src: introduce PullAll method to speed up blob.text/arrayBuffer

Refs: nodejs/performance#118

Author: debadree25

lib/internal/blob.js

@@ -274,28 +274,17 @@ class Blob {
 
     const { promise, resolve, reject } = createDeferredPromise();
     const reader = this[kHandle].getReader();
-    const buffers = [];
-    const readNext = () => {
-      reader.pull((status, buffer) => {
-        if (status === 0) {
-          // EOS, concat & resolve
-          // buffer should be undefined here
-          resolve(concat(buffers));
-          return;
-        } else if (status < 0) {
-          // The read could fail for many different reasons when reading
-          // from a non-memory resident blob part (e.g. file-backed blob).
-          // The error details the system error code.
-          const error = lazyDOMException('The blob could not be read', 'NotReadableError');
-          reject(error);
-          return;
-        }
-        if (buffer !== undefined)
-          buffers.push(buffer);
-        queueMicrotask(() => readNext());
-      });
-    };
-    readNext();
+    reader.pullAll((status, buffer) => {
+      if (status === 0) {
+        resolve(buffer);
+      } else if (status < 0) {
+        // The read could fail for many different reasons when reading
+        // from a non-memory resident blob part (e.g. file-backed blob).
+        // The error details the system error code.
+        const error = lazyDOMException('The blob could not be read', 'NotReadableError');
+        reject(error);
+      }
+    })
     return promise;
   }
 

src/node_blob.cc

@@ -291,6 +291,7 @@ Local<FunctionTemplate> Blob::Reader::GetConstructorTemplate(Environment* env) {
         BaseObject::kInternalFieldCount);
     tmpl->SetClassName(FIXED_ONE_BYTE_STRING(env->isolate(), "BlobReader"));
     SetProtoMethod(env->isolate(), tmpl, "pull", Pull);
+    SetProtoMethod(env->isolate(), tmpl, "pullAll", PullAll);
     env->set_blob_reader_constructor_template(tmpl);
   }
   return tmpl;
@@ -379,6 +380,95 @@ void Blob::Reader::Pull(const FunctionCallbackInfo<Value>& args) {
       std::move(next), node::bob::OPTIONS_END, nullptr, 0));
 }
 
+void Blob::Reader::PullAll(const FunctionCallbackInfo<Value>& args) {
+  Environment* env = Environment::GetCurrent(args);
+  Blob::Reader* reader;
+  ASSIGN_OR_RETURN_UNWRAP(&reader, args.Holder());
+
+  CHECK(args[0]->IsFunction());
+  Local<Function> fn = args[0].As<Function>();
+  CHECK(!fn->IsConstructor());
+
+  if (reader->eos_) {
+    Local<Value> arg = Int32::New(env->isolate(), bob::STATUS_EOS);
+    reader->MakeCallback(fn, 1, &arg);
+    return args.GetReturnValue().Set(bob::STATUS_EOS);
+  }
+
+  struct View {
+    std::shared_ptr<BackingStore> store;
+    size_t length;
+    size_t offset = 0;
+  };
+
+  struct Impl {
+    BaseObjectPtr<Blob::Reader> reader;
+    Global<Function> callback;
+    Environment* env;
+    size_t total = 0;
+    std::vector<View> views;
+    int status = 1;
+  };
+
+  Impl* impl = new Impl();
+  impl->reader = BaseObjectPtr<Blob::Reader>(reader);
+  impl->callback.Reset(env->isolate(), fn);
+  impl->env = env;
+
+  auto next = [impl](int status,
+                     const DataQueue::Vec* vecs,
+                     size_t count,
+                     bob::Done doneCb) mutable {
+    Environment* env = impl->env;
+    if (status == bob::STATUS_EOS) impl->reader->eos_ = true;
+
+    if (count > 0) {
+      // Copy the returns vectors into a single ArrayBuffer.
+      size_t total = 0;
+      for (size_t n = 0; n < count; n++) total += vecs[n].len;
+
+      std::shared_ptr<BackingStore> store =
+          v8::ArrayBuffer::NewBackingStore(env->isolate(), total);
+      auto ptr = static_cast<uint8_t*>(store->Data());
+      for (size_t n = 0; n < count; n++) {
+        std::copy(vecs[n].base, vecs[n].base + vecs[n].len, ptr);
+        ptr += vecs[n].len;
+      }
+      // Since we copied the data buffers, signal that we're done with them.
+      std::move(doneCb)(0);
+      impl->views.push_back(View{store, total});
+      impl->total += total;
+    }
+
+    impl->status = status;
+    return;
+  };
+
+  while (impl->status > 0) {
+    impl->reader->inner_->Pull(
+        next, node::bob::OPTIONS_END, nullptr, 0);
+  };
+
+  std::shared_ptr<BackingStore> store = ArrayBuffer::NewBackingStore(
+      env->isolate(), impl->total);
+  auto ptr = static_cast<uint8_t*>(store->Data());
+  for (size_t n = 0; n < impl->views.size(); n++) {
+    uint8_t* from =
+        static_cast<uint8_t*>(impl->views[n].store->Data()) + impl->views[n].offset;
+    std::copy(from, from + impl->views[n].length, ptr);
+    ptr += impl->views[n].length;
+  }
+
+  Local<Value> argv[2] = {
+      Int32::New(env->isolate(), impl->status),
+      ArrayBuffer::New(env->isolate(), store),
+  };
+
+  impl->reader->MakeCallback(fn, arraysize(argv), argv);
+  auto dropMe = std::unique_ptr<Impl>(impl);
+  args.GetReturnValue().Set(impl->status);
+}
+
 BaseObjectPtr<BaseObject>
 Blob::BlobTransferData::Deserialize(
     Environment* env,
@@ -560,6 +650,7 @@ void Blob::RegisterExternalReferences(ExternalReferenceRegistry* registry) {
   registry->Register(Blob::GetDataObject);
   registry->Register(Blob::RevokeObjectURL);
   registry->Register(Blob::Reader::Pull);
+  registry->Register(Blob::Reader::PullAll);
   registry->Register(Concat);
   registry->Register(BlobFromFilePath);
 }

src/node_blob.h

@@ -82,6 +82,7 @@ class Blob : public BaseObject {
     static BaseObjectPtr<Reader> Create(Environment* env,
                                         BaseObjectPtr<Blob> blob);
     static void Pull(const v8::FunctionCallbackInfo<v8::Value>& args);
+    static void PullAll(const v8::FunctionCallbackInfo<v8::Value>& args);
 
     explicit Reader(Environment* env,
                     v8::Local<v8::Object> obj,