From 771c88736831b9d0b0fd33c98cd29c27836f876d Mon Sep 17 00:00:00 2001
From: Quint Daenen <quint@daenen.email>
Date: Wed, 18 Feb 2026 11:42:08 +0100
Subject: [PATCH] fix: prevent WASM out-of-bounds trap in concurrent generate
 calls (#109)

When multiple icpBindgen plugin instances run concurrently (e.g.
several .did files processed during Vite's buildStart), the WASM
GenerateResult object could be held across await boundaries in
writeBindings(). This was observed to cause intermittent "Out of
bounds memory access" traps on the service_ts getter.

Extract all strings from the WASM object synchronously immediately
after wasmGenerate() and free it explicitly, so that writeBindings
operates only on plain JS strings.
---
 src/core/generate/index.ts | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/src/core/generate/index.ts b/src/core/generate/index.ts
index 961d954..bbf7350 100644
--- a/src/core/generate/index.ts
+++ b/src/core/generate/index.ts
@@ -1,7 +1,7 @@
 import { basename, resolve } from 'node:path';
 import { prepareBinding } from './bindings.ts';
 import { ensureDir, writeFileSafe } from './fs.ts';
-import { type WasmGenerateResult, wasmGenerate, wasmInit } from './rs.ts';
+import { wasmGenerate, wasmInit } from './rs.ts';
 
 const DID_FILE_EXTENSION = '.did';
 
@@ -122,8 +122,22 @@ export async function generate(options: GenerateOptions) {
     },
   });
 
+  // Extract all strings from the WASM object synchronously before any async
+  // work and free it explicitly.  The GenerateResult is backed by WASM linear
+  // memory and registered with a FinalizationRegistry whose cleanup timing
+  // is engine-dependent.  Holding the object across await boundaries has been
+  // observed to cause "Out of bounds memory access" traps when multiple
+  // generate() calls run concurrently (e.g. several Vite plugin instances).
+  const bindings = {
+    declarations_js: result.declarations_js,
+    declarations_ts: result.declarations_ts,
+    interface_ts: result.interface_ts,
+    service_ts: result.service_ts,
+  };
+  result.free();
+
   await writeBindings({
-    bindings: result,
+    bindings,
     outDir,
     outputFileName,
     output,
@@ -131,8 +145,15 @@ export async function generate(options: GenerateOptions) {
   });
 }
 
+type Bindings = {
+  declarations_js: string;
+  declarations_ts: string;
+  interface_ts: string;
+  service_ts: string;
+};
+
 type WriteBindingsOptions = {
-  bindings: WasmGenerateResult;
+  bindings: Bindings;
   outDir: string;
   outputFileName: string;
   output: GenerateOutputOptions;