esp-idf-json

Example of JSON Serialize and Deserialize with ESP-IDF.

ESP-IDF includes this cJSON library.
You can use JSON components as standard.
But the documentation is very poor.
The official documentation for the JSON component is here.

Here is a example by Dave Gamble.

How to use

git clone https://github.com/nopnop2002/esp-idf-json
cd esp-idf-json/json-basic-object
idf.py flash monitor

About cJSON_Print

From print_value() function, the pointer returned is allocated by cJSON_strdup() and it is returned to the caller.
Buffers returned by cJSON_Print must be freed by the caller.
Please use the proper API (cJSON_free) rather than directly calling stdlib free.

char *my_json_string = cJSON_Print(root);
ESP_LOGI(TAG, "my_json_string\n%s",my_json_string);
cJSON_Delete(root);
cJSON_free(my_json_string);

Basic Structure

• Array
  Array, like this, have no name.
  Array starts with [ and ends with ].
  root is defined by cJSON_CreateArray.
  element is added by cJSON_AddItemToArray.

   ["abc", 123, true, false, null]
  

• Object
  Object, like this, have name.
  Object starts with { and ends with }.
  root is defined by cJSON_CreateObject.
  element is added by cJSON_AddItemToObject.

   {
           "version":      "v5.0-dev-3202-ga2d5041492-dirty",
           "cores":        2,
   }
  

Complex structure

• Object in Array

   ["abc", 123, true, false, null, {
                   "version":      "v5.0-dev-3202-ga2d5041492-dirty",
                   "cores":        2
           }]
  

   [{
                   "id":   0,
                   "version":      "v5.0-dev-3202-ga2d5041492-dirty",
                   "cores":        2
           }, {
                   "id":   1,
                   "version":      "v5.0-dev-3202-ga2d5041492-dirty",
                   "cores":        2
           }]
  

• Array in Array

   [["abc", 120], ["abc", 121], ["abc", 122], ["abc", 123], ["abc", 124], ["abc", 125], ["abc", 126], ["abc", 127], ["abc", 128], ["abc", 129]]
  

• Object in Object

   {
           "name": "Jack (\"Bee\") Nimble",
           "format":       {
                   "type": "rect",
                   "width":        1920,
                   "height":       1080,
                   "interlace":    false,
                   "frame rate":   24
           }
   }
  

• Array in Object

   {
           "version":      "v5.0-dev-3202-ga2d5041492-dirty",
           "cores":        2,
           "array":        ["abc", 123, true, false, null]
   }
  

More Complex structure

• Object in Array in Object

   {
           "version":      "v5.0-dev-3202-ga2d5041492-dirty",
           "cores":        2,
           "array":  [{
                           "width":        1280,
                           "height":       720
                   }, {
                           "width":        1920,
                           "height":       1080
                   }, {
                           "width":        3840,
                           "height":       2160
                   }]
   }
  

• Array in Object in Array

   [{
                   "id":   0,
                   "version":      "v5.0-dev-3202-ga2d5041492-dirty",
                   "cores":        2,
                   "array":        ["abc", 123, true, false, null]
           }, {
                   "id":   1,
                   "version":      "v5.0-dev-3202-ga2d5041492-dirty",
                   "cores":        2,
                   "array":        ["abc", 123, true, false, null]
           }]
  

How to Serialize

Serialization starts from the lowest level.
No matter how complex the structure, there are only objects and arrays.

• Target structure

   {
           "version":      "v5.0-dev-3202-ga2d5041492-dirty",
           "cores":        2,
           "array":  [{
                           "width":        1280,
                           "height":       720
                   }, {
                           "width":        1920,
                           "height":       1080
                   }, {
                           "width":        3840,
                           "height":       2160
                   }]
   }
  

  • Create 3 objects
    This is simple object.

                     {
                             "width":        1280,
                             "height":       720
                     }
    

                     {
                             "width":        1920,
                             "height":       1080
                     }
    

                     {
                             "width":        3840,
                             "height":       2160
                     }
    
    

  • Create array
    This is object in array.

                    [{
                             "width":        1280,
                             "height":       720
                     }, {
                             "width":        1920,
                             "height":       1080
                     }, {
                             "width":        3840,
                             "height":       2160
                     }]
    

  • Create object as root
    This is array in object.

     {
             "version":      "v5.0-dev-3202-ga2d5041492-dirty",
             "cores":        2,
             "array":  [{
                             "width":        1280,
                             "height":       720
                     }, {
                             "width":        1920,
                             "height":       1080
                     }, {
                             "width":        3840,
                             "height":       2160
                     }]
     }
    

• Target structure

   [{
                   "id":   0,
                   "version":      "v5.0-dev-3202-ga2d5041492-dirty",
                   "cores":        2,
                   "array":        ["abc", 123, true, false, null]
           }, {
                   "id":   1,
                   "version":      "v5.0-dev-3202-ga2d5041492-dirty",
                   "cores":        2,
                   "array":        ["abc", 123, true, false, null]
           }]
  

  • Create 2 arrays
    This is simple array.

     ["abc", 123, true, false, null]
    

     ["abc", 123, true, false, null]
    

  • Create 2 objects
    This is array in object.

             {
                     "id":   1,
                     "version":      "v5.0-dev-3202-ga2d5041492-dirty",
                     "cores":        2,
                     "array":        ["abc", 123, true, false, null]
             }
    

             {
                     "id":   0,
                     "version":      "v5.0-dev-3202-ga2d5041492-dirty",
                     "cores":        2,
                     "array":        ["abc", 123, true, false, null]
             }
    

  • Create array as root
    This is object in array.

     [{
                     "id":   0,
                     "version":      "v5.0-dev-3202-ga2d5041492-dirty",
                     "cores":        2,
                     "array":        ["abc", 123, true, false, null]
             }, {
                     "id":   1,
                     "version":      "v5.0-dev-3202-ga2d5041492-dirty",
                     "cores":        2,
                     "array":        ["abc", 123, true, false, null]
             }]
    

JSON Data Set Sample

This is a sample JSON data set.
https://opensource.adobe.com/Spry/samples/data_region/JSONDataSetSample.html