Follow up test and fix for https://github.com/lemire/simdjson/issues/345 (#347)

src/parsedjson.cpp

@@ -46,8 +46,11 @@ bool ParsedJson::allocate_capacity(size_t len, size_t max_depth) {
   uint32_t max_structures = ROUNDUP_N(len, 64) + 2 + 7;
   structural_indexes = new (std::nothrow) uint32_t[max_structures];
   // a pathological input like "[[[[..." would generate len tape elements, so
-  // need a capacity of len + 1
-  size_t local_tape_capacity = ROUNDUP_N(len + 1, 64);
+  // need a capacity of at least len + 1, but it is also possible to do
+  // worse with "[7,7,7,7,6,7,7,7,6,7,7,6,[7,7,7,7,6,7,7,7,6,7,7,6,7,7,7,7,7,7,6" 
+  //where len + 1 tape elements are
+  // generated, see issue https://github.com/lemire/simdjson/issues/345
+  size_t local_tape_capacity = ROUNDUP_N(len + 2, 64);
   // a document with only zero-length strings... could have len/3 string
   // and we would need len/3 * 5 bytes on the string buffer
   size_t local_string_capacity = ROUNDUP_N(5 * len / 3 + 32, 64);

tests/basictests.cpp

@@ -153,6 +153,18 @@ bool number_test_powers_of_ten() {
   return true;
 }
 
+
+// adversarial example that once triggred overruns, see https://github.com/lemire/simdjson/issues/345
+bool bad_example() {
+  std::string badjson = "[7,7,7,7,6,7,7,7,6,7,7,6,[7,7,7,7,6,7,7,7,6,7,7,6,7,7,7,7,7,7,6";
+  simdjson::ParsedJson pj = simdjson::build_parsed_json(badjson);
+  if(pj.is_valid()) {
+    printf("This json should not be valid %s.\n", badjson.c_str());
+    return false;
+  }
+  return true;
+}
+
 // returns true if successful
 bool navigate_test() {
   std::string json = "{"
@@ -279,6 +291,8 @@ bool skyprophet_test() {
 
 int main() {
   std::cout << "Running basic tests." << std::endl;
+  if(!bad_example())
+    return EXIT_FAILURE;
   if(!number_test_powers_of_two())
     return EXIT_FAILURE;
   if(!number_test_powers_of_ten())