tower_http

Module limit

Source
Available on crate feature limit only.
Expand description

Middleware for limiting request bodies.

This layer will also intercept requests with a Content-Length header larger than the allowable limit and return an immediate error response before reading any of the body.

Note that payload length errors can be used by adversaries in an attempt to smuggle requests. When an incoming stream is dropped due to an over-sized payload, servers should close the connection or resynchronize by optimistically consuming some data in an attempt to reach the end of the current HTTP frame. If the incoming stream cannot be resynchronized, then the connection should be closed. If you’re using hyper this is automatically handled for you.

§Examples

§Limiting based on Content-Length

If a Content-Length header is present and indicates a payload that is larger than the acceptable limit, then the underlying service will not be called and a 413 Payload Too Large response will be generated.

use bytes::Bytes;
use std::convert::Infallible;
use http::{Request, Response, StatusCode, HeaderValue, header::CONTENT_LENGTH};
use http_body_util::{LengthLimitError};
use tower::{Service, ServiceExt, ServiceBuilder};
use tower_http::{body::Limited, limit::RequestBodyLimitLayer};
use http_body_util::Full;

async fn handle(req: Request<Limited<Full<Bytes>>>) -> Result<Response<Full<Bytes>>, Infallible> {
    panic!("This should not be hit")
}

let mut svc = ServiceBuilder::new()
    // Limit incoming requests to 4096 bytes.
    .layer(RequestBodyLimitLayer::new(4096))
    .service_fn(handle);

// Call the service with a header that indicates the body is too large.
let mut request = Request::builder()
    .header(CONTENT_LENGTH, HeaderValue::from_static("5000"))
    .body(Full::<Bytes>::default())
    .unwrap();

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

assert_eq!(response.status(), StatusCode::PAYLOAD_TOO_LARGE);

§Limiting without known Content-Length

If a Content-Length header is not present, then the body will be read until the configured limit has been reached. If the payload is larger than the limit, the http_body_util::Limited body will return an error. This error can be inspected to determine if it is a http_body_util::LengthLimitError and return an appropriate response in such case.

Note that no error will be generated if the body is never read. Similarly, if the body would be to large, but is never consumed beyond the length limit, then no error is generated, and handling of the remaining incoming data stream is left to the server implementation as described above.

async fn handle(req: Request<Limited<Full<Bytes>>>) -> Result<Response<Full<Bytes>>, BoxError> {
    let data = match req.into_body().collect().await {
        Ok(collected) => collected.to_bytes(),
        Err(err) => {
            if let Some(_) = err.downcast_ref::<LengthLimitError>() {
                let mut resp = Response::new(Full::default());
                *resp.status_mut() = StatusCode::PAYLOAD_TOO_LARGE;
                return Ok(resp);
            } else {
                return Err(err);
            }
        }
    };

    Ok(Response::new(Full::default()))
}

let mut svc = ServiceBuilder::new()
    // Limit incoming requests to 4096 bytes.
    .layer(RequestBodyLimitLayer::new(4096))
    .service_fn(handle);

// Call the service.
let request = Request::new(Full::<Bytes>::default());

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

assert_eq!(response.status(), StatusCode::OK);

// Call the service with a body that is too large.
let request = Request::new(Full::<Bytes>::from(Bytes::from(vec![0u8; 4097])));

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

assert_eq!(response.status(), StatusCode::PAYLOAD_TOO_LARGE);

§Limiting without Content-Length

If enforcement of body size limits is desired without preemptively handling requests with a Content-Length header indicating an over-sized request, consider using MapRequestBody to wrap the request body with http_body_util::Limited and checking for http_body_util::LengthLimitError like in the previous example.

Structs§