feat: clean cache directory when threshold is met

packages/my-app/src/tasks/cleanCacheDirectoryTask.ts

@@ -0,0 +1,117 @@
+/**
+ * Using background fetch trigger which is usually quite infrequent periodically clean the cache directory of the app.
+ * Inspiration https://www.echowaves.com/post/expo-filesystem-cachedirectory-has-to-be-cleaned
+ */
+import { backgroundFetchLog } from '@/logging';
+import * as BackgroundFetch from 'expo-background-fetch';
+import * as TaskManager from 'expo-task-manager';
+import * as FileSystem from 'expo-file-system';
+
+export const CLEAN_CACHE_DIRECTORY_TASK =
+  'clean-cache-directory-background-fetch';
+/**
+ * This is the maximum number of FileSystem.**Async calls to run so we don't exhaust?
+ */
+const FILESYSTEM_ASYNC_OPERATIONS_BATCH_SIZE = 100;
+
+/**
+ * This threshold must be met by the file sizes before cleaning will occur.
+ */
+const TRIGGER_CACHE_SIZE_IN_BYTES = 100_000_000;
+
+/**
+ * Minimum number of files to keep in the cache.
+ */
+const MIN_FILES_TO_KEEP = 100;
+
+const processFilesInBatchesAsync = async <T>(
+  items: string[],
+  processFunction: (item: string) => Promise<T | null>,
+): Promise<T[]> => {
+  const results: T[] = [];
+  for (
+    let i = 0;
+    i < items.length;
+    i += FILESYSTEM_ASYNC_OPERATIONS_BATCH_SIZE
+  ) {
+    const batch = items.slice(i, i + FILESYSTEM_ASYNC_OPERATIONS_BATCH_SIZE);
+    const batchResults = await Promise.all(batch.map(processFunction));
+    results.push(...(batchResults.filter((it) => it !== null) as T[]));
+  }
+  return results;
+};
+
+/**
+ * Function that specifies which files to preseve.  Namely Cache.db* and *.ttf
+ * @param filename
+ */
+const shouldPreserve = (filename: string) => {
+  const preserveCacheDb = filename.startsWith('Cache.db');
+  const preserveTtf = filename.endsWith('.ttf');
+
+  return preserveCacheDb || preserveTtf;
+};
+/**
+ * Traverses the directory and skips some files.
+ * @param directory
+ */
+const traverseDirectorySkipFontsAsync = async (
+  directory: string,
+): Promise<string[]> => {
+  const files: string[] = [];
+  const items = await FileSystem.readDirectoryAsync(directory);
+
+  for (const item of items) {
+    const fullPath = `${directory}/${item}`;
+    const fileInfo = await FileSystem.getInfoAsync(fullPath);
+
+    if (fileInfo.isDirectory) {
+      const nestedFiles = await traverseDirectorySkipFontsAsync(fullPath);
+      files.push(...nestedFiles);
+    } else if (!shouldPreserve(item)) {
+      files.push(fullPath);
+    }
+  }
+  return files;
+};
+
+TaskManager.defineTask('clean-cache', async () => {
+  const files = await traverseDirectorySkipFontsAsync(
+    FileSystem.cacheDirectory!,
+  );
+
+  // Process file info in batches
+  const fileInfos = await processFilesInBatchesAsync(files, async (file) => {
+    const info = await FileSystem.getInfoAsync(file, { size: true });
+    if (info.isDirectory || !info.exists || info.modificationTime === 0) {
+      return null;
+    } else {
+      return info;
+    }
+  });
+
+  const totalSizeOfCacheDirectoryInBytes = fileInfos.reduce(
+    (c, info) => c + info.size,
+    0,
+  );
+
+  backgroundFetchLog.info(
+    `totalSizeOfCacheDirectoryInBytes ${totalSizeOfCacheDirectoryInBytes}, number of files in cache ${fileInfos.length}`,
+  );
+
+  if (
+    totalSizeOfCacheDirectoryInBytes >= TRIGGER_CACHE_SIZE_IN_BYTES ||
+    fileInfos.length > MIN_FILES_TO_KEEP
+  ) {
+    fileInfos.sort((a, b) => a.modificationTime - b.modificationTime);
+    const filesToDelete = fileInfos
+      .slice(0, fileInfos.length - MIN_FILES_TO_KEEP)
+      .map((f) => f.uri);
+
+    // Delete files in batches
+    await processFilesInBatchesAsync(filesToDelete, async (fileUri) => {
+      await FileSystem.deleteAsync(fileUri, { idempotent: true });
+    });
+  }
+  return BackgroundFetch.BackgroundFetchResult.NoData;
+});

packages/my-app/src/tasks/index.ts

@@ -1,6 +1,7 @@
 /**
  * Registers task manager tasks
  */
+export { CLEAN_CACHE_DIRECTORY_TASK } from './cleanCacheDirectoryTask';
 export { BACKGROUND_FETCH_TASK } from './background-fetch';
 export { BACKGROUND_LOCATION_TASK } from './location';
 export { BACKGROUND_NOTIFICATION_TASK } from './notifications';