[json] Port json parser from swssconfig to swss-common so that other

component can take advantage of this tool

Author: Stephen Sun

common/json.cpp

@@ -1,4 +1,7 @@
+#include <stdlib.h>
 #include <sstream>
+#include <fstream>
+#include <iostream>
 #include <limits>
 
 #include "common/json.h"
@@ -36,4 +39,63 @@ void JSon::readJson(const string &jsonstr, vector<FieldValueTuple> &fv)
     }
 }
 
+bool JSon::loadJsonFromFile(ifstream &fs, vector<KeyOpFieldsValuesTuple> &db_items)
+{
+    nlohmann::json json_array;
+    fs >> json_array;
+
+    if (!json_array.is_array())
+    {
+        SWSS_LOG_ERROR("Root element must be an array.");
+        return false;
+    }
+
+    for (size_t i = 0; i < json_array.size(); i++)
+    {
+        auto &arr_item = json_array[i];
+
+        if (arr_item.is_object())
+        {
+            if (el_count != arr_item.size())
+            {
+                SWSS_LOG_ERROR("Chlid elements must have both key and op entry. %s",
+                               arr_item.dump().c_str());
+                return false;
+            }
+
+            db_items.push_back(KeyOpFieldsValuesTuple());
+            auto &cur_db_item = db_items[db_items.size() - 1];
+
+            for (nlohmann::json::iterator child_it = arr_item.begin(); child_it != arr_item.end(); child_it++) {
+                auto cur_obj_key = child_it.key();
+                auto &cur_obj = child_it.value();
+
+                if (cur_obj.is_object()) {
+                    kfvKey(cur_db_item) = cur_obj_key;
+                    for (nlohmann::json::iterator cur_obj_it = cur_obj.begin(); cur_obj_it != cur_obj.end(); cur_obj_it++)
+                    {
+                        string field_str = cur_obj_it.key();
+                        string value_str;
+                        if ((*cur_obj_it).is_number())
+                            value_str = to_string((*cur_obj_it).get<int>());
+                        else if ((*cur_obj_it).is_string())
+                            value_str = (*cur_obj_it).get<string>();
+                        kfvFieldsValues(cur_db_item).push_back(FieldValueTuple(field_str, value_str));
+                    }
+                }
+                else
+                {
+                    kfvOp(cur_db_item) = cur_obj.get<string>();
+                }
+            }
+        }
+        else
+        {
+            SWSS_LOG_ERROR("Child elements must be objects. element:%s", arr_item.dump().c_str());
+            return false;
+        }
+    }
+    return true;
+}
+
 }

common/json.h

@@ -2,6 +2,7 @@
 #define __JSON__
 
 #include <string>
+#include <fstream>
 #include <vector>
 
 #include "table.h"
@@ -10,9 +11,12 @@ namespace swss {
 
 class JSon
 {
+private:
+    static const int el_count = 2;
 public:
-   static std::string buildJson(const std::vector<FieldValueTuple> &fv);
-   static void readJson(const std::string &json, std::vector<FieldValueTuple> &fv);
+    static std::string buildJson(const std::vector<FieldValueTuple> &fv);
+    static void readJson(const std::string &json, std::vector<FieldValueTuple> &fv);
+    static bool loadJsonFromFile(std::ifstream &fs, std::vector<KeyOpFieldsValuesTuple> &db_items);
 };
 
 }