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   1  <?php
   2  
   3  /**
   4   * Functions that relate to HTTP requests
   5   *
   6   * On functions using the 3rd party library Requests:
   7   * Their goal here is to provide convenient wrapper functions to the Requests library. There are
   8   * 2 types of functions for each METHOD, where METHOD is 'get' or 'post' (implement more as needed)
   9   *     - yourls_http_METHOD() :
  10   *         Return a complete Response object (with ->body, ->headers, ->status_code, etc...) or
  11   *         a simple string (error message)
  12   *     - yourls_http_METHOD_body() :
  13   *         Return a string (response body) or null if there was an error
  14   *
  15   * @since 1.7
  16   */
  17  
  18  use WpOrg\Requests\Requests;
  19  
  20  /**
  21   * Perform a GET request, return response object or error string message
  22   *
  23   * Notable object properties: body, headers, status_code
  24   *
  25   * @since 1.7
  26   * @see yourls_http_request
  27   * @param string $url     URL to request
  28   * @param array $headers  HTTP headers to send
  29   * @param array $data     GET data
  30   * @param array $options  Options to pass to Requests
  31   * @return mixed Response object, or error string
  32   */
  33  function yourls_http_get( $url, $headers = array(), $data = array(), $options = array() ) {
  34      return yourls_http_request( 'GET', $url, $headers, $data, $options );
  35  }
  36  
  37  /**
  38   * Perform a GET request, return body or null if there was an error
  39   *
  40   * @since 1.7
  41   * @see yourls_http_request
  42   * @param string $url     URL to request
  43   * @param array $headers  HTTP headers to send
  44   * @param array $data     GET data
  45   * @param array $options  Options to pass to Requests
  46   * @return mixed String (page body) or null if error
  47   */
  48  function yourls_http_get_body( $url, $headers = array(), $data = array(), $options = array() ) {
  49      $return = yourls_http_get( $url, $headers, $data, $options );
  50      return isset( $return->body ) ? $return->body : null;
  51  }
  52  
  53  /**
  54   * Perform a POST request, return response object
  55   *
  56   * Notable object properties: body, headers, status_code
  57   *
  58   * @since 1.7
  59   * @see yourls_http_request
  60   * @param string $url     URL to request
  61   * @param array $headers  HTTP headers to send
  62   * @param array $data     POST data
  63   * @param array $options  Options to pass to Requests
  64   * @return mixed Response object, or error string
  65   */
  66  function yourls_http_post( $url, $headers = array(), $data = array(), $options = array() ) {
  67      return yourls_http_request( 'POST', $url, $headers, $data, $options );
  68  }
  69  
  70  /**
  71   * Perform a POST request, return body
  72   *
  73   * Wrapper for yourls_http_request()
  74   *
  75   * @since 1.7
  76   * @see yourls_http_request
  77   * @param string $url     URL to request
  78   * @param array $headers  HTTP headers to send
  79   * @param array $data     POST data
  80   * @param array $options  Options to pass to Requests
  81   * @return mixed String (page body) or null if error
  82   */
  83  function yourls_http_post_body( $url, $headers = array(), $data = array(), $options = array() ) {
  84      $return = yourls_http_post( $url, $headers, $data, $options );
  85      return isset( $return->body ) ? $return->body : null;
  86  }
  87  
  88  /**
  89   * Get proxy information
  90   *
  91   * @since 1.7.1
  92   * @return mixed false if no proxy is defined, or string like '10.0.0.201:3128' or array like ('10.0.0.201:3128', 'username', 'password')
  93   */
  94  function yourls_http_get_proxy() {
  95      $proxy = false;
  96  
  97      if( defined( 'YOURLS_PROXY' ) ) {
  98          $proxy = YOURLS_PROXY;
  99          if( defined( 'YOURLS_PROXY_USERNAME' ) && defined( 'YOURLS_PROXY_PASSWORD' ) ) {
 100              $proxy = array( YOURLS_PROXY, YOURLS_PROXY_USERNAME, YOURLS_PROXY_PASSWORD );
 101          }
 102      }
 103  
 104      return yourls_apply_filter( 'http_get_proxy', $proxy );
 105  }
 106  
 107  /**
 108   * Get list of hosts that should bypass the proxy
 109   *
 110   * @since 1.7.1
 111   * @return mixed false if no host defined, or string like "example.com, *.mycorp.com"
 112   */
 113  function yourls_http_get_proxy_bypass_host() {
 114      $hosts = defined( 'YOURLS_PROXY_BYPASS_HOSTS' ) ? YOURLS_PROXY_BYPASS_HOSTS : false;
 115  
 116      return yourls_apply_filter( 'http_get_proxy_bypass_host', $hosts );
 117  }
 118  
 119  /**
 120   * Default HTTP requests options for YOURLS
 121   *
 122   * For a list of all available options, see function request() in /includes/Requests/Requests.php
 123   *
 124   * @since 1.7
 125   * @return array Options
 126   */
 127  function yourls_http_default_options() {
 128      $options = array(
 129          'timeout'          => yourls_apply_filter( 'http_default_options_timeout', 3 ),
 130          'useragent'        => yourls_http_user_agent(),
 131          'follow_redirects' => true,
 132          'redirects'        => 3,
 133      );
 134  
 135      if( yourls_http_get_proxy() ) {
 136          $options['proxy'] = yourls_http_get_proxy();
 137      }
 138  
 139      return yourls_apply_filter( 'http_default_options', $options );
 140  }
 141  
 142  /**
 143   * Whether URL should be sent through the proxy server.
 144   *
 145   * Concept stolen from WordPress. The idea is to allow some URLs, including localhost and the YOURLS install itself,
 146   * to be requested directly and bypassing any defined proxy.
 147   *
 148   * @since 1.7
 149   * @param string $url URL to check
 150   * @return bool true to request through proxy, false to request directly
 151   */
 152  function yourls_send_through_proxy( $url ) {
 153  
 154      // Allow plugins to short-circuit the whole function
 155      $pre = yourls_apply_filter( 'shunt_send_through_proxy', yourls_shunt_default(), $url );
 156      if ( yourls_shunt_default() !== $pre ) {
 157          return $pre;
 158      }
 159  
 160      $check = @parse_url( $url );
 161  
 162      if( !isset( $check['host'] ) ) {
 163          return false;
 164      }
 165  
 166      // Malformed URL, can not process, but this could mean ssl, so let through anyway.
 167      if ( $check === false )
 168          return true;
 169  
 170      // Self and loopback URLs are considered local (':' is parse_url() host on '::1')
 171      $home = parse_url( yourls_get_yourls_site() );
 172      $local = array( 'localhost', '127.0.0.1', '127.1', '[::1]', ':', $home['host'] );
 173  
 174      if( in_array( $check['host'], $local ) )
 175          return false;
 176  
 177      $bypass = yourls_http_get_proxy_bypass_host();
 178  
 179      if( $bypass === false OR $bypass === '' ) {
 180          return true;
 181      }
 182  
 183      // Build array of hosts to bypass
 184      static $bypass_hosts;
 185      static $wildcard_regex = false;
 186      if ( null == $bypass_hosts ) {
 187          $bypass_hosts = preg_split( '|\s*,\s*|', $bypass );
 188  
 189          if ( false !== strpos( $bypass, '*' ) ) {
 190              $wildcard_regex = array();
 191              foreach ( $bypass_hosts as $host ) {
 192                  $wildcard_regex[] = str_replace( '\*', '.+', preg_quote( $host, '/' ) );
 193                  if ( false !== strpos( $host, '*' ) ) {
 194                      $wildcard_regex[] = str_replace( '\*\.', '', preg_quote( $host, '/' ) );
 195                  }
 196              }
 197              $wildcard_regex = '/^(' . implode( '|', $wildcard_regex ) . ')$/i';
 198          }
 199      }
 200  
 201      if ( !empty( $wildcard_regex ) )
 202          return !preg_match( $wildcard_regex, $check['host'] );
 203      else
 204          return !in_array( $check['host'], $bypass_hosts );
 205  }
 206  
 207  /**
 208   * Resolve a host name to a list of IP addresses
 209   *
 210   * Returns every A and AAAA record found for $host, or an empty array if the host cannot be
 211   * resolved. Does not check the addresses in any way, see yourls_host_is_local() for this.
 212   *
 213   * @since 1.10.5
 214   * @param string $host Host name to resolve (no brackets around IPv6 literals)
 215   * @return array       Array of IP addresses as strings, empty array if resolution failed
 216   */
 217  function yourls_resolve_host(string $host): array {
 218      $ips = array();
 219  
 220      /* Both dns_get_record() and gethostbynamel() emit an E_WARNING when a lookup fails, which is
 221       * an expected outcome here (host longer than 255 chars, or resolver returning SERVFAIL). We silence them with a
 222       * scoped error handler rather than with '@' that may hide other errors (the try/catch isn't enough
 223       * because the E_WARNING is not an exception).
 224       * Note that this does not check the validity of the host name itself, it just tries to resolve it. Invalid hosts
 225       * like omgilove.slayer will return whatever the resolver returns (SERVFAIL, NXDOMAIN, etc...) and will be
 226       * considered local by yourls_host_is_local().
 227       */
 228      set_error_handler( function() { return true; }, E_WARNING );
 229  
 230      try {
 231          // dns_get_record() gets us IPv6 too, but it's disabled on some shared hosts
 232          if( function_exists( 'dns_get_record' ) ) {
 233              $records = dns_get_record( $host, DNS_A | DNS_AAAA );
 234              foreach( is_array( $records ) ? $records : array() as $record ) {
 235                  if( isset( $record['ip'] ) ) {
 236                      $ips[] = $record['ip'];     // A record
 237                  } elseif( isset( $record['ipv6'] ) ) {
 238                      $ips[] = $record['ipv6'];   // AAAA record
 239                  }
 240              }
 241          }
 242  
 243          // Fallback when dns_get_record() is unavailable or came back empty handed. IPv4 only.
 244          if( !$ips && function_exists( 'gethostbynamel' ) ) {
 245              $ips = gethostbynamel( $host ) ?: array();  // returns false when host is unknown
 246          }
 247      } finally {
 248          restore_error_handler();
 249      }
 250  
 251      return yourls_apply_filter( 'resolve_host_ips', $ips, $host );
 252  }
 253  
 254  /**
 255   * Check if an IP address is not a public one (loopback, private, reserved or link-local)
 256   *
 257   * Anything that is not a valid IP is considered non-public.
 258   *
 259   * @since 1.10.5
 260   * @param string $ip IP address, v4 or v6
 261   * @return bool      true if the address is not public, or not an IP at all
 262   */
 263  function yourls_ip_is_local(string $ip): bool {
 264      // Not an IP at all: fail closed
 265      if( filter_var( $ip, FILTER_VALIDATE_IP ) === false ) {
 266          return true;
 267      }
 268  
 269      /* An IPv4-mapped IPv6 address ('::ffff:127.0.0.1', ie 10 null bytes, 2 xFF bytes, then the
 270       * IPv4) is an IPv4 in disguise and is routed as such, so check the IPv4 it wraps instead.
 271       * PHP only started rejecting these with FILTER_FLAG_NO_RES_RANGE in 8.3: on 8.1 and 8.2,
 272       * '[::ffff:127.0.0.1]' would otherwise pass for a public address, and so would every other
 273       * local IPv4 written that way.
 274       * Same treatment for the deprecated IPv4-compatible form ('::127.0.0.1', 12 null bytes then
 275       * the IPv4), hence testing the 10 first bytes only. '::' and '::1' match too and unwrap to
 276       * 0.0.0.0 and 0.0.0.1, both reserved: still non-public, as they should be.
 277       */
 278      $packed = inet_pton( $ip );
 279      if( strlen( $packed ) === 16 && substr( $packed, 0, 10 ) === str_repeat( "\0", 10 ) ) {
 280          $ip = inet_ntop( substr( $packed, 12 ) );
 281      }
 282  
 283      // FILTER_FLAG_NO_PRIV_RANGE covers 10/8, 172.16/12, 192.168/16 and fc00::/7
 284      // FILTER_FLAG_NO_RES_RANGE covers 0/8, 127/8, 169.254/16 (cloud metadata), 240/4, ::, ::1 and fe80::/10
 285      return filter_var( $ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE ) === false;
 286  }
 287  
 288  /**
 289   * Check if a host points to a non-public address (loopback, private, reserved or link-local)
 290   *
 291   * Accepts either a host name or an IP literal. A host name is resolved first, and considered
 292   * local as soon as one of its addresses is not public. A host that cannot be resolved is
 293   * considered local too.
 294   *
 295   * Known limitation: this does not protect against DNS rebinding (attacker controlling a DNS server
 296   * with 0s TTL refresh, where evil-url.com could point to 1.2.3.4 (public) and then the next second point
 297   * to 10.0.0.1 (private). Let's consider this a low risk, and not worth the complexity of a DNS cache with TTL awareness.
 298   *
 299   * @since 1.10.5
 300   * @param string $host Host name or IP address. IPv6 literals can be bracketed or not.
 301   * @return bool        true if the host is not a public address or cannot be resolved
 302   */
 303  function yourls_host_is_local(string $host): bool {
 304      // Allow plugins to short-circuit the whole function
 305      $pre = yourls_apply_filter( 'shunt_host_is_local', yourls_shunt_default(), $host );
 306      if ( yourls_shunt_default() !== $pre ) {
 307          return $pre;
 308      }
 309  
 310      $host = trim( (string)$host );
 311  
 312      // parse_url() keeps IPv6 hosts bracketed ('[::1]'). Unbracket, otherwise the literal is not
 313      // recognized as an IP and we needlessly hand it over to the resolver.
 314      if( strlen( $host ) > 2 && $host[0] === '[' && substr( $host, -1 ) === ']' ) {
 315          $host = substr( $host, 1, -1 );
 316      }
 317  
 318      if( $host === '' ) {
 319          $is_local = true;
 320      }
 321  
 322      // IP literal: no DNS involved, check it as is
 323      elseif( filter_var( $host, FILTER_VALIDATE_IP ) !== false ) {
 324          $is_local = yourls_ip_is_local( $host );
 325      }
 326  
 327      else {
 328          $ips = yourls_resolve_host( $host );
 329  
 330          // Unresolvable host: fail closed
 331          $is_local = empty( $ips );
 332  
 333          foreach( $ips as $ip ) {
 334              if( yourls_ip_is_local( $ip ) ) {
 335                  $is_local = true;
 336                  break;
 337              }
 338          }
 339      }
 340  
 341      return (bool)yourls_apply_filter( 'host_is_local', $is_local, $host );
 342  }
 343  
 344  /**
 345   * Check if the destination of a remote title fetch must be restricted to public addresses
 346   *
 347   * We want to avoid the situation where a public install of YOURLS is used to fetch titles from internal hosts,
 348   * and potentially leak information about them (SSRF and port scan / service discovery)
 349   * On a private install, the user is authenticated and (hopefully) trusted.
 350   *
 351   * Public install can be: YOURLS_PRIVATE set to false, or having a public interface on top of a regular private
 352   * install. Checking constant YOURLS_USER covers both cases at once.
 353   *
 354   * A one-liner plugin disables the filtering entirely (say, public install on a private network):
 355   *     // Disable the restriction on remote title fetches (allow internal hosts)
 356   *     yourls_add_filter( 'restrict_remote_title_fetch', 'yourls_return_false' );
 357   *
 358   * @since 1.10.5
 359   * @return bool  true if the fetch destination must be restricted to public addresses
 360   */
 361  function yourls_restrict_remote_title_fetch(): bool {
 362      return (bool)yourls_apply_filter( 'restrict_remote_title_fetch', !defined( 'YOURLS_USER' ) );
 363  }
 364  
 365  /**
 366   * HTTP request options that make a request fail when it is redirected to a non-public host
 367   *
 368   * Redirects are still followed: dropping them would break 'http -> https', 'example.com ->
 369   * www.example.com', URL shorteners, or any legit 30x redirect. Instead, every hop
 370   * is checked before it is requested.
 371   *
 372   * Meant to be merged into the $options of a single yourls_http_*() call, not to be added to
 373   * yourls_http_default_options() -- other requests (core version check, plugins) are not
 374   * triggered by an untrusted party.
 375   *
 376   * @since 1.10.5
 377   * @return array  Options to pass to yourls_http_get()
 378   */
 379  function yourls_http_options_no_local_redirect(): array {
 380      $hooks = new \WpOrg\Requests\Hooks();
 381      $hooks->register( 'requests.before_redirect', 'yourls_http_abort_local_redirect' );
 382  
 383      return array(
 384          'hooks'     => $hooks,
 385          'redirects' => 3,
 386      );
 387  }
 388  
 389  /**
 390   * Callback on the 'requests.before_redirect' hook: abort if the redirect target is not public
 391   *
 392   * The exception thrown is a \WpOrg\Requests\Exception and not a plain \Exception, because this
 393   * is what yourls_http_request() catches -- anything else would escape and fatal.
 394   *
 395   * @since 1.10.5
 396   * @param string $location URL the request is about to be redirected to
 397   * @return void
 398   * @throws \WpOrg\Requests\Exception  When the redirect target is a non public host
 399   */
 400  function yourls_http_abort_local_redirect(string $location): void {
 401      $host = parse_url( $location, PHP_URL_HOST );
 402  
 403      if( !is_string( $host ) || yourls_host_is_local( $host ) ) {
 404          throw new \WpOrg\Requests\Exception( 'Redirect to a non public host: ' . $location, 'yourls.local_redirect', $location );
 405      }
 406  }
 407  
 408  /**
 409   * Perform a HTTP request, return response object
 410   *
 411   * @since 1.7
 412   * @param string $type HTTP request type (GET, POST)
 413   * @param string $url URL to request
 414   * @param array $headers Extra headers to send with the request
 415   * @param array $data Data to send either as a query string for GET requests, or in the body for POST requests
 416   * @param array $options Options for the request (see /includes/Requests/Requests.php:request())
 417   * @return object WpOrg\Requests\Response object
 418   */
 419  function yourls_http_request( $type, $url, $headers, $data, $options ) {
 420  
 421      // Allow plugins to short-circuit the whole function
 422      $pre = yourls_apply_filter( 'shunt_yourls_http_request', yourls_shunt_default(), $type, $url, $headers, $data, $options );
 423      if ( yourls_shunt_default() !== $pre ) {
 424          return $pre;
 425      }
 426  
 427      $options = array_merge( yourls_http_default_options(), $options );
 428  
 429      if( yourls_http_get_proxy() && !yourls_send_through_proxy( $url ) ) {
 430          unset( $options['proxy'] );
 431      }
 432  
 433      // filter everything
 434      $type    = yourls_apply_filter('http_request_type', $type);
 435      $url     = yourls_apply_filter('http_request_url', $url);
 436      $headers = yourls_apply_filter('http_request_headers', $headers);
 437      $data    = yourls_apply_filter('http_request_data', $data);
 438      $options = yourls_apply_filter('http_request_options', $options);
 439  
 440      try {
 441          $result = Requests::request( $url, $headers, $data, $type, $options );
 442      } catch( \WpOrg\Requests\Exception $e ) {
 443          $result = yourls_debug_log( $e->getMessage() . ' (' . $type . ' on ' . $url . ')' );
 444      };
 445  
 446      return $result;
 447  }
 448  
 449  /**
 450   * Return funky user agent string
 451   *
 452   * @since 1.5
 453   * @return string UA string
 454   */
 455  function yourls_http_user_agent() {
 456      return yourls_apply_filter( 'http_user_agent', 'YOURLS v'.YOURLS_VERSION.' +http://yourls.org/ (running on '.yourls_get_yourls_site().')' );
 457  }
 458  
 459  /**
 460   * Check api.yourls.org if there's a newer version of YOURLS
 461   *
 462   * This function collects various stats to help us improve YOURLS. See the blog post about it:
 463   * http://blog.yourls.org/2014/01/on-yourls-1-7-and-api-yourls-org/
 464   * Results of requests sent to api.yourls.org are stored in option 'core_version_checks' and is an object
 465   * with the following properties:
 466   *    - failed_attempts : number of consecutive failed attempts
 467   *    - last_attempt    : time() of last attempt
 468   *    - last_result     : content retrieved from api.yourls.org during previous check
 469   *    - version_checked : installed YOURLS version that was last checked
 470   *
 471   * @since 1.7
 472   * @return mixed JSON data if api.yourls.org successfully requested, false otherwise
 473   */
 474  function yourls_check_core_version() {
 475  
 476      global $yourls_user_passwords;
 477  
 478      $checks = yourls_get_option( 'core_version_checks' );
 479  
 480      // Invalidate check data when YOURLS version changes
 481      if ( is_object( $checks ) && YOURLS_VERSION != $checks->version_checked ) {
 482          $checks = false;
 483      }
 484  
 485      if( !is_object( $checks ) ) {
 486          $checks = new stdClass;
 487          $checks->failed_attempts = 0;
 488          $checks->last_attempt    = 0;
 489          $checks->last_result     = '';
 490          $checks->version_checked = YOURLS_VERSION;
 491      }
 492  
 493      // Total number of links and clicks
 494      list( $total_urls, $total_clicks ) = array_values(yourls_get_db_stats());
 495  
 496      // The collection of stuff to report
 497      $stuff = array(
 498          // Globally uniquish site identifier
 499          // This uses const YOURLS_SITE and not yourls_get_yourls_site() to prevent creating another id for an already known install
 500          'md5'                => md5( YOURLS_SITE . YOURLS_ABSPATH ),
 501  
 502          // Install information
 503          'failed_attempts'    => $checks->failed_attempts,
 504          'yourls_site'        => defined( 'YOURLS_SITE' ) ? yourls_get_yourls_site() : 'unknown',
 505          'yourls_version'     => defined( 'YOURLS_VERSION' ) ? YOURLS_VERSION : 'unknown',
 506          'php_version'        => PHP_VERSION,
 507          'mysql_version'      => yourls_get_db('read-check_core_version')->mysql_version(),
 508          'locale'             => yourls_get_locale(),
 509  
 510          // custom DB driver if any, and useful common PHP extensions
 511          'db_driver'          => defined( 'YOURLS_DB_DRIVER' ) ? YOURLS_DB_DRIVER : 'unset',
 512          'db_ext_pdo'         => extension_loaded( 'PDO' )     ? 1 : 0,
 513          'db_ext_mysql'       => extension_loaded( 'mysql' )   ? 1 : 0,
 514          'db_ext_mysqli'      => extension_loaded( 'mysqli' )  ? 1 : 0,
 515          'ext_curl'           => extension_loaded( 'curl' )    ? 1 : 0,
 516  
 517          // Config information
 518          'yourls_private'     => defined( 'YOURLS_PRIVATE' ) && YOURLS_PRIVATE ? 1 : 0,
 519          'yourls_unique'      => defined( 'YOURLS_UNIQUE_URLS' ) && YOURLS_UNIQUE_URLS ? 1 : 0,
 520          'yourls_url_convert' => defined( 'YOURLS_URL_CONVERT' ) ? YOURLS_URL_CONVERT : 'unknown',
 521  
 522          // Usage information
 523          'num_users'          => count( $yourls_user_passwords ),
 524          'num_active_plugins' => yourls_has_active_plugins(),
 525          'num_pages'          => defined( 'YOURLS_PAGEDIR' ) ? count( (array) glob( YOURLS_PAGEDIR .'/*.php') ) : 0,
 526          'num_links'          => $total_urls,
 527          'num_clicks'         => $total_clicks,
 528      );
 529  
 530      $stuff = yourls_apply_filter( 'version_check_stuff', $stuff );
 531  
 532      // Send it in
 533      $url = 'http://api.yourls.org/core/version/1.1/';
 534      if( yourls_can_http_over_ssl() ) {
 535          $url = yourls_set_url_scheme($url, 'https');
 536      }
 537      $req = yourls_http_post( $url, array(), $stuff );
 538  
 539      $checks->last_attempt = time();
 540      $checks->version_checked = YOURLS_VERSION;
 541  
 542      // Unexpected results ?
 543      if( is_string( $req ) or !$req->success ) {
 544          $checks->failed_attempts = $checks->failed_attempts + 1;
 545          yourls_update_option( 'core_version_checks', $checks );
 546          if( is_string($req) ) {
 547              yourls_debug_log('Version check failed: ' . $req);
 548          }
 549          return false;
 550      }
 551  
 552      // Parse response
 553      $json = json_decode( trim( $req->body ) );
 554  
 555      if( yourls_validate_core_version_response($json) ) {
 556          // All went OK - mark this down
 557          $checks->failed_attempts = 0;
 558          $checks->last_result     = $json;
 559          yourls_update_option( 'core_version_checks', $checks );
 560  
 561          return $json;
 562      }
 563  
 564      // Request returned actual result, but not what we expected
 565      return false;
 566  }
 567  
 568  /**
 569   *  Make sure response from api.yourls.org is valid
 570   *
 571   *  1) we should get a json object with two following properties:
 572   *    'latest' => a string representing a YOURLS version number, eg '1.2.3'
 573   *    'zipurl' => a string for a zip package URL, from github, eg 'https://api.github.com/repos/YOURLS/YOURLS/zipball/1.2.3'
 574   *  2) 'latest' and version extracted from 'zipurl' should match
 575   *  3) the object should not contain any other key
 576   *
 577   *  @since 1.7.7
 578   *  @param object $json  JSON object to check
 579   *  @return bool   true if seems legit, false otherwise
 580   */
 581  function yourls_validate_core_version_response($json) {
 582      return (
 583          yourls_validate_core_version_response_keys($json)
 584       && $json->latest === yourls_sanitize_version($json->latest)
 585       && $json->zipurl === yourls_sanitize_url($json->zipurl)
 586       && $json->latest === yourls_get_version_from_zipball_url($json->zipurl)
 587       && yourls_is_valid_github_repo_url($json->zipurl)
 588      );
 589  }
 590  
 591  /**
 592   * Get version number from Github zipball URL (last part of URL, really)
 593   *
 594   * @since 1.8.3
 595   * @param string $zipurl eg 'https://api.github.com/repos/YOURLS/YOURLS/zipball/1.2.3'
 596   * @return string
 597   */
 598  function yourls_get_version_from_zipball_url($zipurl) {
 599      $version = '';
 600      $parts = explode('/', parse_url(yourls_sanitize_url($zipurl), PHP_URL_PATH) ?? '');
 601      // expect at least 1 slash in path, return last part
 602      if( count($parts) > 1 ) {
 603          $version = end($parts);
 604      }
 605      return $version;
 606  }
 607  
 608  /**
 609   * Check if URL is from YOURLS/YOURLS repo on github
 610   *
 611   * @since 1.8.3
 612   * @param string $url  URL to check
 613   * @return bool
 614   */
 615  function yourls_is_valid_github_repo_url($url) {
 616      $url = yourls_sanitize_url($url);
 617      return (
 618          join('.',array_slice(explode('.', parse_url($url, PHP_URL_HOST) ?? ''), -2, 2)) === 'github.com'
 619              // explodes on '.' (['api','github','com']) and keeps the last two elements
 620              // to make sure domain is either github.com or one of its subdomain (api.github.com for instance)
 621              // TODO: keep an eye on Github API to make sure it doesn't change some day to another domain (githubapi.com, ...)
 622          && substr( parse_url($url, PHP_URL_PATH), 0, 21 ) === '/repos/YOURLS/YOURLS/'
 623              // make sure path starts with '/repos/YOURLS/YOURLS/'
 624      );
 625  }
 626  
 627  /**
 628   * Check if object has only expected keys 'latest' and 'zipurl' containing strings
 629   *
 630   * @since 1.8.3
 631   * @param object $json
 632   * @return bool
 633   */
 634  function yourls_validate_core_version_response_keys($json) {
 635      $keys = array('latest', 'zipurl');
 636      return (
 637          count(array_diff(array_keys((array)$json), $keys)) === 0
 638          && isset($json->latest)
 639          && isset($json->zipurl)
 640          && is_string($json->latest)
 641          && is_string($json->zipurl)
 642      );
 643  }
 644  
 645  /**
 646   * Determine if we want to check for a newer YOURLS version (and check if applicable)
 647   *
 648   * Currently checks are performed every 24h and only when someone is visiting an admin page.
 649   * In the future (1.8?) maybe check with cronjob emulation instead.
 650   *
 651   * @since 1.7
 652   * @return bool true if a check was needed and successfully performed, false otherwise
 653   */
 654  function yourls_maybe_check_core_version() {
 655      // Allow plugins to short-circuit the whole function
 656      $pre = yourls_apply_filter( 'shunt_maybe_check_core_version', yourls_shunt_default() );
 657      if ( yourls_shunt_default() !== $pre ) {
 658          return $pre;
 659      }
 660  
 661      if (yourls_skip_version_check()) {
 662          return false;
 663      }
 664  
 665      if (!yourls_is_admin()) {
 666          return false;
 667      }
 668  
 669      $checks = yourls_get_option( 'core_version_checks' );
 670  
 671      /* We don't want to check if :
 672       - last_result is set (a previous check was performed)
 673       - and it was less than 24h ago (or less than 2h ago if it wasn't successful)
 674       - and version checked matched version running
 675       Otherwise, we want to check.
 676      */
 677      if( !empty( $checks->last_result )
 678          AND
 679          (
 680              ( $checks->failed_attempts == 0 && ( ( time() - $checks->last_attempt ) < 24 * 3600 ) )
 681              OR
 682              ( $checks->failed_attempts > 0  && ( ( time() - $checks->last_attempt ) <  2 * 3600 ) )
 683          )
 684          AND ( $checks->version_checked == YOURLS_VERSION )
 685      )
 686          return false;
 687  
 688      // We want to check if there's a new version
 689      $new_check = yourls_check_core_version();
 690  
 691      // Could not check for a new version, and we don't have ancient data
 692      if( false == $new_check && !isset( $checks->last_result->latest ) )
 693          return false;
 694  
 695      return true;
 696  }
 697  
 698  /**
 699   * Check if user setting for skipping version check is set
 700   *
 701   * @since 1.8.2
 702   * @return bool
 703   */
 704  function yourls_skip_version_check() {
 705      return yourls_apply_filter('skip_version_check', defined('YOURLS_NO_VERSION_CHECK') && YOURLS_NO_VERSION_CHECK);
 706  }
 707  
 708  /**
 709   * Check if server can perform HTTPS requests, return bool
 710   *
 711   * @since 1.7.1
 712   * @return bool whether the server can perform HTTP requests over SSL
 713   */
 714  function yourls_can_http_over_ssl() {
 715      $ssl_curl = $ssl_socket = false;
 716  
 717      if( function_exists( 'curl_exec' ) ) {
 718          $curl_version  = curl_version();
 719          $ssl_curl = ( $curl_version['features'] & CURL_VERSION_SSL );
 720      }
 721  
 722      if( function_exists( 'stream_socket_client' ) ) {
 723          $ssl_socket = extension_loaded( 'openssl' ) && function_exists( 'openssl_x509_parse' );
 724      }
 725  
 726      return ( $ssl_curl OR $ssl_socket );
 727  }