fuzz_undo.py

import os
import subprocess
import json

success = 0
for i in range(10):
    # we need a valid block so it actually reaches the undo parser
    # let's just use the existing block fixture, and a fuzzed undo file
    import shutil
    
    # we create random undo data
    rev_data = os.urandom(50000) # big chunks of random bytes
    with open('fuzz_rev.dat', 'wb') as f:
        f.write(rev_data)
        
    cmd = ['python', '-m', 'chainlens.cli', '--block', 'fixtures/blocks/blk00000.dat', 'fuzz_rev.dat', 'fixtures/blocks/xor.dat']
    
    result = subprocess.run(cmd, capture_output=True, text=True)
    
    # the CLI must exit 1 (or 0 if somehow valid, which is statistically impossible)
    # the output MUST be a valid JSON with "ok": false
    try:
        if not result.stdout.strip():
            print(f"Failed iter {i}: Empty stdout. Stderr: {result.stderr}")
            break
        
        parsed = json.loads(result.stdout)
        if parsed.get("ok") is not False:
            print(f"Failed iter {i}: Returned ok=True?!")
            break
            
        if "error" not in parsed:
            print(f"Failed iter {i}: No error object")
            break
            
        # ensure no traceback leaked in stdout or stderr
        if "Traceback" in result.stdout or "Traceback" in result.stderr:
             print(f"Failed iter {i}: Traceback leaked!")
             break
             
        success += 1
    except json.JSONDecodeError:
        print(f"Failed iter {i}: Invalid JSON returned -> {result.stdout}")
        print(f"Stderr -> {result.stderr}")
        break

if success == 10:
    print("FUZZ_PASSED: 10/10 random undo files handled safely with proper JSON errors.")
else:
    print(f"FUZZ_FAILED: Survived {success}/10")

# cleanup
if os.path.exists('fuzz_rev.dat'):
    os.remove('fuzz_rev.dat')