seanmonstar/warp · error

invalid header name

Error message

invalid header name

What it means

Thrown inside warp::test::request().header(key, value) when the key string cannot be parsed as a valid HTTP HeaderName (e.g. contains characters outside the legal token set or is empty). The TryFrom<HeaderName> conversion fails and the code .expect("invalid header name") panics, aborting the test process rather than returning a Result.

Solutions

1. Use a valid HTTP header name: lowercase token characters only (letters, digits, and !#$%&'*+-.^_`|~), non-empty
2. Use constants from the http crate such as http::header::ACCEPT instead of hand-written strings
3. Pre-validate the header name with HeaderName::try_from(key) and handle the Err before calling .header()
4. Fix typos in header names, e.g. "Accept" is valid but names with spaces or invalid symbols are not

When it happens

Trigger: Thrown at src/test.rs:231 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of seanmonstar/warp@ff34d7213e (2026-09-09). Data as JSON: /api/errors/8a3daaa1aa35c2b4. Report an issue: GitHub.

Appendix: source

Thrown at src/test.rs:231

    /// # Example
    ///
    /// ```
    /// let req = warp::test::request()
    ///     .header("accept", "application/json");
    /// ```
    ///
    /// # Panic
    ///
    /// This panics if the passed strings are not able to be parsed as a valid
    /// `HeaderName` and `HeaderValue`.
    pub fn header<K, V>(mut self, key: K, value: V) -> Self
    where
        HeaderName: TryFrom<K>,
        HeaderValue: TryFrom<V>,
    {
        let name: HeaderName = TryFrom::try_from(key)
            .map_err(|_| ())
            .expect("invalid header name");
        let value = TryFrom::try_from(value)
            .map_err(|_| ())
            .expect("invalid header value");
        self.req.headers_mut().insert(name, value);
        self
    }

    /// Set the remote address of this request
    ///
    /// Default is no remote address.
    ///
    /// # Example
    /// ```
    /// use std::net::{IpAddr, Ipv4Addr, SocketAddr};
    ///
    /// let req = warp::test::request()
    ///     .remote_addr(SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8080));
    /// ```

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