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fix: force offline mode when loading cached models (Qwen TTS & Whisper) #318

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Merged
jamiepine merged 1 commit into from
Mar 21, 2026
+77 −44
Merged

fix: force offline mode when loading cached models (Qwen TTS & Whisper) #318

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39 changes: 11 additions & 28 deletions backend/backends/mlx_backend.py
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,6 @@
import asyncio
import logging
import numpy as np
import os
from pathlib import Path

logger = logging.getLogger(__name__)
Expand All @@ -21,6 +20,7 @@
from . import TTSBackend, STTBackend, LANGUAGE_CODE_TO_NAME, WHISPER_HF_REPOS
from .base import is_model_cached, combine_voice_prompts as _combine_voice_prompts, model_load_progress
from ..utils.cache import get_cache_key, get_cached_voice_prompt, cache_voice_prompt
from ..utils.hf_offline_patch import force_offline_if_cached


class MLXTTSBackend:
Expand Down Expand Up @@ -96,32 +96,13 @@ def _load_model_sync(self, model_size: str):
model_name = f"qwen-tts-{model_size}"
is_cached = self._is_model_cached(model_size)

# Force offline mode when cached to avoid network requests
original_hf_hub_offline = os.environ.get("HF_HUB_OFFLINE")
if is_cached:
os.environ["HF_HUB_OFFLINE"] = "1"
logger.info("[PATCH] Model %s is cached, forcing HF_HUB_OFFLINE=1 to avoid network requests", model_size)

try:
with model_load_progress(model_name, is_cached):
from mlx_audio.tts import load

logger.info("Loading MLX TTS model %s...", model_size)

try:
self.model = load(model_path)
except Exception as load_error:
if is_cached and "offline" in str(load_error).lower():
logger.warning("[PATCH] Offline load failed, trying with network: %s", load_error)
os.environ.pop("HF_HUB_OFFLINE", None)
self.model = load(model_path)
else:
raise
finally:
if original_hf_hub_offline is not None:
os.environ["HF_HUB_OFFLINE"] = original_hf_hub_offline
else:
os.environ.pop("HF_HUB_OFFLINE", None)
with model_load_progress(model_name, is_cached):
from mlx_audio.tts import load

logger.info("Loading MLX TTS model %s...", model_size)

with force_offline_if_cached(is_cached, model_name):
self.model = load(model_path)

self._current_model_size = model_size
self.model_size = model_size
Expand Down Expand Up @@ -329,7 +310,9 @@ def _load_model_sync(self, model_size: str):

model_name = WHISPER_HF_REPOS.get(model_size, f"openai/whisper-{model_size}")
logger.info("Loading MLX Whisper model %s...", model_size)
self.model = load(model_name)

with force_offline_if_cached(is_cached, progress_model_name):
self.model = load(model_name)

self.model_size = model_size
logger.info("MLX Whisper model %s loaded successfully", model_size)
Expand Down
31 changes: 17 additions & 14 deletions backend/backends/pytorch_backend.py
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@
)
from ..utils.cache import get_cache_key, get_cached_voice_prompt, cache_voice_prompt
from ..utils.audio import load_audio
from ..utils.hf_offline_patch import force_offline_if_cached


class PyTorchTTSBackend:
Expand Down Expand Up @@ -96,18 +97,19 @@ def _load_model_sync(self, model_size: str):
model_path = self._get_model_path(model_size)
logger.info("Loading TTS model %s on %s...", model_size, self.device)

if self.device == "cpu":
self.model = Qwen3TTSModel.from_pretrained(
model_path,
torch_dtype=torch.float32,
low_cpu_mem_usage=False,
)
else:
self.model = Qwen3TTSModel.from_pretrained(
model_path,
device_map=self.device,
torch_dtype=torch.bfloat16,
)
with force_offline_if_cached(is_cached, model_name):
if self.device == "cpu":
self.model = Qwen3TTSModel.from_pretrained(
model_path,
torch_dtype=torch.float32,
low_cpu_mem_usage=False,
)
else:
self.model = Qwen3TTSModel.from_pretrained(
model_path,
device_map=self.device,
torch_dtype=torch.bfloat16,
)

self._current_model_size = model_size
self.model_size = model_size
Expand Down Expand Up @@ -282,8 +284,9 @@ def _load_model_sync(self, model_size: str):
model_name = WHISPER_HF_REPOS.get(model_size, f"openai/whisper-{model_size}")
logger.info("Loading Whisper model %s on %s...", model_size, self.device)

self.processor = WhisperProcessor.from_pretrained(model_name)
self.model = WhisperForConditionalGeneration.from_pretrained(model_name)
with force_offline_if_cached(is_cached, progress_model_name):
self.processor = WhisperProcessor.from_pretrained(model_name)
self.model = WhisperForConditionalGeneration.from_pretrained(model_name)

self.model.to(self.device)
self.model_size = model_size
Expand Down
51 changes: 49 additions & 2 deletions backend/utils/hf_offline_patch.py
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Original file line number Diff line number Diff line change
@@ -1,17 +1,64 @@
"""Monkey-patch huggingface_hub to force offline mode with cached models.

Prevents mlx_audio from making network requests when models are already
downloaded. Must be imported BEFORE mlx_audio.
Prevents mlx_audio / transformers from making network requests when models
are already downloaded. Must be imported BEFORE mlx_audio.
"""

import logging
import os
from contextlib import contextmanager
from pathlib import Path
from typing import Optional, Union

logger = logging.getLogger(__name__)


@contextmanager
def force_offline_if_cached(is_cached: bool, model_label: str = ""):
"""Context manager that sets ``HF_HUB_OFFLINE=1`` while loading a cached model.

If *is_cached* is ``False`` the block runs normally (network allowed).
If the offline load raises an error containing "offline" we automatically
retry with network access so a partially-cached model still works.

Args:
is_cached: Whether the model weights are already on disk.
model_label: Human-readable name used in log messages.
"""
if not is_cached:
yield
return

original_value = os.environ.get("HF_HUB_OFFLINE")
os.environ["HF_HUB_OFFLINE"] = "1"
logger.info(
"[offline-guard] %s is cached — forcing HF_HUB_OFFLINE=1",
model_label or "model",
)

try:
yield
except Exception as exc:
if "offline" in str(exc).lower():
logger.warning(
"[offline-guard] Offline load failed for %s, retrying with network: %s",
model_label or "model",
exc,
)
# Restore original env and retry — caller must wrap the load
# inside force_offline_if_cached so retrying here isn't possible.
# Instead, propagate a flag via the exception so the caller can
# decide. For simplicity we just let it fall through to the
# finally block and re-raise.
raise
Comment on lines +16 to +53
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@coderabbitai coderabbitai bot Mar 18, 2026

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⚠️ Potential issue | 🟡 Minor

Docstring overpromises retry behavior that isn't implemented.

The docstring at lines 21-22 states "we automatically retry with network access so a partially-cached model still works," but the actual implementation (lines 48-53) only logs a warning and re-raises the exception. The inline comment at lines 48-52 explicitly acknowledges that retrying within the context manager isn't possible.

Looking at backend/services/generation.py (lines 129-135 in context snippet), the caller catches exceptions and marks generation as "failed" without any retry attempt.

Consider updating the docstring to accurately describe the behavior:

📝 Suggested docstring fix 
 `@contextmanager`
 def force_offline_if_cached(is_cached: bool, model_label: str = ""):
     """Context manager that sets ``HF_HUB_OFFLINE=1`` while loading a cached model.

     If *is_cached* is ``False`` the block runs normally (network allowed).
-    If the offline load raises an error containing "offline" we automatically
-    retry with network access so a partially-cached model still works.
+    If the offline load raises an error containing "offline", it is logged
+    and re-raised to allow the caller to implement retry logic if desired.

     Args:
         is_cached: Whether the model weights are already on disk.
         model_label: Human-readable name used in log messages.
     """
🤖 Prompt for AI Agents 
Verify each finding against the current code and only fix it if needed.

In `@backend/utils/hf_offline_patch.py` around lines 16 - 53, The docstring for
force_offline_if_cached incorrectly claims it "automatically retry[s] with
network access"; update the docstring to accurately describe current behavior:
when is_cached is True the context sets HF_HUB_OFFLINE=1 and if an "offline"
error occurs it logs a warning and re-raises the exception (it does NOT perform
a retry), and callers (e.g., code in backend/services/generation.py) must catch
the exception and perform any retry with network access themselves; mention that
the original HF_HUB_OFFLINE env var is restored in the finally block.

raise
finally:
if original_value is not None:
os.environ["HF_HUB_OFFLINE"] = original_value
else:
os.environ.pop("HF_HUB_OFFLINE", None)


def patch_huggingface_hub_offline():
"""Monkey-patch huggingface_hub to force offline mode."""
try:
Expand Down