Rust actix-web middleware modifying request data

Question

Is there a recommended way of modifying the request received on actix-web.

Is there an example on how to modify I am looking for way to add data to the request object and have it available for processing by downstream middlewares and handlers.

The Middleware documentation at "https://actix.rs/docs/middleware/" says the following "Actix-web’s middleware system allows us to add additional behavior to request/response processing. Middleware can hook into an incoming request process, enabling us to modify requests as well as halt request processing to return a response early."

The page doesn't have an example on how to modify the Request.

Let take the code below (obtained from "https://actix.rs/docs/middleware/"), what would be the code to somehow add data to the request?

use std::pin::Pin;
use std::task::{Context, Poll};

use actix_service::{Service, Transform};
use actix_web::{dev::ServiceRequest, dev::ServiceResponse, Error};
use futures::future::{ok, Ready};
use futures::Future;

// There are two steps in middleware processing.
// 1. Middleware initialization, middleware factory gets called with
//    next service in chain as parameter.
// 2. Middleware's call method gets called with normal request.
pub struct SayHi;

// Middleware factory is `Transform` trait from actix-service crate
// `S` - type of the next service
// `B` - type of response's body
impl<S, B> Transform<S> for SayHi
where
    S: Service<Request = ServiceRequest, Response = ServiceResponse<B>, Error = Error>,
    S::Future: 'static,
    B: 'static,
{
    type Request = ServiceRequest;
    type Response = ServiceResponse<B>;
    type Error = Error;
    type InitError = ();
    type Transform = SayHiMiddleware<S>;
    type Future = Ready<Result<Self::Transform, Self::InitError>>;

    fn new_transform(&self, service: S) -> Self::Future {
        ok(SayHiMiddleware { service })
    }
}

pub struct SayHiMiddleware<S> {
    service: S,
}

impl<S, B> Service for SayHiMiddleware<S>
where
    S: Service<Request = ServiceRequest, Response = ServiceResponse<B>, Error = Error>,
    S::Future: 'static,
    B: 'static,
{
    type Request = ServiceRequest;
    type Response = ServiceResponse<B>;
    type Error = Error;
    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>>>>;

    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        self.service.poll_ready(cx)
    }

    fn call(&mut self, req: ServiceRequest) -> Self::Future {
        println!("Hi from start. You requested: {}", req.path());

        let fut = self.service.call(req);

        Box::pin(async move {
            let res = fut.await?;

            println!("Hi from response");
            Ok(res)
        })
    }
}

Answer 1

I was just looking at how to do this as well, disappointing that they talk about it in their docs but do not show any examples.

I found that you can either edit the headers or extensions as follows, I'm not sure how to edit it otherwise.

Headers

• Grab the headers from the Service request, let headers = req.headers_mut()
• Take the HeaderMap and you can from there either insert, remove, clear, etc
• Insert example: headers.insert(HeaderName::from_lowercase(b"content-length").unwrap(), HeaderValue::from_static("hello"));

Extensions

• Get the extensions for the request let extensions = req.extensions_mut()
• Add to the extension extensions.insert("foo".to_string());
• One liner: req.extensions_mut().insert("foo".to_string());
• Get that extension later: req.extensions().get::<String>()

Answer 2

It's certainly possible to modify a request and the associated response from middleware. Here is a brief example(this works with Actix v4):

use x_contrib::{actix_http, actix_web, body, futures, log, HttpMessage, HttpResponseBuilder};
use std::cell::RefCell;

use log::Level;
use std::pin::Pin;

use actix_web::dev::{Service, ServiceRequest, ServiceResponse, Transform};
use actix_web::Error;
use futures::future::{ok, Ready};
use futures::task::{Context, Poll};
use std::future::Future;
use std::rc::Rc;
use std::str;

use crate::middleware::utility::{ApiMiddlewareUtility, MiddlewareUtility};
use crate::request;
use x_common::prelude::*;
use x_common::settings;
use x_contrib::actix_http::h1::Payload;
use x_contrib::body::{EitherBody, MessageBody};
use x_contrib::futures::future::err;
use x_contrib::futures::StreamExt;
use x_contrib::web::{Buf, BytesMut};

pub struct LogEvents;

impl<S: 'static, B> Transform<S, ServiceRequest> for LogEvents
where
    S: Service<ServiceRequest, Response = ServiceResponse<B>, Error = Error>,
    S::Future: 'static,
    B: MessageBody + 'static,
{
    type Response = ServiceResponse<EitherBody<B>>;
    type Error = Error;
    type Transform = LogEventsMiddleware<S>;
    type InitError = ();
    type Future = Ready<Result<Self::Transform, Self::InitError>>;

    fn new_transform(&self, service: S) -> Self::Future {
        ok(LogEventsMiddleware {
            service: Rc::new(RefCell::new(service)),
        })
    }
}

pub struct LogEventsMiddleware<S> {
    service: Rc<RefCell<S>>,
}

impl<S: 'static, B> Service<ServiceRequest> for LogEventsMiddleware<S>
where
    S: Service<ServiceRequest, Response = ServiceResponse<B>, Error = Error>,
    S::Future: 'static,
    B: MessageBody + 'static,
{
    type Response = ServiceResponse<EitherBody<B>>;
    type Error = Error;
    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>>>>;

    actix_web::dev::forward_ready!(service);

    fn call(&self, mut req: ServiceRequest) -> Self::Future {
        let svc = self.service.clone();
        let log_level = settings::get_setting("log_level").unwrap_or("info".to_owned());

        Box::pin(async move {
            match log_level.as_str() {
                "debug" | "trace" | "info" => {
                    let route = req.path().to_owned();

                    /* we only process requests that are json */
                    if !MiddlewareUtility::is_json_request(&req) {
                        let res: ServiceResponse = svc.call(req).await?.map_into_boxed_body();
                        return Ok(res.map_into_right_body());
                    }

                    /* extract and log the request */
                    let mut request_body = BytesMut::new();
                    while let Some(chunk) = req.take_payload().next().await {
                        request_body.extend_from_slice(&chunk?);
                    }

                    match str::from_utf8(&request_body.to_vec().as_slice()) {
                        Ok(str) => {
                            /* identify routes that we will redact the body from,
                            these are items that contain sensitive information we do not want to log
                             */
                            match route.as_str() {
                                "/x/protected_endpoint" => {
                                    tracing::info!({ body = "Redacted" }, "HTTP Request");
                                }
                                _ => {
                                    tracing::info!({body = %str}, "HTTP Request");
                                }
                            }
                        }
                        Err(_) => {}
                    };

                    let (payload_sender, mut orig_payload) = Payload::create(true);
                    orig_payload.unread_data(request_body.freeze());
                    req.set_payload(actix_http::Payload::from(orig_payload));

                    /* extract and log the response */
                    let res: ServiceResponse = svc.call(req).await?.map_into_boxed_body();
                    if !MiddlewareUtility::is_json_response(&res) {
                        return Ok(res.map_into_right_body());
                    }

                    let res_status = res.status().clone();
                    let res_headers = res.headers().clone();
                    let new_request = res.request().clone();
                    let body_bytes = body::to_bytes(res.into_body()).await?;
                    match str::from_utf8(&body_bytes) {
                        Ok(str) => {
                            tracing::info!({body = %str}, "HTTP Response");
                            str
                        }
                        Err(_) => "Unknown",
                    };

                    /* build an identical response */
                    let mut new_response = HttpResponseBuilder::new(res_status);
                    for (header_name, header_value) in res_headers {
                        new_response.insert_header((header_name.as_str(), header_value));
                    }
                    let new_response = new_response.body(body_bytes.to_vec());

                    Ok(ServiceResponse::new(
                        new_request,
                        new_response.map_into_right_body(),
                    ))
                }
                _ => {
                    let res: ServiceResponse = svc.call(req).await?.map_into_boxed_body();
                    Ok(res.map_into_right_body())
                }
            }
        })
    }
}

This particular example integrates with tracing_actix_web, a fantastic telemetry tool and logs the request/response to jaeger if the request/response is json.

One thing to note, as far as I know, once you read out the request, you have to reassemble it, same with the response. Hence what the example is doing.