feat(ext/ffi): Add support to get ArrayBuffers from UnsafePointerView (#15143)

ext/ffi/00_ffi.js

@@ -10,7 +10,6 @@
     ObjectPrototypeIsPrototypeOf,
     PromisePrototypeThen,
     TypeError,
-    Uint8Array,
   } = window.__bootstrap.primordials;
 
   function unpackU64([hi, lo]) {
@@ -107,9 +106,11 @@
     }
 
     getArrayBuffer(byteLength, offset = 0) {
-      const uint8array = new Uint8Array(byteLength);
-      this.copyInto(uint8array, offset);
-      return uint8array.buffer;
+      return core.opSync(
+        "op_ffi_get_buf",
+        offset ? this.pointer + BigInt(offset) : this.pointer,
+        byteLength,
+      );
     }
 
     copyInto(destination, offset = 0) {

ext/ffi/lib.rs

@@ -165,6 +165,7 @@ pub fn init<P: FfiPermissions + 'static>(unstable: bool) -> Extension {
       op_ffi_call_ptr::decl::<P>(),
       op_ffi_call_ptr_nonblocking::decl::<P>(),
       op_ffi_ptr_of::decl::<P>(),
+      op_ffi_get_buf::decl::<P>(),
       op_ffi_buf_copy_into::decl::<P>(),
       op_ffi_cstr_read::decl::<P>(),
       op_ffi_read_u8::decl::<P>(),
@@ -1912,6 +1913,50 @@ where
   Ok(big_int.into())
 }
 
+unsafe extern "C" fn noop_deleter_callback(
+  _data: *mut c_void,
+  _byte_length: usize,
+  _deleter_data: *mut c_void,
+) {
+}
+
+#[op(v8)]
+fn op_ffi_get_buf<FP, 'scope>(
+  scope: &mut v8::HandleScope<'scope>,
+  state: &mut deno_core::OpState,
+  src: serde_v8::Value<'scope>,
+  len: usize,
+) -> Result<serde_v8::Value<'scope>, AnyError>
+where
+  FP: FfiPermissions + 'static,
+{
+  check_unstable(state, "Deno.UnsafePointerView#arrayBuffer");
+
+  let permissions = state.borrow_mut::<FP>();
+  permissions.check(None)?;
+
+  let value = v8::Local::<v8::BigInt>::try_from(src.v8_value)
+    .map_err(|_| type_error("Invalid FFI pointer value, expected BigInt"))?;
+  let ptr = value.u64_value().0 as usize as *mut c_void;
+  if std::ptr::eq(ptr, std::ptr::null()) {
+    return Err(type_error("Invalid FFI pointer value, got nullptr"));
+  }
+
+  // SAFETY: Trust the user to have provided a real pointer, and a valid matching size to it. Since this is a foreign pointer, we should not do any deletion.
+  let backing_store = unsafe {
+    v8::ArrayBuffer::new_backing_store_from_ptr(
+      ptr,
+      len,
+      noop_deleter_callback,
+      std::ptr::null_mut(),
+    )
+  }
+  .make_shared();
+  let array_buffer: v8::Local<v8::Value> =
+    v8::ArrayBuffer::with_backing_store(scope, &backing_store).into();
+  Ok(array_buffer.into())
+}
+
 #[op]
 fn op_ffi_buf_copy_into<FP>(
   state: &mut deno_core::OpState,

test_ffi/src/lib.rs

@@ -393,4 +393,4 @@ pub struct Structure {
 }
 
 #[no_mangle]
-pub static static_ptr: Structure = Structure { _data: 42 };
+pub static mut static_ptr: Structure = Structure { _data: 42 };

test_ffi/tests/integration_tests.rs

@@ -101,6 +101,11 @@ fn basic() {
     Static i64: -1242464576485n\n\
     Static ptr: true\n\
     Static ptr value: 42\n\
+    arrayBuffer.byteLength: 4\n\
+    uint32Array.length: 1\n\
+    uint32Array[0]: 42\n\
+    uint32Array[0] after mutation: 55\n\
+    Static ptr value after mutation: 55\n\
     Correct number of resources\n";
   assert_eq!(stdout, expected);
   assert_eq!(stderr, "");

test_ffi/tests/test.js

@@ -3,7 +3,9 @@
 
 // Run using cargo test or `--v8-options=--allow-natives-syntax`
 
-import { assertThrows } from "../../test_util/std/testing/asserts.ts";
+import {
+  assertThrows,
+} from "../../test_util/std/testing/asserts.ts";
 
 const targetDir = Deno.execPath().replace(/[^\/\\]+$/, "");
 const [libPrefix, libSuffix] = {
@@ -442,6 +444,15 @@ console.log(
 const view = new Deno.UnsafePointerView(dylib.symbols.static_ptr);
 console.log("Static ptr value:", view.getUint32());
 
+const arrayBuffer = view.getArrayBuffer(4);
+const uint32Array = new Uint32Array(arrayBuffer);
+console.log("arrayBuffer.byteLength:", arrayBuffer.byteLength);
+console.log("uint32Array.length:", uint32Array.length);
+console.log("uint32Array[0]:", uint32Array[0]);
+uint32Array[0] = 55; // MUTATES!
+console.log("uint32Array[0] after mutation:", uint32Array[0]);
+console.log("Static ptr value after mutation:", view.getUint32());
+
 (function cleanup() {
   dylib.close();
   throwCallback.close();