feat(core): safe file write, and also cleanup function using exit-hook package

packages/core/src/storage/json-file.ts

@@ -5,14 +5,59 @@ try {
     fs = require('fs')
 } catch (e) {}
 
+let exitHook: any = null
+try {
+    exitHook = require('exit-hook')
+} catch (e) {}
+
 export class JsonFileStorage extends JsonMemoryStorage {
     private readonly _filename: string
+    private readonly _safe: boolean
+    private readonly _cleanup: boolean
 
-    constructor(filename: string) {
+    private readonly _unsubscribe: () => void
+
+    constructor(
+        filename: string,
+        params?: {
+            /**
+             * Whether to save file "safely", meaning that the file will first be saved
+             * to `${filename}.tmp`, and then renamed to `filename`,
+             * instead of writing directly to `filename`.
+             *
+             * This solves the issue with the storage being saved as
+             * a blank file because of the app being stopped while
+             * the storage is being written.
+             *
+             * Defaults to `true`
+             */
+            safe?: boolean
+
+            /**
+             * Whether to save file on process exit.
+             * Uses [`exit-hook`](https://www.npmjs.com/package/exit-hook)
+             *
+             * Defaults to `true` if `exit-hook` is installed, otherwise `false`
+             */
+            cleanup?: boolean
+        }
+    ) {
         super()
         if (!fs) throw new Error('Node fs module is not available!')
 
         this._filename = filename
+        this._safe = params?.safe ?? true
+        this._cleanup = params?.cleanup ?? !!exitHook
+
+        if (this._cleanup && !exitHook) {
+            throw new Error(
+                'Cleanup on exit is supported through `exit-hook` library, install it first!'
+            )
+        }
+
+        if (this._cleanup) {
+            this._unsubscribe = exitHook(this._onProcessExit.bind(this))
+        }
     }
 
     async load(): Promise<void> {
@@ -32,19 +77,45 @@ export class JsonFileStorage extends JsonMemoryStorage {
 
     save(): Promise<void> {
         return new Promise((resolve, reject) => {
-            // calling writeFile immediately seems to destroy session when using debugger
-            setTimeout(
-                () =>
             fs.writeFile(
-                        this._filename,
+                this._safe ? this._filename + '.tmp' : this._filename,
                 this._saveJson(),
+                (err?: Error) => {
+                    if (this._safe) {
+                        fs.rename(
+                            this._filename + '.tmp',
+                            this._filename,
                             (err?: Error) => {
                                 if (err) reject(err)
                                 else resolve()
                             }
-                    ),
-                0
+                        )
+                    } else {
+                        if (err) reject(err)
+                        else resolve()
+                    }
+                }
             )
         })
     }
+
+    private _onProcessExit(): void {
+        // on exit handler must be synchronous, thus we use sync methods here
+
+        try {
+            fs.writeFileSync(this._filename, this._saveJson())
+        } catch (e) {}
+
+        if (this._safe) {
+            try {
+                fs.unlinkSync(this._filename + '.tmp')
+            } catch (e) {}
+        }
+    }
+
+    destroy(): void {
+        if (this._cleanup) {
+            this._unsubscribe()
+        }
+    }
 }