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Minimalist JSON Parser for Arduino

Cobbled together by Laurence A. Lee ([email protected]) from the following original sources:

• jsmn - JSON Lexical Scanner and Tokenizer (http://zserge.com/jsmn.html)
• jsmn-example - JSON Parser Example for Jsmn (https://github.com/alisdair/jsmn-example)

This library is intended to be a lightweight alternative to AJSON, specifically for memory-constrained products like the DigiSpark that run on the ATTINY85 processor.

Limitations

NESTED STRUCTURES NOT SUPPORTED (YET)

Currently, this library only handles Key-Value pairs at the Top Level of the JSON String.

This is not a shortcoming of the Jsmn library used under the hood - it's a design-decision to keep the memory footprint as small as possible.

If you feel the need to fork and enhance, I would suggest putting such enhancements within an #ifdef block (say, #ifdef JSON_ALLOW_NESTED) to allow end-users to have finer control over what enhancements they may or may not need.

Usage Example

// NOTE1: As the Caller, you are responsible for the memory management (calling create_token_list() and release_token_list())
// of the Hashmap used to maintain the Key/Value pairs.
// NOTE2: The Key/Value strings in the HashMap reference strings as tokenized within the original JSON String.

#include <json_arduino.h>

char json_string[256];
char* command;
int toggle;

token_list_t *token_list = NULL;

void setup() {
  Serial.begin(115200);
}

void loop() {

  if (toggle>0){
    strcpy(json_string, "{command:hello, to:world}");
  } else {
    // Demonstrates quotation-marks around tokens are handled by Jsmn OK.
    strcpy(json_string, "{\\"command\\":\\"goodbye\\", \\"say_to\\":\\"World\\"}"); 
  }

  token_list = create_token_list(25); // Create the Token List.
  json_to_token_list(json_string, token_list); // Convert JSON String to a Hashmap of Key/Value Pairs

  command = json_get_value(token_list, "command");
  if (strcmp(command,"hello")==0){
    // do something for the Hello Command ...
    Serial.print("Hello, ");
    Serial.println( json_get_value(token_list,"to") );
  } else if (strcmp(command,"goodbye")==0) {
    // do something for the Goodbye Command ...
    Serial.print("Goodbye, Cruel ");
    Serial.println( json_get_value(token_list,"say_to") );
  } else {
    Serial.println("** BONK **");
  } 

  release_token_list(token_list); // Release or Wipe the Token List, else memory-leak at your own peril.
  
  toggle = (++toggle % 2); // Weenie way to do "Odd or Even".
  delay(25); // Give the loop some time to breathe.
  
}