entitymap: add json file loading if present

Step 3 to handle the entity-map transition from YAML to JSON.  This
patchset adds a method that will process the json file, if present to
build the map.

Tested: This patchset has not been tested.
Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I79297aef59844a21f20c0a77de7a21264e2ed96a

1 files changed, 22 insertions, 0 deletions

diff --git a/entity_map_json.cpp b/entity_map_json.cpp
index db45b05..b6fc6d6 100644
--- a/entity_map_json.cpp
+++ b/entity_map_json.cpp
@@ -1,6 +1,7 @@
 #include "entity_map_json.hpp"
 
 #include <exception>
+#include <fstream>
 #include <ipmid/types.hpp>
 #include <nlohmann/json.hpp>
 #include <string>
@@ -11,6 +12,27 @@ namespace ipmi
 namespace sensor
 {
 
+EntityInfoMap buildEntityMapFromFile()
+{
+    const char* entityMapJsonFilename =
+        "/usr/share/ipmi-providers/entity-map.json";
+    EntityInfoMap builtMap;
+
+    std::ifstream mapFile(entityMapJsonFilename);
+    if (!mapFile.is_open())
+    {
+        return builtMap;
+    }
+
+    auto data = nlohmann::json::parse(mapFile, nullptr, false);
+    if (data.is_discarded())
+    {
+        return builtMap;
+    }
+
+    return buildJsonEntityMap(data);
+}
+
 EntityInfoMap buildJsonEntityMap(const nlohmann::json& data)
 {
     EntityInfoMap builtMap;