Add ArrayBuffer::detach() and is_detachable() (denoland#648)

Fixes denoland#646.

src/array_buffer.rs

@@ -33,6 +33,8 @@ extern "C" {
     isolate: *mut Isolate,
     backing_store: *const SharedRef<BackingStore>,
   ) -> *const ArrayBuffer;
+  fn v8__ArrayBuffer__Detach(this: *const ArrayBuffer);
+  fn v8__ArrayBuffer__IsDetachable(this: *const ArrayBuffer) -> bool;
   fn v8__ArrayBuffer__ByteLength(this: *const ArrayBuffer) -> usize;
   fn v8__ArrayBuffer__GetBackingStore(
     this: *const ArrayBuffer,
@@ -351,6 +353,23 @@ impl ArrayBuffer {
     unsafe { v8__ArrayBuffer__ByteLength(self) }
   }
 
+  /// Returns true if this ArrayBuffer may be detached.
+  pub fn is_detachable(&self) -> bool {
+    unsafe { v8__ArrayBuffer__IsDetachable(self) }
+  }
+
+  /// Detaches this ArrayBuffer and all its views (typed arrays).
+  /// Detaching sets the byte length of the buffer and all typed arrays to zero,
+  /// preventing JavaScript from ever accessing underlying backing store.
+  /// ArrayBuffer should have been externalized and must be detachable.
+  pub fn detach(&self) {
+    // V8 terminates when the ArrayBuffer is not detachable. Non-detachable
+    // buffers are buffers that are in use by WebAssembly or asm.js.
+    if self.is_detachable() {
+      unsafe { v8__ArrayBuffer__Detach(self) }
+    }
+  }
+
   /// Get a shared pointer to the backing store of this array buffer. This
   /// pointer coordinates the lifetime management of the internal storage
   /// with any live ArrayBuffers on the heap, even across isolates. The embedder

src/binding.cc

@@ -737,6 +737,14 @@ two_pointers_t v8__ArrayBuffer__GetBackingStore(const v8::ArrayBuffer& self) {
   return make_pod<two_pointers_t>(ptr_to_local(&self)->GetBackingStore());
 }
 
+void v8__ArrayBuffer__Detach(const v8::ArrayBuffer& self) {
+  ptr_to_local(&self)->Detach();
+}
+
+bool v8__ArrayBuffer__IsDetachable(const v8::ArrayBuffer& self) {
+  return ptr_to_local(&self)->IsDetachable();
+}
+
 void* v8__BackingStore__Data(const v8::BackingStore& self) {
   return self.Data();
 }

tests/test_api.rs

@@ -439,6 +439,11 @@ fn array_buffer() {
     let ab = v8::ArrayBuffer::new(scope, 42);
     assert_eq!(42, ab.byte_length());
 
+    assert!(ab.is_detachable());
+    ab.detach();
+    assert_eq!(0, ab.byte_length());
+    ab.detach(); // Calling it twice should be a no-op.
+
     let bs = v8::ArrayBuffer::new_backing_store(scope, 84);
     assert_eq!(84, bs.byte_length());
     assert_eq!(false, bs.is_shared());