core: reimplement logging using ndn-cxx's facility

Change-Id: Ifc7c5d70a61ad405dc1f1adfa522a2c0ad1586ab
Refs: #4580
diff --git a/core/log-config-section.cpp b/core/log-config-section.cpp
new file mode 100644
index 0000000..6f6f0ab
--- /dev/null
+++ b/core/log-config-section.cpp
@@ -0,0 +1,96 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2014-2018,  Regents of the University of California,
+ *                           Arizona Board of Regents,
+ *                           Colorado State University,
+ *                           University Pierre & Marie Curie, Sorbonne University,
+ *                           Washington University in St. Louis,
+ *                           Beijing Institute of Technology,
+ *                           The University of Memphis.
+ *
+ * This file is part of NFD (Named Data Networking Forwarding Daemon).
+ * See AUTHORS.md for complete list of NFD authors and contributors.
+ *
+ * NFD is free software: you can redistribute it and/or modify it under the terms
+ * of the GNU General Public License as published by the Free Software Foundation,
+ * either version 3 of the License, or (at your option) any later version.
+ *
+ * NFD 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
+ * NFD, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "log-config-section.hpp"
+
+#include <ndn-cxx/util/logger.hpp>
+#include <ndn-cxx/util/logging.hpp>
+
+namespace nfd {
+namespace log {
+
+static ndn::util::LogLevel
+parseLogLevel(const ConfigSection& item, const std::string& key)
+{
+  try {
+    return ndn::util::parseLogLevel(item.get_value<std::string>());
+  }
+  catch (const std::invalid_argument& e) {
+    BOOST_THROW_EXCEPTION(ConfigFile::Error("Invalid setting for log." + key + ": " + e.what()));
+  }
+}
+
+static void
+onConfig(const ConfigSection& section, bool isDryRun, const std::string&)
+{
+  // log
+  // {
+  //   ; default_level specifies the logging level for modules
+  //   ; that are not explicitly named. All debugging levels
+  //   ; listed above the selected value are enabled.
+  //
+  //   default_level INFO
+  //
+  //   ; You may also override the default for specific modules:
+  //
+  //   FibManager DEBUG
+  //   Forwarder WARN
+  // }
+
+  auto defaultLevel = ndn::util::LogLevel::INFO;
+  auto item = section.get_child_optional("default_level");
+  if (item) {
+    defaultLevel = parseLogLevel(*item, "default_level");
+  }
+  if (!isDryRun) {
+    // default_level applies only to NFD loggers
+    ndn::util::Logging::setLevel("nfd.*", defaultLevel);
+  }
+
+  for (const auto& i : section) {
+    if (i.first == "default_level") {
+      // do nothing
+    }
+    else {
+      auto level = parseLogLevel(i.second, i.first);
+      if (!isDryRun) {
+        if (i.first.find('.') == std::string::npos)
+          // backward compat: assume unqualified logger names refer to NFD loggers
+          ndn::util::Logging::setLevel("nfd." + i.first, level);
+        else
+          ndn::util::Logging::setLevel(i.first, level);
+      }
+    }
+  }
+}
+
+void
+setConfigFile(ConfigFile& config)
+{
+  config.addSectionHandler("log", &onConfig);
+}
+
+} // namespace log
+} // namespace nfd