fix: block writing empty files with 0 quota

Signed-off-by: Robin Appelman <robin@icewind.nl>

Author: icewind1991

lib/private/Files/Storage/Wrapper/Quota.php

@@ -120,19 +120,20 @@ public function copy(string $source, string $target): bool {
 
 	#[\Override]
 	public function fopen(string $path, string $mode) {
-		if (!$this->hasQuota()) {
+		if (!$this->hasQuota() || $this->isPartFile($path)) {
 			return $this->getWrapperStorage()->fopen($path, $mode);
 		}
-		$source = $this->getWrapperStorage()->fopen($path, $mode);
 
-		// don't apply quota for part files
-		if (!$this->isPartFile($path)) {
-			$free = $this->free_space($path);
-			if ($source && (is_int($free) || is_float($free)) && $free >= 0 && $mode !== 'r' && $mode !== 'rb') {
-				// only apply quota for files, not metadata, trash or others
-				if ($this->shouldApplyQuota($path)) {
-					return \OC\Files\Stream\Quota::wrap($source, $free);
-				}
+		$free = $this->free_space($path);
+		if ($this->shouldApplyQuota($path) && $free == 0) {
+			return false;
+		}
+
+		$source = $this->getWrapperStorage()->fopen($path, $mode);
+		if ($source && (is_int($free) || is_float($free)) && $free >= 0 && $mode !== 'r' && $mode !== 'rb') {
+			// only apply quota for files, not metadata, trash or others
+			if ($this->shouldApplyQuota($path)) {
+				return \OC\Files\Stream\Quota::wrap($source, $free);
 			}
 		}
 

tests/lib/Files/Storage/Wrapper/QuotaTest.php

@@ -229,4 +229,10 @@ public function testNoTouchQuotaZero(): void {
 		$instance = $this->getLimitedStorage(0.0);
 		$this->assertFalse($instance->touch('foobar'));
 	}
+
+	public function testNoFopenQuotaZero(): void {
+		$instance = $this->getLimitedStorage(0.0);
+		$fh = $instance->fopen('files/test.txt', 'w');
+		$this->assertFalse($fh);
+	}
 }