Problem with nested objects

[bcatalin]

Hi,

I have a issue reading (or writing) a nested JSON on an ESP8266.
What I try to have is a file is [ {"m":1, "h":2} , {"m":10, "h":20} , {"m":100, "h":200} ]

I am using SPIFFS to write the JSON to a file then to read it.

For one object is working fine, but for nested array does not working at all.

Code below:

Not working case:

#include <ESP8266WiFi.h>
#include <ESP8266WebServer.h>
#include <ArduinoJson.h>
#include "FS.h"

void setup() {
// put your setup code here, to run once:
Serial.begin(115200);
delay(2000);
int i=0;
if( SPIFFS.begin() )
{
File my_file = SPIFFS.open("xfile.json", "w");
if (!my_file) {
Serial.println("failed to open xfile.json file for writing :-(");
return; //==============>
}
StaticJsonBuffer<300> jsonBuffer;
JsonArray& my_array = jsonBuffer.createArray();
for(i=0;i<3;i++)
{
JsonObject& my_entry = my_array.createNestedObject();
my_entry["m"] = 20;
my_entry["h"] = 14;
}
my_array.printTo(Serial);
Serial.println("");
my_array.printTo(my_file);
my_file.close();
delay(1000);
//---------------------------- READ ----------------------------------
File myFile = SPIFFS.open("xfile.json", "r");
if (myFile)
{
Serial.println("opened xfile.json file");
size_t size = myFile.size();
// Allocate a buffer to store contents of the file.
std::unique_ptr<char[]> buf(new char[size]);
Serial.println(size);
Serial.println(buf.get());
myFile.readBytes(buf.get(), size);
DynamicJsonBuffer jsonBuffer;
//StaticJsonBuffer<200> jsonBuffer;
JsonObject& jsona = jsonBuffer.parseObject(buf.get());
jsona.printTo(Serial);
Serial.println("");
if (jsona.success())
{
Serial.println("READ OK");
}
else
{
Serial.println("Json invalid");
}
}
myFile.close();
}//end SPIFFS.begin
}//end setup
void loop() {
// put your main code here, to run repeatedly:
}

and working case:

#include <ESP8266WiFi.h>
#include <ESP8266WebServer.h>
#include <ArduinoJson.h>
#include "FS.h"

void setup() {
// put your setup code here, to run once:
Serial.begin(115200);
delay(2000);
int i=0;
if( SPIFFS.begin() )
{
File my_file = SPIFFS.open("xfile.json", "w");
if (!my_file) {
Serial.println("failed to open xfile.json file for writing :-(");
return; //==============>
}

StaticJsonBuffer<300> jsonBuffer;
JsonObject& my_entry = jsonBuffer.createObject();
my_entry["m"] = 20;
my_entry["h"] = 14;

my_entry.printTo(Serial); 
Serial.println("");
my_entry.printTo(my_file);
my_file.close();

delay(1000);
//---------------------------- READ ----------------------------------

File myFile = SPIFFS.open("xfile.json", "r");
if (myFile) 
{
    Serial.println("opened xfile.json file");
    size_t size = myFile.size();
    // Allocate a buffer to store contents of the file.
    std::unique_ptr<char[]> buf(new char[size]);
    Serial.println(size);
    Serial.println(buf.get());
    myFile.readBytes(buf.get(), size);
    DynamicJsonBuffer jsonBuffer;
    //StaticJsonBuffer<200> jsonBuffer;        
    JsonObject& jsona = jsonBuffer.parseObject(buf.get());
    jsona.printTo(Serial);
    Serial.println("");
    if (jsona.success()) 
    { 
      Serial.println("READ OK");
    }
    else
    {
      Serial.println("Json invalid");
    }
}
myFile.close();

}//end SPIFFS.begin
}//end setup

void loop() {
// put your main code here, to run repeatedly:

}

[bblanchon]

Hi,

I don't know what's wrong, but I think you should simplify your code by removing buf:

File myFile = SPIFFS.open("xfile.json", "r");
if (myFile) 
{
    DynamicJsonBuffer jsonBuffer;
    JsonObject& jsona = jsonBuffer.parseObject(myFile);
    // ...
}
myFile.close();

I didn't test, but I think it should work as File derives from Stream.

[bcatalin]

Ok, I'll give it a try, But if I provide to parseObject a String like [{"a":1,"b":2},{"a":12,"b":22}] it will able to parse it right ?

[bblanchon]

Yes, but this approach uses more memory because you make a full copy of the file in memory.

See:

• How to reduce memory usage?

[bcatalin]

That is correct, but the array I need will have maximum 10 objects in it and only during the start of the card, so is fine for my project. But you are right about memory.

[bcatalin]

I've found that the SPIFFS might have a problem reading data that starts an ends with [], but is not clear for me why this library can not decode an array of JSONs.
This basic code is failing.

#include <ArduinoJson.h>

void setup() {
  Serial.begin(115200);
  Serial.println("");
  StaticJsonBuffer<200> jsonBuffer;

  char json[] = "[{\"a\":1, \"b\":2},{\"a\":11, \"b\":22}]";

  JsonObject& root = jsonBuffer.parseObject(json);

  // Test parsing.
  if (!root.success()) 
    Serial.println("parseObject() failed");    
  else
    Serial.println("all good");
}

void loop() {
  // not used 
}

My expectation is that after root.success returns TRUE, to iterate over the number of JSONs like

int elements = 2;
int i=0;
for(i=0; i<elements; i++)
{
  Serial.println(root["a"]; //print 1 first, print 11 on second pass
  Serial.println(root["b"]; //print 2 first, print 22 on second pass
}

It is possible ?
In the non Arduino IDE I've used cJSON to do it and was ok, but now I am moving all the code to Arduino IDE and this is the last issue I have. Thanks.

[bblanchon]

Hello Catalin,

You need to call parseArray() instead of parseObject().

See:

• FAQ: Why parsing fails?

[bcatalin]

Right! Another case for RTFM :-)

[bblanchon]

That was not my point.
I'm adding a link to the FAQ so that other users will find it.

You're not the first to make that mistake, so I probably missed something as a library author.
What could have prevented you from making that mistake?
Would JsonObject& obj = jsonBuffer.parse<JsonObject>(json); be better?