aio-libs/aiohttp · warning · LookupError

Proxying is disallowed for `{url.host!r}`

Error message

Proxying is disallowed for `{url.host!r}`

What it means

Raised by get_env_proxy_for_url when urllib.request.proxy_bypass(url.host) returns True, i.e. the host is on the no-proxy list (NO_PROXY env var or system bypass rules). LookupError signals that although env proxies exist, this destination must not be proxied.

Source

Thrown at aiohttp/helpers.py:293

        if proxy.scheme in ("https", "wss"):
            client_logger.warning(
                "%s proxies %s are not supported, ignoring", proxy.scheme.upper(), proxy
            )
            continue
        if netrc_obj and auth is None:
            if proxy.host is not None:
                try:
                    auth = _auth_header_from_netrc(netrc_obj, proxy.host)
                except LookupError:
                    auth = None
        ret[proto] = ProxyInfo(proxy, auth)
    return ret


def get_env_proxy_for_url(url: URL) -> tuple[URL, str | None]:
    """Get a permitted proxy for the given URL from the env."""
    if url.host is not None and proxy_bypass(url.host):
        raise LookupError(f"Proxying is disallowed for `{url.host!r}`")

    proxies_in_env = proxies_from_env()
    try:
        proxy_info = proxies_in_env[url.scheme]
    except KeyError:
        raise LookupError(f"No proxies found for `{url!s}` in the env")
    else:
        return proxy_info.proxy, proxy_info.proxy_auth


@frozen_dataclass_decorator
class MimeType:
    type: str
    subtype: str
    suffix: str
    parameters: "MultiDictProxy[str]"

View on GitHub (pinned to c0ef574e29)

Solutions

1. Respect the bypass: do not call get_env_proxy_for_url for hosts in NO_PROXY.
2. Check proxy_bypass(host) yourself before requesting a proxy.
3. Adjust NO_PROXY env if the host genuinely should be proxied.

Example fix

// before
proxy, auth = get_env_proxy_for_url(url)  # raises for internal hosts
// after
from urllib.request import proxy_bypass
if not proxy_bypass(url.host):
    proxy, auth = get_env_proxy_for_url(url)
else:
    proxy, auth = None, None

from urllib.request import proxy_bypass
def maybe_proxy(url):
    if url.host and proxy_bypass(url.host):
        return None, None
    return get_env_proxy_for_url(url)

try:
    proxy, auth = get_env_proxy_for_url(url)
except LookupError:
    proxy, auth = None, None

When it happens

Trigger: Calling get_env_proxy_for_url(url) for a host listed in NO_PROXY='localhost,127.0.0.1,.internal'. Common when an app tries to forcibly route a localhost/internal request through an env-configured proxy.

Common situations: Corporate NO_PROXY includes the target domain; localhost/loopback explicitly bypassed; '*.corp' internal domains bypassed but code still requests a proxy.

Related errors

• No .netrc file found
• No proxies found for `{url!s}` in the env
• No entry for {host!s} found in the `.netrc` file.
• Invalid upgrade header
• Invalid connection header

AI-assisted analysis of aio-libs/aiohttp@c0ef574e29 (2026-08-04). Data as JSON: /data/errors/9fe2ff57d14a7b84.json. Report an issue: GitHub.