[inspector] Add fromUTF16LE function to string-16

Bug: v8:9355
Change-Id: I317bb52952ad5b347d627d4f6096f251bca1a815
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1652558
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62342}

src/inspector/string-16.cc

@@ -200,6 +200,23 @@ String16 String16::fromUTF8(const char* stringStart, size_t length) {
   return String16(UTF8ToUTF16(stringStart, length));
 }
 
+String16 String16::fromUTF16LE(const UChar* stringStart, size_t length) {
+#ifdef V8_TARGET_BIG_ENDIAN
+  // Need to flip the byte order on big endian machines.
+  String16Builder builder;
+  builder.reserveCapacity(length);
+  for (size_t i = 0; i < length; i++) {
+    const UChar utf16be_char =
+        utf16le_str[i] << 8 | (utf16le_str[i] >> 8 & 0x00FF);
+    builder.append(utf16be_char);
+  }
+  return builder.toString();
+#else
+  // No need to do anything on little endian machines.
+  return String16(stringStart, length);
+#endif  // V8_TARGET_BIG_ENDIAN
+}
+
 std::string String16::utf8() const {
   return UTF16ToUTF8(m_impl.data(), m_impl.size());
 }

src/inspector/string-16.h

@@ -66,8 +66,13 @@ class String16 {
   }
 
   // Convenience methods.
-  std::string utf8() const;
-  static String16 fromUTF8(const char* stringStart, size_t length);
+  V8_EXPORT std::string utf8() const;
+  V8_EXPORT static String16 fromUTF8(const char* stringStart, size_t length);
+
+  // Instantiates a String16 in native endianness from UTF16 LE.
+  // On Big endian architectures, byte order needs to be flipped.
+  V8_EXPORT static String16 fromUTF16LE(const UChar* stringStart,
+                                        size_t length);
 
   std::size_t hash() const {
     if (!hash_code) {

src/inspector/string-util.h

@@ -74,6 +74,10 @@ class StringUtil {
     return String16(data, length);
   }
 
+  static String fromUTF16LE(const uint16_t* data, size_t length) {
+    return String16::fromUTF16LE(data, length);
+  }
+
   static const uint8_t* CharactersLatin1(const String& s) { return nullptr; }
   static const uint8_t* CharactersUTF8(const String& s) { return nullptr; }
   static const uint16_t* CharactersUTF16(const String& s) {

test/cctest/test-inspector.cc

@@ -9,7 +9,9 @@
 #include "include/v8-inspector.h"
 #include "include/v8.h"
 #include "src/inspector/protocol/Runtime.h"
+#include "src/inspector/string-16.h"
 
+using v8_inspector::String16;
 using v8_inspector::StringBuffer;
 using v8_inspector::StringView;
 using v8_inspector::V8ContextInfo;
@@ -63,3 +65,16 @@ TEST(WrapInsideWrapOnInterrupt) {
   isolate->RequestInterrupt(&WrapOnInterrupt, session.get());
   session->wrapObject(env.local(), v8::Null(isolate), object_group_view, false);
 }
+
+TEST(String16EndianTest) {
+  const char* utf8 =
+      "Hello, \xf0\x9f\x8c\x8e.";  // "Hello, earth." in utf8 encoding
+  const uint16_t* utf16le = reinterpret_cast<const uint16_t*>(
+      "H\0e\0l\0l\0o\0,\0 \0\x3c\xd8\x0e\xdf.\0");  // Same text in UTF16LE
+                                                    // encoding
+
+  String16 utf16_str = String16::fromUTF16LE(utf16le, 10);
+  String16 utf8_str = String16::fromUTF8(utf8, strlen(utf8));
+
+  CHECK_EQ(utf16_str.utf8(), utf8_str.utf8());
+}