Create CSV from data returned from API

I'm trying to use Mailchimp's Export API to generate a CSV file of all members of a given list. Here' the documentation and the example PHP code they give:

$apikey = 'YOUR_API_KEY';
$list_id = 'YOUR_LIST_ID';
$chunk_size = 4096; //in bytes
$url = 'http://ift.tt/1PaEXCC'.$apikey.'&id='.$list_id;

/** a more robust client can be built using fsockopen **/
$handle = @fopen($url,'r');
if (!$handle) {
  echo "failed to access url\n";
} else {
  $i = 0;
  $header = array();
  while (!feof($handle)) {
    $buffer = fgets($handle, $chunk_size);
    if (trim($buffer)!=''){
      $obj = json_decode($buffer);
      if ($i==0){
        //store the header row
        $header = $obj;
      } else {
        //echo, write to a file, queue a job, etc.
        echo $header[0].': '.$obj[0]."\n";
      }
      $i++;
    }
  }
  fclose($handle);
}

This works well for me and when I run this file, I end up with a bunch of data in this format:

Email Address: xdf@example.com
Email Address: bob@example.com
Email Address: gerry@example.io

What I want to do is turn this into a CSV (to pass to a place on my server) instead of echoing the data. Is there a library or simple syntax/snippit I can use to make this happen?

via Chebli Mohamed