fix: CustomOutputStream 사용

src/main/java/com/woowacamp/storage/domain/file/controller/MultipartFileController.java

@@ -93,14 +93,22 @@ public void handleFileUpload(HttpServletRequest request) throws Exception {
 		}
 	}
 
+	static class CustomOutputStream extends ByteArrayOutputStream {
+		@Override
+		public synchronized void reset() {
+			super.reset();
+			buf = new byte[32];
+		}
+	}
+
 	/**
 	 * 클라이언트 요청을 buffer 단위로 읽어서 processBuffer 메소드를 호출합니다.
 	 * processBuffer 메소드에서 헤더 파싱을 하고 boundary 체크를 하여 각 파트를 구분합니다.
 	 */
 	private void processMultipartData(InputStream inputStream, UploadContext context) throws Exception {
 		byte[] buffer = new byte[bufferSize];
-		ByteArrayOutputStream lineBuffer = new ByteArrayOutputStream();
-		ByteArrayOutputStream contentBuffer = new ByteArrayOutputStream();
+		ByteArrayOutputStream lineBuffer = new CustomOutputStream();
+		ByteArrayOutputStream contentBuffer = new CustomOutputStream();
 		PartContext partContext = new PartContext();
 		UploadState state = new UploadState();
 
@@ -389,7 +397,6 @@ ResponseEntity<InputStreamResource> download(@CheckField(FieldType.FILE_ID) @Pat
 		headers.add(HttpHeaders.CONTENT_DISPOSITION,
 			"attachment; filename=\"" + encodedFileName + "\"; filename*=UTF-8''" + encodedFileName);
 
-
 		return ResponseEntity.ok()
 			.headers(headers)
 			.contentType(MediaType.APPLICATION_OCTET_STREAM)