encoding: use AliasedUint32Array for encodeInto results

Getting the buffer from a TypedArray created from the JS land
incurs a copy. For encodeInto() results we can just use an
AliasedArray and let the binding always own the store.

lib/internal/encoding.js

@@ -13,7 +13,6 @@ const {
   StringPrototypeSlice,
   Symbol,
   SymbolToStringTag,
-  Uint32Array,
   Uint8Array,
 } = primordials;
 
@@ -49,12 +48,12 @@ const {
   validateString,
   validateObject,
 } = require('internal/validators');
-
+const binding = internalBinding('encoding');
 const {
   encodeInto,
   encodeUtf8String,
   decodeUTF8,
-} = internalBinding('encoding');
+} = binding;
 
 const { Buffer } = require('buffer');
 
@@ -318,8 +317,6 @@ function getEncodingFromLabel(label) {
   return encodings.get(trimAsciiWhitespace(label.toLowerCase()));
 }
 
-const encodeIntoResults = new Uint32Array(2);
-
 class TextEncoder {
   constructor() {
     this[kEncoder] = true;
@@ -340,8 +337,10 @@ class TextEncoder {
     validateString(src, 'src');
     if (!dest || !isUint8Array(dest))
       throw new ERR_INVALID_ARG_TYPE('dest', 'Uint8Array', dest);
-    encodeInto(src, dest, encodeIntoResults);
-    return { read: encodeIntoResults[0], written: encodeIntoResults[1] };
+
+    encodeInto(src, dest);
+    const { 0: read, 1: written } = binding.encodeIntoResults;
+    return { read, written };
   }
 
   [inspect](depth, opts) {

src/encoding.cc

@@ -25,11 +25,24 @@ using v8::Uint8Array;
 using v8::Uint32Array;
 using v8::Value;
 
-BindingData::BindingData(Environment* env, Local<Object> object)
-    : SnapshotableObject(env, object, type_int) {}
+void BindingData::MemoryInfo(MemoryTracker* tracker) const {
+  tracker->TrackField("encode_into_results_buffer", encode_into_results_buffer_);
+}
+
+BindingData::BindingData(Environment* env, v8::Local<v8::Object> object)
+    : SnapshotableObject(env, object, type_int),
+      encode_into_results_buffer_(env->isolate(), kEncodeIntoResultsLength) {
+  object->Set(env->context(),
+            FIXED_ONE_BYTE_STRING(env->isolate(), "encodeIntoResults"),
+            encode_into_results_buffer_.GetJSArray())
+  .Check();
+}
 
 bool BindingData::PrepareForSerialization(Local<Context> context,
                                           v8::SnapshotCreator* creator) {
+  // We'll just re-initialize the buffers in the constructor since their
+  // contents can be thrown away once consumed in the previous call.
+  encode_into_results_buffer_.Release();
   // Return true because we need to maintain the reference to the binding from
   // JS land.
   return true;
@@ -57,10 +70,10 @@ void BindingData::Deserialize(Local<Context> context,
 void BindingData::EncodeInto(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
   Isolate* isolate = env->isolate();
-  CHECK_GE(args.Length(), 3);
+  CHECK_GE(args.Length(), 2);
   CHECK(args[0]->IsString());
   CHECK(args[1]->IsUint8Array());
-  CHECK(args[2]->IsUint32Array());
+  BindingData* binding_data = Environment::GetBindingData<BindingData>(args);
 
   Local<String> source = args[0].As<String>();
 
@@ -69,21 +82,16 @@ void BindingData::EncodeInto(const FunctionCallbackInfo<Value>& args) {
   char* write_result = static_cast<char*>(buf->Data()) + dest->ByteOffset();
   size_t dest_length = dest->ByteLength();
 
-  // results = [ read, written ]
-  Local<Uint32Array> result_arr = args[2].As<Uint32Array>();
-  uint32_t* results = reinterpret_cast<uint32_t*>(
-      static_cast<char*>(result_arr->Buffer()->Data()) +
-      result_arr->ByteOffset());
-
   int nchars;
   int written = source->WriteUtf8(
       isolate,
       write_result,
       dest_length,
       &nchars,
       String::NO_NULL_TERMINATION | String::REPLACE_INVALID_UTF8);
-  results[0] = nchars;
-  results[1] = written;
+
+  binding_data->encode_into_results_buffer_[0] = nchars;
+  binding_data->encode_into_results_buffer_[1] = written;
 }
 
 // Encode a single string to a UTF-8 Uint8Array (not Buffer).

src/encoding.h

@@ -21,7 +21,7 @@ class BindingData : public SnapshotableObject {
   SERIALIZABLE_OBJECT_METHODS()
   SET_BINDING_ID(encoding_binding_data)
 
-  SET_NO_MEMORY_INFO()
+  void MemoryInfo(MemoryTracker* tracker) const override;
   SET_SELF_SIZE(BindingData)
   SET_MEMORY_INFO_NAME(BindingData)
 
@@ -35,6 +35,10 @@ class BindingData : public SnapshotableObject {
                          void* priv);
   static void RegisterTimerExternalReferences(
       ExternalReferenceRegistry* registry);
+
+private:
+  static constexpr size_t kEncodeIntoResultsLength = 2;
+  AliasedUint32Array encode_into_results_buffer_;
 };
 
 }  // namespace encoding_binding