Module request 

Available on crate feature set-header only.

Middleware for setting headers on HTTP requests.

This module provides middleware for setting one or more headers on HTTP requests, either with fixed values or values determined dynamically from the request.

Single Header

Use SetRequestHeaderLayer and SetRequestHeader to set a single header. The header value can be a fixed value or computed dynamically using a closure. See crate::set_header::MakeHeaderValue for details.

Example: Fixed Value

use http::{Request, Response, header::{self, HeaderValue}};
use tower::{Service, ServiceExt, ServiceBuilder};
use tower_http::set_header::SetRequestHeaderLayer;
use http_body_util::Full;
use bytes::Bytes;

let mut svc = ServiceBuilder::new()
    .layer(
        // Layer that sets `User-Agent: my very cool app` on requests.
        //
        // `if_not_present` will only insert the header if it does not already
        // have a value.
        SetRequestHeaderLayer::if_not_present(
            header::USER_AGENT,
            HeaderValue::from_static("my very cool app"),
        )
    )
    .service(http_client);

let request = Request::new(Full::default());

let response = svc.ready().await?.call(request).await?;

Setting a header based on a value determined dynamically from the request:

use http::{Request, Response, header::{self, HeaderValue}};
use tower::{Service, ServiceExt, ServiceBuilder};
use tower_http::set_header::SetRequestHeaderLayer;
use bytes::Bytes;
use http_body_util::Full;

fn date_header_value() -> HeaderValue {
    // ...
}

let mut svc = ServiceBuilder::new()
    .layer(
        // Layer that sets `Date` to the current date and time.
        //
        // `overriding` will insert the header and override any previous values it
        // may have.
        SetRequestHeaderLayer::overriding(
            header::DATE,
            |request: &Request<Full<Bytes>>| {
                Some(date_header_value())
            }
        )
    )
    .service(http_client);

let request = Request::new(Full::default());

let response = svc.ready().await?.call(request).await?;

Multiple Headers

Use SetMultipleRequestHeadersLayer and SetMultipleRequestHeader to set multiple headers at once. Each header can have a fixed value or be computed dynamically.

Note: this layer uses boxing (allocation + dynamic dispatch) to support mixed producer types in a single vec. Stacking multiple SetRequestHeaderLayer instances avoids this at the cost of a more complex composed service type.

Example: Multiple Dynamic Values

use http::{Request, Response, header::{self, HeaderValue}};
use tower::{Service, ServiceExt, ServiceBuilder};
use tower_http::set_header::{HeaderMetadata, request::{SetMultipleRequestHeadersLayer}};
use bytes::Bytes;
use http_body_util::Full;


let mut svc = ServiceBuilder::new()
    .layer(
        SetMultipleRequestHeadersLayer::overriding(vec![
            (header::DATE, |_: &Request<Full<Bytes>>| {
                Some(HeaderValue::from_static("now"))
            }).into(),
        ])
    )
    .service(tower::service_fn(|req: Request<Full<Bytes>>| async move {
        assert_eq!(req.headers()["date"], "now");
        Ok::<_, std::convert::Infallible>(Response::new(Full::<Bytes>::default()))
    }));

let request = Request::new(Full::default());

let _response = svc.ready().await?.call(request).await?;

Modes

• overriding: If a previous value exists for the same header, it is removed and replaced with the new value.
• appending: The new header is always added, preserving any existing values. If previous values exist, the header will have multiple values.
• if_not_present: If a previous value exists for the header, the new value is not inserted.

See SetRequestHeaderLayer, SetRequestHeader, SetMultipleRequestHeadersLayer, and SetMultipleRequestHeader for more details.

Structs

SetMultipleRequestHeader

Middleware that sets multiple headers on the request.

SetMultipleRequestHeadersLayer

Layer that applies SetMultipleRequestHeader which adds multiple request headers.

SetRequestHeader

Middleware that sets a header on the request.

SetRequestHeaderLayer

Layer that applies SetRequestHeader which adds a request header.