From 662b1d8da12f47a268eeea2035138c40438542df Mon Sep 17 00:00:00 2001
From: Yagiz Nizipli <yagiz@nizipli.com>
Date: Mon, 30 Sep 2024 21:18:32 -0400
Subject: [PATCH] improve stringwrapper bytestring unwrap

---
 src/workerd/jsg/BUILD.bazel |  2 +-
 src/workerd/jsg/value.h     | 28 ++++++++++++++++------------
 2 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/src/workerd/jsg/BUILD.bazel b/src/workerd/jsg/BUILD.bazel
index 8cce150449b..b84b00b48b7 100644
--- a/src/workerd/jsg/BUILD.bazel
+++ b/src/workerd/jsg/BUILD.bazel
@@ -52,7 +52,6 @@ wd_cc_library(
         "web-idl.h",
         "wrappable.h",
     ],
-    implementation_deps = ["@simdutf"],
     visibility = ["//visibility:public"],
     deps = [
         ":exception",
@@ -65,6 +64,7 @@ wd_cc_library(
         "//src/workerd/util:thread-scopes",
         "//src/workerd/util:uuid",
         "@capnp-cpp//src/kj",
+        "@simdutf",
         "@workerd-v8//:v8",
     ],
 )
diff --git a/src/workerd/jsg/value.h b/src/workerd/jsg/value.h
index a71a0947747..54c7fca2d63 100644
--- a/src/workerd/jsg/value.h
+++ b/src/workerd/jsg/value.h
@@ -8,6 +8,7 @@
 // Handling of various basic value types: numbers, booleans, strings, optionals, maybes, variants,
 // arrays, buffers, dicts.
 
+#include "simdutf.h"
 #include "util.h"
 #include "web-idl.h"
 #include "wrappable.h"
@@ -468,20 +469,23 @@ class StringWrapper {
       kj::Maybe<v8::Local<v8::Object>> parentObject) {
     // TODO(cleanup): Move to a HeaderStringWrapper in the api directory.
     v8::Local<v8::String> str = check(handle->ToString(context));
-    auto result =
-        ByteString(KJ_ASSERT_NONNULL(tryUnwrap(context, str, (kj::String*)nullptr, parentObject)));
-    if (str->ContainsOnlyOneByte()) {
-      auto buf = kj::heapArray<kj::byte>(str->Length() + 1);
-      str->WriteOneByte(context->GetIsolate(), buf.begin());
-      for (auto b: buf) {
-        if (b >= 128) {
-          result.warning = ByteString::Warning::CONTAINS_EXTENDED_ASCII;
-          break;
-        }
+    auto result = ByteString(KJ_ASSERT_NONNULL(
+        tryUnwrap(context, str, static_cast<kj::String*>(nullptr), parentObject)));
+
+    if (!simdutf::validate_ascii(result.begin(), result.size())) {
+      // If storage is one-byte or the string contains only one-byte
+      // characters, we know that it contains extended ASCII characters.
+      //
+      // The order of execution matters, since ContainsOnlyOneByte()
+      // will scan the whole string for two-byte storage.
+      if (str->ContainsOnlyOneByte()) {
+        result.warning = ByteString::Warning::CONTAINS_EXTENDED_ASCII;
+      } else {
+        // Storage is two-bytes and it contains two-byte characters.
+        result.warning = ByteString::Warning::CONTAINS_UNICODE;
       }
-    } else {
-      result.warning = ByteString::Warning::CONTAINS_UNICODE;
     }
+
     return kj::mv(result);
   }
 };