From 350671db4758890116fa6709be90189231958bdb Mon Sep 17 00:00:00 2001
From: Alex Gleason <alex@alexgleason.me>
Date: Wed, 25 Sep 2024 14:31:01 -0500
Subject: [PATCH] DittoPglite: prevent starting PGlite instances in worker
 threads

---
 src/db/adapters/DittoPglite.ts | 19 +++++++++++++------
 src/utils/worker.test.ts       | 30 ++++++++++++++++++++++++++++++
 src/utils/worker.ts            |  9 +++++++++
 3 files changed, 52 insertions(+), 6 deletions(-)
 create mode 100644 src/utils/worker.test.ts
 create mode 100644 src/utils/worker.ts

diff --git a/src/db/adapters/DittoPglite.ts b/src/db/adapters/DittoPglite.ts
index 2455fc37..6e4ae488 100644
--- a/src/db/adapters/DittoPglite.ts
+++ b/src/db/adapters/DittoPglite.ts
@@ -6,16 +6,23 @@ import { Kysely } from 'kysely';
 import { DittoDatabase, DittoDatabaseOpts } from '@/db/DittoDatabase.ts';
 import { DittoTables } from '@/db/DittoTables.ts';
 import { KyselyLogger } from '@/db/KyselyLogger.ts';
+import { isWorker } from '@/utils/worker.ts';
 
 export class DittoPglite {
   static create(databaseUrl: string, opts?: DittoDatabaseOpts): DittoDatabase {
+    const url = new URL(databaseUrl);
+
+    if (url.protocol === 'file:' && isWorker()) {
+      throw new Error('PGlite is not supported in worker threads.');
+    }
+
+    const pglite = new PGlite(databaseUrl, {
+      extensions: { pg_trgm },
+      debug: opts?.debug,
+    });
+
     const kysely = new Kysely<DittoTables>({
-      dialect: new PgliteDialect({
-        database: new PGlite(databaseUrl, {
-          extensions: { pg_trgm },
-          debug: opts?.debug,
-        }),
-      }),
+      dialect: new PgliteDialect({ database: pglite }),
       log: KyselyLogger,
     });
 
diff --git a/src/utils/worker.test.ts b/src/utils/worker.test.ts
new file mode 100644
index 00000000..89845e2b
--- /dev/null
+++ b/src/utils/worker.test.ts
@@ -0,0 +1,30 @@
+import { assertEquals } from '@std/assert';
+
+import { isWorker } from '@/utils/worker.ts';
+
+Deno.test('isWorker from the main thread returns false', () => {
+  assertEquals(isWorker(), false);
+});
+
+Deno.test('isWorker from a worker thread returns true', async () => {
+  const script = `
+    import { isWorker } from '@/utils/worker.ts';
+    postMessage(isWorker());
+    self.close();
+  `;
+
+  const worker = new Worker(
+    URL.createObjectURL(new Blob([script], { type: 'application/javascript' })),
+    { type: 'module' },
+  );
+
+  const result = await new Promise<boolean>((resolve) => {
+    worker.onmessage = (e) => {
+      resolve(e.data);
+    };
+  });
+
+  worker.terminate();
+
+  assertEquals(result, true);
+});
diff --git a/src/utils/worker.ts b/src/utils/worker.ts
new file mode 100644
index 00000000..ce94caee
--- /dev/null
+++ b/src/utils/worker.ts
@@ -0,0 +1,9 @@
+/**
+ * Detect if this thread is running in a Worker context.
+ *
+ * https://stackoverflow.com/a/18002694
+ */
+export function isWorker(): boolean {
+  // @ts-ignore This is fine.
+  return typeof WorkerGlobalScope !== 'undefined' && self instanceof WorkerGlobalScope;
+}