perf(web): Optimize `TextDecoder` by adding a new `U16String` type (#13923)

2 files changed, 63 insertions, 0 deletions

diff --git a/serde_v8/src/magic/mod.rs b/serde_v8/src/magic/mod.rs
index 941a69d41..e90b5ab60 100644
--- a/serde_v8/src/magic/mod.rs
+++ b/serde_v8/src/magic/mod.rs
@@ -3,6 +3,7 @@ pub mod buffer;
 pub mod bytestring;
 mod field;
 pub mod string_or_buffer;
+pub mod u16string;
 mod value;
 pub mod zero_copy_buf;
 
diff --git a/serde_v8/src/magic/u16string.rs b/serde_v8/src/magic/u16string.rs
new file mode 100644
index 000000000..a75af016b
--- /dev/null
+++ b/serde_v8/src/magic/u16string.rs
@@ -0,0 +1,62 @@
+use std::ops::{Deref, DerefMut};
+
+use serde::Serialize;
+
+pub const NAME: &str = "$__v8_magic_u16string";
+pub const FIELD_PTR: &str = "$__v8_magic_u16string_ptr";
+pub const FIELD_LEN: &str = "$__v8_magic_u16string_len";
+
+#[derive(Default, PartialEq, Eq)]
+pub struct U16String(pub Vec<u16>);
+
+impl U16String {
+  pub fn with_zeroes(length: usize) -> U16String {
+    U16String(vec![0u16; length])
+  }
+
+  pub fn truncate(&mut self, new_length: usize) {
+    self.0.truncate(new_length);
+    self.0.shrink_to_fit()
+  }
+}
+
+impl Deref for U16String {
+  type Target = [u16];
+  fn deref(&self) -> &[u16] {
+    self.0.deref()
+  }
+}
+
+impl DerefMut for U16String {
+  fn deref_mut(&mut self) -> &mut [u16] {
+    self.0.deref_mut()
+  }
+}
+
+impl AsRef<[u16]> for U16String {
+  fn as_ref(&self) -> &[u16] {
+    self.0.as_ref()
+  }
+}
+
+impl AsMut<[u16]> for U16String {
+  fn as_mut(&mut self) -> &mut [u16] {
+    self.0.as_mut()
+  }
+}
+
+impl Serialize for U16String {
+  fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+  where
+    S: serde::Serializer,
+  {
+    use serde::ser::SerializeStruct;
+
+    let mut s = serializer.serialize_struct(NAME, 3)?;
+    s.serialize_field(FIELD_PTR, &(self.0.as_ptr() as usize))?;
+    s.serialize_field(FIELD_LEN, &self.0.len())?;
+    s.end()
+  }
+}
+
+// TODO: Deserialize