lbry.com/controller/action/DownloadActions.class.php

<?php

class DownloadActions extends Actions
{
    public static function executeGetAppRedirect(string $ext)
    {
        return Controller::redirect(GitHub::getAppDownloadUrl(OS::getOsForExtension($ext)) ?: '/get', 302);
    }

    public static function executeGetAppPrereleaseRedirect(string $ext)
    {
        return Controller::redirect(GitHub::getAppPrereleaseDownloadUrl(OS::getOsForExtension($ext)) ?: '/get', 302);
    }


    public static function executeGetDaemonRedirect(string $os)
    {
        $uri  = null;
        $oses = Os::getAll();

        if (isset($oses[$os])) {
            $uri = GitHub::getDaemonDownloadUrl($os);
        }

        return Controller::redirect($uri ?: '/quickstart', 302);
    }

    public static function executeGet()
    {
        $osChoices = OS::getAll();

        $os = static::guessOS();

        if (isset($os) && isset($osChoices[$os])) {
            list($uri, $osTitle, $osIcon, $buttonLabel, $analyticsLabel) = $osChoices[$os];
            $asset = Github::getAppAsset($os);
            $param = ['osTitle' => $osTitle, 'osIcon' => $osIcon, 'os' => $os, 'downloadUrl' => $asset ? $asset['browser_download_url'] : null];
            return ['download/get', $param];
        } else {
            return ['download/get-no-os'];
        }
    }

    public static function prepareListPartial(array $vars)
    {
        return $vars + ['osChoices' => isset($vars['excludeOs']) ?
      array_diff_key(OS::getAll(), [$vars['excludeOs'] => null]) :
      OS::getAll()
    ];
    }

    protected static function guessOs()
    {
        //if exact OS is requested, use that
        $uri = Request::getRelativeUri();
        foreach (OS::getAll() as $os => $osChoice) {
            if ($osChoice[0] == $uri) {
                return $os;
            }
        }

        if (Request::isRobot()) {
            return null;
        }

        //otherwise guess from UA
        $ua = Request::getUserAgent();
        if (stripos($ua, 'OS X') !== false) {
            return strpos($ua, 'iPhone') !== false || stripos($ua, 'iPad') !== false ? OS::OS_IOS : OS::OS_OSX;
        }
        if (stripos($ua, 'Linux') !== false || strpos($ua, 'X11') !== false) {
            return strpos($ua, 'Android') !== false ? OS::OS_ANDROID : OS::OS_LINUX;
        }
        if (stripos($ua, 'Windows') !== false) {
            return OS::OS_WINDOWS;
        }
    }

    protected static function getEmailParam()
    {
        $email = Request::getParam('e');

        if (!$email) {
            $encoded = Request::getParam('ec');
            if ($encoded) {
                $email = Smaz::decode(Encoding::base64DecodeUrlsafe($encoded), Smaz::CODEBOOK_EMAIL);
                if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
                    $email = null;
                }
            }
        }

        return $email;
    }

    public static function prepareDownloadButtonPartial(array $vars)
    {
        $osChoices = OS::getAll();

        $os = static::guessOS();

        if ($os && isset($osChoices[$os])) {
            list($uri, $osTitle, $osIcon, $buttonLabel, $analyticsLabel) = $osChoices[$os];
            $release = Github::getAppRelease();
            $asset = Github::getAppAsset($os);

            $vars += [
          'analyticsLabel' => $analyticsLabel,
          'buttonLabel' => $buttonLabel,
          'downloadUrl' => $asset ? $asset['browser_download_url'] : null,
          'meta' => true,
          'os' => $os,
          'osTitle' => $osTitle,
          'osIcon' => $osIcon,
          'releaseTimestamp' => $release ? strtotime($release['created_at']) : null,
          'size' => $asset ? $asset['size'] / (1024 * 1024) : 0, //bytes -> MB
          'sourceLink' => false,
          'version' => $release ? $release['name'] : null,
          'isAuto' => Request::getParam('auto'),
      ];
        }

        return $vars;
    }
}