THRIFT-6043: Limit struct read/write recursion depth in Python library

[Jens-G]

Summary

Adds a configurable recursion depth limit (default 64) to struct and exception read/write in the Python library.

What is changed:

• compiler/cpp/src/thrift/generate/t_py_generator.cc: generated read()/write() methods now wrap the body in increment_recursion_depth() / try / finally: decrement_recursion_depth().
• lib/py/src/protocol/TProtocol.py: TProtocolBase gains _recursion_depth, DEFAULT_RECURSION_DEPTH = 64, increment_recursion_depth() (raises TProtocolException.DEPTH_LIMIT when exceeded), and decrement_recursion_depth().
• lib/py/src/ext/protocol.h / protocol.tcc: The fastbinary C extension (TBinaryProtocolAccelerated, TCompactProtocolAccelerated) is also guarded. ProtocolBase gains a recursionDepth_ counter; readStruct() and encodeValue(T_STRUCT) use a RAII RecursionGuard that raises TProtocolException(DEPTH_LIMIT, …) via the Python C API when the limit is exceeded.
• lib/py/test/test_recursion_depth.py + lib/py/Makefile.am: Generated-code round-trip tests over test/Recursive.thrift (RecTree struct, CoError exception) for TBinaryProtocol, TBinaryProtocolAccelerated, TCompactProtocol, TCompactProtocolAccelerated, and TJSONProtocol.

Note: The guard is placed after the fast-path early return in generated read(), so TBinaryProtocol (non-accelerated) and TJSONProtocol are protected via the Python path; TBinaryProtocolAccelerated and TCompactProtocolAccelerated are protected via the C extension guard. The limit (64) is hardcoded in the C extension; making it read from TConfiguration can be a follow-up.

skip() remains independently bounded via TProtocolBase.skip(max_depth=64) (unchanged).

Test plan

• make -C lib/py check passes (Python 3.10–3.14, with and without skip-build-ext)
• 12/12 round-trip tests in test_recursion_depth.py pass locally (Docker thrift:jammy)
• Baseline proof: stripping the generator guard from the generated RecTree.read()/write() causes 8 over-limit assertions to fail

🤖 Generated with Claude Code

Co-Authored-By: Claude Sonnet 4.6 noreply@anthropic.com