From ed8257f220192d041d86e90e3158d897cab09231 Mon Sep 17 00:00:00 2001
From: Archkon <180910180+Archkon@users.noreply.github.com>
Date: Sun, 26 Jul 2026 10:42:59 +0800
Subject: [PATCH] src: handle empty external string resources

V8 requires external string resources to have a non-null data pointer,
even when their length is zero. Empty vectors may return a null data
pointer, causing NewExternalTwoByte() to abort the process.

Signed-off-by: Archkon <180910180+Archkon@users.noreply.github.com>
---
 src/node_union_bytes.h   |  4 ++++
 src/util.cc              |  6 ++++++
 test/cctest/test_util.cc | 14 ++++++++++++++
 3 files changed, 24 insertions(+)

diff --git a/src/node_union_bytes.h b/src/node_union_bytes.h
index 4a3f67980fdc92..28d6f1a9846b79 100644
--- a/src/node_union_bytes.h
+++ b/src/node_union_bytes.h
@@ -66,6 +66,10 @@ class UnionBytes {
   UnionBytes& operator=(UnionBytes&&) = default;
 
   bool is_one_byte() const { return one_byte_resource_ != nullptr; }
+  size_t length() const {
+    return is_one_byte() ? one_byte_resource_->length()
+                         : two_byte_resource_->length();
+  }
 
   v8::Local<v8::String> ToStringChecked(v8::Isolate* isolate) const;
 
diff --git a/src/util.cc b/src/util.cc
index 317b8db0daac69..72fcffde991e22 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -636,6 +636,12 @@ void SetConstructorFunction(Isolate* isolate,
 }
 
 Local<String> UnionBytes::ToStringChecked(Isolate* isolate) const {
+  if (length() == 0) [[unlikely]] {
+    // V8 requires non-null data pointers for empty external strings,
+    // but we don't guarantee that. Solve this by not creating an
+    // external string at all in that case.
+    return String::Empty(isolate);
+  }
   if (is_one_byte()) {
     return String::NewExternalOneByte(isolate, one_byte_resource_)
         .ToLocalChecked();
diff --git a/test/cctest/test_util.cc b/test/cctest/test_util.cc
index c3beea15f2dfc4..d2631182910d65 100644
--- a/test/cctest/test_util.cc
+++ b/test/cctest/test_util.cc
@@ -3,6 +3,7 @@
 #include "gtest/gtest.h"
 #include "node_options-inl.h"
 #include "node_test_fixture.h"
+#include "node_union_bytes.h"
 #include "simdutf.h"
 #include "util-inl.h"
 #include "v8-function-callback.h"
@@ -312,6 +313,19 @@ TEST_F(UtilTest, DumpJavaScriptStackWithNoIsolate) {
   node::DumpJavaScriptBacktrace(stderr);
 }
 
+TEST_F(UtilTest, EmptyUnionBytesToString) {
+  const v8::HandleScope handle_scope(isolate_);
+  node::StaticExternalOneByteResource one_byte_resource(nullptr, 0, nullptr);
+  node::StaticExternalTwoByteResource two_byte_resource(nullptr, 0, nullptr);
+
+  EXPECT_EQ(
+      0,
+      node::UnionBytes(&one_byte_resource).ToStringChecked(isolate_)->Length());
+  EXPECT_EQ(
+      0,
+      node::UnionBytes(&two_byte_resource).ToStringChecked(isolate_)->Length());
+}
+
 TEST_F(UtilTest, DetermineSpecificErrorType) {
   const v8::HandleScope handle_scope(isolate_);
   Argv argv;