Test Case Reducer

Fuzzer found a crash with a 50KB JSON input. The bug is probably triggered by 3 bytes of it. Reduction finds those 3 bytes.

The interestingness test

Everything hinges on a boolean oracle: does this (smaller) input still trigger the bug?

def interesting(input_bytes):
    proc = subprocess.run(["./parser", "-"], input=input_bytes,
                          capture_output=True, timeout=5)
    return proc.returncode == -11   # SIGSEGV

Make it specific. "Crashes" is too loose — you might reduce to a different crash. Check for the same stack trace, same error message, same assertion.

Delta debugging (ddmin) — the general algorithm