unsloth/studio/backend/tests/test_hf_xet_fallback.py

# SPDX-License-Identifier: AGPL-3.0-only
# Copyright 2026-present the Unsloth AI Inc. team. All rights reserved. See /studio/LICENSE.AGPL-3.0

"""Tests for the Unsloth shim over the shared unsloth_zoo Xet -> HTTP fallback.

The transport-policy matrix is tested once in unsloth_zoo; here we assert only the
Unsloth seam: re-exporting the shared API and injecting the marker-aware
prepare_cache_for_transport on the HTTP retry. CPU-only, no network, no real subprocess.
"""

from __future__ import annotations

import sys
import types as _types
from pathlib import Path

import pytest

_BACKEND_DIR = str(Path(__file__).resolve().parent.parent)
if _BACKEND_DIR not in sys.path:
    sys.path.insert(0, _BACKEND_DIR)

# Stub heavy/unavailable deps before importing the module under test. Use real structlog when present;
# a bare stub would break later modules that log at import time.
_loggers_stub = _types.ModuleType("loggers")
_loggers_stub.get_logger = lambda name: __import__("logging").getLogger(name)
sys.modules.setdefault("loggers", _loggers_stub)
try:
    import structlog  # noqa: F401
except ImportError:
    sys.modules["structlog"] = _types.ModuleType("structlog")

import huggingface_hub

try:
    import unsloth_zoo.hf_xet_fallback as _shared_mod
    shared = _shared_mod
except Exception:  # noqa: BLE001 - still collect degraded-path tests when unsloth_zoo is unavailable
    shared = None

import utils.hf_xet_fallback as xf


DL_REPO, FILE = "ztest/xet-dl", "model-Q4_K_XL.gguf"


def _requires_shared():
    if shared is None:
        pytest.skip("unsloth_zoo.hf_xet_fallback is not installed in this environment")


def test_shim_reexports_shared_api():
    _requires_shared()
    assert xf.DownloadStallError is shared.DownloadStallError
    for name in (
        "start_watchdog",
        "get_hf_download_state",
        "child_should_disable_xet",
        "hf_hub_download_with_xet_fallback",
        "snapshot_download_with_xet_fallback",
    ):
        assert hasattr(xf, name), f"shim missing {name}"


def test_child_should_disable_xet_truth_table():
    assert xf.child_should_disable_xet({"disable_xet": True}) is True
    assert xf.child_should_disable_xet({"disable_xet": False}) is False
    assert xf.child_should_disable_xet({}) is False


def test_shim_injects_studio_prepare_on_http_retry(monkeypatch):
    """A Xet stall retries over HTTP and the shim runs Unsloth's marker-aware
    ``prepare_cache_for_transport(..., 'http')`` before the retry."""
    _requires_shared()
    for var in ("UNSLOTH_DISABLE_XET", "UNSLOTH_STABLE_DOWNLOADS", "HF_HUB_DISABLE_XET"):
        monkeypatch.delenv(var, raising = False)
    monkeypatch.setattr(huggingface_hub, "try_to_load_from_cache", lambda *a, **k: None)

    seen_disable_xet = []

    def fake_attempt(
        repo_id,
        *,
        kind,
        params,
        token,
        repo_type,
        disable_xet,
        cancel_event,
        stall_timeout,
        interval,
        grace_period,
        on_status,
        force_download = False,
    ):
        seen_disable_xet.append(disable_xet)
        return ("ok", "/cache/model.gguf") if disable_xet else ("stall", None)

    monkeypatch.setattr(shared, "_run_download_attempt", fake_attempt)

    prepared = []
    monkeypatch.setattr(
        "hub.utils.download_registry.prepare_cache_for_transport",
        lambda repo_type, repo_id, mode, *a, **k: prepared.append((repo_type, repo_id, mode)),
    )

    out = xf.hf_hub_download_with_xet_fallback(DL_REPO, FILE, None)
    assert out == "/cache/model.gguf"
    assert seen_disable_xet == [False, True]  # Xet first, then HTTP
    assert prepared == [("model", DL_REPO, "http")], "shim must run Unsloth's marker-aware prep"


def test_shim_snapshot_injects_studio_prepare(monkeypatch):
    """The snapshot wrapper forwards Unsloth's marker-aware prep, like the file wrapper."""
    captured = {}

    def fake_snapshot(repo_id, **kwargs):
        captured["repo_id"] = repo_id
        captured["prepare_for_http_fn"] = kwargs.get("prepare_for_http_fn")
        return "/tmp/snap-dir"

    monkeypatch.setattr(xf, "_shared_snapshot_download_with_xet_fallback", fake_snapshot)
    out = xf.snapshot_download_with_xet_fallback("org/model")
    assert out == "/tmp/snap-dir"
    assert captured["repo_id"] == "org/model"
    assert captured["prepare_for_http_fn"] is xf._studio_prepare_for_http


def test_degrades_gracefully_without_shared_helper(monkeypatch):
    """On an older unsloth_zoo lacking the shared helper, the shim still imports (Unsloth
    boots) and exposes stub API doing plain HF downloads with the watchdog disabled."""
    import importlib

    class _BlockShared:
        def find_spec(
            self,
            name,
            path = None,
            target = None,
        ):
            if name == "unsloth_zoo.hf_xet_fallback":
                raise ModuleNotFoundError(f"No module named '{name}'", name = name)
            return None

    finder = _BlockShared()
    saved_shared = sys.modules.pop("unsloth_zoo.hf_xet_fallback", None)
    saved_shim = sys.modules.pop("utils.hf_xet_fallback", None)
    sys.meta_path.insert(0, finder)
    try:
        degraded = importlib.import_module("utils.hf_xet_fallback")

        # Boots without raising and mirrors the shared API surface.
        assert issubclass(degraded.DownloadStallError, RuntimeError)
        assert degraded.child_should_disable_xet({"disable_xet": True}) is True
        assert degraded.get_hf_download_state(["x"]) is None  # unmeasurable
        event = degraded.start_watchdog(repo_ids = ["x"], on_stall = lambda m: None)
        assert hasattr(event, "set") and not event.is_set()  # never fires

        # Degraded mode still emits heartbeats so the inactivity deadline is not tripped.
        import time as _time

        beats = []
        hb_stop = degraded.start_watchdog(
            repo_ids = ["x"],
            on_stall = lambda m: None,
            on_heartbeat = beats.append,
            interval = 0.02,
        )
        try:
            deadline = _time.monotonic() + 2.0
            while not beats and _time.monotonic() < deadline:
                _time.sleep(0.02)
            assert beats, "degraded watchdog emitted no heartbeat"
        finally:
            hb_stop.set()

        # Downloads fall back to plain huggingface_hub (no watchdog, no crash).
        called = {}

        def _fake_snapshot(repo_id, **kwargs):
            called["repo_id"] = repo_id
            return "/snap-dir"

        monkeypatch.setattr(huggingface_hub, "snapshot_download", _fake_snapshot)
        assert degraded.snapshot_download_with_xet_fallback("org/model") == "/snap-dir"
        assert called["repo_id"] == "org/model"

        # Cancellation still holds: an already-set cancel_event aborts before the HF download.
        import threading as _threading

        cancelled = _threading.Event()
        cancelled.set()
        called.clear()
        with pytest.raises(RuntimeError, match = "Cancelled"):
            degraded.snapshot_download_with_xet_fallback("org/model", cancel_event = cancelled)
        assert "repo_id" not in called, "degraded download ran despite cancellation"
    finally:
        sys.meta_path.remove(finder)
        sys.modules.pop("utils.hf_xet_fallback", None)
        if saved_shared is not None:
            sys.modules["unsloth_zoo.hf_xet_fallback"] = saved_shared
        if saved_shim is not None:
            sys.modules["utils.hf_xet_fallback"] = saved_shim


def test_degrades_when_unsloth_zoo_entirely_absent():
    """When unsloth_zoo is absent entirely, the import raises
    ModuleNotFoundError(name='unsloth_zoo') (top-level package). Guard that the shim still
    degrades and does not re-raise, breaking every Unsloth import that pulls it in."""
    import importlib

    class _BlockZoo:
        def find_spec(
            self,
            name,
            path = None,
            target = None,
        ):
            # Whole package absent, so ModuleNotFoundError.name is the top-level 'unsloth_zoo'.
            if name == "unsloth_zoo" or name.startswith("unsloth_zoo."):
                raise ModuleNotFoundError("No module named 'unsloth_zoo'", name = "unsloth_zoo")
            return None

    finder = _BlockZoo()
    saved = {
        k: v
        for k, v in list(sys.modules.items())
        if k == "unsloth_zoo" or k.startswith("unsloth_zoo.")
    }
    for k in saved:
        del sys.modules[k]
    saved_shim = sys.modules.pop("utils.hf_xet_fallback", None)
    sys.meta_path.insert(0, finder)
    try:
        degraded = importlib.import_module("utils.hf_xet_fallback")
        # Boots without raising and exposes the stub API.
        assert issubclass(degraded.DownloadStallError, RuntimeError)
        assert degraded.get_hf_download_state(["x"]) is None
        event = degraded.start_watchdog(repo_ids = ["x"], on_stall = lambda m: None)
        assert hasattr(event, "set") and not event.is_set()
    finally:
        sys.meta_path.remove(finder)
        sys.modules.pop("utils.hf_xet_fallback", None)
        sys.modules.update(saved)
        if saved_shim is not None:
            sys.modules["utils.hf_xet_fallback"] = saved_shim


def test_degrades_when_shared_helper_import_raises_importerror():
    """unsloth_zoo can be installed yet fail to import when torch is missing (llama.cpp/GGUF-only
    Unsloth), raising ImportError not ModuleNotFoundError. The shim must degrade for that too."""
    import importlib

    class _BlockWithImportError:
        def find_spec(
            self,
            name,
            path = None,
            target = None,
        ):
            if name == "unsloth_zoo.hf_xet_fallback":
                # Mirror a torch-less install: a plain ImportError with no .name.
                raise ImportError("Unsloth: Pytorch is not installed.")
            return None

    finder = _BlockWithImportError()
    saved_shared = sys.modules.pop("unsloth_zoo.hf_xet_fallback", None)
    saved_zoo = sys.modules.pop("unsloth_zoo", None)
    saved_shim = sys.modules.pop("utils.hf_xet_fallback", None)
    sys.meta_path.insert(0, finder)
    try:
        degraded = importlib.import_module("utils.hf_xet_fallback")
        assert issubclass(degraded.DownloadStallError, RuntimeError)
        assert degraded.get_hf_download_state(["x"]) is None
        event = degraded.start_watchdog(repo_ids = ["x"], on_stall = lambda m: None)
        assert hasattr(event, "set") and not event.is_set()
    finally:
        sys.meta_path.remove(finder)
        sys.modules.pop("utils.hf_xet_fallback", None)
        if saved_shared is not None:
            sys.modules["unsloth_zoo.hf_xet_fallback"] = saved_shared
        if saved_zoo is not None:
            sys.modules["unsloth_zoo"] = saved_zoo
        if saved_shim is not None:
            sys.modules["utils.hf_xet_fallback"] = saved_shim


def test_retries_under_light_gpu_init_when_import_fails(monkeypatch):
    """GPU detection in unsloth_zoo's __init__ raises NotImplementedError on a GPU-less host. The shim
    retries under UNSLOTH_ZOO_DISABLE_GPU_INIT=1, restores the env, and degrades if the retry fails.
    The backend loads lazily (first use of a heavy helper), so this triggers the load explicitly
    before asserting the retry/degrade behavior."""
    import importlib
    import os

    monkeypatch.delenv("UNSLOTH_ZOO_DISABLE_GPU_INIT", raising = False)
    seen_env = []

    class _GpuGatedBlocker:
        def find_spec(
            self,
            name,
            path = None,
            target = None,
        ):
            # Crash is in unsloth_zoo's __init__, so intercept "unsloth_zoo" itself (the parent).
            if name == "unsloth_zoo":
                # Record the env each attempt sees; raise the no-GPU error both times so the shim
                # degrades.
                seen_env.append(os.environ.get("UNSLOTH_ZOO_DISABLE_GPU_INIT"))
                raise NotImplementedError("Unsloth cannot find any torch accelerator")
            return None

    finder = _GpuGatedBlocker()
    saved = {
        k: v
        for k, v in list(sys.modules.items())
        if k == "unsloth_zoo" or k.startswith("unsloth_zoo.")
    }
    for k in saved:
        del sys.modules[k]
    saved_shim = sys.modules.pop("utils.hf_xet_fallback", None)
    sys.meta_path.insert(0, finder)
    try:
        degraded = importlib.import_module("utils.hf_xet_fallback")
        # Import is light (lazy backend); unsloth_zoo not loaded yet.
        assert seen_env == [], seen_env
        # First use of a heavy helper triggers the load (attempt without the light env, then a retry
        # with it set); accessing DownloadStallError drives it via __getattr__.
        stall_error = degraded.DownloadStallError
        assert seen_env == [None, "1"], seen_env
        # Both attempts raised -> Unsloth still boots in degraded mode.
        assert issubclass(stall_error, RuntimeError)
        # The env override must not leak past the load.
        assert os.environ.get("UNSLOTH_ZOO_DISABLE_GPU_INIT") is None
    finally:
        sys.meta_path.remove(finder)
        sys.modules.pop("utils.hf_xet_fallback", None)
        sys.modules.update(saved)
        if saved_shim is not None:
            sys.modules["utils.hf_xet_fallback"] = saved_shim


def test_importing_child_should_disable_xet_stays_light(monkeypatch):
    """Regression guard for the stale-transformers-sidecar bug: importing the shim (and
    ``child_should_disable_xet``) must NOT pull in ``transformers``/``unsloth_zoo``. The worker calls
    this at startup to decide the Xet env flip BEFORE activating the sidecar; an eager import here
    would cache the default transformers 4.57.x in sys.modules, defeating the sidecar sys.path prepend
    and breaking 5.x models (Qwen3.5/GLM/gemma-4)."""
    import importlib

    for name in [
        m
        for m in list(sys.modules)
        if m == "transformers"
        or m.startswith("transformers.")
        or m == "unsloth_zoo"
        or m.startswith("unsloth_zoo.")
        or m == "utils.hf_xet_fallback"
    ]:
        monkeypatch.delitem(sys.modules, name, raising = False)

    mod = importlib.import_module("utils.hf_xet_fallback")
    # The lightweight decision works without the heavy backend.
    assert mod.child_should_disable_xet({"disable_xet": True}) is True
    assert mod.child_should_disable_xet({}) is False
    # And nothing heavy was imported as a side effect.
    assert "transformers" not in sys.modules, "importing the shim must not import transformers"
    assert "unsloth_zoo" not in sys.modules, "importing the shim must not import unsloth_zoo"