MDL-34290 repository_equella: do not download files when not needed

repository_equella::get_file_by_reference respects request timeouts, downloads only images (for thumbnail generation),
does not use cache_file class (content is cached in moodle filepool if needed);
also repository_equella has counter of unsuccessfull connect attempts and do not perform any more if 3 failed
(within one request)

repository/equella/lib.php

@@ -122,6 +122,49 @@ public function get_file_reference($source) {
         return $source;
     }
 
+    /**
+     * Counts the number of failed connections.
+     *
+     * If we received the connection timeout more than 3 times in a row, we don't attemt to
+     * connect to the server any more during this request.
+     *
+     * This function is used by {@link repository_equella::get_file_by_reference()} that
+     * synchronises the file size of referenced files.
+     *
+     * @param int $errno omit if we just want to know the return value, the last curl_errno otherwise
+     * @return bool true if we had less than 3 failed connections, false if no more connections
+     * attempts recommended
+     */
+    private function connection_result($errno = null) {
+        static $countfailures = array();
+        $sess = sesskey();
+        if (!array_key_exists($sess, $countfailures)) {
+            $countfailures[$sess] = 0;
+        }
+        if ($errno !== null) {
+            if ($errno == 0) {
+                // reset count of failed connections
+                $countfailures[$sess] = 0;
+            } else if ($errno == 7 /*CURLE_COULDNT_CONNECT*/ || $errno == 9 /*CURLE_REMOTE_ACCESS_DENIED*/) {
+                // problems with server
+                $countfailures[$sess]++;
+            }
+        }
+        return ($countfailures[$sess] < 3);
+    }
+
+    /**
+     * Decide whether or not the file should be synced
+     *
+     * @param stored_file $storedfile
+     * @return bool
+     */
+    public function sync_individual_file(stored_file $storedfile) {
+        // if we had several unsuccessfull attempts to connect to server - do not try any more
+        return $this->connection_result();
+    }
+
+
     /**
      * Download a file, this function can be overridden by subclass. {@link curl}
      *
@@ -155,35 +198,50 @@ public function get_file($reference, $filename = '') {
 
     /**
      * Returns information about file in this repository by reference
-     * {@link repository::get_file_reference()}
-     * {@link repository::get_file()}
      *
+     * If the file is an image we download the contents and save it in our filesystem
+     * so we can generate thumbnails. Otherwise we just request the file size.
      * Returns null if file not found or can not be accessed
      *
      * @param stdClass $reference file reference db record
-     * @return null|stdClass containing attribute 'filepath'
+     * @return stdClass|null contains one of the following:
+     *   - 'filesize' (for non-image files or files we failed to retrieve fully because of timeout)
+     *   - 'filepath' (for image files that we retrieived and saved)
      */
     public function get_file_by_reference($reference) {
-        $ref = unserialize(base64_decode($reference->reference));
-        $url = $this->appendtoken($ref->url);
-
-        if (!$url) {
+        global $USER;
+        $ref = @unserialize(base64_decode($reference->reference));
+        if (!isset($ref->url) || !($url = $this->appendtoken($ref->url))) {
             // Occurs when the user isn't known..
             return null;
         }
 
-        // We use this cache to get the correct file size.
-        $cachedfilepath = cache_file::get($url, array('ttl' => 0));
-        if ($cachedfilepath === false) {
-            // Cache the file.
-            $path = $this->get_file($url);
-            $cachedfilepath = cache_file::create_from_file($url, $path['path']);
+        $return = null;
+        $cookiepathname = $this->prepare_file($USER->id. '_'. uniqid('', true). '.cookie');
+        $c = new curl(array('cookie' => $cookiepathname));
+        if (file_extension_in_typegroup($ref->filename, 'web_image')) {
+            $path = $this->prepare_file('');
+            $result = $c->download_one($url, null, array('filepath' => $path, 'followlocation' => true, 'timeout' => self::SYNCIMAGE_TIMEOUT));
+            if ($result === true) {
+                $return = (object)array('filepath' => $path);
             }
+        } else {
+            $result = $c->head($url, array('followlocation' => true, 'timeout' => self::SYNCFILE_TIMEOUT));
+        }
+        // Delete cookie jar.
+        if (file_exists($cookiepathname)) {
+            unlink($cookiepathname);
+        }
 
-        if ($cachedfilepath && is_readable($cachedfilepath)) {
-            return (object)array('filepath' => $cachedfilepath);
+        $this->connection_result($c->get_errno());
+        $curlinfo = $c->get_info();
+        if ($return === null && isset($curlinfo['http_code']) && $curlinfo['http_code'] == 200
+                && array_key_exists('download_content_length', $curlinfo)
+                && $curlinfo['download_content_length'] >= 0) {
+            // we received a correct header and at least can tell the file size
+            $return = (object)array('filesize' => $curlinfo['download_content_length']);
         }
-        return null;
+        return $return;
     }
 
     /**