tower-http 解决什么问题

`async fn(HttpRequest) -> Result<HttpResponse, Error>`

All middleware uses the [http] and [http-body] crates as the HTTP abstractions. That means
they're compatible with any library or framework that also uses those crates, such as
[hyper], [tonic], and [warp].

tower-http = { version = "=0.7.1", features = ["compression-gzip"] }
tower = { version = "=0.5.3", features = ["util"] }
axum = { version = "=0.8.9", default-features = false }
tokio = { version = "=1.54.1", features = ["macros", "rt"] }
http = "1"
http-body = "1"
http-body-util = "0.1"
bytes = "1"

use bytes::Bytes;
use http::{header, Request, Response};
use http_body_util::{BodyExt, Full};
use std::convert::Infallible;
use tower::{Layer, Service, ServiceExt};
use tower_http::compression::CompressionLayer;

fn short<T>(_: &T) -> String {
  // 去掉路径，只留类型名，方便看
  let mut out = String::new();
  for part in std::any::type_name::<T>().split_inclusive(['<', '>', ',']) {
    out.push_str(part.trim_start().rsplit("::").next().unwrap());
  }
  out
}

async fn hit<S, B, RB>(name: &str, svc: S, req: Request<B>)
where
  S: Service<Request<B>, Response = Response<RB>>,
  S::Error: std::fmt::Debug,
  RB: http_body::Body<Data = Bytes>,
  RB::Error: std::fmt::Debug,
{
  let res = svc.oneshot(req).await.unwrap();
  println!("{name}");
  println!("  body type:        {}", short(res.body()));
  println!("  content-encoding: {:?}", res.headers().get(header::CONTENT_ENCODING));
  let bytes = res.into_body().collect().await.unwrap().to_bytes();
  println!("  {} bytes on the wire, gzip magic: {:02x?}", bytes.len(), &bytes[..2]);
}

#[tokio::main(flavor = "current_thread")]
async fn main() {
  let text = "tower-http ".repeat(100);
  let layer = CompressionLayer::new();

  // 1. 一个纯 tower 服务：请求、响应都是 http 的类型，body 用 http-body-util 的 Full
  let t = text.clone();
  let plain = tower::service_fn(move |_req: Request<Full<Bytes>>| {
    let t = t.clone();
    async move { Ok::<_, Infallible>(Response::new(Full::new(Bytes::from(t)))) }
  });
  let req = Request::get("/").header(header::ACCEPT_ENCODING, "gzip").body(Full::default()).unwrap();
  hit("tower service_fn", layer.layer(plain), req).await;

  // 2. axum 的 Router：同一个 layer 值
  let app = axum::Router::new().route("/", axum::routing::get(move || async move { text }));
  let req = Request::get("/").header(header::ACCEPT_ENCODING, "gzip").body(axum::body::Body::empty()).unwrap();
  hit("axum Router", layer.layer(app), req).await;
}

tower service_fn
  body type:        CompressionBody<Full<Bytes>>
  content-encoding: Some("gzip")
  51 bytes on the wire, gzip magic: [1f, 8b]
axum Router
  body type:        CompressionBody<Body>
  content-encoding: Some("gzip")
  51 bytes on the wire, gzip magic: [1f, 8b]