-        VariableValues *l) override;
+    void evaluate(const Transaction *transaction,
+        VariableValues *l) const noexcept override;
 
     virtual Variable *clone() override {
         return new XML_WithNSPath(*this);