Fix dropbox storage to not store the whole file in memory

Since the library can only store the full response in memory on
download, we use an alternate client lib and set the correct headers to
be able to stream the content to a temp file.

apps/files_external/3rdparty/Dropbox/OAuth/Curl.php

@@ -196,7 +196,7 @@ private function getOAuthBaseParams() {
      * @return array Array for request's headers section like
      * array('Authorization' => 'OAuth ...');
      */
-    private function getOAuthHeader($uri, $params, $method = 'GET', $oAuthParams = null) {
+    public function getOAuthHeader($uri, $params, $method = 'GET', $oAuthParams = null) {
         $oAuthParams = $oAuthParams ? $oAuthParams : $this->getOAuthBaseParams();
 
         // create baseString to encode for the sent parameters

apps/files_external/lib/dropbox.php

@@ -39,6 +39,7 @@ class Dropbox extends \OC\Files\Storage\Common {
 	private $root;
 	private $id;
 	private $metaData = array();
+	private $oauth;
 
 	private static $tempFiles = array();
 
@@ -51,10 +52,10 @@ public function __construct($params) {
 		) {
 			$this->root = isset($params['root']) ? $params['root'] : '';
 			$this->id = 'dropbox::'.$params['app_key'] . $params['token']. '/' . $this->root;
-			$oauth = new \Dropbox_OAuth_Curl($params['app_key'], $params['app_secret']);
-			$oauth->setToken($params['token'], $params['token_secret']);
+			$this->oauth = new \Dropbox_OAuth_Curl($params['app_key'], $params['app_secret']);
+			$this->oauth->setToken($params['token'], $params['token_secret']);
 			// note: Dropbox_API connection is lazy
-			$this->dropbox = new \Dropbox_API($oauth, 'auto');
+			$this->dropbox = new \Dropbox_API($this->oauth, 'auto');
 		} else {
 			throw new \Exception('Creating \OC\Files\Storage\Dropbox storage failed');
 		}
@@ -248,10 +249,31 @@ public function fopen($path, $mode) {
 		switch ($mode) {
 			case 'r':
 			case 'rb':
-				$tmpFile = \OCP\Files::tmpFile();
 				try {
-					$data = $this->dropbox->getFile($path);
-					file_put_contents($tmpFile, $data);
+					// slashes need to stay
+					$encodedPath = str_replace('%2F', '/', rawurlencode(trim($path, '/')));
+					$downloadUrl = 'https://api-content.dropbox.com/1/files/auto/' . $encodedPath;
+					$headers = $this->oauth->getOAuthHeader($downloadUrl, [], 'GET');
+
+					$client = \OC::$server->getHTTPClientService()->newClient();
+					try {
+						$tmpFile = \OC::$server->getTempManager()->getTemporaryFile();
+						$client->get($downloadUrl, [
+							'headers' => $headers,
+							'save_to' => $tmpFile,
+						]);
+					} catch (RequestException $e) {
+						if (!is_null($e->getResponse())) {
+							if ($e->getResponse()->getStatusCode() === 404) {
+								return false;
+							} else {
+								throw $e;
+							}
+						} else {
+							throw $e;
+						}
+					}
+
 					return fopen($tmpFile, 'r');
 				} catch (\Exception $exception) {
 					\OCP\Util::writeLog('files_external', $exception->getMessage(), \OCP\Util::ERROR);