json: raise wuffs cursor nesting bound to 16

source/common/json/wuffs_json/wuffs_json_cursor.h

@@ -241,11 +241,13 @@ class WuffsJsonCursor {
   bool wuffs_done_{false};
 
   // Exclusive upper bound for per-depth state tracking: depths 1 through
-  // kMaxTrackedDepth-1 (currently 1–8) have full key/dup/path tracking.
-  // Value covers the deepest known OpenAI/Anthropic schema paths:
-  //   tools[i].function.parameters.properties.<arg>.type  (depth 7)
-  //   messages[i].content[j].content[k].text              (depth 7)
-  // plus one buffer level for schemas with one extra level of nesting.
+  // kMaxTrackedDepth-1 (currently 1–16) have full key/dup/path tracking.
+  // Value covers the deepest known provider schema paths:
+  //   tools[i].function.parameters.properties.<arg>.type      (depth 7)
+  //   messages[i].content[j].content[k].text                  (depth 7)
+  //   [i].candidates[j].content.parts[k].functionCall.args.*  (depth 9+,
+  //     Gemini streamed root arrays; `args` is an arbitrary object)
+  // plus headroom for nested tool arguments.
   //
   // Nesting beyond kMaxTrackedDepth-1 is rejected with InvalidArgumentError.
   // Key/dup/path tracking accuracy is bounded by kMaxTrackedDepth-1 because
@@ -256,7 +258,7 @@ class WuffsJsonCursor {
   // losing tracking accuracy. This removes the hard compile-time cap at the
   // cost of per-push heap allocation; evaluate against the request-path perf
   // budget before doing so.
-  static constexpr int kMaxTrackedDepth = 9;
+  static constexpr int kMaxTrackedDepth = 17;
   // Cap key length at 256 bytes: well above any legitimate schema field name
   // (longest observed ~25B, e.g. "input_audio_transcription") while bounding
   // per-key allocation and guarding against DoS via unbounded key lengths.

test/common/json/wuffs_json/wuffs_json_cursor_test.cc

@@ -598,17 +598,25 @@ TEST(WuffsJsonCursorTest, ByteRangeKeyValueFieldString) {
 
 // Depth limit tests
 
-// 8 levels of nesting must be accepted (boundary value for default max_depth=8).
+// 16 levels of nesting must be accepted (boundary value for the tracked
+// depth limit; Gemini streamed root arrays reach depth 9+ through
+// candidates[].content.parts[].functionCall.args).
 TEST(WuffsJsonCursorTest, MaxDepthAccepted) {
   CapturingHandler h;
-  // 8 nested objects, scalar at the innermost level.
-  EXPECT_OK(parse(R"({"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":1}}}}}}}})", h));
+  // 16 nested objects, scalar at the innermost level.
+  EXPECT_OK(parse(
+      R"({"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":1}}}}}}}}}}}}}}}})",
+      h));
 }
 
-// 9 levels of nesting must be rejected (fail-closed).
+// 17 levels of nesting must be rejected (fail-closed).
 TEST(WuffsJsonCursorTest, ExceedMaxDepthRejected) {
   CapturingHandler h;
-  EXPECT_THAT(parse(R"({"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":1}}}}}}}}})", h), Not(IsOk()));
+  EXPECT_THAT(
+      parse(
+          R"({"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":1}}}}}}}}}}}}}}}}})",
+          h),
+      Not(IsOk()));
 }
 
 // Path-tracking tests

test/extensions/filters/http/ai_protocol_manager/json_with_ext_buf_parser_test.cc

@@ -372,6 +372,20 @@ TEST_F(JsonWithExtBufParserTest, MixedInlineAndOffloadedValues) {
   EXPECT_LT(system_ref.offset, user_ref.offset);
 }
 
+// Gemini streamed root arrays reach candidates[].content.parts[].functionCall
+// .args (depth 9+, and `args` is an arbitrary object): well within the raised
+// nesting bound.
+TEST_F(JsonWithExtBufParserTest, GeminiFunctionCallDepthParses) {
+  JsonWithExtBufParser parser({});
+  const std::string body =
+      R"([{"candidates":[{"content":{"parts":[{"functionCall":{"name":"f",)"
+      R"("args":{"location":{"city":"sf"}}}}]}}],)"
+      R"("usageMetadata":{"promptTokenCount":6,"candidatesTokenCount":9,"totalTokenCount":15}}])";
+  ASSERT_TRUE(parser.feed(body, /*end_stream=*/true).ok());
+  const auto doc = parser.takeDocument();
+  EXPECT_EQ(doc.json()[0]["usageMetadata"]["totalTokenCount"], 15);
+}
+
 } // namespace
 } // namespace AiProtocolManager
 } // namespace HttpFilters