Added index to SQL TTL cache (#142)

1. Added index to SQL TTL cache by leveraging latest `dwn-sql-store`
1. Added handling of an edge race condition.

---------

Co-authored-by: Liran Cohen <c.liran.c@gmail.com>

package.json

@@ -1,7 +1,7 @@
 {
   "name": "@web5/dwn-server",
   "type": "module",
-  "version": "0.4.0",
+  "version": "0.4.1",
   "files": [
     "dist",
     "src"
@@ -27,7 +27,7 @@
   },
   "dependencies": {
     "@tbd54566975/dwn-sdk-js": "0.4.0",
-    "@tbd54566975/dwn-sql-store": "0.6.0",
+    "@tbd54566975/dwn-sql-store": "0.6.1",
     "better-sqlite3": "^8.5.0",
     "body-parser": "^1.20.2",
     "bytes": "3.1.2",

src/web5-connect/sql-ttl-cache.ts

@@ -8,11 +8,13 @@ export class SqlTtlCache {
   private static readonly cacheTableName = 'cacheEntries';
   private static readonly cleanupIntervalInSeconds = 60;
 
+  private sqlDialect: Dialect;
   private db: Kysely<CacheDatabase>;
   private cleanupTimer: NodeJS.Timeout;
 
   private constructor(sqlDialect: Dialect) {
     this.db = new Kysely<CacheDatabase>({ dialect: sqlDialect });
+    this.sqlDialect = sqlDialect;
   }
 
   /**
@@ -27,14 +29,26 @@ export class SqlTtlCache {
   }
 
   private async initialize(): Promise<void> {
-    await this.db.schema
-      .createTable(SqlTtlCache.cacheTableName)
-      .ifNotExists()
-      // 512 chars to accommodate potentially large `state` in Web5 Connect flow
-      .addColumn('key', 'varchar(512)', (column) => column.primaryKey())
-      .addColumn('value', 'text', (column) => column.notNull())
-      .addColumn('expiry', 'integer', (column) => column.notNull())
-      .execute();
+
+    // create table if it doesn't exist
+    const tableExists = await this.sqlDialect.hasTable(this.db, SqlTtlCache.cacheTableName);
+    if (!tableExists) {
+      await this.db.schema
+        .createTable(SqlTtlCache.cacheTableName)
+        .ifNotExists() // kept to show supported by all dialects in contrast to ifNotExists() below, though not needed due to tableExists check above
+        // 512 chars to accommodate potentially large `state` in Web5 Connect flow
+        .addColumn('key', 'varchar(512)', (column) => column.primaryKey())
+        .addColumn('value', 'text', (column) => column.notNull())
+        .addColumn('expiry', 'integer', (column) => column.notNull())
+        .execute();
+
+      await this.db.schema
+        .createIndex('index_expiry')
+        // .ifNotExists() // intentionally kept commented out code to show that it is not supported by all dialects (ie. MySQL)
+        .on(SqlTtlCache.cacheTableName)
+        .column('expiry')
+        .execute();
+    }
 
     // Start the cleanup timer
     this.startCleanupTimer();
@@ -102,7 +116,7 @@ export class SqlTtlCache {
   }
 
   /**
-   * Periodically clean up expired cache entries.
+   * Cleans up expired cache entries.
    */
   public async cleanUpExpiredEntries(): Promise<void> {
     await this.db

src/web5-connect/web5-connect-server.ts

@@ -83,10 +83,15 @@ export class Web5ConnectServer {
    * Returns the Web5 Connect Request object. The request ID can only be used once.
    */
   public async getWeb5ConnectRequest(requestId: string): Promise<Web5ConnectRequest | undefined> {
-    const request = this.cache.get(`request:${requestId}`);
+    const request = await this.cache.get(`request:${requestId}`);
 
-    // Delete the Request Object from the data store now that it has been retrieved.
-    this.cache.delete(`request:${requestId}`);
+    // Delete the Request Object from cache once it has been retrieved.
+    // IMPORTANT: only delete if the object exists, otherwise there could be a race condition
+    // where the object does not exist in this call but becomes available immediately after,
+    // we would end up deleting it before it is successfully retrieved.
+    if (request !== undefined) {
+      this.cache.delete(`request:${requestId}`);
+    }
 
     return request;
   }
@@ -102,10 +107,15 @@ export class Web5ConnectServer {
    * Gets the Web5 Connect Response object. The `state` string can only be used once.
    */
   public async getWeb5ConnectResponse(state: string): Promise<Web5ConnectResponse | undefined> {
-    const response = this. cache.get(`response:${state}`);
-
-    // Delete the Response object from the data store now that it has been retrieved.
-    this.cache.delete(`response:${state}`);
+    const response = await this.cache.get(`response:${state}`);
+
+    // Delete the Response object from the cache once it has been retrieved.
+    // IMPORTANT: only delete if the object exists, otherwise there could be a race condition
+    // where the object does not exist in this call but becomes available immediately after,
+    // we would end up deleting it before it is successfully retrieved.
+    if (response !== undefined) {
+      this.cache.delete(`response:${state}`);
+    }
 
     return response;
   }