fseek: $whence parameter is not properly passed to underlying stream.

S3 driver: override appendUploadedData() function as the streamWrapper does not support "a+" mode.

core/src/plugins/access.fs/class.fsAccessWrapper.php

@@ -290,7 +290,7 @@ public function stream_open($path, $mode, $options, &$context)
 
     public function stream_seek($offset , $whence = SEEK_SET)
     {
-        fseek($this->fp, $offset, SEEK_SET);
+        fseek($this->fp, $offset, $whence);
     }
 
     public function stream_tell()

core/src/plugins/access.s3/class.s3AccessDriver.php

@@ -145,6 +145,41 @@ protected function parseSpecificContributions(&$contribNode)
         $this->disableArchiveBrowsingContributions($contribNode);
     }
 
+    /**
+     * We have to overwrite original FS function as S3 wrapper does not support "a+" open mode.
+     *
+     * @param String $folder Folder destination
+     * @param String $source Maybe updated by the function
+     * @param String $target Existing part to append data
+     * @return bool If the target file already existed or not.
+     * @throws Exception
+     */
+    protected function appendUploadedData($folder, $source, $target){
+
+        $already_existed = false;
+        if($source == $target){
+            throw new Exception("Something nasty happened: trying to copy $source into itself, it will create a loop!");
+        }
+        // S3 does not really support append. Let's grab the remote target first.
+        if (file_exists($folder ."/" . $target)) {
+            $already_existed = true;
+            $this->logDebug("Should copy stream from $source to $target - folder is ($folder)");
+            $partO = fopen($folder."/".$source, "r");
+            $appendF = fopen($folder ."/". $target, 'a');
+            while (!feof($partO)) {
+                $buf = fread($partO, 1024);
+                fwrite($appendF, $buf);
+            }
+            fclose($partO);
+            fclose($appendF);
+            $this->logDebug("Done, closing streams!");
+        }
+        @unlink($folder."/".$source);
+        return $already_existed;
+
+    }
+
+
     public function isWriteable($dir, $type="dir")
     {
         return true;