Add MakeStringViewWithNulChars().

This new function can be used to construct an instance of a
string view from a string literal that contains NUL characters
internally.

Change-Id: I35555934922c00684263d143bbd63a5b08279c8e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5691499
Reviewed-by: danakj <[email protected]>
Commit-Queue: Patrick Monette <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1326367}

base/strings/string_util.h

@@ -604,6 +604,16 @@ BASE_EXPORT std::u16string ReplaceStringPlaceholders(
     const std::u16string& a,
     size_t* offset);
 
+// Helper function for creating a std::string_view from a string literal that
+// preserves internal NUL characters.
+template <class CharT, size_t N>
+std::basic_string_view<CharT> MakeStringViewWithNulChars(
+    const CharT (&lit LIFETIME_BOUND)[N])
+    ENABLE_IF_ATTR(lit[N - 1u] == CharT{0},
+                   "requires string literal as input") {
+  return std::basic_string_view<CharT>(lit, N - 1u);
+}
+
 }  // namespace base
 
 #if BUILDFLAG(IS_WIN)

base/strings/string_util_unittest.cc

@@ -1571,6 +1571,34 @@ TEST(StringUtilTest, IsUnicodeWhitespace) {
   EXPECT_TRUE(IsUnicodeWhitespace(L'\n'));
 }
 
+// Tests that MakeStringViewWithNulChars preserves internal NUL characters.
+TEST(StringUtilTest, MakeStringViewWithNulChars) {
+  {
+    const char kTestString[] = "abd\0def";
+    auto s = MakeStringViewWithNulChars(kTestString);
+    EXPECT_EQ(s.size(), 7u);
+    EXPECT_EQ(base::span(s), base::span_from_cstring(kTestString));
+  }
+  {
+    const wchar_t kTestString[] = L"abd\0def";
+    auto s = MakeStringViewWithNulChars(kTestString);
+    EXPECT_EQ(s.size(), 7u);
+    ASSERT_TRUE(base::span(s) == base::span_from_cstring(kTestString));
+  }
+  {
+    const char16_t kTestString[] = u"abd\0def";
+    auto s = MakeStringViewWithNulChars(kTestString);
+    EXPECT_EQ(s.size(), 7u);
+    EXPECT_TRUE(base::span(s) == base::span_from_cstring(kTestString));
+  }
+  {
+    const char32_t kTestString[] = U"abd\0def";
+    auto s = MakeStringViewWithNulChars(kTestString);
+    EXPECT_EQ(s.size(), 7u);
+    EXPECT_TRUE(base::span(s) == base::span_from_cstring(kTestString));
+  }
+}
+
 class WriteIntoTest : public testing::Test {
  protected:
   static void WritesCorrectly(size_t num_chars) {