Add more details if extract fails.

Signed-off-by: Daniel Kesselberg <mail@danielkesselberg.de>

lib/private/Archive/TAR.php

@@ -381,4 +381,14 @@ class TAR extends Archive {
 		$types = [null, 'gz', 'bz'];
 		$this->tar = new \Archive_Tar($this->path, $types[self::getTarType($this->path)]);
 	}
+
+	/**
+	 * Get error object from archive_tar.
+	 */
+	public function getError(): ?\PEAR_Error {
+		if ($this->tar instanceof \Archive_Tar && $this->tar->error_object instanceof \PEAR_Error) {
+			return $this->tar->error_object;
+		}
+		return null;
+	}
 }

lib/private/Installer.php

@@ -294,12 +294,14 @@ class Installer {
 
 					if ($archive) {
 						if (!$archive->extract($extractDir)) {
-							throw new \Exception(
-								sprintf(
-									'Could not extract app %s',
-									$appId
-								)
-							);
+							$errorMessage = 'Could not extract app ' . $appId;
+
+							$archiveError = $archive->getError();
+							if ($archiveError instanceof \PEAR_Error) {
+								$errorMessage .= ': ' . $archiveError->getMessage();
+							}
+
+							throw new \Exception($errorMessage);
 						}
 						$allFiles = scandir($extractDir);
 						$folders = array_diff($allFiles, ['.', '..']);