dvlden/extract-cookies.php

## extract-cookies.php
<?php

function extractCookies ($string) {
    $cookies = array();

    $lines = explode("\n", $string);

    // iterate over lines
    foreach ($lines as $line) {
        // we only care for valid cookie def lines
        if (isset($line[0]) && substr_count($line, "\t") == 6) {
            // get tokens in an array
            $tokens = explode("\t", $line);

            // trim the tokens
            $tokens = array_map('trim', $tokens);

            $cookie = array();

            // Extract the data
            $cookie['domain'] = $tokens[0];
            $cookie['flag'] = (bool) $tokens[1];
            $cookie['path'] = $tokens[2];
            $cookie['secure'] = (bool) $tokens[3];

            // Convert date to a readable format
            $cookie['expiration'] = date('Y-m-d h:i:s', $tokens[4]);

            $cookie['name'] = $tokens[5];
            $cookie['value'] = $tokens[6];

            // Record the cookie.
            $cookies[] = $cookie;
        }
    }

    return $cookies;
}

## index.php
<?php

require('extract-cookies.php'); // require the file from above...

if (isset($_FILES['file'])) {
    $inputName = $_FILES['file']['tmp_name'];
    $contents = file_get_contents($inputName);
    $outputName = 'cookies.json';
    $convertContents = extractCookies($contents);

    file_put_contents($outputName, json_encode($convertContents));

    if (file_exists($outputName)) {
        header('Content-Description: File Transfer');
        header('Content-Type: application/octet-stream');
        header('Content-Disposition: attachment; filename="'.basename($outputName).'"');
        header('Expires: 0');
        header('Cache-Control: must-revalidate');
        header('Pragma: public');
        header('Content-Length: ' . filesize($outputName));

        readfile($outputName);
        unlink($outputName);

        exit;
    }
}

?>

<!doctype html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <title>Convert Cookies from "txt" to "json" format</title>

    <link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet">
</head>

<body>
    <div class="container my-5">
        <p class="lead mb-5">
            Browse an `cookies.txt` for upload <i>(file name doesn't matter)</i> and begin converting.
        </p>

        <form method="POST" enctype="multipart/form-data">
            <label class="btn btn-lg btn-block btn-secondary">
                <input type="file" id="file" name="file" hidden>
                Browse
            </label>

            <button type="submit" class="btn btn-block btn-primary">Convert!</button>
        </form>
    </div>
</body>
</html>
	<?php

	function extractCookies ($string) {
	$cookies = array();

	$lines = explode("\n", $string);

	// iterate over lines
	foreach ($lines as $line) {
	// we only care for valid cookie def lines
	if (isset($line[0]) && substr_count($line, "\t") == 6) {
	// get tokens in an array
	$tokens = explode("\t", $line);

	// trim the tokens
	$tokens = array_map('trim', $tokens);

	$cookie = array();

	// Extract the data
	$cookie['domain'] = $tokens[0];
	$cookie['flag'] = (bool) $tokens[1];
	$cookie['path'] = $tokens[2];
	$cookie['secure'] = (bool) $tokens[3];

	// Convert date to a readable format
	$cookie['expiration'] = date('Y-m-d h:i:s', $tokens[4]);

	$cookie['name'] = $tokens[5];
	$cookie['value'] = $tokens[6];

	// Record the cookie.
	$cookies[] = $cookie;
	}
	}

	return $cookies;
	}
	<?php

	require('extract-cookies.php'); // require the file from above...

	if (isset($_FILES['file'])) {
	$inputName = $_FILES['file']['tmp_name'];
	$contents = file_get_contents($inputName);
	$outputName = 'cookies.json';
	$convertContents = extractCookies($contents);

	file_put_contents($outputName, json_encode($convertContents));

	if (file_exists($outputName)) {
	header('Content-Description: File Transfer');
	header('Content-Type: application/octet-stream');
	header('Content-Disposition: attachment; filename="'.basename($outputName).'"');
	header('Expires: 0');
	header('Cache-Control: must-revalidate');
	header('Pragma: public');
	header('Content-Length: ' . filesize($outputName));

	readfile($outputName);
	unlink($outputName);

	exit;
	}
	}

	?>

	<!doctype html>
	<html lang="en">
	<head>
	<meta charset="utf-8">
	<title>Convert Cookies from "txt" to "json" format</title>

	<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet">
	</head>

	<body>
	<div class="container my-5">
	<p class="lead mb-5">
	Browse an `cookies.txt` for upload <i>(file name doesn't matter)</i> and begin converting.
	</p>

	<form method="POST" enctype="multipart/form-data">
	<label class="btn btn-lg btn-block btn-secondary">
	<input type="file" id="file" name="file" hidden>
	Browse
	</label>

	<button type="submit" class="btn btn-block btn-primary">Convert!</button>
	</form>
	</div>
	</body>
	</html>