sgl-project/sglang · error · ValueError

Unsupported config file {path} (config format: {ext})

Error message

Unsupported config file {path} (config format: {ext})

What it means

_parse_storage_backend_extra_config accepts a storage backend extra config either as a JSON string or as a path to a file. When it looks like a path, it dispatches on the file extension: .toml via tomllib, .yaml/.yml via yaml.safe_load; any other extension (or no recognized extension) raises this ValueError listing the offending path and extension.

Source

Thrown at python/sglang/srt/mem_cache/hiradix_cache.py:739

        if storage_backend_extra_config:
            try:
                if storage_backend_extra_config.startswith("@"):
                    # Read config from a json/toml/yaml file
                    path = storage_backend_extra_config[1:]
                    ext = os.path.splitext(path)[1].lower()
                    with open(path, "rb" if ext == ".toml" else "r") as f:
                        if ext == ".json":
                            extra_config = json.load(f)
                        elif ext == ".toml":
                            import tomllib

                            extra_config = tomllib.load(f)
                        elif ext in (".yaml", ".yml"):
                            import yaml

                            extra_config = yaml.safe_load(f)
                        else:
                            raise ValueError(
                                f"Unsupported config file {path} (config format: {ext})"
                            )
                else:
                    # read config from JSON string
                    extra_config = json.loads(storage_backend_extra_config)
            except Exception as e:
                logger.error(f"Invalid backend extra config JSON: {e}")
                raise e

        defaults = PrefetchTimeoutConfig()
        prefetch_threshold = extra_config.pop("prefetch_threshold", 256)  # tokens
        prefetch_timeout_base = extra_config.pop(
            "prefetch_timeout_base", defaults.base
        )  # seconds
        prefetch_timeout_per_ki_token = extra_config.pop(
            "prefetch_timeout_per_ki_token", defaults.per_ki_token
        )  # seconds per 1024 tokens
        prefetch_timeout_max = extra_config.pop(

View on GitHub (pinned to 0132848349)

Solutions

1. Rename the config file to .yaml, .yml, or .toml (convert JSON contents to one of those formats if needed)
2. Or inline the config as a JSON string instead of a file path: pass the JSON text directly to storage_backend_extra_config
3. Verify the path string doesn't have stray suffixes (.bak, ~, .tmp) that change the detected extension

Example fix

# before: JSON file path is rejected
--storage-backend-extra-config /etc/hicache/config.json

# after: either rename to YAML
--storage-backend-extra-config /etc/hicache/config.yaml
# or pass JSON inline
--storage-backend-extra-config '{"prefetch_threshold": 2}'

import os
ext = os.path.splitext(extra_config_path)[1].lower()
assert ext in (".toml", ".yaml", ".yml") or not os.path.exists(extra_config_path), (
    f"config file must be .toml/.yaml/.yml or an inline JSON string, got {ext}")

def is_supported_config_arg(s: str) -> bool:
    if os.path.exists(s):
        return os.path.splitext(s)[1].lower() in (".toml", ".yaml", ".yml")
    try:
        json.loads(s); return True
    except Exception:
        return False

When it happens

Trigger: Passing --storage-backend-extra-config / hi-cache storage_backend_extra_config as a path to a file whose suffix is not .toml/.yaml/.yml (e.g. .json, .conf, .ini, .txt, or a missing extension).

Common situations: Users naturally try to point at a .json config file (only JSON strings are supported inline, not JSON files); typos in the filename; a config file with a double extension like config.yaml.bak; new users assuming any config format works.

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AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/7817450e537b75e7. Report an issue: GitHub.