Add external ArrayBuffers to JSI

API/hermes/TracingRuntime.cpp

@@ -583,6 +583,11 @@ jsi::Array TracingRuntime::createArray(size_t length) {
   return arr;
 }
 
+jsi::ArrayBuffer TracingRuntime::createArrayBuffer(
+    std::shared_ptr<jsi::MutableBuffer> buffer) {
+  throw std::logic_error("Cannot create external ArrayBuffers in trace mode.");
+}
+
 size_t TracingRuntime::size(const jsi::Array &arr) {
   // Array size inquiries read from the length property, which is
   // non-configurable and thus cannot have side effects.

API/hermes/TracingRuntime.h

@@ -90,6 +90,8 @@ class TracingRuntime : public jsi::RuntimeDecorator<jsi::Runtime> {
   jsi::Value lockWeakObject(jsi::WeakObject &wo) override;
 
   jsi::Array createArray(size_t length) override;
+  jsi::ArrayBuffer createArrayBuffer(
+      std::shared_ptr<jsi::MutableBuffer> buffer) override;
 
   size_t size(const jsi::Array &arr) override;
   size_t size(const jsi::ArrayBuffer &buf) override;

API/hermes/hermes.cpp

@@ -737,6 +737,8 @@ class HermesRuntimeImpl final : public HermesRuntime,
   jsi::Value lockWeakObject(jsi::WeakObject &) override;
 
   jsi::Array createArray(size_t length) override;
+  jsi::ArrayBuffer createArrayBuffer(
+      std::shared_ptr<jsi::MutableBuffer> buffer) override;
   size_t size(const jsi::Array &) override;
   size_t size(const jsi::ArrayBuffer &) override;
   uint8_t *data(const jsi::ArrayBuffer &) override;
@@ -1987,6 +1989,24 @@ jsi::Array HermesRuntimeImpl::createArray(size_t length) {
   return add<jsi::Object>(result->getHermesValue()).getArray(*this);
 }
 
+jsi::ArrayBuffer HermesRuntimeImpl::createArrayBuffer(
+    std::shared_ptr<jsi::MutableBuffer> buffer) {
+  vm::GCScope gcScope(runtime_);
+  auto buf = runtime_.makeHandle(vm::JSArrayBuffer::create(
+      runtime_,
+      vm::Handle<vm::JSObject>::vmcast(&runtime_.arrayBufferPrototype)));
+  auto size = buffer->size();
+  auto *data = buffer->data();
+  auto *ctx = new std::shared_ptr<jsi::MutableBuffer>(std::move(buffer));
+  auto finalize = [](void *ctx) {
+    delete static_cast<std::shared_ptr<jsi::MutableBuffer> *>(ctx);
+  };
+  auto res = vm::JSArrayBuffer::setExternalDataBlock(
+      runtime_, buf, data, size, ctx, finalize);
+  checkStatus(res);
+  return add<jsi::Object>(buf.getHermesValue()).getArrayBuffer(*this);
+}
+
 size_t HermesRuntimeImpl::size(const jsi::Array &arr) {
   vm::GCScope gcScope(runtime_);
   return getLength(arrayHandle(arr));

API/jsi/jsi/decorator.h

@@ -302,6 +302,10 @@ class RuntimeDecorator : public Base, private jsi::Instrumentation {
   Array createArray(size_t length) override {
     return plain_.createArray(length);
   };
+  ArrayBuffer createArrayBuffer(
+      std::shared_ptr<MutableBuffer> buffer) override {
+    return plain_.createArrayBuffer(std::move(buffer));
+  };
   size_t size(const Array& a) override {
     return plain_.size(a);
   };
@@ -701,6 +705,10 @@ class WithRuntimeDecorator : public RuntimeDecorator<Plain, Base> {
     Around around{with_};
     return RD::createArray(length);
   };
+  ArrayBuffer createArrayBuffer(
+      std::shared_ptr<MutableBuffer> buffer) override {
+    return RD::createArrayBuffer(std::move(buffer));
+  };
   size_t size(const Array& a) override {
     Around around{with_};
     return RD::size(a);

API/jsi/jsi/jsi.cpp

@@ -66,6 +66,8 @@ Value callGlobalFunction(Runtime& runtime, const char* name, const Value& arg) {
 
 Buffer::~Buffer() = default;
 
+MutableBuffer::~MutableBuffer() = default;
+
 PreparedJavaScript::~PreparedJavaScript() = default;
 
 Value HostObject::get(Runtime&, const PropNameID&) {

API/jsi/jsi/jsi.h

@@ -31,6 +31,10 @@ class FBJSRuntime;
 namespace facebook {
 namespace jsi {
 
+/// Base class for buffers of data or bytecode that need to be passed to the
+/// runtime. The buffer is expected to be fully immutable, so the result of
+/// size(), data(), and the contents of the pointer returned by data() must not
+/// change after construction.
 class JSI_EXPORT Buffer {
  public:
   virtual ~Buffer();
@@ -52,6 +56,18 @@ class JSI_EXPORT StringBuffer : public Buffer {
   std::string s_;
 };
 
+/// Base class for buffers of data that need to be passed to the runtime. The
+/// result of size() and data() must not change after construction. However, the
+/// region pointed to by data() may be modified by the user or the runtime. The
+/// user must ensure that access to the contents of the buffer is properly
+/// synchronised.
+class JSI_EXPORT MutableBuffer {
+ public:
+  virtual ~MutableBuffer();
+  virtual size_t size() const = 0;
+  virtual uint8_t* data() = 0;
+};
+
 /// PreparedJavaScript is a base class representing JavaScript which is in a
 /// form optimized for execution, in a runtime-specific way. Construct one via
 /// jsi::Runtime::prepareJavaScript().
@@ -336,6 +352,8 @@ class JSI_EXPORT Runtime {
   virtual Value lockWeakObject(WeakObject&) = 0;
 
   virtual Array createArray(size_t length) = 0;
+  virtual ArrayBuffer createArrayBuffer(
+      std::shared_ptr<MutableBuffer> buffer) = 0;
   virtual size_t size(const Array&) = 0;
   virtual size_t size(const ArrayBuffer&) = 0;
   virtual uint8_t* data(const ArrayBuffer&) = 0;
@@ -915,6 +933,9 @@ class JSI_EXPORT ArrayBuffer : public Object {
   ArrayBuffer(ArrayBuffer&&) = default;
   ArrayBuffer& operator=(ArrayBuffer&&) = default;
 
+  ArrayBuffer(Runtime& runtime, std::shared_ptr<MutableBuffer> buffer)
+      : ArrayBuffer(runtime.createArrayBuffer(std::move(buffer))) {}
+
   /// \return the size of the ArrayBuffer, according to its byteLength property.
   /// (C++ naming convention)
   size_t size(Runtime& runtime) const {

unittests/API/APITest.cpp

@@ -10,6 +10,7 @@
 #include <hermes/CompileJS.h>
 #include <hermes/Public/JSOutOfMemoryError.h>
 #include <hermes/hermes.h>
+#include <jsi/instrumentation.h>
 
 #include <tuple>
 
@@ -105,6 +106,68 @@ TEST_F(HermesRuntimeTest, ArrayBufferTest) {
   EXPECT_EQ(buffer[1], 5678);
 }
 
+class HermesRuntimeTestMethodsTest : public HermesRuntimeTestBase {
+ public:
+  HermesRuntimeTestMethodsTest()
+      : HermesRuntimeTestBase(::hermes::vm::RuntimeConfig::Builder()
+                                  .withEnableHermesInternalTestMethods(true)
+                                  .build()) {}
+};
+
+TEST_F(HermesRuntimeTestMethodsTest, ExternalArrayBufferTest) {
+  struct FixedBuffer : MutableBuffer {
+    size_t size() const override {
+      return sizeof(arr);
+    }
+    uint8_t *data() override {
+      return reinterpret_cast<uint8_t *>(arr.data());
+    }
+
+    std::array<uint32_t, 256> arr;
+  };
+
+  {
+    auto buf = std::make_shared<FixedBuffer>();
+    for (uint32_t i = 0; i < buf->arr.size(); i++)
+      buf->arr[i] = i;
+    auto arrayBuffer = ArrayBuffer(*rt, buf);
+    auto square = eval(
+        R"#(
+(function (buf) {
+  var view = new Uint32Array(buf);
+  for(var i = 0; i < view.length; i++) view[i] = view[i] * view[i];
+})
+)#");
+    square.asObject(*rt).asFunction(*rt).call(*rt, arrayBuffer);
+    for (uint32_t i = 0; i < 256; i++)
+      EXPECT_EQ(buf->arr[i], i * i);
+  }
+
+  {
+    auto buf = std::make_shared<FixedBuffer>();
+    std::weak_ptr<FixedBuffer> weakBuf(buf);
+    auto arrayBuffer = ArrayBuffer(*rt, std::move(buf));
+    auto detach = eval(
+        R"#(
+(function (buf) {
+  var view = new Uint32Array(buf);
+  HermesInternal.detachArrayBuffer(buf);
+  view[0] = 5;
+})
+)#");
+    try {
+      detach.asObject(*rt).asFunction(*rt).call(*rt, arrayBuffer);
+      FAIL() << "Expected JSIException";
+    } catch (const JSError &ex) {
+      EXPECT_NE(
+          strstr(ex.what(), "Cannot set a value into a detached ArrayBuffer"),
+          nullptr);
+    }
+    rt->instrumentation().collectGarbage("");
+    EXPECT_TRUE(weakBuf.expired());
+  }
+}
+
 TEST_F(HermesRuntimeTest, BytecodeTest) {
   const uint8_t shortBytes[] = {1, 2, 3};
   EXPECT_FALSE(HermesRuntime::isHermesBytecode(shortBytes, 0));