Recover from aborted or failed model downloads (#358)

Author: GregoryComer

download.py

@@ -4,6 +4,7 @@
 # This source code is licensed under the license found in the
 # LICENSE file in the root directory of this source tree.
 import os
+import shutil
 import urllib.request
 from pathlib import Path
 from typing import Optional, Sequence
@@ -19,26 +20,22 @@
 
 
 def _download_hf_snapshot(
-    model_config: ModelConfig, models_dir: Path, hf_token: Optional[str]
+    model_config: ModelConfig, artifact_dir: Path, hf_token: Optional[str]
 ):
-    model_dir = models_dir / model_config.name
-    os.makedirs(model_dir, exist_ok=True)
-
     from huggingface_hub import snapshot_download
 
     # Download and store the HF model artifacts.
     print(f"Downloading {model_config.name} from HuggingFace...")
     try:
         snapshot_download(
             model_config.distribution_path,
-            local_dir=model_dir,
+            local_dir=artifact_dir,
             local_dir_use_symlinks=False,
             token=hf_token,
             ignore_patterns="*safetensors*",
         )
     except HTTPError as e:
         if e.response.status_code == 401:
-            os.rmdir(model_dir)
             raise RuntimeError(
                 "Access denied. Run huggingface-cli login to authenticate."
             )
@@ -48,20 +45,16 @@ def _download_hf_snapshot(
 
     # Convert the model to the torchchat format.
     print(f"Converting {model_config.name} to torchchat format...")
-    convert_hf_checkpoint(model_dir=model_dir, model_name=model_config.name, remove_bin_files=True)
+    convert_hf_checkpoint(model_dir=artifact_dir, model_name=model_config.name, remove_bin_files=True)
 
 
 def _download_direct(
     model_config: ModelConfig,
-    urls: Sequence[str],
-    models_dir: Path,
+    artifact_dir: Path,
 ):
-    model_dir = models_dir / model_config.name
-    os.makedirs(model_dir, exist_ok=True)
-
-    for url in urls:
+    for url in model_config.distribution_path:
         filename = url.split("/")[-1]
-        local_path = model_dir / filename
+        local_path = artifact_dir / filename
         print(f"Downloading {url}...")
         urllib.request.urlretrieve(url, str(local_path.absolute()))
 
@@ -70,18 +63,38 @@ def download_and_convert(
     model: str, models_dir: Path, hf_token: Optional[str] = None
 ) -> None:
     model_config = resolve_model_config(model)
+    model_dir = models_dir / model_config.name
 
-    if (
-        model_config.distribution_channel
-        == ModelDistributionChannel.HuggingFaceSnapshot
-    ):
-        _download_hf_snapshot(model_config, models_dir, hf_token)
-    elif model_config.distribution_channel == ModelDistributionChannel.DirectDownload:
-        _download_direct(model_config, model_config.distribution_path, models_dir)
-    else:
-        raise RuntimeError(
-            f"Unknown distribution channel {model_config.distribution_channel}."
-        )
+    # Download into a temporary directory. We'll move to the final location once
+    # the download and conversion is complete. This allows recovery in the event
+    # that the download or conversion fails unexpectedly.
+    temp_dir = models_dir / "downloads" / model_config.name
+    if os.path.isdir(temp_dir):
+        shutil.rmtree(temp_dir)
+    os.makedirs(temp_dir, exist_ok=True)
+
+    try:
+        if (
+            model_config.distribution_channel
+            == ModelDistributionChannel.HuggingFaceSnapshot
+        ):
+            _download_hf_snapshot(model_config, temp_dir, hf_token)
+        elif model_config.distribution_channel == ModelDistributionChannel.DirectDownload:
+            _download_direct(model_config, temp_dir)
+        else:
+            raise RuntimeError(
+                f"Unknown distribution channel {model_config.distribution_channel}."
+            )
+        
+        # Move from the temporary directory to the intended location,
+        # overwriting if necessary.
+        if os.path.isdir(model_dir):
+            shutil.rmtree(model_dir)
+        os.rename(temp_dir, model_dir)
+
+    finally:
+        if os.path.isdir(temp_dir):
+            shutil.rmtree(temp_dir)
 
 
 def is_model_downloaded(model: str, models_dir: Path) -> bool: