can1357/oh-my-pi · error · ValueError

scheme must be a non-empty string

Error message

scheme must be a non-empty string

What it means

host_uri() registers a custom URI scheme (e.g. 'omp://...') with the host, and it refuses to register a scheme that is empty or whitespace-only. The scheme is cleaned via `(scheme or '').strip().lower()` before validation, so None, empty strings, and strings of only spaces all fail. This is an upfront programmer-error guard so registrations with typos or unpopulated variables fail loudly instead of producing unusable URIs.

Source

Thrown at python/omp-rpc/src/omp_rpc/host_uris.py:85

    description: str | None = None
    immutable: bool = False

    @property
    def writable(self) -> bool:
        return self.write is not None


def host_uri(
    *,
    scheme: str,
    read: HostUriReadHandler,
    write: HostUriWriteHandler | None = None,
    description: str | None = None,
    immutable: bool = False,
) -> HostUri[None]:
    cleaned = (scheme or "").strip().lower()
    if not cleaned:
        raise ValueError("scheme must be a non-empty string")
    return HostUri(
        scheme=cleaned,
        read=read,
        write=write,
        description=description,
        immutable=immutable,
    )


def normalize_read_result(value: HostUriReadValue) -> JsonObject:
    """Convert a handler's `read` return into the wire-frame fields.

    Returns a dict suitable for spreading into a `host_uri_result` payload.
    """

    if isinstance(value, str):
        return {"content": value}
    if not isinstance(value, dict):

View on GitHub (pinned to 9690622007)

Solutions

1. Pass a non-empty literal scheme string, e.g. host_uri('mydata') (no '://' suffix; the function lowercases and strips it for you)
2. Check the config/env source that supplied the scheme and give it a real value or a non-empty default
3. Add a caller-side check: if not scheme or not scheme.strip(): raise/skip the registration

Example fix

// before
scheme = os.environ.get('OMP_SCHEME', '')
h = host_uri(scheme, read=read_handler)
// after
scheme = os.environ.get('OMP_SCHEME') or 'mydata'
h = host_uri(scheme, read=read_handler)

def validate_scheme(scheme):
    if not isinstance(scheme, str) or not scheme.strip():
        raise ValueError(f"scheme must be a non-empty string, got {scheme!r}")
    return scheme

def is_valid_scheme(scheme) -> bool:
    return isinstance(scheme, str) and bool(scheme.strip())

try:
    h = host_uri(scheme, read=read_handler)
except ValueError as e:
    logger.error('host_uri registration failed: %s (scheme=%r)', e, scheme)
    raise

When it happens

Trigger: Calling host_uri('') or host_uri(None), passing a scheme read from an unset config/env variable that resolves to an empty string, or a scheme variable populated via a lookup that returned '' (e.g. dict.get('scheme') missing). Note whitespace-only strings like ' ' also trigger it after stripping.

Common situations: Config files with `scheme:` left blank, env vars like OMP_URI_SCHEME unset and defaulted to '', f-string/format placeholders that stayed empty, or a refactoring that split the scheme out of a full URI string but produced an empty prefix.

Related errors

• Unsupported content_type: {content_type!r}
• Failed to load tree-sitter language: {err}
• Host URI scheme must be a non-empty string
• Host URI scheme contains invalid characters: ${raw.scheme}
• Host URI scheme is reserved by OMP: ${scheme}://

AI-assisted analysis of can1357/oh-my-pi@9690622007 (2026-08-31). Data as JSON: /api/errors/95ffb49d99f026a8. Report an issue: GitHub.