[web snapshots] Add two-byte string support

Bug: v8:11525
Change-Id: I7dee1987160d3811054a7be43280993630bca5be
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3320426Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78295}

src/web-snapshot/web-snapshot.cc

@@ -398,8 +398,13 @@ void WebSnapshotSerializer::SerializeString(Handle<String> string,
     string_serializer_.WriteRawBytes(chars.begin(),
                                      chars.length() * sizeof(uint8_t));
   } else if (flat.IsTwoByte()) {
-    // TODO(v8:11525): Support two-byte strings.
-    UNREACHABLE();
+    v8::Isolate* v8_isolate = reinterpret_cast<v8::Isolate*>(isolate_);
+    v8::Local<v8::String> api_string = Utils::ToLocal(string);
+    int length = api_string->Utf8Length(v8_isolate);
+    std::unique_ptr<char[]> buffer(new char[length]);
+    api_string->WriteUtf8(v8_isolate, buffer.get(), length);
+    string_serializer_.WriteUint32(length);
+    string_serializer_.WriteRawBytes(buffer.get(), length * sizeof(uint8_t));
   } else {
     UNREACHABLE();
   }
@@ -1127,8 +1132,7 @@ void WebSnapshotDeserializer::DeserializeStrings() {
   STATIC_ASSERT(kMaxItemCount <= FixedArray::kMaxLength);
   strings_ = isolate_->factory()->NewFixedArray(string_count_);
   for (uint32_t i = 0; i < string_count_; ++i) {
-    // TODO(v8:11525): Read strings as UTF-8.
-    MaybeHandle<String> maybe_string = deserializer_->ReadOneByteString();
+    MaybeHandle<String> maybe_string = deserializer_->ReadUtf8String();
     Handle<String> string;
     if (!maybe_string.ToHandle(&string)) {
       Throw("Malformed string");

test/mjsunit/web-snapshot/web-snapshot.js

@@ -99,6 +99,34 @@ function takeAndUseWebSnapshot(createObjects, exports) {
   assertFalse(b);
 })();
 
+(function TestStringWithNull() {
+  function createObjects() {
+    globalThis.s = 'l\0l';
+  }
+  const { s } = takeAndUseWebSnapshot(createObjects, ['s']);
+  assertEquals(108, s.charCodeAt(0));
+  assertEquals(0, s.charCodeAt(1));
+  assertEquals(108, s.charCodeAt(2));
+})();
+
+(function TestTwoByteString() {
+  function createObjects() {
+    globalThis.s = '\u{1F600}';
+  }
+  const { s } = takeAndUseWebSnapshot(createObjects, ['s']);
+  assertEquals('\u{1F600}', s);
+})();
+
+(function TestTwoByteStringWithNull() {
+  function createObjects() {
+    globalThis.s = 'l\0l\u{1F600}';
+  }
+  const { s } = takeAndUseWebSnapshot(createObjects, ['s']);
+  assertEquals(108, s.charCodeAt(0));
+  assertEquals(0, s.charCodeAt(1));
+  assertEquals(108, s.charCodeAt(2));
+})();
+
 (function TestFunction() {
   function createObjects() {
     globalThis.foo = {