iota.lib.js/lib/utils/extractJson.js

Javascript Library for IOTA

var ascii = require("./asciiToTrytes");
var inputValidator = require("./inputValidator");

/**
*   extractJson takes a bundle as input and from the signatureMessageFragments extracts the correct JSON
*   data which was encoded and sent with the transaction.
*
*   @method extractJson
*   @param {array} bundle
*   @returns {Object}
**/
function extractJson(bundle) {

    // if wrong input return null
    if ( !inputValidator.isArray(bundle) || bundle[0] === undefined ) return null;


    // Sanity check: if the first tryte pair is not opening bracket, it's not a message
    var firstTrytePair = bundle[0].signatureMessageFragment[0] + bundle[0].signatureMessageFragment[1];

    if (firstTrytePair !== "OD") return null;

    var index = 0;
    var notEnded = true;
    var trytesChunk = '';
    var trytesChecked = 0;
    var preliminaryStop = false;
    var finalJson = '';

    while (index < bundle.length && notEnded) {

        var messageChunk = bundle[index].signatureMessageFragment;

        // We iterate over the message chunk, reading 9 trytes at a time
        for (var i = 0; i < messageChunk.length; i += 9) {

            // get 9 trytes
            var trytes = messageChunk.slice(i, i + 9);
            trytesChunk += trytes;

            // Get the upper limit of the tytes that need to be checked
            // because we only check 2 trytes at a time, there is sometimes a leftover
            var upperLimit = trytesChunk.length - trytesChunk.length % 2;

            var trytesToCheck = trytesChunk.slice(trytesChecked, upperLimit);

            // We read 2 trytes at a time and check if it equals the closing bracket character
            for (var j = 0; j < trytesToCheck.length; j += 2) {

                var trytePair = trytesToCheck[j] + trytesToCheck[j + 1];

                // If closing bracket char was found, and there are only trailing 9's
                // we quit and remove the 9's from the trytesChunk.
                if ( preliminaryStop && trytePair === '99' ) {

                    notEnded = false;
                    // TODO: Remove the trailing 9's from trytesChunk
                    //var closingBracket = trytesToCheck.indexOf('QD') + 1;

                    //trytesChunk = trytesChunk.slice( 0, ( trytesChunk.length - trytesToCheck.length ) + ( closingBracket % 2 === 0 ? closingBracket : closingBracket + 1 ) );

                    break;
                }

                finalJson += ascii.fromTrytes(trytePair);

                // If tryte pair equals closing bracket char, we set a preliminary stop
                // the preliminaryStop is useful when we have a nested JSON object
                if (trytePair === "QD") {
                    preliminaryStop = true;
                }
            }

            if (!notEnded)
                break;

            trytesChecked += trytesToCheck.length;
        }

        // If we have not reached the end of the message yet, we continue with the next
        // transaction in the bundle
        index += 1;

    }

    // If we did not find any JSON, return null
    if (notEnded) {

        return null;

    } else {

        return finalJson;

    }
}

module.exports = extractJson;