fix(config): Throw PreconditionException always when it didn't match

Previously even when the precondition did not match, the call "passed"
when the after value was the expected one. This however can lead to
race conditions, duplicate code excutions and other things.

Signed-off-by: Joas Schilling <coding@schilljs.com>

2 files changed, 39 insertions, 3 deletions

diff --git a/lib/private/AllConfig.php b/lib/private/AllConfig.php
index 263b5283133..f08e5125a47 100644
--- a/lib/private/AllConfig.php
+++ b/lib/private/AllConfig.php
@@ -242,10 +242,10 @@ class AllConfig implements IConfig {
 		$prevValue = $this->getUserValue($userId, $appName, $key, null);
 
 		if ($prevValue !== null) {
-			if ($prevValue === (string)$value) {
-				return;
-			} elseif ($preCondition !== null && $prevValue !== (string)$preCondition) {
+			if ($preCondition !== null && $prevValue !== (string)$preCondition) {
 				throw new PreConditionNotMetException();
+			} elseif ($prevValue === (string)$value) {
+				return;
 			} else {
 				$qb = $this->connection->getQueryBuilder();
 				$qb->update('preferences')
diff --git a/tests/lib/AllConfigTest.php b/tests/lib/AllConfigTest.php
index 92793a75ae6..73a62c6b8f2 100644
--- a/tests/lib/AllConfigTest.php
+++ b/tests/lib/AllConfigTest.php
@@ -182,6 +182,42 @@ class AllConfigTest extends \Test\TestCase {
 		$config->deleteUserValue('userPreCond1', 'appPreCond', 'keyPreCond');
 	}
 
+	public function testSetUserValueWithPreConditionFailureWhenResultStillMatches(): void {
+		$this->expectException(\OCP\PreConditionNotMetException::class);
+
+		$config = $this->getConfig();
+
+		$selectAllSQL = 'SELECT `userid`, `appid`, `configkey`, `configvalue` FROM `*PREFIX*preferences` WHERE `userid` = ?';
+
+		$config->setUserValue('userPreCond1', 'appPreCond', 'keyPreCond', 'valuePreCond');
+
+		$result = $this->connection->executeQuery($selectAllSQL, ['userPreCond1'])->fetchAll();
+
+		$this->assertCount(1, $result);
+		$this->assertEquals([
+			'userid' => 'userPreCond1',
+			'appid' => 'appPreCond',
+			'configkey' => 'keyPreCond',
+			'configvalue' => 'valuePreCond'
+		], $result[0]);
+
+		// test if the method throws with invalid precondition when the value is the same
+		$config->setUserValue('userPreCond1', 'appPreCond', 'keyPreCond', 'valuePreCond', 'valuePreCond3');
+
+		$result = $this->connection->executeQuery($selectAllSQL, ['userPreCond1'])->fetchAll();
+
+		$this->assertCount(1, $result);
+		$this->assertEquals([
+			'userid' => 'userPreCond1',
+			'appid' => 'appPreCond',
+			'configkey' => 'keyPreCond',
+			'configvalue' => 'valuePreCond'
+		], $result[0]);
+
+		// cleanup
+		$config->deleteUserValue('userPreCond1', 'appPreCond', 'keyPreCond');
+	}
+
 	public function testSetUserValueUnchanged() {
 		// TODO - FIXME until the dependency injection is handled properly (in AllConfig)
 		$this->markTestSkipped('Skipped because this is just testable if database connection can be injected');