Add support for log-handler

This handler is based off of version handler with major differences in
handler_builder

Tested:
created the blackbox blob successfully using this lib.
Read the data from the blob using a host side tool

Signed-off-by: Gaurav Gandhi <gauravgandhi@google.com>
Change-Id: I9ef775af752156a1647453ff3831ef4c0449d546
diff --git a/bmc/log-handler/log_handlers_builder.cpp b/bmc/log-handler/log_handlers_builder.cpp
new file mode 100644
index 0000000..2781534
--- /dev/null
+++ b/bmc/log-handler/log_handlers_builder.cpp
@@ -0,0 +1,125 @@
+// Copyright 2021 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "log_handlers_builder.hpp"
+
+#include "file_handler.hpp"
+#include "fs.hpp"
+#include "skip_action.hpp"
+
+#include <nlohmann/json.hpp>
+
+#include <algorithm>
+#include <cstdio>
+#include <exception>
+#include <fstream>
+#include <memory>
+#include <regex>
+#include <string>
+#include <vector>
+
+namespace ipmi_flash
+{
+
+std::vector<HandlerConfig<LogBlobHandler::ActionPack>>
+    LogHandlersBuilder::buildHandlerFromJson(const nlohmann::json& data)
+{
+    std::vector<HandlerConfig<LogBlobHandler::ActionPack>> handlers;
+
+    for (const auto& item : data)
+    {
+        try
+        {
+            HandlerConfig<LogBlobHandler::ActionPack> output;
+
+            /* at() throws an exception when the key is not present. */
+            item.at("blob").get_to(output.blobId);
+
+            /* name must be: /log/ */
+            std::regex regexpr("^\\/(?:log)\\/(.+)");
+            std::smatch matches;
+            if (!std::regex_search(output.blobId, matches, regexpr))
+            {
+                continue;
+            }
+            /* log must have handler */
+            const auto& h = item.at("handler");
+
+            const std::string& handlerType = h.at("type");
+            if (handlerType == "file")
+            {
+                const auto& path = h.at("path");
+                output.handler = std::make_unique<FileHandler>(path);
+            }
+            else
+            {
+                throw std::runtime_error("Invalid handler type: " +
+                                         handlerType);
+            }
+
+            /* actions are required (presently). */
+            const auto& a = item.at("actions");
+            auto pack = std::make_unique<LogBlobHandler::ActionPack>();
+
+            /* to make an action optional, assign type "skip" */
+            const auto& onOpen = a.at("open");
+            const std::string& onOpenType = onOpen.at("type");
+            if (onOpenType == "systemd")
+            {
+                pack->onOpen = std::move(buildSystemd(onOpen));
+            }
+            else if (onOpenType == "skip")
+            {
+                pack->onOpen = SkipAction::CreateSkipAction();
+            }
+            else
+            {
+                throw std::runtime_error("Invalid preparation type: " +
+                                         onOpenType);
+            }
+
+            const auto& onDelete = a.at("delete");
+            const std::string& onDeleteType = onOpen.at("type");
+            if (onOpenType == "systemd")
+            {
+                pack->onDelete = std::move(buildSystemd(onDelete));
+            }
+            else if (onOpenType == "skip")
+            {
+                pack->onDelete = SkipAction::CreateSkipAction();
+            }
+            else
+            {
+                throw std::runtime_error("Invalid preparation type: " +
+                                         onDeleteType);
+            }
+
+            output.actions = std::move(pack);
+            handlers.push_back(std::move(output));
+        }
+        catch (const std::exception& e)
+        {
+            /* TODO: Once phosphor-logging supports unit-test injection, fix
+             * this to log.
+             */
+            std::fprintf(stderr,
+                         "Excepted building HandlerConfig from json: %s\n",
+                         e.what());
+        }
+    }
+
+    return handlers;
+}
+
+} // namespace ipmi_flash