[desktop] Improve export_status.json writes

desktop/src/main/ipc.ts

@@ -41,6 +41,7 @@ import {
     fsRm,
     fsRmdir,
     fsWriteFile,
+    fsWriteFileViaBackup,
 } from "./services/fs";
 import { convertToJPEG, generateImageThumbnail } from "./services/image";
 import { logout } from "./services/logout";
@@ -154,6 +155,12 @@ export const attachIPCHandlers = () => {
         fsWriteFile(path, contents),
     );
 
+    ipcMain.handle(
+        "fsWriteFileViaBackup",
+        (_, path: string, contents: string) =>
+            fsWriteFileViaBackup(path, contents),
+    );
+
     ipcMain.handle("fsIsDir", (_, dirPath: string) => fsIsDir(dirPath));
 
     ipcMain.handle("fsFindFiles", (_, folderPath: string) =>

desktop/src/main/services/fs.ts

@@ -24,6 +24,12 @@ export const fsReadTextFile = async (filePath: string) =>
 export const fsWriteFile = (path: string, contents: string) =>
     fs.writeFile(path, contents, { flush: true });
 
+export const fsWriteFileViaBackup = async (path: string, contents: string) => {
+    const backupPath = path + ".backup";
+    await fs.writeFile(backupPath, contents, { flush: true });
+    return fs.rename(backupPath, path);
+};
+
 export const fsIsDir = async (dirPath: string) => {
     if (!existsSync(dirPath)) return false;
     const stat = await fs.stat(dirPath);

desktop/src/preload.ts

@@ -178,6 +178,9 @@ const fsReadTextFile = (path: string) =>
 const fsWriteFile = (path: string, contents: string) =>
     ipcRenderer.invoke("fsWriteFile", path, contents);
 
+const fsWriteFileViaBackup = (path: string, contents: string) =>
+    ipcRenderer.invoke("fsWriteFileViaBackup", path, contents);
+
 const fsIsDir = (dirPath: string) => ipcRenderer.invoke("fsIsDir", dirPath);
 
 // - Conversion
@@ -373,6 +376,7 @@ contextBridge.exposeInMainWorld("electron", {
         rm: fsRm,
         readTextFile: fsReadTextFile,
         writeFile: fsWriteFile,
+        writeFileViaBackup: fsWriteFileViaBackup,
         isDir: fsIsDir,
         findFiles: fsFindFiles,
     },

web/apps/photos/src/services/export/index.ts

@@ -888,7 +888,7 @@ class ExportService {
         try {
             const exportRecord = await this.getExportRecord(folder);
             const newRecord: ExportRecord = { ...exportRecord, ...newData };
-            await ensureElectron().fs.writeFile(
+            await ensureElectron().fs.writeFileViaBackup(
                 joinPath(folder, exportRecordFileName),
                 JSON.stringify(newRecord, null, 2),
             );

web/packages/base/types/ipc.ts

@@ -259,6 +259,18 @@ export interface Electron {
          */
         writeFile: (path: string, contents: string) => Promise<void>;
 
+        /**
+         * A variant of {@link writeFile} that first writes the file to a backup
+         * file, and then renames the backup file to the actual path. This both
+         * makes the write atomic (as far as the node's fs.rename guarantees
+         * atomicity), and also keeps the backup file around for recovery if
+         * something goes wrong during the rename.
+         *
+         * This behaviour of this function is tailored around for writes to the
+         * "export_status.json" during exports.
+         */
+        writeFileViaBackup: (path: string, contents: string) => Promise<void>;
+
         /**
          * Return true if there is an item at {@link dirPath}, and it is as
          * directory.