Fix bookdrop race condition processing files before fully written (#2267) (#2785)

Co-authored-by: acx10 <acx10@users.noreply.github.com>

booklore-api/src/main/java/org/booklore/service/bookdrop/BookdropEventHandlerService.java

@@ -15,6 +15,7 @@ import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.stereotype.Service;
 
+import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.StandardWatchEventKinds;
@@ -35,6 +36,10 @@ public class BookdropEventHandlerService {
     private final AppSettingService appSettingService;
     private final BookdropMetadataService bookdropMetadataService;
 
+    private static final long STABILITY_CHECK_INTERVAL_MS = 500;
+    private static final int STABILITY_REQUIRED_CHECKS = 3;
+    private static final long STABILITY_MAX_WAIT_MS = 30_000;
+
     private final BlockingQueue<BookDropFileEvent> fileQueue = new LinkedBlockingQueue<>();
     private volatile boolean running = true;
     private Thread workerThread;
@@ -100,6 +105,11 @@ public class BookdropEventHandlerService {
                     return;
                 }
 
+                if (!waitForFileStability(file)) {
+                    log.warn("File did not stabilize within timeout, skipping: {}", file);
+                    return;
+                }
+
                 log.info("Handling new bookdrop file: {}", file);
 
                 int queueSize = fileQueue.size();
@@ -158,4 +168,41 @@ public class BookdropEventHandlerService {
             bookdropNotificationService.sendBookdropFileSummaryNotification();
         }
     }
+
+    private boolean waitForFileStability(Path file) {
+        long startTime = System.currentTimeMillis();
+        long lastSize = -1;
+        int stableCount = 0;
+
+        while (System.currentTimeMillis() - startTime < STABILITY_MAX_WAIT_MS) {
+            try {
+                if (!Files.exists(file)) {
+                    return false;
+                }
+
+                long currentSize = Files.size(file);
+
+                if (currentSize == lastSize && currentSize > 0) {
+                    stableCount++;
+                    if (stableCount >= STABILITY_REQUIRED_CHECKS) {
+                        return true;
+                    }
+                } else {
+                    stableCount = 0;
+                }
+
+                lastSize = currentSize;
+                Thread.sleep(STABILITY_CHECK_INTERVAL_MS);
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+                return false;
+            } catch (IOException e) {
+                log.warn("Error checking file size for stability: {}", file, e);
+                return false;
+            }
+        }
+
+        log.warn("File size did not stabilize after {}ms: {}", STABILITY_MAX_WAIT_MS, file);
+        return false;
+    }
 }

booklore-api/src/main/java/org/booklore/service/bookdrop/BookdropMetadataService.java

@@ -21,6 +21,8 @@ import org.springframework.transaction.annotation.Transactional;
 import tools.jackson.core.JacksonException;
 import tools.jackson.databind.ObjectMapper;
 
+import org.apache.commons.io.FilenameUtils;
+
 import java.io.File;
 import java.io.IOException;
 import java.time.Instant;
@@ -46,6 +48,12 @@ public class BookdropMetadataService {
     public BookdropFileEntity attachInitialMetadata(Long bookdropFileId) throws JacksonException {
         BookdropFileEntity entity = getOrThrow(bookdropFileId);
         BookMetadata initial = extractInitialMetadata(entity);
+        if (initial == null) {
+            log.warn("Metadata extraction returned null for file: {}. Using filename as fallback.", entity.getFileName());
+            initial = BookMetadata.builder()
+                    .title(FilenameUtils.getBaseName(entity.getFileName()))
+                    .build();
+        }
         extractAndSaveCover(entity);
         String initialJson = objectMapper.writeValueAsString(initial);
         entity.setOriginalMetadata(initialJson);

booklore-api/src/main/java/org/booklore/service/metadata/MetadataRefreshService.java

@@ -413,6 +413,11 @@ public class MetadataRefreshService {
 
     private FetchMetadataRequest buildFetchMetadataRequestFromBook(Book book) {
         BookMetadata metadata = book.getMetadata();
+        if (metadata == null) {
+            return FetchMetadataRequest.builder()
+                    .bookId(book.getId())
+                    .build();
+        }
         String isbn = metadata.getIsbn13();
         if (isbn == null || isbn.isBlank()) {
             isbn = metadata.getIsbn10();