Add persistency for events

Persist event D-bus objects using cereal

Resolves openbmc/openbmc#2319

Change-Id: Ifa15d944fe1d1026761f65eeb647dcbdf6afdba0
Signed-off-by: Dhruvaraj Subhashchandran <dhruvaraj@in.ibm.com>
diff --git a/src/event_serialize.cpp b/src/event_serialize.cpp
new file mode 100644
index 0000000..c7e78d9
--- /dev/null
+++ b/src/event_serialize.cpp
@@ -0,0 +1,97 @@
+#include <cereal/types/string.hpp>
+#include <cereal/types/vector.hpp>
+#include <cereal/archives/binary.hpp>
+#include <fstream>
+
+#include "event_serialize.hpp"
+#include <phosphor-logging/log.hpp>
+#include "config.h"
+
+// Register class version
+// From cereal documentation;
+// "This macro should be placed at global scope"
+CEREAL_CLASS_VERSION(phosphor::events::Entry, CLASS_VERSION);
+
+namespace phosphor
+{
+namespace events
+{
+
+using namespace phosphor::logging;
+
+/** @brief Function required by Cereal to perform serialization.
+ *  @tparam Archive - Cereal archive type (binary in our case).
+ *  @param[in] archive - reference to Cereal archive.
+ *  @param[in] event - const reference to event entry.
+ *  @param[in] version - Class version that enables handling
+ *                       a serialized data across code levels
+ */
+template <class Archive>
+void save(Archive& archive, const Entry& event, const std::uint32_t version)
+{
+    archive(event.timestamp(), event.message(), event.additionalData());
+}
+
+/** @brief Function required by Cereal to perform deserialization.
+ *  @tparam Archive - Cereal archive type (binary in our case).
+ *  @param[in] archive - reference to Cereal archive.
+ *  @param[in] event - reference to event entry.
+ *  @param[in] version - Class version that enables handling
+ *                       a serialized data across code levels
+ */
+template <class Archive>
+void load(Archive& archive, Entry& event, const std::uint32_t version)
+{
+    using namespace sdbusplus::xyz::openbmc_project::Logging::server;
+
+    uint64_t timestamp{};
+    std::string message{};
+    std::vector<std::string> additionalData{};
+
+    archive(timestamp, message, additionalData);
+
+    event.timestamp(timestamp);
+    event.message(message);
+    event.additionalData(additionalData);
+}
+
+fs::path serialize(const Entry& event, const std::string& eventName)
+{
+    fs::path dir(EVENTS_PERSIST_PATH);
+    auto path = dir / eventName;
+    fs::create_directories(path);
+    path /= std::to_string(event.timestamp());
+    std::ofstream os(path.string(), std::ios::binary);
+    cereal::BinaryOutputArchive oarchive(os);
+    oarchive(event);
+    return path;
+}
+
+bool deserialize(const fs::path& path, Entry& event)
+{
+    try
+    {
+        if (fs::exists(path))
+        {
+            std::ifstream is(path.c_str(), std::ios::in | std::ios::binary);
+            cereal::BinaryInputArchive iarchive(is);
+            iarchive(event);
+            return true;
+        }
+        return false;
+    }
+    catch (cereal::Exception& e)
+    {
+        log<level::ERR>(e.what());
+        std::error_code ec;
+        fs::remove(path, ec);
+        return false;
+    }
+    catch (const fs::filesystem_error& e)
+    {
+        return false;
+    }
+}
+
+} // namespace event
+} // namespace phosphor