From 0612f15aad69b80bb1ca9097fb2ae12275160408 Mon Sep 17 00:00:00 2001
From: Andras Schmelczer <andras@schmelczer.dev>
Date: Sun, 23 Feb 2025 10:04:20 +0000
Subject: [PATCH] Add FileNotFoundError error

---
 .../src/file-operations/file-operations.ts    | 11 ++-
 .../safe-filesystem-operations.ts             | 88 +++++++++++++++++++
 2 files changed, 96 insertions(+), 3 deletions(-)
 create mode 100644 frontend/sync-client/src/file-operations/safe-filesystem-operations.ts

diff --git a/frontend/sync-client/src/file-operations/file-operations.ts b/frontend/sync-client/src/file-operations/file-operations.ts
index 8fe2a3fd..4bd29402 100644
--- a/frontend/sync-client/src/file-operations/file-operations.ts
+++ b/frontend/sync-client/src/file-operations/file-operations.ts
@@ -2,12 +2,17 @@ import type { Logger } from "src/tracing/logger";
 import type { FileSystemOperations } from "./filesystem-operations";
 import type { RelativePath } from "src/persistence/database";
 import { isBinary, isFileTypeMergable, mergeText } from "sync_lib";
+import { SafeFileSystemOperations } from "./safe-filesystem-operations";
 
 export class FileOperations {
+	private readonly fs: SafeFileSystemOperations;
+
 	public constructor(
 		private readonly logger: Logger,
-		private readonly fs: FileSystemOperations
-	) {}
+		fs: FileSystemOperations
+	) {
+		this.fs = new SafeFileSystemOperations(fs);
+	}
 
 	public async listAllFiles(): Promise<RelativePath[]> {
 		const files = await this.fs.listAllFiles();
@@ -43,7 +48,7 @@ export class FileOperations {
 	}
 
 	public async exists(path: RelativePath): Promise<boolean> {
-		this.logger.debug(`Checking existance of ${path}`);
+		this.logger.debug(`Checking existence of ${path}`);
 		return this.fs.exists(path);
 	}
 
diff --git a/frontend/sync-client/src/file-operations/safe-filesystem-operations.ts b/frontend/sync-client/src/file-operations/safe-filesystem-operations.ts
new file mode 100644
index 00000000..3776e63a
--- /dev/null
+++ b/frontend/sync-client/src/file-operations/safe-filesystem-operations.ts
@@ -0,0 +1,88 @@
+import { FileSystemOperations } from "dist/types";
+import type { RelativePath } from "src/persistence/database";
+
+export class FileNotFoundError extends Error {
+	constructor(message: string) {
+		super(message);
+		this.name = "FileNotFoundError";
+	}
+}
+
+// Decorate FileSystemOperations replacing errors with FileNotFoundError
+// if the accessed file doesn't exist.
+export class SafeFileSystemOperations implements FileSystemOperations {
+	public constructor(private readonly fs: FileSystemOperations) {}
+
+	public listAllFiles(): Promise<RelativePath[]> {
+		return this.fs.listAllFiles();
+	}
+
+	public async read(path: RelativePath): Promise<Uint8Array> {
+		return this.safeOperation(path, () => this.fs.read(path));
+	}
+
+	public async write(path: RelativePath, content: Uint8Array): Promise<void> {
+		return this.fs.write(path, content);
+	}
+
+	public async atomicUpdateText(
+		path: RelativePath,
+		updater: (currentContent: string) => string
+	): Promise<string> {
+		return this.safeOperation(path, () =>
+			this.fs.atomicUpdateText(path, updater)
+		);
+	}
+
+	public async getFileSize(path: RelativePath): Promise<number> {
+		return this.safeOperation(path, () => this.fs.getFileSize(path));
+	}
+
+	public async getModificationTime(path: RelativePath): Promise<Date> {
+		return this.safeOperation(path, () =>
+			this.fs.getModificationTime(path)
+		);
+	}
+
+	public async exists(path: RelativePath): Promise<boolean> {
+		return this.fs.exists(path);
+	}
+
+	public async createDirectory(path: RelativePath): Promise<void> {
+		return this.fs.createDirectory(path);
+	}
+
+	public async delete(path: RelativePath): Promise<void> {
+		return this.fs.delete(path);
+	}
+
+	public async rename(
+		oldPath: RelativePath,
+		newPath: RelativePath
+	): Promise<void> {
+		return this.safeOperation(oldPath, () =>
+			this.fs.rename(oldPath, newPath)
+		);
+	}
+
+	private async safeOperation<T>(
+		path: RelativePath,
+		operation: () => Promise<T>
+	): Promise<T> {
+		// Without locking the file, this isn't atomic, however, it's good enough practicaly.
+		// This will only break if the file exists, gets deleted and then immediately
+		// recreated while `operation` is running.
+		if (!(await this.fs.exists(path))) {
+			throw new FileNotFoundError(path);
+		}
+		try {
+			return await operation();
+		} catch (error) {
+			if (await this.fs.exists(path)) {
+				throw error;
+			} else {
+				throw new FileNotFoundError(path);
+			}
+		}
+	}
+}