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Merge pull request #660 from adam-vessey/7.x-avoid-chunking-race-condition

Chunking/byte-range datastream request race condition
pull/669/head
Jared Whiklo 8 years ago committed by GitHub
parent
commit
03b6afeb6f
  1. 76
      includes/datastream.inc

76
includes/datastream.inc

@ -437,6 +437,12 @@ function islandora_view_datastream_deliver_chunks(AbstractDatastream $datastream
/**
* Creates/returns the file URI for the content of a datastream for chunking.
*
* File locks are used to ensure the datastream is completely downloaded before
* attempting to serve up chunks from the file.
*
* @throws RepositoryException|Exception
* Exceptions may be thrown if the file was unable to be reliably acquired.
*
* @param AbstractDatastream $datastream
* An AbstractDatastream representing a datastream on a Fedora object.
*
@ -445,17 +451,71 @@ function islandora_view_datastream_deliver_chunks(AbstractDatastream $datastream
*/
function islandora_view_datastream_retrieve_file_uri(AbstractDatastream $datastream) {
module_load_include('inc', 'islandora', 'includes/mimetype.utils');
module_load_include('inc', 'islandora', 'includes/utilities');
$extension = islandora_get_extension_for_mimetype($datastream->mimetype);
$file_uri = 'temporary://chunk_' . $datastream->parent->id . '_' . $datastream->id . '_' . $datastream->createdDate->getTimestamp() . '.' . $extension;
if (!file_exists($file_uri)) {
$file = new stdClass();
$file->uri = $file_uri;
$file->filename = drupal_basename($file_uri);
$file->filemime = $datastream->mimeType;
$file->status = 0;
$datastream->getContent($file_uri);
file_save($file);
touch(drupal_realpath($file_uri));
$fp = fopen($file_uri, 'r+b');
if (flock($fp, LOCK_SH)) {
try {
fseek($fp, 0, SEEK_END);
if (ftell($fp) === 0 && $datastream->size > 0) {
// Just opened at beginning of file, if beginning == EOF, need to grab
// it.
if (!flock($fp, LOCK_EX | LOCK_NB)) {
// Hypothetically, two threads could have a "shared" lock with an
// unpopulated file, so to avoid deadlock on the "exclusive" lock,
// drop the "shared" lock before blocking to obtain the "exclusive"
// lock.
flock($fp, LOCK_UN);
}
if (flock($fp, LOCK_EX)) {
// Get exclusive lock, write file.
$file = islandora_temp_file_entry($file_uri, $datastream->mimeType);
if ($file->filesize == $datastream->size) {
// Populated in another thread while we were waiting for the
// "exclusive" lock; drop lock and return.
flock($fp, LOCK_UN);
fclose($fp);
return $file_uri;
}
try {
$datastream->getContent($file->uri);
clearstatcache($file->uri);
$file = file_save($file);
if ($file->filesize != $datastream->size) {
throw new RepositoryException(t('Size of file downloaded for chunking does not match: Got @apparent bytes when expecting @actual.', array(
'@apparent' => $file->filesize,
'@actual' => $datastream->size,
)));
}
}
catch (RepositoryException $e) {
file_delete($file);
throw $e;
}
}
else {
throw new Exception(t('Failed to acquire write lock when downloading @pid/@dsid for chunking.', array(
'@pid' => $datastream->parent->id,
'@dsid' => $datastream->id,
)));
}
}
flock($fp, LOCK_UN);
fclose($fp);
return $file_uri;
}
catch (Exception $e) {
flock($fp, LOCK_UN);
fclose($fp);
throw $e;
}
}
throw new Exception(t('Failed to acquire shared lock when chunking @pid/@dsid.', array(
'@pid' => $datastream->parent->id,
'@dsid' => $datastream->id,
)));
}

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