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Minimalist JSON Parser for Arduino

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

• jsmn - JSON Parser (http://zserge.com/jsmn.html)
• jsmn-example - State-Machine JSON Parser Example for Jsmn (https://github.com/alisdair/jsmn-example)
• map_lib - Associative Array Library (http://www.mailsend-online.com/blog/a-simple-associative-array-library-in-c.html)

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 JSON Parsing library used under the hood - it's a design-decision of how I trivially stitched together Jsmn and map_lib 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

#include <json_arduino.h>

// NOTE1: As the Caller, you are responsible for the memory management (calling map_create() and map_destroy())
// 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.

char json_string[256];
int toggle;
struct map_t *json_hash = NULL;

void setup() {
  Serial.begin(9600);
}

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

  json_to_hash(json_string, json_hash); // Convert JSON String to a Hashmap of Key/Value Pairs
  char* command = map_get(json_hash, "command");
  if (strcmp(command,"hello")==0){
    // do something for the Hello Command ...
    Serial.print("Hello, ");
    Serial.println(map_get(json_hash,"to"));
  } else if (strcmp(command,"goodbye")==0) {
    // do something for the Goodbye Command ...
    Serial.print("Goodbye, Cruel ");
    Serial.println(map_get(json_hash,"say_to"));
  }
  map_destroy(json_hash); // Release the Hashmap, else memory-leak at your own peril.
  toggle = (++toggle % 2); // Weenie way to do "Odd or Even".
  
  delay(500); // Give the loop some time to breathe.
}