aio-libs/aiohttp · error · ValueError

Scheme not supported

Error message

Scheme not supported

What it means

Raised as ValueError by Domain.validation when the domain string contains '://' — indicating a scheme (e.g. 'https://example.com') was passed where only a bare host is expected. Domain matches on the Host header, which never includes a scheme, so a schemed input is rejected.

Source

Thrown at aiohttp/web_urldispatcher.py:786

class Domain(AbstractRuleMatching):
    re_part = re.compile(r"(?!-)[a-z\d-]{1,63}(?<!-)")

    def __init__(self, domain: str) -> None:
        super().__init__()
        self._domain = self.validation(domain)

    @property
    def canonical(self) -> str:
        return self._domain

    def validation(self, domain: str) -> str:
        if not isinstance(domain, str):
            raise TypeError("Domain must be str")
        domain = domain.rstrip(".").lower()
        if not domain:
            raise ValueError("Domain cannot be empty")
        elif "://" in domain:
            raise ValueError("Scheme not supported")
        url = URL("http://" + domain)
        assert url.raw_host is not None
        if not all(self.re_part.fullmatch(x) for x in url.raw_host.split(".")):
            raise ValueError("Domain not valid")
        if url.port == 80:
            return url.raw_host
        return f"{url.raw_host}:{url.port}"

    async def match(self, request: Request) -> bool:
        host = request.headers.get(hdrs.HOST)
        if not host:
            return False
        return self.match_domain(host)

    def match_domain(self, host: str) -> bool:
        return host.lower() == self._domain

    def get_info(self) -> _InfoDict:

View on GitHub (pinned to c0ef574e29)

Solutions

1. Pass only the host (optionally with port): Domain('example.com') or Domain('example.com:8080').
2. Strip the scheme before constructing: extract host via yarl: URL(url).raw_host.
3. If you meant path-based mounting, use app.add_sub_app(prefix, sub_app) instead of add_domain.

Example fix

# before
app.add_domain('https://api.example.com', sub_app)

# after
from yarl import URL
host = URL('https://api.example.com').raw_host
app.add_domain(host, sub_app)

from yarl import URL

def host_from_url(value: str) -> str:
    if '://' in value:
        u = URL(value)
        host = u.raw_host
        if u.port and u.port != 80:
            host = f'{host}:{u.port}'
        return host
    return value

def is_bare_host(domain) -> bool:
    return isinstance(domain, str) and '://' not in domain and bool(domain.strip())

try:
    app.add_domain(host, sub_app)
except ValueError as e:
    if 'Scheme not supported' in str(e):
        from yarl import URL
        app.add_domain(URL(host).raw_host, sub_app)
    else:
        raise

When it happens

Trigger: Constructing aiohttp.web.Domain('https://example.com'), Domain('http://api.example.com:8080'), or app.add_domain('https://example.com', sub_app). Passing a full URL instead of just the host.

Common situations: Copy-pasting a full URL from a browser/address bar into domain config; reading base URLs from config and passing them whole; confusing add_domain (host-based) with prefix-based sub-app mounting.

Related errors

• Domain cannot be empty
• '{directory}' is not a directory
• Domain must be str
• base_url must have a trailing '/'
• {url}

AI-assisted analysis of aio-libs/aiohttp@c0ef574e29 (2026-08-04). Data as JSON: /data/errors/f21cd9bf2b1f56c0.json. Report an issue: GitHub.