limesurvey_ynh/sources/application/helpers/admin/export/JsonWriter.php

<?php
class JsonWriter extends Writer
{
    private $output;
    /**
     * The open filehandle
     */
    private $file = null;
    /**
     * first don't need seperator
     */
    protected $havePrev = false;

    function __construct()
    {
        $this->output = '';
    }

    public function init(SurveyObj $survey, $sLanguageCode, FormattingOptions $oOptions)
    {
        parent::init($survey, $sLanguageCode, $oOptions);
        $sStartOutput='{'.json_encode("responses").': [';
        if ($oOptions->output=='display') {
            header("Content-type: application/json");
            echo $sStartOutput;
        } elseif ($oOptions->output == 'file') {
            $this->file = fopen($this->filename, 'w');
            fwrite($this->file, $sStartOutput);
        }
        
    }
    
    protected function outputRecord($headers, $values, FormattingOptions $oOptions)
    {
        $aJson[$values[0]]=array_combine ($headers,$values);
        $sJson=json_encode($aJson);
        Yii::log($this->havePrev, 'info', 'info');
        if($this->havePrev){
            $sJson=','.$sJson;

        }
        $this->havePrev=true;
        if ($oOptions->output=='display')
        {
            echo $sJson;
            $this->output = '';
        } elseif ($oOptions->output == 'file') {
            $this->output .= $sJson;
            fwrite($this->file, $this->output);
            $this->output='';
        }

    }

    public function close()
    {
        $sEndOutput=']}';
        if (!$this->file)
        {
            echo $sEndOutput;
        }
        else
        {
            $this->output .= $sEndOutput;
            fwrite($this->file, $this->output);
            fclose($this->file);
        }
    }
}