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codetracer-python-recorder

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## CodeTracer Recorders (Monorepo)

This repository hosts **two recorders by design**:

- **codetracer-python-recorder** — the production recorder. A
  Rust-backed Python extension (PyO3 + maturin) with structured errors
  and tighter tooling; emits CTFS v3 binary trace bundles per
  `codetracer-specs/Recorder-CLI-Conventions.md` §4. Use this in real
  deployments.
- **codetracer-pure-python-recorder** — a pure-Python *reference
  implementation* that deliberately emits the legacy JSON trace
  shape. It is the cross-validation oracle that keeps the native
  recorder honest: the test suite runs the same programs through both
  recorders and uses `ct print --json-events` to bring the native
  recorder's CTFS output back into a comparable JSON shape (see
  `codetracer-python-recorder/tests/python/test_cli_integration.py`).
  **Do not migrate it to CTFS** without coordinating with the test
  framework; see
  [`codetracer-pure-python-recorder/README.md`](codetracer-pure-python-recorder/README.md)
  for the full rationale.

Both projects are still in motion. Expect breaking changes while we finish the error-handling rollout.

### Structured errors (Rust-backed recorder)

The Rust module wraps every failure in a `RecorderError` hierarchy that reaches Python with a stable `code`, a readable `kind`, and a `context` dict.

- `UsageError` → bad input or calling pattern. Codes like `ERR_ALREADY_TRACING`.
- `EnvironmentError` → IO or OS problems. Codes like `ERR_IO`.
- `TargetError` → the traced program raised or refused inspection. Codes like `ERR_TRACE_INCOMPLETE`.
- `InternalError` → a recorder bug or panic. Codes default to `ERR_UNKNOWN` unless classified.

Quick catch example:

```python
from codetracer_python_recorder import RecorderError, start, stop

try:
    session = start("/tmp/trace", format="json")
except RecorderError as err:
    print(f"Recorder failed: {err.code}")
    for key, value in err.context.items():
        print(f"  {key}: {value}")
else:
    try:
        ...  # run work here
    finally:
        session.flush()
        stop()
```

All subclasses carry the same attributes, so existing handlers can migrate by catching `RecorderError` once and branching on `err.code` if needed.

### CLI exit behaviour and JSON trailers

`python -m codetracer_python_recorder` returns:

- `0` when the recorder finishes cleanly, even if the traced script exits non-zero. The script's status is still recorded in `trace_metadata.json`, and a warning on stderr highlights the suppressed status.
- `1` when a `RecorderError` bubbles out of startup or shutdown (policy failures, `require_trace`, flush/stop issues).
- `2` when the CLI arguments are incomplete or invalid.

Opt into mirroring the script's exit code with `--propagate-script-exit` (or `CODETRACER_PROPAGATE_SCRIPT_EXIT=true`). Use `--no-propagate-script-exit` to force suppression, even if the environment enables mirroring.

Pass `--json-errors` (or set the policy via `configure_policy(json_errors=True)`) to stream a one-line JSON trailer on stderr. The payload includes `run_id`, `trace_id`, `error_code`, `error_kind`, `message`, and the `context` map so downstream tooling can log failures without scraping text.

### IO capture configuration

Line-aware capture (see [ADR 0008](design-docs/adr/0008-line-aware-io-capture.md)) installs `LineAwareStdout`, `LineAwareStderr`, and `LineAwareStdin` proxies so every chunk carries `{path_id, line, frame_id}` metadata. The proxies forward writes immediately to keep TTY behaviour unchanged and the batching sink emits newline/flush/step-delimited chunks. When the FD mirror fallback observes bytes that bypassed the proxies, the resulting `IoChunk` carries the `mirror` flag so downstream tooling can highlight native writers separately. Recorder logs and telemetry use `ScopedMuteIoCapture` to avoid recursive capture.

Control the feature through the policy layer:

- CLI: `python -m codetracer_python_recorder --io-capture=off script.py` disables capture, while `--io-capture=proxies+fd` also mirrors raw file-descriptor writes.
- Python: `configure_policy(io_capture_line_proxies=False)` toggles proxies, and `configure_policy(io_capture_fd_fallback=True)` enables the FD fallback.
- Environment: set `CODETRACER_CAPTURE_IO=off`, `proxies`, or `proxies+fd` (`,` is also accepted) to match the CLI and Python helpers.

Manual smoke check: `python -m codetracer_python_recorder examples/stdout_script.py` should report the proxied output while leaving the console live.

#### Troubleshooting replaced stdout/stderr

Third-party tooling occasionally replaces `sys.stdout` / `sys.stderr` after the proxies install. When that happens, IO metadata stops updating and the recorder falls back to passthrough behaviour. You can verify the binding at runtime:

```python
import sys
from codetracer_python_recorder.runtime import LineAwareStdout, LineAwareStderr

print(type(sys.stdout).__name__, isinstance(sys.stdout, LineAwareStdout))
print(type(sys.stderr).__name__, isinstance(sys.stderr, LineAwareStderr))
```

Both `isinstance` checks should return `True`. If they do not:

1. Re-run `configure_policy(io_capture_line_proxies=True)` (or restart tracing) to reinstall the proxies before the other tool mutates the streams.
2. Fall back to FD mirroring by enabling `CODETRACER_CAPTURE_IO=proxies+fd` so native writes still reach the ledger-backed mirror.
3. As a last resort, disable IO capture (`--io-capture=off`) and rely on console output while investigating the conflicting integration.

### Migration checklist for downstream tools

- Catch `RecorderError` (or a subclass) instead of `RuntimeError`.
- Switch any string matching over to `err.code` values like `ERR_TRACE_DIR_CONFLICT`.
- Expect structured log lines (JSON) on stderr. Use the `error_code` field instead of parsing text.
- Opt in to JSON trailers for machine parsing and keep human output short.
- Update policy wiring to use `configure_policy` / `policy_snapshot()` rather than hand-rolled env parsing.
- Read `docs/onboarding/error-handling.md` for detailed migration steps and assertion rules.

### Logging defaults

The recorder now installs a JSON logger on first import. Logs include `run_id`, optional `trace_id`, and an `error_code` field when set.

- Control the log filter with `RUST_LOG=target=level` (standard env syntax).
- Override from Python with `configure_policy(log_level="info")` or `log_file=...` for file output.
- Metrics counters record dropped events, detach reasons, and caught panics; plug your own sink via the Rust API when embedding.

### codetracer-pure-python-recorder

Install from PyPI:

```bash
pip install codetracer-pure-python-recorder
```

CLI usage:

```bash
codetracer-record <path to python file>
# produces several trace json files in the current directory
# or in the folder of `$CODETRACER_DB_TRACE_PATH` if such an env var is defined
```

During development you can also run it directly:

```bash
python src/trace.py <path to python file>
# produces several trace json files in the current directory
# or in the folder of `$CODETRACER_DB_TRACE_PATH` if such an env var is defined
```

### codetracer-python-recorder (Rust-backed)

A separate Python module implemented in Rust with PyO3 and built via maturin lives under:
crates/codetracer-python-recorder/

Basic workflow:

- Build/dev install the Rust module:
  - maturin develop -m crates/codetracer-python-recorder/Cargo.toml
- Use in Python:
  - from codetracer_python_recorder import hello
  - hello()

#### Testing & Coverage

- Run the full split test suite (Rust nextest + Python pytest): `just test`
- Run only Rust integration/unit tests: `just cargo-test`
- Run only Python tests (including the pure-Python recorder to guard regressions): `just py-test`
- Exercise the trace-filter benchmarks (Rust Criterion + Python smoke, JSON output under `codetracer-python-recorder/target/perf`): `just bench`
- Collect coverage artefacts locally (LCOV + Cobertura/JSON): `just coverage`

The CI workflow mirrors these commands. Pull requests get an automated comment with the latest Rust/Python coverage tables and downloadable artefacts (`lcov.info`, `coverage.xml`, `coverage.json`).

#### Debug logging

Rust-side logging defaults to `warn` so test output stays readable. Export
`RUST_LOG` when you need more detail:

```bash
RUST_LOG=codetracer_python_recorder=debug pytest \
  codetracer-python-recorder/tests/python/unit/test_backend_exceptions.py -q
```

Any filter accepted by `env_logger` still works, so you can switch to
`RUST_LOG=codetracer_python_recorder=info` or silence everything with
`RUST_LOG=off`.

### Future directions

The current Python support is an unfinished prototype. We can finish it. In the future, it may be expanded to function in a way to similar to the more complete implementations, e.g. [Noir](https://github.com/blocksense-network/noir/tree/blocksense/tooling/tracer).

Currently it's very similar to our [Ruby tracer](https://github.com/metacraft-labs/ct-ruby-tracer)

#### Current approach: sys.settrace API

Currently we're using the sys.settrace API: https://docs.python.org/3/library/sys.html#sys.settrace .
This is very flexible and can function with probably multiple Python versions out of the box. 
However, this is limited:

* it's not optimal
* it can't track more detailed info/state, needed for some CodeTracer features(or for more optimal replays).

For other languages, we've used a more deeply integrated approach: patching the interpreter or VM itself (e.g. Noir).

#### Patching the VM

This can be a good approach for Python as well: it can let us record more precisely subvalues, assignments and subexpressions and to let
some CodeTracer features work in a deeper/better way.

One usually needs to add additional logic to places where new opcodes/lines are being ran, and to call entries/exits. Additionally
tracking assignments can be a great addition, but it really depends on the interpreter internals.

#### Filtering

It would be useful to have a way to record in detail only certain periods of the program, or certain functions or modules: 
we plan on expanding the [trace format](https://github.com/metacraft-labs/runtime_tracing/) and CodeTracer' support, so that this is possible. It would let one be able to record interesting
parts of even long-running or more heavy programs.

### Contributing

We'd be very happy if the community finds this useful, and if anyone wants to:

* Use and test the Python support or CodeTracer.
* Provide feedback and discuss alternative implementation ideas: in the issue tracker, or in our [discord](https://discord.gg/qSDCAFMP).
* Contribute code to enhance the Python support of CodeTracer.
* Provide [sponsorship](https://opencollective.com/codetracer), so we can hire dedicated full-time maintainers for this project.

### Direct-storage upload (Enterprise on-prem)

For Enterprise on-prem deployments, the recorder produces materialized
trace artifacts on the local filesystem and a separate
`codetracer-managed-upload direct-materialized-finalize` invocation
PUTs them directly to the customer's storage server, then posts a
metadata-only finalize to codetracer-ci. Trace bytes never traverse
the codetracer-ci control plane.

The `codetracer-managed-upload` helper is shipped in the
`codetracer-trace-format` workspace
(`codetracer_ctfs/src/bin/codetracer-managed-upload.rs`). It takes
a static `codetracer.trace-storage.v1` JSON config that points at
the storage server, the control plane, and the Enterprise lease
checkout endpoint. After the recorder produces the materialized
artifact set, drive the helper:

```bash
codetracer-managed-upload direct-materialized-finalize \
  --storage-config /etc/codetracer/trace-storage.json \
  --recording-id "${SESSION_ID}" \
  --object-key-prefix "traces/${TENANT_ID}/${SESSION_ID}/python-direct" \
  --idempotency-key "${SESSION_ID}-python" \
  --artifact-dir "${RECORDER_OUT_DIR}" \
  --language python
```

The full data-path overview, the static-config schema, and the
Enterprise lease lifecycle are documented at
[`codetracer-specs/Observability-Platform/docs/direct-storage-data-path.md`](../codetracer-specs/Observability-Platform/docs/direct-storage-data-path.md).
The HTTP endpoint reference is at
[`codetracer-ci/rewrite-docs/04-apis-events/http-api.md`](../codetracer-ci/rewrite-docs/04-apis-events/http-api.md)
section 4.10.

End-to-end coverage:
`StoragePolicyModelTests.e2e_python_recorder_materialized_direct_upload_with_static_config`
(M38 slice 5A) and the M39 NixOS test
`codetracer-ci-rewrite-multitenant-infra-materialized-recorders-incus`
(live recorder running inside an Incus container per tenant).

### Legal info

LICENSE: MIT

codetracer-python-recorder

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