JSONWriter should support adding non containers at max depth

The JSON fuzzing tests failed to write JSON via JSONWriter::Write that
was successfully read with JSONReader.  This was due to an edge case
where we are writing the JSON and have reached max depth (200) but have
non-container leaf entries at that level and nothing deeper.  This case
should be supported by the JSONWriter to match the JSONReader and
JSONParser. Also added a unit test for this case.

Bug: 1138450, 1013934
Change-Id: I98fcd63c957ab4e85a322d923bef18b981220383
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2477239Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Chris Davis <chrdavis@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#818212}

base/json/json_writer.cc

@@ -61,8 +61,6 @@ JSONWriter::JSONWriter(int options, std::string* json, size_t max_depth)
 
 bool JSONWriter::BuildJSONString(const Value& node, size_t depth) {
   internal::StackMarker depth_check(max_depth_, &stack_depth_);
-  if (depth_check.IsTooDeep())
-    return false;
 
   switch (node.type()) {
     case Value::Type::NONE:
@@ -113,6 +111,9 @@ bool JSONWriter::BuildJSONString(const Value& node, size_t depth) {
       return true;
 
     case Value::Type::LIST: {
+      if (depth_check.IsTooDeep())
+        return false;
+
       json_string_->push_back('[');
       if (pretty_print_)
         json_string_->push_back(' ');
@@ -142,6 +143,9 @@ bool JSONWriter::BuildJSONString(const Value& node, size_t depth) {
     }
 
     case Value::Type::DICTIONARY: {
+      if (depth_check.IsTooDeep())
+        return false;
+
       json_string_->push_back('{');
       if (pretty_print_)
         json_string_->append(kPrettyPrintLineEnding);

base/json/json_writer_unittest.cc

@@ -3,9 +3,11 @@
 // found in the LICENSE file.
 
 #include "base/json/json_writer.h"
+#include "base/json/json_reader.h"
 
 #include "base/containers/span.h"
 #include "base/memory/ptr_util.h"
+#include "base/strings/stringprintf.h"
 #include "base/values.h"
 #include "build/build_config.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -186,4 +188,26 @@ TEST(JSONWriterTest, StackOverflow) {
   }
 }
 
+TEST(JSONWriterTest, TestMaxDepthWithValidNodes) {
+  // Create JSON to the max depth - 1.  Nodes at that depth are still valid
+  // for writing which matches the JSONParser logic.
+  std::string nested_json;
+  for (int i = 0; i < 199; ++i) {
+    std::string node = "[";
+    for (int j = 0; j < 5; j++) {
+      node.append(StringPrintf("%d,", j));
+    }
+    nested_json.insert(0, node);
+    nested_json.append("]");
+  }
+
+  // Ensure we can read and write the JSON
+  JSONReader::ValueWithError json_val = JSONReader::ReadAndReturnValueWithError(
+      nested_json, JSON_ALLOW_TRAILING_COMMAS);
+  EXPECT_TRUE(json_val.value);
+  const Value& value = json_val.value.value();
+  std::string serialized;
+  EXPECT_TRUE(JSONWriter::Write(value, &serialized));
+}
+
 }  // namespace base