# actix_web::http::header::VARY - Rust
API documentation for the Rust `VARY` constant in crate `actix_web`.
Keywords: rust, rustlang, rust-lang, VARY

# Constant actix_web::http::header::VARY [−] [src]

    pub const VARY: HeaderName = HeaderName{inner: Repr::Standard(StandardHeader::Vary),}

Determines how to match future requests with cached responses.

The `vary` HTTP response header determines how to match future request headers to decide whether a cached response can be used rather than requesting a fresh one from the origin server. It is used by the server to indicate which headers it used when selecting a representation of a resource in a content negotiation algorithm.

The `vary` header should be set on a 304 Not Modified response exactly like it would have been set on an equivalent 200 OK response.

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