add compaction.failed event

API.md

@@ -241,7 +241,7 @@ Will return pointers to matched elements (shallow copies), returning full copies
 
 **Kind**: global class  
 **Extends**: [<code>EventEmitter</code>](http://nodejs.org/api/events.html)  
-**Emits**: <code>Datastore#event:&quot;compaction.done&quot;</code>  
+**Emits**: <code>Datastore#event:&quot;compaction.done&quot;</code>, <code>Datastore#event:&quot;compaction.failed&quot;</code>  
 
 * [Datastore](#Datastore) ⇐ [<code>EventEmitter</code>](http://nodejs.org/api/events.html)
     * [new Datastore(options)](#new_Datastore_new)
@@ -282,6 +282,7 @@ Will return pointers to matched elements (shallow copies), returning full copies
         * [.remove(query, [options], [cb])](#Datastore+remove)
         * [.removeAsync(query, [options])](#Datastore+removeAsync) ⇒ <code>Promise.&lt;number&gt;</code>
         * ["event:compaction.done"](#Datastore+event_compaction.done)
+        * ["event:compaction.failed"](#Datastore+event_compaction.failed)
     * _inner_
         * [~countCallback](#Datastore..countCallback) : <code>function</code>
         * [~findOneCallback](#Datastore..findOneCallback) : <code>function</code>
@@ -743,6 +744,16 @@ if the update did not actually modify them.</p>
 <p>Compaction event. Happens when the Datastore's Persistence has been compacted.
 It happens when calling [compactDatafileAsync](#Datastore+compactDatafileAsync), which is called periodically if you have called
 [setAutocompactionInterval](#Datastore+setAutocompactionInterval).</p>
+<p>In case of failure, it emits [Datastore#event:"compaction.failed"](Datastore#event:"compaction.failed") instead.</p>
+
+**Kind**: event emitted by [<code>Datastore</code>](#Datastore)  
+<a name="Datastore+event_compaction.failed"></a>
+
+### "event:compaction.failed"
+<p>Compaction event. Happens when the Datastore's Persistence compaction task has failed.
+It may happen when calling [compactDatafileAsync](#Datastore+compactDatafileAsync), which is called periodically if you have called
+[setAutocompactionInterval](#Datastore+setAutocompactionInterval).</p>
+<p>In case of success, it emits [Datastore#event:"compaction.done"](Datastore#event:"compaction.done") instead.</p>
 
 **Kind**: event emitted by [<code>Datastore</code>](#Datastore)  
 <a name="Datastore..countCallback"></a>

CHANGELOG.md

@@ -11,6 +11,9 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 - Explicitly import `buffer` [#34](https://github.com/seald/nedb/pull/34).
 - Fix `Cursor`'s typings [#45](https://github.com/seald/nedb/issues/45)
 
+### Added
+- Added a `compaction.failed` event [#28](https://github.com/seald/nedb/issues/28)
+
 ## [4.0.3] - 2023-12-13
 ### Fixed
 - Fixed EPERM Exception when datastore is at the root of a disk on Windows [#48](https://github.com/seald/nedb/issues/48)

lib/datastore.js

@@ -60,10 +60,23 @@ const { isDate, pick, filterIndexNames } = require('./utils.js')
  * It happens when calling {@link Datastore#compactDatafileAsync}, which is called periodically if you have called
  * {@link Datastore#setAutocompactionInterval}.
  *
+ * In case of failure, it emits {@link Datastore#event:"compaction.failed"} instead.
+ *
  * @event Datastore#event:"compaction.done"
  * @type {undefined}
  */
 
+/**
+ * Compaction event. Happens when the Datastore's Persistence compaction task has failed.
+ * It may happen when calling {@link Datastore#compactDatafileAsync}, which is called periodically if you have called
+ * {@link Datastore#setAutocompactionInterval}.
+ *
+ * In case of success, it emits {@link Datastore#event:"compaction.done"} instead.
+ *
+ * @event Datastore#event:"compaction.failed"
+ * @type {Error}
+ */
+
 /**
  * Generic document in NeDB.
  * It consists of an Object with anything you want inside.
@@ -143,6 +156,7 @@ const { isDate, pick, filterIndexNames } = require('./utils.js')
  * @classdesc The `Datastore` class is the main class of NeDB.
  * @extends external:EventEmitter
  * @emits Datastore#event:"compaction.done"
+ * @emits Datastore#event:"compaction.failed"
  * @typicalname NeDB
  */
 class Datastore extends EventEmitter {

lib/persistence.js

@@ -96,27 +96,31 @@ class Persistence {
    * @private
    */
   async persistCachedDatabaseAsync () {
-    const lines = []
-
-    if (this.inMemoryOnly) return
+    try {
+      const lines = []
 
-    this.db.getAllData().forEach(doc => {
-      lines.push(this.afterSerialization(model.serialize(doc)))
-    })
-    Object.keys(this.db.indexes).forEach(fieldName => {
-      if (fieldName !== '_id') { // The special _id index is managed by datastore.js, the others need to be persisted
-        lines.push(this.afterSerialization(model.serialize({
-          $$indexCreated: {
-            fieldName: this.db.indexes[fieldName].fieldName,
-            unique: this.db.indexes[fieldName].unique,
-            sparse: this.db.indexes[fieldName].sparse
-          }
-        })))
-      }
-    })
+      if (this.inMemoryOnly) return
+      this.db.getAllData().forEach(doc => {
+        lines.push(this.afterSerialization(model.serialize(doc)))
+      })
+      Object.keys(this.db.indexes).forEach(fieldName => {
+        if (fieldName !== '_id') { // The special _id index is managed by datastore.js, the others need to be persisted
+          lines.push(this.afterSerialization(model.serialize({
+            $$indexCreated: {
+              fieldName: this.db.indexes[fieldName].fieldName,
+              unique: this.db.indexes[fieldName].unique,
+              sparse: this.db.indexes[fieldName].sparse
+            }
+          })))
+        }
+      })
 
-    await storage.crashSafeWriteFileLinesAsync(this.filename, lines, this.modes)
-    this.db.emit('compaction.done')
+      await storage.crashSafeWriteFileLinesAsync(this.filename, lines, this.modes)
+      this.db.emit('compaction.done')
+    } catch (error) {
+      this.db.emit('compaction.failed', error)
+      throw error
+    }
   }
 
   /**

test/persistence.async.test.js

@@ -368,6 +368,7 @@ describe('Persistence async', function () {
   })
 
   it('Can listen to compaction events', async () => {
+    d.insertAsync({ a: 2 })
     const compacted = new Promise(resolve => {
       d.once('compaction.done', function () {
         resolve()
@@ -375,6 +376,21 @@ describe('Persistence async', function () {
     })
     await d.compactDatafileAsync()
     await compacted // should already be resolved when the function returns, but still awaiting for it
+
+    const failure = new Promise(resolve => {
+      d.once('compaction.failed', function (error) {
+        resolve(error)
+      })
+    })
+
+    const afterSerializationOriginal = d.persistence.afterSerialization
+    d.persistence.afterSerialization = () => { throw new Error('synthetic error') }
+    await d.compactDatafileAsync().then(() => { throw new Error('should have failed') }, error => {
+      if (!error || !(error instanceof Error) || error.message !== 'synthetic error') throw error
+    })
+    const error = await failure
+    if (!error || !(error instanceof Error) || error.message !== 'synthetic error') throw error
+    d.persistence.afterSerialization = afterSerializationOriginal
   })
 
   it('setAutocompaction fails gracefully when passed a NaN', async () => {