seanmonstar/warp · error

missing scheme

Error message

missing scheme

What it means

IntoOrigin for &str splits the input on '://' and expects both a scheme and a remainder, panicking with 'missing scheme' otherwise. So cors().allow_origins(&["example.com"]) (no scheme) panics during filter construction.

Solutions

1. Always include the scheme: "https://example.com" instead of "example.com"
2. Preprocess config origins to prepend "https://" when the scheme is absent (if that matches intent)
3. Validate origins at config load time and fail fast with a clear message

Example fix

// before
warp::cors().allow_origin("example.com")
// after
warp::cors().allow_origin("https://example.com")

fn has_scheme(origin: &str) -> bool { origin.contains("://") }
for o in origins { assert!(has_scheme(o), "origin '{}' missing scheme", o); }

fn as_origin(s: &str) -> Option<String> { s.contains("://").then(|| s.to_string()) }

When it happens

Trigger: Calling allow_origins/allow_origin with an origin string lacking '://', e.g. "example.com", "localhost:8080" — splitn yields only one part and the second expect fires.

Common situations: Writing hosts from config without the https:// prefix; assuming bare hostnames are acceptable origins; migrating configs from other CORS libraries that accept bare hosts.

Understand the failure class

Background: "Invalid URL" errors: why new URL(), URI.parse, and reqwest::Url reject your string — missing scheme, whitespace, and bad path format — this error's family across 39 libraries.

Related errors

• Origin is always a valid HeaderValue
• illegal Method
• illegal Header
• invalid Origin
• polled after complete

AI-assisted analysis of seanmonstar/warp@ff34d7213e (2026-09-09). Data as JSON: /api/errors/6c97ee684af45145. Report an issue: GitHub.

Appendix: source

Thrown at src/filters/cors.rs:617

        fn seconds(self) -> u64 {
            self.into()
        }
    }

    impl Seconds for ::std::time::Duration {
        fn seconds(self) -> u64 {
            self.as_secs()
        }
    }

    pub trait IntoOrigin {
        fn into_origin(self) -> Origin;
    }

    impl<'a> IntoOrigin for &'a str {
        fn into_origin(self) -> Origin {
            let mut parts = self.splitn(2, "://");
            let scheme = parts.next().expect("missing scheme");
            let rest = parts.next().expect("missing scheme");

            Origin::try_from_parts(scheme, rest, None).expect("invalid Origin")
        }
    }
}

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