convert_csv_to_json.js

// This function takes an array containing the field names, and another that
// contains field values, and returns a json dictionary that combines them.
function convert_csv_to_dict(csv_headers_row, csv_values_row) {
  var json_from_csv =  csv_values_row.reduce(function(result, field, index) {
    result[csv_headers_row[index]] = field;
    return result;
  }, {})

  return json_from_csv;
}


// Define the Javascript function that will be used to combine the 
// header row with subsequent rows in the CSV file
var headers_fn = (function() {
  var csv_headers_row = null; 

  // Use a javascript closure to store the header line (csv_headers_row), 
  // so that we can use the header values for all subsequent CSV entries. 
  return function(csv_arr) {

    var json_from_csv = null;

    if (!csv_headers_row) {
      // if this is the first row, store the headers
      csv_headers_row = csv_arr;
    } else {
      // combine the csv_headers_row with the values to get a dict
      json_from_csv = convert_csv_to_dict(csv_headers_row, csv_arr)
    }
    return json_from_csv;
  }

})();  


// This function is called for each "event" 
// (eg. called once for each line in the log file)
function process(event) {
    var csv_arr = event.Get("decoded_csv_arr");
    var json_from_csv = headers_fn(csv_arr);

    // If the current event was triggered to process the header row,
    // then the json_from_csv will be empty - it only returns a json dict
    // for subsequent rows. Cancel the event so that nothing
    // is sent to the output.
    if (!json_from_csv) {
      event.Cancel();
    }
    event.Put("json_from_csv", json_from_csv);
}