Allow deno_buf with null alloc_ptr to be memcpy'd

This is a temporary hack to allow for easier restructuring of
the serialization code as we move Flatbuffer stuff from C++ to Rust.

js/mock_runtime.js

@@ -134,3 +134,14 @@ global.ErrorHandling = () => {
   };
   eval("\n\n notdefined()\n//# sourceURL=helloworld.js");
 };
+
+global.SendNullAllocPtr = () => {
+  deno.recv(msg => {
+    assert(msg instanceof Uint8Array);
+    assert(msg.byteLength === 4);
+    assert(msg[0] === "a".charCodeAt(0));
+    assert(msg[1] === "b".charCodeAt(0));
+    assert(msg[2] === "c".charCodeAt(0));
+    assert(msg[3] === "d".charCodeAt(0));
+  });
+};

src/binding.cc

@@ -120,6 +120,14 @@ void Print(const v8::FunctionCallbackInfo<v8::Value>& args) {
 }
 
 static v8::Local<v8::Uint8Array> ImportBuf(v8::Isolate* isolate, deno_buf buf) {
+  if (buf.alloc_ptr == nullptr) {
+    // If alloc_ptr isn't set, we memcpy.
+    // This is currently used for flatbuffers created in Rust.
+    auto ab = v8::ArrayBuffer::New(isolate, buf.data_len);
+    memcpy(ab->GetContents().Data(), buf.data_ptr, buf.data_len);
+    auto view = v8::Uint8Array::New(ab, 0, buf.data_len);
+    return view;
+  } else {
     auto ab = v8::ArrayBuffer::New(
         isolate, reinterpret_cast<void*>(buf.alloc_ptr), buf.alloc_len,
         v8::ArrayBufferCreationMode::kInternalized);
@@ -127,6 +135,7 @@ static v8::Local<v8::Uint8Array> ImportBuf(v8::Isolate* isolate, deno_buf buf) {
         v8::Uint8Array::New(ab, buf.data_ptr - buf.alloc_ptr, buf.data_len);
     return view;
   }
+}
 
 static deno_buf ExportBuf(v8::Isolate* isolate,
                           v8::Local<v8::ArrayBufferView> view) {

src/mock_runtime_test.cc

@@ -34,6 +34,17 @@ deno_buf strbuf(const char* str) {
   return buf;
 }
 
+// Same as strbuf but with null alloc_ptr.
+deno_buf StrBufNullAllocPtr(const char* str) {
+  auto len = strlen(str);
+  deno_buf buf;
+  buf.alloc_ptr = nullptr;
+  buf.alloc_len = 0;
+  buf.data_ptr = reinterpret_cast<uint8_t*>(strdup(str));
+  buf.data_len = len;
+  return buf;
+}
+
 TEST(MockRuntimeTest, SendSuccess) {
   Deno* d = deno_new(nullptr, nullptr);
   EXPECT_TRUE(deno_execute(d, "a.js", "SendSuccess()"));
@@ -176,3 +187,15 @@ TEST(MockRuntimeTest, ErrorHandling) {
   EXPECT_EQ(count, 1);
   deno_delete(d);
 }
+
+TEST(MockRuntimeTest, SendNullAllocPtr) {
+  static int count = 0;
+  Deno* d = deno_new(nullptr, [](auto _, auto buf) { count++; });
+  EXPECT_TRUE(deno_execute(d, "a.js", "SendNullAllocPtr()"));
+  deno_buf buf = StrBufNullAllocPtr("abcd");
+  EXPECT_EQ(buf.alloc_ptr, nullptr);
+  EXPECT_EQ(buf.data_len, 4u);
+  EXPECT_TRUE(deno_send(d, buf));
+  EXPECT_EQ(count, 0);
+  deno_delete(d);
+}