Change SkipRestOfBlock to be iterative instead of recursive to avoid stack

overflows on invalid input with many unbalanced `{` characters.

PiperOrigin-RevId: 562806350

src/google/protobuf/compiler/parser.cc

@@ -38,6 +38,7 @@
 
 #include <float.h>
 
+#include <cstddef>
 #include <cstdint>
 #include <limits>
 #include <string>
@@ -555,14 +556,15 @@ void Parser::SkipStatement() {
 }
 
 void Parser::SkipRestOfBlock() {
+  size_t block_count = 1;
   while (true) {
     if (AtEnd()) {
       return;
     } else if (LookingAtType(io::Tokenizer::TYPE_SYMBOL)) {
       if (TryConsumeEndOfDeclaration("}", nullptr)) {
-        return;
+        if (--block_count == 0) break;
       } else if (TryConsume("{")) {
-        SkipRestOfBlock();
+        ++block_count;
       }
     }
     input_->Next();

src/google/protobuf/compiler/parser_unittest.cc

@@ -117,8 +117,9 @@ class ParserTest : public testing::Test {
   ParserTest() : require_syntax_identifier_(false) {}
 
   // Set up the parser to parse the given text.
-  void SetupParser(const char* text) {
-    raw_input_ = absl::make_unique<io::ArrayInputStream>(text, strlen(text));
+  void SetupParser(absl::string_view text) {
+    raw_input_ =
+        absl::make_unique<io::ArrayInputStream>(text.data(), text.size());
     input_ =
         absl::make_unique<io::Tokenizer>(raw_input_.get(), &error_collector_);
     parser_ = absl::make_unique<Parser>();
@@ -169,7 +170,8 @@ class ParserTest : public testing::Test {
 
   // Same as above but does not expect that the parser parses the complete
   // input.
-  void ExpectHasEarlyExitErrors(const char* text, const char* expected_errors) {
+  void ExpectHasEarlyExitErrors(absl::string_view text,
+                                absl::string_view expected_errors) {
     SetupParser(text);
     SourceLocationTable source_locations;
     parser_->RecordSourceLocationsTo(&source_locations);
@@ -286,6 +288,16 @@ TEST_F(ParserTest, WarnIfFieldNameContainsNumberImmediatelyFollowUnderscore) {
                   "song_name_1.") != std::string::npos);
 }
 
+TEST_F(ParserTest, RegressionNestedOpenBraceDoNotStackOverflow) {
+  std::string input("edition=\"a\000;", 12);
+  input += std::string(100000, '{');
+  ExpectHasEarlyExitErrors(
+      input,
+      "0:10: Unexpected end of string.\n"
+      "0:10: Invalid control characters encountered in text.\n"
+      "0:12: Expected top-level statement (e.g. \"message\").\n");
+}
+
 // ===================================================================
 
 typedef ParserTest ParseMessageTest;