HttpCaching.php

<?php
class HttpCaching {

  private $cacheControlDirectives = array();
  private $ages = array('max-age' => -1, 's-maxage' => -1);
  private $lastModified;
  private $eTag;

  function sendStatusAndHeaders($die) {
    $isFresh = $_SERVER['REQUEST_METHOD'] == "GET" ? $this->isFresh() : false;
    // Send back a 304?
    if ($isFresh == true) {
      header('HTTP/1.1 304 Not Modified');
    }
    $this->sendHeaders();
    // Die if 304?
    if ($isFresh == true && $die == true) {
      exit();
    }
    return $isFresh;
  }

  function sendHeaders() {
    // Expires corresponds to max-age
    if ($this->ages['max-age'] >= 0) {
      header('Expires: ' . self::formatDate(time() + $this->ages['max-age']), 1);
    }
    // Cache-Control
    if (!is_array($this->cacheControlDirectives)) {
      $this->cacheControlDirectives = array();
    }
    foreach($this->ages as $dir => $value) {
      if ($value >= 0) {
        array_push($this->cacheControlDirectives, "$dir=$value");
      }
    }
    if (count($this->cacheControlDirectives) > 0) {
      header('Cache-Control: ' .
             implode(', ', $this->cacheControlDirectives), 1);
    }
    // At least one of ETags of Last-Modified will be sent for cacheability
    if ($this->eTag) {
      header('ETag: ' . $this->eTag);
    }
    if ($this->lastModified) {
      $lm = $this->lastModified;
    } else if (!$this->eTag) {
      $lm = time();
    }
    if ($lm) {
      header('Last-Modified: ' . self::formatDate($lm));
    }
  }

  function isFresh() {
    if (!isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) &&
        !isset($_SERVER['HTTP_IF_NONE_MATCH'])) {
      // No information provided by the client
      return false;
    }

    if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
      if (!$this->lastModified) {
        return false;
      }
      // Split the If-Modified-Since (Netscape < v6 gets this wrong)
      $ifModifiedSince = explode(';', $_SERVER['HTTP_IF_MODIFIED_SINCE']);
      // Turn the client request If-Modified-Since into a timestamp
      $ifModifiedSince = strtotime($ifModifiedSince[0]);
      // Compare timestamps (FIXME: make this test '!='?)
      if ($this->lastModified > $ifModifiedSince) {
        return false;
      }
    }

    if (isset($_SERVER['HTTP_IF_NONE_MATCH'])) {
      if ($_SERVER['HTTP_IF_NONE_MATCH'] == '*') {
        return true;
      }
      if (!$this->eTag) {
        return false;
      }
      $etags = preg_split('/,\s*/', $_SERVER['HTTP_IF_NONE_MATCH']);
      foreach($etags as $e) {
        if ($this->etagMatch($e)) {
          return true;
        }
      }
      return false;
    }

    return true;
  }

  function etagMatch($etag) {
    if (!$this->eTag) {
      return false;
    }
    if ((self::isEtagWeak($this->eTag) || self::isEtagWeak($etag))
        &&
        ($_SERVER['REQUEST_METHOD'] != "GET" || isset($_SERVER['HTTP_RANGE'])))
    {
      // Weak validation only works for non-subrange GET requests
      return false;
    }
    if (self::etagValidator($this->eTag) == self::etagValidator($etag)) {
      return true;
    } else {
      return false;
    }
  }

  static function isEtagWeak($etag) {
    return (substr_compare($etag, 'W/', 0, 2) == 0);
  }

  static function etagValidator($etag) {
    if (self::isEtagWeak($etag)) {
      return substr($etag, 2);
    } else {
      return $etag;
    }
  }

  function getDuration($type) {
    if ($type != "max-age" && $type != "s-maxage") {
      throw new Exception("Invalid type");
    }
    return $this->ages[$type];
  }

  function setDuration($type, $time) {
    if ($type != "max-age" && $type != "s-maxage") {
      throw new Exception("Invalid type");
    }
    if (is_numeric($time)) {
      $time = intval($time);
      if ($time < 0) {
        $time = -1;
      }
    } else {
      if ($time == 'now') {
        $time = 0;
      } else {
        $time = strtotime($time) - time();
      }
      if ($time < 0) {
        throw new Exception("Bad interval specified to strtotime()");
      }
    }
    return $this->ages[$type] = $time;
  }

  function freshFor($time) {
    return $this->setDuration('max-age', $time);
  }

  function setCacheControlDirective($type, $set) {
    if ($set == true) {
      if (!in_array($type, $this->cacheControlDirectives)) {
        array_push($this->cacheControlDirectives, $type);
      }
    } else {
      $this->cacheControlDirectives = array_diff($this->cacheControlDirectives,
                                                 array($type));
    }
  }

  function ccPublic($set) {
    $this->setCacheControlDirective('public', $set);
  }

  function ccNoCache($set) {
    $this->setCacheControlDirective('no-cache', $set);
  }

  function ccNoStore($set) {
    $this->setCacheControlDirective('no-store', $set);
  }

  function ccMustRevalidate($set) {
    $this->setCacheControlDirective('must-revalidate', $set);
  }

  function ccProxyRevalidate($set) {
    $this->setCacheControlDirective('proxy-revalidate', $set);
  }

  function etag($value) {
    $this->eTag = '"' . $value . '"';
  }

  function weakEtag($value) {
    $this->etag($value);
    $this->eTag = "W/" . $this->eTag;
  }

  function lastModified($value) {
    $this->lastModified = $value;
  }

  function setLastModifiedFromFile($file) {
    $finfo = stat($file);
    if (!$finfo) {
      return;
    }
    $this->lastModified($finfo['mtime']);
  }

  static function sendHeadersSpecifyingFreshness($time) {
    $hc = new HttpCaching();
    $hc->freshFor($time);
    $hc->ccMustRevalidate(true);
    $hc->sendHeaders();
  }

  static function formatDate($time) {
    return gmdate("D, d M Y H:i:s", $time) . ' GMT';
  }
}

?>

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PHP HTTP Caching