THRIFT-5855: Add py fuzzers

Add fuzzers for py support, to improve the reliability/robustness of the implementation
diff --git a/lib/py/test/fuzz/fuzz_common.py b/lib/py/test/fuzz/fuzz_common.py
new file mode 100644
index 0000000..f472047
--- /dev/null
+++ b/lib/py/test/fuzz/fuzz_common.py
@@ -0,0 +1,134 @@
+import glob
+import sys
+import os
+import atheris
+
+def setup_thrift_imports():
+    """Set up the Python path to include Thrift libraries and generated code."""
+
+    # For oss-fuzz, we need to package it using pyinstaller and set up paths properly
+    if getattr(sys, 'frozen', False) and hasattr(sys, '_MEIPASS'):
+        print('running in a PyInstaller bundle')
+        sys.path.insert(0, "thrift_lib")
+        sys.path.insert(0, "gen-py")
+    else:
+        print('running in a normal Python process')
+        SCRIPT_DIR = os.path.realpath(os.path.dirname(__file__))
+        ROOT_DIR = os.path.dirname(os.path.dirname(os.path.dirname(os.path.dirname(SCRIPT_DIR))))
+
+        for libpath in glob.glob(os.path.join(ROOT_DIR, 'lib', 'py', 'build', 'lib.*')):
+            for pattern in ('-%d.%d', '-%d%d'):
+                postfix = pattern % (sys.version_info[0], sys.version_info[1])
+                if libpath.endswith(postfix):
+                    sys.path.insert(0, libpath)
+                    break
+
+        gen_path = os.path.join(
+            os.path.dirname(os.path.dirname(os.path.abspath(__file__))), "..", "gen-py"
+        )
+        sys.path.append(gen_path)
+    print(sys.path)
+
+setup_thrift_imports()
+
+from thrift.transport import TTransport
+from thrift.TSerialization import serialize, deserialize
+from fuzz.ttypes import FuzzTest
+
+def create_parser_fuzzer(protocol_factory_class):
+    """
+    Create a parser fuzzer function for a specific protocol.
+    
+    Args:
+        protocol_factory_class: The Thrift protocol factory class to use
+    
+    Returns:
+        A function that can be used with atheris.Setup()
+    """
+    def TestOneInput(data):
+        if len(data) < 2:
+            return
+
+        try:
+            # Create a memory buffer with the fuzzed data
+            buf = TTransport.TMemoryBuffer(data)
+            transport = TTransport.TBufferedTransportFactory().getTransport(buf)
+            factory = protocol_factory_class(string_length_limit=1000, container_length_limit=1000)
+
+            # Try to deserialize the fuzzed data into the test class
+            test_instance = deserialize(FuzzTest(), data, factory)
+
+        except Exception as e:
+            # We expect various exceptions during fuzzing
+            pass
+
+    return TestOneInput
+
+def create_roundtrip_fuzzer(protocol_factory_class):
+    """
+    Create a roundtrip fuzzer function for a specific protocol.
+    
+    Args:
+        protocol_factory_class: The Thrift protocol factory class to use
+    
+    Returns:
+        A function that can be used with atheris.Setup()
+    """
+    def TestOneInput(data):
+        if len(data) < 2:
+            return
+
+        try:
+            # Create a memory buffer with the fuzzed data
+            buf = TTransport.TMemoryBuffer(data)
+            transport = TTransport.TBufferedTransportFactory().getTransport(buf)
+            factory = protocol_factory_class(string_length_limit=1000, container_length_limit=1000)
+
+            # Try to deserialize the fuzzed data into the test class
+            test_instance = deserialize(FuzzTest(), data, factory)
+            # If deserialization succeeds, try to serialize it back
+            serialized = serialize(test_instance, factory)
+            # Deserialize again
+            deserialized = deserialize(FuzzTest(), serialized, factory)
+            # Verify the objects are equal after a second deserialization
+            assert test_instance == deserialized
+
+        except AssertionError as e:
+            raise e
+        except Exception as e:
+            # We expect various exceptions during fuzzing
+            pass
+
+    return TestOneInput
+
+def _run_fuzzer(fuzzer_function):
+    """
+    Set up and run the fuzzer for a specific protocol.
+    
+    Args:
+        fuzzer_function: The fuzzer function to use
+    """
+    setup_thrift_imports()
+    atheris.instrument_all()
+    atheris.Setup(sys.argv, fuzzer_function, enable_python_coverage=True)
+    atheris.Fuzz()
+
+
+def run_roundtrip_fuzzer(protocol_factory_class):
+    """
+    Set up and run the fuzzer for a specific protocol.
+    
+    Args:
+        protocol_factory_class: The Thrift protocol factory class to use
+    """
+    _run_fuzzer(create_roundtrip_fuzzer(protocol_factory_class))
+
+
+def run_parser_fuzzer(protocol_factory_class):
+    """
+    Set up and run the fuzzer for a specific protocol.
+    
+    Args:
+        protocol_factory_class: The Thrift protocol factory class to use
+    """
+    _run_fuzzer(create_parser_fuzzer(protocol_factory_class))
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