DioxusLabs/dioxus · error

SetHeader must have data to set

Error message

SetHeader must have data to set

What it means

Internal invariant: SetHeader was used as a response part but its data field was None. The type was constructed through a path that skipped new(), which always sets data; firing indicates an externally constructed invalid value.

Source

Thrown at packages/fullstack/src/payloads/header.rs:27

}

impl<T: Header> SetHeader<T> {
    pub fn new(
        value: impl TryInto<HeaderValue, Error = InvalidHeaderValue>,
    ) -> Result<Self, headers::Error> {
        let values = value.try_into().map_err(|_| headers::Error::invalid())?;

        let res = T::decode(&mut std::iter::once(&values))?;

        Ok(Self { data: Some(res) })
    }
}

impl<T: Header> IntoResponseParts for SetHeader<T> {
    type Error = ();

    fn into_response_parts(self, res: ResponseParts) -> Result<ResponseParts, Self::Error> {
        let data = self.data.expect("SetHeader must have data to set");

        let mut headers = vec![];
        data.encode(&mut headers);

        Ok(axum::response::AppendHeaders(
            headers.into_iter().map(|value| (T::name().clone(), value)),
        )
        .into_response_parts(res)
        .unwrap())
    }
}

impl<T: Header> FromResponseParts for SetHeader<T> {
    fn from_response_parts(parts: &mut axum::http::response::Parts) -> Result<Self, ServerFnError> {
        let Some(header) = parts.headers.remove(T::name()) else {
            return Ok(SetHeader { data: None });
        };

View on GitHub (pinned to 24f6a829df)

Solutions

1. Provide header data when constructing the SetHeader payload; an empty SetHeader cannot be applied.

When it happens

Trigger: Thrown at packages/fullstack/src/payloads/header.rs:27 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of DioxusLabs/dioxus@24f6a829df (2026-08-23). Data as JSON: /api/errors/9e210f5575bb2b34. Report an issue: GitHub.