fix(napi): Buffer value lifetime should align the Rust lifetime

crates/napi/src/bindgen_runtime/js_values/buffer.rs

@@ -3,15 +3,33 @@ use std::{mem, ptr};
 
 use crate::{bindgen_prelude::*, check_status, sys, Result, ValueType};
 
-/// zero copy u8 vector shared between rust and napi
+/// Zero copy u8 vector shared between rust and napi.
+/// Auto reference the raw JavaScript value, and release it when dropped.
+/// So it is safe to use it in `async fn`, the `&[u8]` under the hood will not be dropped until the `drop` called.
 pub struct Buffer {
   inner: mem::ManuallyDrop<Vec<u8>>,
+  raw: Option<(sys::napi_ref, sys::napi_env)>,
 }
 
+impl Drop for Buffer {
+  fn drop(&mut self) {
+    if let Some((ref_, env)) = self.raw {
+      check_status_or_throw!(
+        env,
+        unsafe { sys::napi_delete_reference(env, ref_) },
+        "Failed to delete Buffer reference in drop"
+      );
+    }
+  }
+}
+
+unsafe impl Send for Buffer {}
+
 impl From<Vec<u8>> for Buffer {
   fn from(data: Vec<u8>) -> Self {
     Buffer {
       inner: mem::ManuallyDrop::new(data),
+      raw: None,
     }
   }
 }
@@ -68,7 +86,11 @@ impl FromNapiValue for Buffer {
   unsafe fn from_napi_value(env: sys::napi_env, napi_val: sys::napi_value) -> Result<Self> {
     let mut buf = ptr::null_mut();
     let mut len = 0;
-
+    let mut ref_ = ptr::null_mut();
+    check_status!(
+      unsafe { sys::napi_create_reference(env, napi_val, 1, &mut ref_) },
+      "Failed to create reference from Buffer"
+    )?;
     check_status!(
       unsafe { sys::napi_get_buffer_info(env, napi_val, &mut buf, &mut len as *mut usize) },
       "Failed to convert napi buffer into rust Vec<u8>"
@@ -76,12 +98,27 @@ impl FromNapiValue for Buffer {
 
     Ok(Self {
       inner: mem::ManuallyDrop::new(unsafe { Vec::from_raw_parts(buf as *mut _, len, len) }),
+      raw: Some((ref_, env)),
     })
   }
 }
 
 impl ToNapiValue for Buffer {
   unsafe fn to_napi_value(env: sys::napi_env, mut val: Self) -> Result<sys::napi_value> {
+    // From Node.js value, not from `Vec<u8>`
+    if let Some((ref_, _)) = val.raw {
+      let mut buf = ptr::null_mut();
+      check_status!(
+        unsafe { sys::napi_get_reference_value(env, ref_, &mut buf) },
+        "Failed to get Buffer value from reference"
+      )?;
+      check_status!(
+        unsafe { sys::napi_delete_reference(env, ref_) },
+        "Failed to delete Buffer reference"
+      )?;
+      val.raw = None; // Prevent double free
+      return Ok(buf);
+    }
     let len = val.inner.len();
     let mut ret = ptr::null_mut();
     check_status!(

examples/napi/__test__/typegen.spec.ts.md

@@ -152,6 +152,7 @@ Generated by [AVA](https://avajs.dev).
     export function createExternalTypedArray(): Uint32Array␊
     export function mutateTypedArray(input: Float32Array): void␊
     export function derefUint8Array(a: Uint8Array, b: Uint8ClampedArray): number␊
+    export function bufferPassThrough(buf: Buffer): Promise<Buffer>␊
     /**␊
      * \`constructor\` option for \`struct\` requires all fields to be public,␊
      * otherwise tag impl fn as constructor␊

examples/napi/__test__/values.spec.ts

@@ -86,6 +86,7 @@ import {
   chronoDateToMillis,
   derefUint8Array,
   chronoDateAdd1Minute,
+  bufferPassThrough,
 } from '../'
 
 test('export const', (t) => {
@@ -382,6 +383,12 @@ test('async move', async (t) => {
   t.is(await asyncMultiTwo(2), 4)
 })
 
+test('buffer passthrough', async (t) => {
+  const fixture = Buffer.from('hello world')
+  const ret = await bufferPassThrough(fixture)
+  t.deepEqual(ret, fixture)
+})
+
 test('either', (t) => {
   t.is(eitherStringOrNumber(2), 2)
   t.is(eitherStringOrNumber('hello'), 'hello'.length)

examples/napi/index.d.ts

@@ -142,6 +142,7 @@ export function convertU32Array(input: Uint32Array): Array<number>
 export function createExternalTypedArray(): Uint32Array
 export function mutateTypedArray(input: Float32Array): void
 export function derefUint8Array(a: Uint8Array, b: Uint8ClampedArray): number
+export function bufferPassThrough(buf: Buffer): Promise<Buffer>
 /**
  * `constructor` option for `struct` requires all fields to be public,
  * otherwise tag impl fn as constructor

examples/napi/src/typed_array.rs

@@ -33,3 +33,8 @@ fn mutate_typed_array(mut input: Float32Array) {
 fn deref_uint8_array(a: Uint8Array, b: Uint8ClampedArray) -> u32 {
   (a.len() + b.len()) as u32
 }
+
+#[napi]
+async fn buffer_pass_through(buf: Buffer) -> Result<Buffer> {
+  Ok(buf)
+}