feat(napi): AsMut and DerefMut for JsBuffer

napi/src/js_values/arraybuffer.rs

@@ -1,5 +1,5 @@
 use std::mem;
-use std::ops::Deref;
+use std::ops::{Deref, DerefMut};
 use std::os::raw::c_void;
 use std::ptr;
 
@@ -196,6 +196,12 @@ impl Deref for JsArrayBufferValue {
   }
 }
 
+impl DerefMut for JsArrayBufferValue {
+  fn deref_mut(&mut self) -> &mut Self::Target {
+    self.data.as_mut_slice()
+  }
+}
+
 impl JsTypedArray {
   /// get TypeArray info
   /// https://nodejs.org/api/n-api.html#n_api_napi_get_typedarray_info

napi/src/js_values/buffer.rs

@@ -1,5 +1,5 @@
 use std::mem;
-use std::ops::Deref;
+use std::ops::{Deref, DerefMut};
 use std::ptr;
 
 use super::Value;
@@ -76,6 +76,12 @@ impl AsRef<[u8]> for JsBufferValue {
   }
 }
 
+impl AsMut<[u8]> for JsBufferValue {
+  fn as_mut(&mut self) -> &mut [u8] {
+    self.data.as_mut_slice()
+  }
+}
+
 impl Deref for JsBufferValue {
   type Target = [u8];
 
@@ -83,3 +89,9 @@ impl Deref for JsBufferValue {
     self.data.as_slice()
   }
 }
+
+impl DerefMut for JsBufferValue {
+  fn deref_mut(&mut self) -> &mut Self::Target {
+    self.data.as_mut_slice()
+  }
+}

test_module/__test__/buffer.spec.ts

@@ -32,3 +32,9 @@ test('should create borrowed buffer with finalize', (t) => {
     Buffer.from([1, 2, 3]),
   )
 })
+
+test('should be able to mutate buffer', (t) => {
+  const fixture = Buffer.from([0, 1])
+  bindings.mutateBuffer(fixture)
+  t.is(fixture[1], 42)
+})

test_module/src/buffer.rs

@@ -3,7 +3,7 @@ use std::str;
 
 use napi::{
   noop_finalize, CallContext, ContextlessResult, Env, Error, JsBuffer, JsNumber, JsObject,
-  JsString, Result, Status,
+  JsString, JsUndefined, Result, Status,
 };
 
 #[js_function(1)]
@@ -57,6 +57,13 @@ pub fn create_borrowed_buffer_with_finalize(env: Env) -> ContextlessResult<JsBuf
   .map(|b| Some(b.into_raw()))
 }
 
+#[js_function(1)]
+fn mutate_buffer(ctx: CallContext) -> Result<JsUndefined> {
+  let buffer = &mut ctx.get::<JsBuffer>(0)?.into_value()?;
+  buffer[1] = 42;
+  ctx.env.get_undefined()
+}
+
 pub fn register_js(exports: &mut JsObject) -> Result<()> {
   exports.create_named_method("getBufferLength", get_buffer_length)?;
   exports.create_named_method("bufferToString", buffer_to_string)?;
@@ -69,5 +76,6 @@ pub fn register_js(exports: &mut JsObject) -> Result<()> {
     "createBorrowedBufferWithFinalize",
     create_borrowed_buffer_with_finalize,
   )?;
+  exports.create_named_method("mutateBuffer", mutate_buffer)?;
   Ok(())
 }