differential-fuzzer

# Differential Fuzzer Always load [Debugging skill for reference](../debugging/) The differential fuzzer compares Turso results against SQLite for generated SQL statements to find correctness bugs. ## Location `testing/differential-oracle/fuzzer/` ## Running the Fuzzer ### Single Run ```bash # Basic run (100 statements, random seed) cargo run --bin differential_fuzzer # With specific seed for reproducibility cargo run --bin differential_fuzzer -- --seed 12345 # More statements with verbose output cargo run --bin differential_fuzzer -- -n 1000 --verbose # Keep database files after run (for debugging) cargo run --bin differential_fuzzer -- --seed 12345 --keep-files # All options cargo run --bin differential_fuzzer -- \ --seed <SEED> # Deterministic seed -n <NUM> # Number of statements (default: 100) -t <NUM> # Number of tables (default: 2) -c <NUM> # Columns per table (default: 5) --verbose # Print each SQL statement --keep-files # Persist .db files to disk ``` ### Continuous Fuzzing (Loop Mode) ```bash # Run forever with random seeds cargo run --bin differential_fuzzer -- loop # Run 50 iterations cargo run --bin differential_fuzzer -- loop 50 ``` ### Docker Runner (CI/Production) ```bash # Build and run from repo root docker build -f testing/differential-oracle/fuzzer/docker-runner/Dockerfile -t fuzzer . docker run -e GITHUB_TOKEN=xxx -e SLACK_WEBHOOK_URL=xxx fuzzer ``` Environment variables for docker-runner: - `TIME_LIMIT_MINUTES` - Total runtime (default: 1440 = 24h) - `PER_RUN_TIMEOUT_SECONDS` - Per-run timeout (default: 1200 = 20min) - `NUM_STATEMENTS` - Statements per run (default: 1000) - `LOG_TO_STDOUT` - Print fuzzer output (default: false) - `GITHUB_TOKEN` - For auto-filing issues - `SLACK_WEBHOOK_URL` - For notifications ## Output Files All output goes to `simulator-output/` directory: | File | Description | |------|-------------| | `test.sql` | All executed SQL statements. Failed statements prefixed with `-- FAILED:`, errors with `-- ERROR:` | | `schema.json` | Database schema at end of run (or at failure) | | `test.db` | Turso database file (only with `--keep-files`) | | `test-sqlite.db` | SQLite database file (only with `--keep-files`) | ## Reproducing Errors Always follow these steps 1. **Find the seed and profile** in the error output: ``` INFO: Starting differential_fuzzer with config: SimConfig { seed: 12345, ..., weight_profile: Writes } ``` 2. **Re-run with that seed and profile** (a seed only replays under the same profile): ```bash cargo run --bin differential_fuzzer -- --seed 12345 --profile writes --verbose --keep-files ``` 3. **Read the minimized reproduction first.** On an oracle failure the fuzzer writes these files to `simulator-output/`: - `minimized.sql` - a shrunken state script plus the shrunken failing statement, produced automatically. Start here. - `turso-state.sql` / `sqlite-state.sql` - each engine's full state as a replayable script, when you need more than the minimized version kept. - `test.sql` - every executed statement (the failing one is marked `-- FAILED:`). The minimizer falls back to replaying this history when the failure depends on how the state was built, not just its contents. - `schema.json` - table structure at failure time. 4. **Probe the reproduction with `differential_probe`.** It runs a statement-per-line script on Turso and SQLite side by side, prints both outcomes for every statement, marks divergences, and compares the final table contents. Exit code 1 means something diverged. ```bash cargo run -q -p differential-fuzzer --bin differential_probe -- \ simulator-output/minimized.sql ``` Use it instead of piping SQL into the two shells: the tursodb shell cannot `ATTACH ':memory:' AS aux`, so fuzzer reproductions with an `aux` schema only run correctly through the probe. Reading from stdin also works: `echo "SELECT ~X'96';" | cargo run -q -p differential-fuzzer --bin differential_probe`. 5. **Bisect by editing the script.** Copy `minimized.sql`, simplify one thing at a time (replace an expression with a constant, drop a column, drop a state line), and re-run the probe after each edit. The divergence marker tells you immediately whether the edit kept the bug. This loop usually ends at a one-line kernel you can hand to `EXPLAIN` on both engines. 6. **Create a regression test** in `.sqltest` (preferred) or `.rs` from the kernel. Always load the [Debugging skill for reference](../debugging/). ## Understanding Failures ### Oracle Failure Types 1. **Row set mismatch** - Turso returned different rows than SQLite 2. **Turso errored but SQLite succeeded** - Turso rejected valid SQL 3. **SQLite errored but Turso succeeded** - Turso accepted invalid SQL 4. **Schema mismatch** - Tables/columns differ after DDL ### Warning (non-fatal) - **Unordered LIMIT mismatch** - LIMIT without ORDER BY may return different valid rows ## Key Source Files | File | Purpose | |------|---------| | `main.rs` | CLI parsing, entry point | | `runner.rs` | Main simulation loop, executes statements on both DBs | | `oracle.rs` | Compares Turso vs SQLite results | | `schema.rs` | Introspects schema from both databases | | `memory/` | In-memory IO for deterministic simulation | ## Tracing Set `RUST_LOG` for more detailed output: ```bash RUST_LOG=debug cargo run --bin differential_fuzzer -- --seed 12345 ```