perf(serde_v8): optimize ByteString deserialization (#13853)

2 files changed, 19 insertions, 18 deletions

diff --git a/serde_v8/src/de.rs b/serde_v8/src/de.rs
index 2deb5da39..318894c22 100644
--- a/serde_v8/src/de.rs
+++ b/serde_v8/src/de.rs
@@ -370,25 +370,25 @@ impl<'de, 'a, 'b, 's, 'x> de::Deserializer<'de>
 
     // Magic ByteString
     if name == magic::bytestring::NAME {
-      if let Some(v8_string) = self.input.to_string(self.scope) {
-        if v8_string.contains_only_onebyte() {
-          let mut buffer: Vec<u8> = vec![0u8; v8_string.length()];
-          let written = v8_string.write_one_byte(
-            self.scope,
-            &mut buffer,
-            0,
-            v8::WriteOptions::NO_NULL_TERMINATION,
-          );
-          assert!(written == v8_string.length());
-          return visitor.visit_byte_buf(buffer);
-        } else {
-          return Err(Error::Message(
-            "Expected a valid ByteString.".to_string(),
-          ));
-        }
-      } else {
-        return Err(Error::ExpectedString);
+      let v8str = v8::Local::<v8::String>::try_from(self.input)
+        .map_err(|_| Error::ExpectedString)?;
+      if !v8str.contains_only_onebyte() {
+        return Err(Error::ExpectedLatin1);
+      }
+      let len = v8str.length();
+      let mut buffer = Vec::with_capacity(len);
+      #[allow(clippy::uninit_vec)]
+      unsafe {
+        buffer.set_len(len);
       }
+      let written = v8str.write_one_byte(
+        self.scope,
+        &mut buffer,
+        0,
+        v8::WriteOptions::NO_NULL_TERMINATION,
+      );
+      assert!(written == len);
+      return visitor.visit_byte_buf(buffer);
     }
 
     // Regular struct
diff --git a/serde_v8/src/error.rs b/serde_v8/src/error.rs
index 6f4305536..e4f7f363b 100644
--- a/serde_v8/src/error.rs
+++ b/serde_v8/src/error.rs
@@ -19,6 +19,7 @@ pub enum Error {
   ExpectedBuffer,
 
   ExpectedUtf8,
+  ExpectedLatin1,
 
   LengthMismatch,
 }