Attempt #1 on preserving savegame files

Author: tobspr

electron/index.js

@@ -3,10 +3,11 @@
 const { app, BrowserWindow, Menu, MenuItem, session } = require("electron");
 const path = require("path");
 const url = require("url");
-const childProcess = require("child_process");
 const { ipcMain, shell } = require("electron");
 const fs = require("fs");
-const steam = require('./steam');
+const steam = require("./steam");
+const asyncLock = require("async-lock");
+
 const isDev = process.argv.indexOf("--dev") >= 0;
 const isLocal = process.argv.indexOf("--local") >= 0;
 
@@ -153,7 +154,82 @@ ipcMain.on("exit-app", (event, flag) => {
     app.quit();
 });
 
-function performFsJob(job) {
+let renameCounter = 1;
+
+const fileLock = new asyncLock({
+    timeout: 30000,
+    maxPending: 1000,
+});
+
+function niceFileName(filename) {
+    return filename.replace(storePath, "@");
+}
+
+async function writeFileSafe(filename, contents) {
+    ++renameCounter;
+    const prefix = "[ " + renameCounter + ":" + niceFileName(filename) + " ] ";
+    const transactionId = String(new Date().getTime()) + "." + renameCounter;
+
+    if (fileLock.isBusy()) {
+        console.warn(prefix, "Concurrent write process on", filename);
+    }
+
+    fileLock.acquire(filename, async () => {
+        console.log(prefix, "Starting write on", niceFileName(filename), "in transaction", transactionId);
+
+        if (!fs.existsSync(filename)) {
+            // this one is easy
+            console.log(prefix, "Writing file instantly because it does not exist:", niceFileName(filename));
+            await fs.promises.writeFile(filename, contents, { encoding: "utf8" });
+            return;
+        }
+
+        // first, write a temporary file (.tmp-XXX)
+        const tempName = filename + ".tmp-" + transactionId;
+        console.log(prefix, "Writing temporary file", niceFileName(tempName));
+        await fs.promises.writeFile(tempName, contents, { encoding: "utf8" });
+
+        // now, rename the original file to (.backup-XXX)
+        const oldTemporaryName = filename + ".backup-" + transactionId;
+        console.log(
+            prefix,
+            "Renaming old file",
+            niceFileName(filename),
+            "to",
+            niceFileName(oldTemporaryName)
+        );
+        await fs.promises.rename(filename, oldTemporaryName);
+
+        // now, rename the temporary file (.tmp-XXX) to the target
+        console.log(
+            prefix,
+            "Renaming the temporary file",
+            niceFileName(tempName),
+            "to the original",
+            niceFileName(filename)
+        );
+        await fs.promises.rename(tempName, filename);
+
+        // we are done now, try to create a backup, but don't fail if the backup fails
+        try {
+            // check if there is an old backup file
+            const backupFileName = filename + ".backup";
+            if (fs.existsSync(backupFileName)) {
+                console.log(prefix, "Deleting old backup file", niceFileName(backupFileName));
+                // delete the old backup
+                await fs.promises.unlink(backupFileName);
+            }
+
+            // rename the old file to the new backup file
+            console.log(prefix, "Moving", niceFileName(oldTemporaryName), "to the backup file location");
+            await fs.promises.rename(oldTemporaryName, backupFileName);
+        } catch (ex) {
+            console.error(prefix, "Failed to switch backup files:", ex);
+        }
+    });
+}
+
+async function performFsJob(job) {
     const fname = path.join(storePath, job.filename);
 
     switch (job.type) {
@@ -165,38 +241,35 @@ function performFsJob(job) {
                 };
             }
 
-            let contents = "";
             try {
-                contents = fs.readFileSync(fname, { encoding: "utf8" });
+                const data = await fs.promises.readFile(fname, { encoding: "utf8" });
+                return {
+                    success: true,
+                    data,
+                };
             } catch (ex) {
                 return {
                     error: ex,
                 };
             }
-
-            return {
-                success: true,
-                data: contents,
-            };
         }
         case "write": {
             try {
-                fs.writeFileSync(fname, job.contents);
+                await writeFileSafe(fname, job.contents);
+                return {
+                    success: true,
+                    data: job.contents,
+                };
             } catch (ex) {
                 return {
                     error: ex,
                 };
             }
-
-            return {
-                success: true,
-                data: job.contents,
-            };
         }
 
         case "delete": {
             try {
-                fs.unlinkSync(fname);
+                await fs.promises.unlink(fname);
             } catch (ex) {
                 return {
                     error: ex,
@@ -214,15 +287,10 @@ function performFsJob(job) {
     }
 }
 
-ipcMain.on("fs-job", (event, arg) => {
-    const result = performFsJob(arg);
+ipcMain.on("fs-job", async (event, arg) => {
+    const result = await performFsJob(arg);
     event.reply("fs-response", { id: arg.id, result });
 });
 
-ipcMain.on("fs-sync-job", (event, arg) => {
-    const result = performFsJob(arg);
-    event.returnValue = result;
-});
-
 steam.init(isDev);
 steam.listen();

electron/package.json

@@ -14,5 +14,8 @@
     },
     "optionalDependencies": {
         "shapez.io-private-artifacts": "github:tobspr/shapez.io-private-artifacts#abi-v85"
+    },
+    "dependencies": {
+        "async-lock": "^1.2.8"
     }
 }

electron/yarn.lock

@@ -35,6 +35,11 @@
   resolved "https://registry.npmjs.org/@types/node/-/node-12.20.5.tgz"
   integrity sha512-5Oy7tYZnu3a4pnJ//d4yVvOImExl4Vtwf0D40iKUlU+XlUsyV9iyFWyCFlwy489b72FMAik/EFwRkNLjjOdSPg==
 
+async-lock@^1.2.8:
+  version "1.2.8"
+  resolved "https://registry.yarnpkg.com/async-lock/-/async-lock-1.2.8.tgz#7b02bdfa2de603c0713acecd11184cf97bbc7c4c"
+  integrity sha512-G+26B2jc0Gw0EG/WN2M6IczuGepBsfR1+DtqLnyFSH4p2C668qkOCtEkGNVEaaNAVlYwEMazy1+/jnLxltBkIQ==
+
 boolean@^3.0.1:
   version "3.0.2"
   resolved "https://registry.npmjs.org/boolean/-/boolean-3.0.2.tgz"

src/js/platform/browser/storage.js

@@ -58,11 +58,6 @@ export class StorageImplBrowser extends StorageInterface {
         });
     }
 
-    writeFileSyncIfSupported(filename, contents) {
-        window.localStorage.setItem(filename, contents);
-        return true;
-    }
-
     readFileAsync(filename) {
         if (this.currentBusyFilename === filename) {
             logger.warn("Attempt to read", filename, "while write progress on it is ongoing!");

src/js/platform/browser/storage_indexed_db.js

@@ -94,12 +94,6 @@ export class StorageImplBrowserIndexedDB extends StorageInterface {
         });
     }
 
-    writeFileSyncIfSupported(filename, contents) {
-        // Not supported
-        this.writeFileAsync(filename, contents);
-        return true;
-    }
-
     readFileAsync(filename) {
         if (!this.database) {
             return Promise.reject("Storage not ready");

src/js/platform/electron/storage.js

@@ -46,14 +46,6 @@ export class StorageImplElectron extends StorageInterface {
         });
     }
 
-    writeFileSyncIfSupported(filename, contents) {
-        return getIPCRenderer().sendSync("fs-sync-job", {
-            type: "write",
-            filename,
-            contents,
-        });
-    }
-
     readFileAsync(filename) {
         return new Promise((resolve, reject) => {
             // ipcMain

src/js/platform/storage.js

@@ -30,16 +30,6 @@ export class StorageInterface {
         return Promise.reject();
     }
 
-    /**
-     * Tries to write a file synchronously, used in unload handler
-     * @param {string} filename
-     * @param {string} contents
-     */
-    writeFileSyncIfSupported(filename, contents) {
-        abstract;
-        return false;
-    }
-
     /**
      * Reads a string asynchronously. Returns Promise<FILE_NOT_FOUND> if file was not found.
      * @param {string} filename