Reduce stack frame size of `TextFormat::Printer::PrintUnknownFields` by offloading `std::string` temporaries into a separate function.

PiperOrigin-RevId: 513627351

src/google/protobuf/text_format.cc

@@ -2699,18 +2699,23 @@ void TextFormat::Printer::PrintFieldValue(const Message& message,
   return Parser().ParseFieldValueFromString(input, field, message);
 }
 
+template <typename... T>
+PROTOBUF_NOINLINE void TextFormat::OutOfLinePrintString(
+    BaseTextGenerator* generator, const T&... values) {
+  generator->PrintString(absl::StrCat(values...));
+}
+
 void TextFormat::Printer::PrintUnknownFields(
     const UnknownFieldSet& unknown_fields, BaseTextGenerator* generator,
     int recursion_budget) const {
   for (int i = 0; i < unknown_fields.field_count(); i++) {
     const UnknownField& field = unknown_fields.field(i);
-    std::string field_number = absl::StrCat(field.number());
 
     switch (field.type()) {
       case UnknownField::TYPE_VARINT:
-        generator->PrintString(field_number);
+        OutOfLinePrintString(generator, field.number());
         generator->PrintMaybeWithMarker(MarkerToken(), ": ");
-        generator->PrintString(absl::StrCat(field.varint()));
+        OutOfLinePrintString(generator, field.varint());
         if (single_line_mode_) {
           generator->PrintLiteral(" ");
         } else {
@@ -2718,10 +2723,10 @@ void TextFormat::Printer::PrintUnknownFields(
         }
         break;
       case UnknownField::TYPE_FIXED32: {
-        generator->PrintString(field_number);
+        OutOfLinePrintString(generator, field.number());
         generator->PrintMaybeWithMarker(MarkerToken(), ": ", "0x");
-        generator->PrintString(
-            absl::StrCat(absl::Hex(field.fixed32(), absl::kZeroPad8)));
+        OutOfLinePrintString(generator,
+                             absl::Hex(field.fixed32(), absl::kZeroPad8));
         if (single_line_mode_) {
           generator->PrintLiteral(" ");
         } else {
@@ -2730,10 +2735,10 @@ void TextFormat::Printer::PrintUnknownFields(
         break;
       }
       case UnknownField::TYPE_FIXED64: {
-        generator->PrintString(field_number);
+        OutOfLinePrintString(generator, field.number());
         generator->PrintMaybeWithMarker(MarkerToken(), ": ", "0x");
-        generator->PrintString(
-            absl::StrCat(absl::Hex(field.fixed64(), absl::kZeroPad16)));
+        OutOfLinePrintString(generator,
+                             absl::Hex(field.fixed64(), absl::kZeroPad16));
         if (single_line_mode_) {
           generator->PrintLiteral(" ");
         } else {
@@ -2742,7 +2747,7 @@ void TextFormat::Printer::PrintUnknownFields(
         break;
       }
       case UnknownField::TYPE_LENGTH_DELIMITED: {
-        generator->PrintString(field_number);
+        OutOfLinePrintString(generator, field.number());
         const std::string& value = field.length_delimited();
         // We create a CodedInputStream so that we can adhere to our recursion
         // budget when we attempt to parse the data. UnknownFieldSet parsing is
@@ -2783,7 +2788,7 @@ void TextFormat::Printer::PrintUnknownFields(
         break;
       }
       case UnknownField::TYPE_GROUP:
-        generator->PrintString(field_number);
+        OutOfLinePrintString(generator, field.number());
         if (single_line_mode_) {
           generator->PrintMaybeWithMarker(MarkerToken(), " ", "{ ");
         } else {

src/google/protobuf/text_format.h

@@ -141,7 +141,7 @@ class PROTOBUF_EXPORT TextFormat {
     // Print text to the output stream.
     virtual void Print(const char* text, size_t size) = 0;
 
-    void PrintString(const std::string& str) { Print(str.data(), str.size()); }
+    void PrintString(absl::string_view str) { Print(str.data(), str.size()); }
 
     template <size_t n>
     void PrintLiteral(const char (&text)[n]) {
@@ -724,6 +724,11 @@ class PROTOBUF_EXPORT TextFormat {
                                     ParseLocationRange location);
   static inline ParseInfoTree* CreateNested(ParseInfoTree* info_tree,
                                             const FieldDescriptor* field);
+  // To reduce stack frame bloat we use an out-of-line function to print
+  // strings. This avoid local std::string temporaries.
+  template <typename... T>
+  static void OutOfLinePrintString(BaseTextGenerator* generator,
+                                   const T&... values);
 };
 
 

src/google/protobuf/text_format_unittest.cc

@@ -297,6 +297,22 @@ TEST_F(TextFormatTest, PrintUnknownFields) {
             message.DebugString());
 }
 
+TEST_F(TextFormatTest, PrintUnknownFieldsDeepestStackWorks) {
+  // Test printing of unknown fields in a message.
+
+  unittest::TestEmptyMessage message;
+  UnknownFieldSet* unknown_fields = message.mutable_unknown_fields();
+
+  for (int i = 0; i < 200; ++i) {
+    unknown_fields = unknown_fields->AddGroup(1);
+  }
+
+  unknown_fields->AddVarint(2, 100);
+
+  std::string str;
+  EXPECT_TRUE(TextFormat::PrintToString(message, &str));
+}
+
 TEST_F(TextFormatTest, PrintUnknownFieldsHidden) {
   // Test printing of unknown fields in a message when suppressed.
 
@@ -2350,6 +2366,7 @@ TEST(TextFormatFloatingPointTest, PreservesNegative0) {
             std::signbit(out_message.optional_double()));
 }
 
+
 }  // namespace text_format_unittest
 }  // namespace protobuf
 }  // namespace google