feat: save/restore database snapshots (#78)

packages/core/src/database/database.js

@@ -41,9 +41,8 @@ class Database {
   }
 
   databaseInitialize(cb) {
-    // TODO: save in the db results by using a combination of concatMap and scan, to save results in batches
     fromEvent(this.events, "updateDB").subscribe(({eventKey, eventData}) => {
-      if (eventData.removed) { 
+      if (eventData.removed) {
         this.deleteEvent(eventKey, eventData.id);
         return;
       }
@@ -56,6 +55,25 @@ class Database {
     });
   }
 
+  serialize() {
+    return this.db.serialize();
+  }
+
+  restore(serializedDb, forced) {
+    return new Promise((resolve, reject) => {
+      const collections = this.db.listCollections();
+      if (!collections?.length || forced) {
+        this.db.loadJSON(serializedDb);
+        this.db.saveDatabase(err => {
+          if(err) {
+            reject(err);
+          }
+          resolve();
+        });
+      }
+    });
+  }
+
   getLastKnownEvent(eventKey) {
     const collection = this.db.getCollection(eventKey);
     if (collection?.count()) {
@@ -99,9 +117,10 @@ class Database {
   deleteEvent(eventKey, eventId) {
     const collection = this.db.getCollection(eventKey);
     if (collection)
-      collection.chain()
+      collection
-                .find({id: eventId})
+        .chain()
-                .remove();
+        .find({id: eventId})
+        .remove();
   }
 
   deleteNewestBlocks(eventKey, gteBlockNum) {
@@ -109,9 +128,10 @@ class Database {
 
     const collection = this.db.getCollection(eventKey);
     if (collection)
-      collection.chain()
+      collection
-                .find({blockNumber: {$gte: gteBlockNum}})
+        .chain()
-                .remove();
+        .find({blockNumber: {$gte: gteBlockNum}})
+        .remove();
   }
 }
 

packages/core/src/subspace.js

@@ -33,6 +33,7 @@ export default class Subspace {
     this.options.callInterval = options.callInterval;
     this.options.dbFilename = options.dbFilename ?? "subspace.db";
     this.options.disableDatabase = options.disableDatabase;
+    this.options.snapshot = options.snapshot;
 
     this.networkId = undefined;
     this.isWebsocketProvider = options.disableSubscriptions ? false : !!web3?.currentProvider?.on;
@@ -44,6 +45,11 @@ export default class Subspace {
     } else {
       this._db = new Database(this.options.dbFilename, this.events);
     }
+    
+    if(this.options.snapshot) {
+      await this._db.restore(this.options.snapshot);
+    }
+
     this.eventSyncer = new EventSyncer(this.web3.eth, this.events, this._db, this.isWebsocketProvider);
     this.logSyncer = new LogSyncer(this.web3.eth, this.events, this._db);
 
@@ -308,4 +314,12 @@ export default class Subspace {
   close() {
     this.eventSyncer.close();
   }
+
+  snapshot() {
+    return this._db.serialize();
+  }
+
+  async loadSnapshot(serializedDb) {
+    return this._db.restore(serializedDb, true);
+  }
 }

packages/core/types/index.d.ts

@@ -19,6 +19,8 @@ export default class Subspace {
   trackGasPrice(): Observable<string>;
   trackAverageBlocktime(): Observable<number>;
   close(): void;
+  snapshot(): string;
+  async loadSnapshot(serializedDb: string): void;
 }
 
 export interface ContractLike {