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+/*
+ * This file is part of PowerDNS or dnsdist.
+ * Copyright -- PowerDNS.COM B.V. and its contributors
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * In addition, for the avoidance of any doubt, permission is granted to
+ * link this program with OpenSSL and to (re)distribute the binaries
+ * produced as the result of such linking.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#pragma once
+
+#include "config.h"
+
+#ifdef RECURSOR
+
+#include <map>
+#include <memory>
+#include <string>
+#include <sstream>
+#include <boost/optional.hpp>
+
+#include "logr.hh"
+#include "dnsname.hh"
+#include "iputils.hh"
+
+namespace Logging
+{
+
+struct Entry
+{
+  boost::optional<std::string> name; // name parts joined with '.'
+  std::string message; // message as send to log call
+  boost::optional<std::string> error; // error if .Error() was called
+  struct timeval d_timestamp; // time of entry generation
+  std::map<std::string, std::string> values; // key-value pairs
+  size_t level; // level at which this was logged
+  Logr::Priority d_priority; // (syslog) priority)
+};
+
+// Warning: some meta-programming is going on.  We define helper
+// templates that can be used to see if specific string output
+// functions are available.  If so, we use those instead of << into an
+// ostringstream. Note that this decision happpens compile time.
+// Some hints taken from https://www.cppstories.com/2019/07/detect-overload-from-chars/
+// (I could not get function templates with enabled_if<> to work in this case)
+//
+// Default: std::string(T) is not available
+template <typename T, typename = void>
+struct is_to_string_available : std::false_type
+{
+};
+
+// If std::string(T) is available this template is used
+template <typename T>
+struct is_to_string_available<T, std::void_t<decltype(std::to_string(std::declval<T>()))>> : std::true_type
+{
+};
+
+// Same mechanism for t.toLogString()
+template <typename T, typename = void>
+struct is_toLogString_available : std::false_type
+{
+};
+
+template <typename T>
+struct is_toLogString_available<T, std::void_t<decltype(std::declval<T>().toLogString())>> : std::true_type
+{
+};
+
+template <typename T, typename = void>
+struct is_toString_available : std::false_type
+{
+};
+
+template <typename T>
+struct is_toString_available<T, std::void_t<decltype(std::declval<T>().toString())>> : std::true_type
+{
+};
+
+template <typename T>
+struct Loggable : public Logr::Loggable
+{
+  const T& _t;
+  Loggable(const T& v) :
+    _t(v)
+  {
+  }
+  std::string to_string() const
+  {
+    if constexpr (std::is_same_v<T, std::string>) {
+      return _t;
+    }
+    else if constexpr (is_toLogString_available<T>::value) {
+      return _t.toLogString();
+    }
+    else if constexpr (is_toString_available<T>::value) {
+      return _t.toString();
+    }
+    else if constexpr (is_to_string_available<T>::value) {
+      return std::to_string(_t);
+    }
+    else {
+      std::ostringstream oss;
+      oss << _t;
+      return oss.str();
+    }
+  }
+};
+
+template <typename T>
+struct IterLoggable : public Logr::Loggable
+{
+  const T& _t1;
+  const T& _t2;
+  IterLoggable(const T& v1, const T& v2) :
+    _t1(v1), _t2(v2)
+  {
+  }
+  std::string to_string() const
+  {
+    std::ostringstream oss;
+    bool first = true;
+    for (auto i = _t1; i != _t2; i++) {
+      if (!first) {
+        oss << ' ';
+      }
+      else {
+        first = false;
+      }
+      oss << *i;
+    }
+    return oss.str();
+  }
+};
+
+typedef void (*EntryLogger)(const Entry&);
+
+class Logger : public Logr::Logger, public std::enable_shared_from_this<const Logger>
+{
+public:
+  bool enabled(Logr::Priority) const override;
+
+  void info(const std::string& msg) const override;
+  void info(Logr::Priority, const std::string& msg) const override;
+  void error(int err, const std::string& msg) const override;
+  void error(const std::string& err, const std::string& msg) const override;
+  void error(Logr::Priority, int err, const std::string& msg) const override;
+  void error(Logr::Priority, const std::string& err, const std::string& msg) const override;
+
+  std::shared_ptr<Logr::Logger> v(size_t level) const override;
+  std::shared_ptr<Logr::Logger> withValues(const std::map<std::string, std::string>& values) const override;
+  virtual std::shared_ptr<Logr::Logger> withName(const std::string& name) const override;
+
+  static std::shared_ptr<Logger> create(EntryLogger callback);
+  static std::shared_ptr<Logger> create(EntryLogger callback, const std::string& name);
+
+  Logger(EntryLogger callback);
+  Logger(EntryLogger callback, boost::optional<std::string> name);
+  Logger(std::shared_ptr<const Logger> parent, boost::optional<std::string> name, size_t verbosity, size_t lvl, EntryLogger callback);
+  virtual ~Logger();
+
+  size_t getVerbosity() const;
+  void setVerbosity(size_t verbosity);
+
+private:
+  void logMessage(const std::string& msg, boost::optional<const std::string> err) const;
+  void logMessage(const std::string& msg, Logr::Priority p, boost::optional<const std::string> err) const;
+  std::shared_ptr<const Logger> getptr() const;
+
+  std::shared_ptr<const Logger> _parent{nullptr};
+  EntryLogger _callback;
+  boost::optional<std::string> _name;
+  std::map<std::string, std::string> _values;
+  // current Logger's level. the higher the more verbose.
+  size_t _level{0};
+  // verbosity settings. messages with level higher's than verbosity won't appear
+  size_t _verbosity{0};
+};
+}
+
+extern std::shared_ptr<Logging::Logger> g_slog;
+
+// Prefer structured logging?
+extern bool g_slogStructured;
+
+// A helper macro to switch between old-style logging and new-style (structured logging)
+// A typical use:
+//
+// SLOG(g_log<<Logger::Warning<<"Unable to parse configuration file '"<<configname<<"'"<<endl,
+//      startupLog->error("No such file", "Unable to parse configuration file", "config_file", Logging::Loggable(configname));
+//
+#define SLOG(oldStyle, slogCall) \
+  do {                           \
+    if (g_slogStructured) {      \
+      slogCall;                  \
+    }                            \
+    else {                       \
+      oldStyle;                  \
+    }                            \
+  } while (0);
+
+#else // No structured logging (e.g. auth)
+#define SLOG(oldStyle, slogCall) \
+  do {                           \
+    oldStyle;                    \
+  } while (0);
+#endif // RECURSOR