Added part files for when writing chunks

Whenever a chunk is being written, it is now written to a part file
first. This is to avoid a concurrent chunk upload to believe that the
former chunk already exists, even though it's not fully written.

This makes sure that the final file assembly is only done when all
chunks were successfully written.

Also added an extra unique id to chunk parts in case the same chunk is
uploaded twice concurrently.

1 files changed, 13 insertions, 2 deletions

diff --git a/lib/private/cache/file.php b/lib/private/cache/file.php
index 6fa7686ea96..8ec048ccba0 100644
--- a/lib/private/cache/file.php
+++ b/lib/private/cache/file.php
@@ -11,6 +11,7 @@ namespace OC\Cache;
 
 use OC\Files\Filesystem;
 use OC\Files\View;
+use OCP\Security\ISecureRandom;
 
 class File {
 	protected $storage;
@@ -79,12 +80,22 @@ class File {
 		$storage = $this->getStorage();
 		$result = false;
 		$proxyStatus = \OC_FileProxy::$enabled;
+		// unique id to avoid chunk collision, just in case
+		$uniqueId = \OC::$server->getSecureRandom()->getLowStrengthGenerator()->generate(
+			16,
+			ISecureRandom::CHAR_DIGITS . ISecureRandom::CHAR_LOWER . ISecureRandom::CHAR_UPPER
+		);
+
+		// use part file to prevent hasKey() to find the key
+		// while it is being written
+		$keyPart = $key . '.' . $uniqueId . '.part';
 		\OC_FileProxy::$enabled = false;
-		if ($storage and $storage->file_put_contents($key, $value)) {
+		if ($storage and $storage->file_put_contents($keyPart, $value)) {
 			if ($ttl === 0) {
 				$ttl = 86400; // 60*60*24
 			}
-			$result = $storage->touch($key, time() + $ttl);
+			$result = $storage->touch($keyPart, time() + $ttl);
+			$result &= $storage->rename($keyPart, $key);
 		}
 		\OC_FileProxy::$enabled = $proxyStatus;
 		return $result;