Fix validation to detect missing model files before loading

python/sglang/srt/model_loader/weight_validation.py

@@ -1,3 +1,4 @@
+import json
 import logging
 import os
 import re
@@ -36,6 +37,61 @@ def _validate_safetensors_file(file_path: str) -> bool:
         return False
 
 
+def _check_index_files_exist(snapshot_dir: str) -> Tuple[bool, Optional[str]]:
+    """
+    Check if all files listed in safetensors index files actually exist on disk.
+
+    This catches cases where the snapshot directory exists but files are missing
+    (e.g., due to incomplete downloads or corrupted cache).
+
+    Args:
+        snapshot_dir: Path to the model snapshot directory
+
+    Returns:
+        Tuple of (all_exist, error_message)
+    """
+    # Find all safetensors index files
+    index_files = [
+        f for f in os.listdir(snapshot_dir) if f.endswith(".safetensors.index.json")
+    ]
+
+    if not index_files:
+        # No index files means it's not a sharded model, skip this check
+        return True, None
+
+    for index_file in index_files:
+        index_path = os.path.join(snapshot_dir, index_file)
+        try:
+            with open(index_path) as f:
+                index_data = json.load(f)
+
+            weight_map = index_data.get("weight_map", {})
+            if not weight_map:
+                continue
+
+            # Check that all files in weight_map exist
+            required_files = set(weight_map.values())
+            missing_files = []
+
+            for file_name in required_files:
+                file_path = os.path.join(snapshot_dir, file_name)
+                # Check both existence and that it's not a broken symlink
+                if not os.path.exists(file_path):
+                    missing_files.append(file_name)
+
+            if missing_files:
+                return (
+                    False,
+                    f"Missing {len(missing_files)} file(s) from index {index_file}: {missing_files[:3]}{'...' if len(missing_files) > 3 else ''}",
+                )
+
+        except Exception as e:
+            logger.warning("Failed to read index file %s: %s", index_file, e)
+            continue
+
+    return True, None
+
+
 def _validate_sharded_model(
     snapshot_dir: str, weight_files: List[str]
 ) -> Tuple[bool, Optional[str], List[str]]:
@@ -50,6 +106,12 @@ def _validate_sharded_model(
         Tuple of (is_valid, error_message, corrupted_files)
         - corrupted_files: List of file paths that are corrupted (for selective cleanup)
     """
+    # First, check if all files from the index actually exist
+    # This catches missing files that wouldn't be found by glob
+    index_check_valid, index_error = _check_index_files_exist(snapshot_dir)
+    if not index_check_valid:
+        return False, index_error, []
+
     # Pattern for sharded files: model-00001-of-00009.safetensors
     shard_pattern = re.compile(r"(.*?)-(\d+)-of-(\d+)\.(safetensors|bin)")