1 files changed, 136 insertions, 0 deletions
diff --git a/serde_v8/magic/zero_copy_buf.rs b/serde_v8/magic/zero_copy_buf.rs
new file mode 100644
index 000000000..c63d4ba66
--- /dev/null
+++ b/serde_v8/magic/zero_copy_buf.rs
@@ -0,0 +1,136 @@
+// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.
+
+use std::cell::Cell;
+use std::ops::Deref;
+use std::ops::DerefMut;
+
+use super::transl8::FromV8;
+
+/// A ZeroCopyBuf encapsulates a slice that's been borrowed from a JavaScript
+/// ArrayBuffer object. JavaScript objects can normally be garbage collected,
+/// but the existence of a ZeroCopyBuf inhibits this until it is dropped. It
+/// behaves much like an Arc<[u8]>.
+///
+/// # Cloning
+/// Cloning a ZeroCopyBuf does not clone the contents of the buffer,
+/// it creates a new reference to that buffer.
+///
+/// To actually clone the contents of the buffer do
+/// `let copy = Vec::from(&*zero_copy_buf);`
+#[derive(Clone)]
+pub struct ZeroCopyBuf {
+  backing_store: v8::SharedRef<v8::BackingStore>,
+  byte_offset: usize,
+  byte_length: usize,
+}
+
+unsafe impl Send for ZeroCopyBuf {}
+
+impl ZeroCopyBuf {
+  pub fn from_buffer(
+    buffer: v8::Local<v8::ArrayBuffer>,
+    byte_offset: usize,
+    byte_length: usize,
+  ) -> Result<Self, v8::DataError> {
+    let backing_store = buffer.get_backing_store();
+    match backing_store.is_shared() {
+      true => Err(v8::DataError::BadType {
+        actual: "shared ArrayBufferView",
+        expected: "non-shared ArrayBufferView",
+      }),
+      false => Ok(Self {
+        backing_store,
+        byte_offset,
+        byte_length,
+      }),
+    }
+  }
+
+  pub fn from_view(
+    scope: &mut v8::HandleScope,
+    view: v8::Local<v8::ArrayBufferView>,
+  ) -> Result<Self, v8::DataError> {
+    let buffer = view.buffer(scope).ok_or(v8::DataError::NoData {
+      expected: "view to have a buffer",
+    })?;
+    Self::from_buffer(buffer, view.byte_offset(), view.byte_length())
+  }
+}
+
+impl FromV8 for ZeroCopyBuf {
+  fn from_v8(
+    scope: &mut v8::HandleScope,
+    value: v8::Local<v8::Value>,
+  ) -> Result<Self, crate::Error> {
+    if value.is_array_buffer() {
+      value
+        .try_into()
+        .and_then(|b| Self::from_buffer(b, 0, b.byte_length()))
+    } else {
+      value
+        .try_into()
+        .and_then(|view| Self::from_view(scope, view))
+    }
+    .map_err(|_| crate::Error::ExpectedBuffer)
+  }
+}
+
+impl Deref for ZeroCopyBuf {
+  type Target = [u8];
+  fn deref(&self) -> &[u8] {
+    unsafe {
+      get_backing_store_slice(
+        &self.backing_store,
+        self.byte_offset,
+        self.byte_length,
+      )
+    }
+  }
+}
+
+impl DerefMut for ZeroCopyBuf {
+  fn deref_mut(&mut self) -> &mut [u8] {
+    unsafe {
+      get_backing_store_slice_mut(
+        &self.backing_store,
+        self.byte_offset,
+        self.byte_length,
+      )
+    }
+  }
+}
+
+impl AsRef<[u8]> for ZeroCopyBuf {
+  fn as_ref(&self) -> &[u8] {
+    &*self
+  }
+}
+
+impl AsMut<[u8]> for ZeroCopyBuf {
+  fn as_mut(&mut self) -> &mut [u8] {
+    &mut *self
+  }
+}
+
+unsafe fn get_backing_store_slice(
+  backing_store: &v8::SharedRef<v8::BackingStore>,
+  byte_offset: usize,
+  byte_length: usize,
+) -> &[u8] {
+  let cells: *const [Cell<u8>] =
+    &backing_store[byte_offset..byte_offset + byte_length];
+  let bytes = cells as *const [u8];
+  &*bytes
+}
+
+#[allow(clippy::mut_from_ref)]
+unsafe fn get_backing_store_slice_mut(
+  backing_store: &v8::SharedRef<v8::BackingStore>,
+  byte_offset: usize,
+  byte_length: usize,
+) -> &mut [u8] {
+  let cells: *const [Cell<u8>] =
+    &backing_store[byte_offset..byte_offset + byte_length];
+  let bytes = cells as *const _ as *mut [u8];
+  &mut *bytes
+}