json: Added nlohmann's JSON C++ header

Adding JSON header for serializing/deserializing library descriptor JSON
files.

    * Added header
    * Added simple unit test to verify functionality

Signed-off-by: Noel Eck <noel.eck@intel.com>

CMakeLists.txt

@@ -489,4 +489,4 @@ endif()
 # Install C headers
 install(DIRECTORY include/ DESTINATION include/upm
     COMPONENT ${CMAKE_PROJECT_NAME}-dev
-    FILES_MATCHING PATTERN "*.h")
+    FILES_MATCHING PATTERN "*.h" PATTERN "*.hpp")

tests/unit/CMakeLists.txt

@@ -7,6 +7,13 @@ if(NOT GTEST_FOUND)
     return ()
 endif()
 
+# Unit tests - utilities library
 add_executable(utilities_tests utilities/utilities_tests.cxx)
 target_link_libraries(utilities_tests utilities GTest::GTest GTest::Main)
 gtest_add_tests(utilities_tests "" AUTO)
+
+# Unit tests - Json header
+add_executable(json_tests json/json_tests.cxx)
+target_link_libraries(json_tests GTest::GTest GTest::Main)
+target_include_directories(json_tests PRIVATE "${UPM_COMMON_HEADER_DIRS}/")
+gtest_add_tests(json_tests "" AUTO)

tests/unit/json/json_tests.cxx

@@ -0,0 +1,86 @@
+#include "gtest/gtest.h"
+#include "external/json/json.hpp"
+
+namespace
+{
+    class source
+    {
+        public:
+            std::string unit;
+            float max;
+            float min;
+            float accuracy;
+    };
+
+    void to_json(nlohmann::json& j, const source& p) {
+        j = nlohmann::json{
+            {"unit", p.unit},
+                {"min", p.min},
+                {"max", p.max},
+                {"accuracy", p.accuracy}};
+    }
+
+    void from_json(const nlohmann::json& j, source& p) {
+        p.unit = j.at("unit").get<std::string>();
+        p.min = j.at("min").get<float>();
+        p.max = j.at("max").get<float>();
+        p.accuracy = j.at("accuracy").get<float>();
+    }
+
+    bool operator==(const source& lhs, const source& rhs)
+    {
+        return lhs.unit == rhs.unit && lhs.min == rhs.min;
+    }
+}
+
+/* Json test fixture */
+class json_unit : public ::testing::Test
+{
+    protected:
+        /* One-time setup logic if needed */
+        json_unit() {}
+
+        /* One-time tear-down logic if needed */
+        virtual ~json_unit() {}
+
+        /* Per-test setup logic if needed */
+        virtual void SetUp() {}
+
+        /* Per-test tear-down logic if needed */
+        virtual void TearDown() {}
+};
+
+/* Test basic json serialization */
+TEST_F(json_unit, test_basic_class_serialization)
+{
+    source s_temp {"C", -40.0, 85.0, 1.0};
+    source s_humi {"%", 0.0, 100.0, 1.0};
+
+    /* Create the json objects */
+    nlohmann::json j_temp = s_temp;
+    nlohmann::json j_humi = s_humi;
+
+    /* Serialize/deserialize the originals */
+    source clone_temp = j_temp;
+    source clone_humi = j_humi;
+    ASSERT_EQ(s_temp, clone_temp);
+
+    /* Populate an stl container */
+    std::map<std::string, source> sources;
+    sources["temperature"] = s_temp;
+    sources["humidity-relative"] = s_humi;
+
+    /* Create the json object */
+    nlohmann::json j_sources = sources;
+
+    /* Serialize/deserialize the container */
+    std::map<std::string, source> clone_sources = j_sources;
+    ASSERT_EQ(sources, j_sources);
+}
+
+/* Currently no need for a custom main (use gtest's)
+int main(int argc, char **argv) {
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}
+*/