Simple warp filter does not compile

help
1

RUST noob here.
I am trying to create a simple Warp filter that can give me the remote ip address of the caller. I got this from here
#![deny(warnings)]

use std::net::SocketAddr;
use warp::Filter;
#[tokio::main]

async fn main() {
    let addrfilter = warp::addr::remote()
        .map(|addr: Option<SocketAddr>| {
            println!("remote address = {:?}", addr);
        });
    warp::serve(addrfilter).run(([127, 0, 0, 1], 3030)).await;
}

When I compile this, I get the following errors

$ cargo build
   Compiling hello-warp v0.1.0 (E:\rust_projects\hello-warp)
error[E0277]: the trait bound `(): Reply` is not satisfied
  --> src\main.rs:12:17
   |
12 |     warp::serve(addrfilter).run(([127, 0, 0, 1], 3030)).await;
   |                 ^^^^^^^^^^ the trait `Reply` is not implemented for `()`
   | 
  ::: C:\Users\rokugver\.cargo\registry\src\github.com-1ecc6299db9ec823\warp-0.3.1\src\server.rs:26:17
   |
26 |     F::Extract: Reply,
   |                 ----- required by this bound in `serve`
   |
   = note: required because of the requirements on the impl of `Reply` for `((),)`

error[E0277]: the trait bound `(): Reply` is not satisfied
  --> src\main.rs:12:29
   |
12 |     warp::serve(addrfilter).run(([127, 0, 0, 1], 3030)).await;
   |                             ^^^ the trait `Reply` is not implemented for `()`
   |
   = note: required because of the requirements on the impl of `Reply` for `((),)`
error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0277`.
error: could not compile `hello-warp`
To learn more, run the command again with --verbose.

What am I missing here considering that I am using a documented example almost as it is?

2

Warp expects your serve filter to output something that implements Reply, so that it can know how to respond to requests. If you make your map closure return a Reply value (like a http::StatusCode or a String), your code should work:

let addrfilter = warp::addr::remote()
        .map(|addr: Option<SocketAddr>| {
            println!("remote address = {:?}", addr);
            StatusCode::OK
        });
3

Thanks, returning a string worked.

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4

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