Implement a new way of unpacking json to structs

The existing way of decoding json structures, while fast has some disadvantages.
1. it's very verbose to write.
2. It requires in depth knowlege of redfish error messages to get
correct.
3. It _can_ lead to undesired behavior, like half of a patch being
applied, if only some of the values have bad types.

This commit implements a new interface for decoding redfish json
named.... readJson.  It is a templated function, that lets you decode
json values based on type easily, while still handling all the correct
error codes that were handled previously.  Use is done similar to the
example below:

std::string required;
boost::optional<std::string> optional;
if (!json_util::readJson(req, res, "OptionalParam", optional,
"RequiredParam", required))
{
    return;
}

if (optional){
   //  optional param was given, take action.
}

As part of this patchset, the systems schema is moved to the new
interface, which deletes some of the code involved and shows the
improvement in clarity.

Change-Id: I041a97c84d294df8cd4de4c2702e5ee22c0bc120
Signed-off-by: Ed Tanous <ed.tanous@intel.com>

1 files changed, 122 insertions, 2 deletions

diff --git a/redfish-core/include/utils/json_utils.hpp b/redfish-core/include/utils/json_utils.hpp
index bde81ce..3263c73 100644
--- a/redfish-core/include/utils/json_utils.hpp
+++ b/redfish-core/include/utils/json_utils.hpp
@@ -14,11 +14,13 @@
 // limitations under the License.
 */
 #pragma once
+
 #include <crow/http_request.h>
 #include <crow/http_response.h>
 
+#include <bitset>
+#include <error_messages.hpp>
 #include <nlohmann/json.hpp>
-
 namespace redfish
 {
 
@@ -296,7 +298,125 @@ Result getDouble(const char* fieldName, const nlohmann::json& json,
  */
 bool processJsonFromRequest(crow::Response& res, const crow::Request& req,
                             nlohmann::json& reqJson);
+namespace details
+{
+template <typename Type> struct unpackValue
+{
+    using isRequired = std::true_type;
+    using JsonType = std::add_const_t<std::add_pointer_t<Type>>;
+};
 
-} // namespace json_util
+template <typename OptionalType>
+struct unpackValue<boost::optional<OptionalType>>
+{
+    using isRequired = std::false_type;
+    using JsonType = std::add_const_t<std::add_pointer_t<OptionalType>>;
+};
+
+template <size_t Count, size_t Index>
+void readJsonValues(const std::string& key, nlohmann::json& jsonValue,
+                    crow::Response& res, std::bitset<Count>& handled)
+{
+    BMCWEB_LOG_DEBUG << "Unable to find variable for key" << key;
+    messages::addMessageToErrorJson(res.jsonValue,
+                                    messages::propertyUnknown(key));
+    res.result(boost::beast::http::status::bad_request);
+}
+
+template <size_t Count, size_t Index, typename ValueType,
+          typename... UnpackTypes>
+void readJsonValues(const std::string& key, nlohmann::json& jsonValue,
+                    crow::Response& res, std::bitset<Count>& handled,
+                    const char* keyToCheck, ValueType& valueToFill,
+                    UnpackTypes&... in)
+{
+    if (key != keyToCheck)
+    {
+        readJsonValues<Count, Index + 1>(key, jsonValue, res, handled, in...);
+        return;
+    }
+
+    handled.set(Index);
+
+    using UnpackType = typename unpackValue<ValueType>::JsonType;
+    UnpackType value = jsonValue.get_ptr<UnpackType>();
+    if (value == nullptr)
+    {
+        BMCWEB_LOG_DEBUG << "Value for key " << key
+                         << " was incorrect type: " << jsonValue.type_name();
+        messages::addMessageToErrorJson(
+            res.jsonValue,
+            messages::propertyValueTypeError(jsonValue.dump(), key));
+        res.result(boost::beast::http::status::bad_request);
 
+        return;
+    }
+
+    valueToFill = *value;
+}
+
+template <size_t Index = 0, size_t Count>
+void handleMissing(std::bitset<Count>& handled, crow::Response& res)
+{
+}
+
+template <size_t Index = 0, size_t Count, typename ValueType,
+          typename... UnpackTypes>
+void handleMissing(std::bitset<Count>& handled, crow::Response& res,
+                   const char* key, ValueType& unused, UnpackTypes&... in)
+{
+    if (!handled.test(Index) && unpackValue<ValueType>::isRequired::value)
+    {
+        messages::addMessageToErrorJson(res.jsonValue,
+                                        messages::propertyMissing(key));
+        res.result(boost::beast::http::status::bad_request);
+    }
+    details::handleMissing<Index + 1, Count>(handled, res, in...);
+}
+} // namespace details
+
+template <typename... UnpackTypes>
+bool readJson(const crow::Request& req, crow::Response& res, const char* key,
+              UnpackTypes&... in)
+{
+    nlohmann::json jsonRequest;
+    if (!json_util::processJsonFromRequest(res, req, jsonRequest))
+    {
+        BMCWEB_LOG_DEBUG << "Json value not readable";
+        return false;
+    }
+    if (!jsonRequest.is_object())
+    {
+        BMCWEB_LOG_DEBUG << "Json value is not an object";
+        messages::addMessageToErrorJson(res.jsonValue,
+                                        messages::unrecognizedRequestBody());
+        res.result(boost::beast::http::status::bad_request);
+        return false;
+    }
+
+    if (jsonRequest.empty())
+    {
+        BMCWEB_LOG_DEBUG << "Json value is empty";
+        messages::addMessageToErrorJson(res.jsonValue, messages::emptyJSON());
+        res.result(boost::beast::http::status::bad_request);
+        return false;
+    }
+
+    std::bitset<(sizeof...(in) + 1) / 2> handled(0);
+    for (const auto& item : jsonRequest.items())
+    {
+        details::readJsonValues<(sizeof...(in) + 1) / 2, 0, UnpackTypes...>(
+            item.key(), item.value(), res, handled, key, in...);
+    }
+
+    if (!handled.all())
+    {
+        details::handleMissing(handled, res, key, in...);
+
+        return false;
+    }
+    return res.result() == boost::beast::http::status::ok;
+}
+
+} // namespace json_util
 } // namespace redfish