Binance get historical data

binance.php

<?
header("Content-type: text/html; charset=utf-8");

//get list of symbols
$xinfo = json_decode(file_get_contents("https://api.binance.com/api/v1/exchangeInfo"), true);

$symbols = [];
foreach($xinfo["symbols"] as $sym) $symbols[] = $sym["symbol"];
asort($symbols);

echo '<form method="get">';
echo '<select name="symbol">';
foreach($symbols as $sym) echo '<option val="'.$sym.'">'.$sym.'</option>';
echo '</select>';
echo '<input type="submit"></form>';

$intervals = array("1h","30m","15m","5m","1m");

if ($_GET["symbol"] != "") echo $_GET["symbol"] . "<br>";

foreach ($intervals as $int)
{
	echo "-----------------<br>";
	echo $int . "<br>";
	$filename = "binance_".$_GET["symbol"]."_".$int.".json";
	if (file_exists ( $filename ))
	{
		echo "file ".$filename." exists. Skipping.<br>";
		continue;
	}

	$ts_ms = round(microtime(true)*1000); //current GMT UNIX time in miliseconds
	$qty = 10;
	$ts_last = 1483243199000; //1.1.2017 milisec

	while ($ts_last < $ts_ms && $qty > 0)
	{
		echo gmdate("Y-m-d\TH:i:s\Z", $ts_last/1000) . "<br>";
		$string = file_get_contents("https://api.binance.com/api/v1/klines?symbol=".$_GET["symbol"]."&interval=".$int."&startTime=".$ts_last);

		//print_r($http_response_header);//global variable, always filled
		if ( $http_response_header[0] != "HTTP/1.1 200 OK") {echo $string . "<br>" . $http_response_header[0]; exit;}

		$json = json_decode($string, true);

		//json trim [ /not first/
		if ($ts_last != 1483243199000) $string = substr($string, 1);

		$ts_last = $json[count($json)-1][6]; $ts_last++;
		$qty = count($json);
		echo $qty  . "<br>";

		//json trim ] add, /not last, should have less than 500, 0.2% chance/
		if ($qty == 500) {$string = substr($string, 0, -1); $string .= ",\n";}

		file_put_contents($filename, $string, FILE_APPEND | LOCK_EX);
		echo str_repeat(' ',1024*64);
		flush();
		ob_flush();
		usleep(200000);
		set_time_limit (60);
	}
	echo "Done! " . $filename . "<br>";
}