限了 1 MiB，handler 还是读到了 10 MiB

tower-http = { version = "=0.7.1", features = ["limit", "decompression-gzip"] }
axum = { version = "=0.8.9", default-features = false }
tower = { version = "=0.5.3", features = ["util"] }
tokio = { version = "=1.54.1", features = ["macros", "rt"] }
flate2 = "1"

use axum::body::{Body, Bytes};
use axum::extract::DefaultBodyLimit;
use axum::http::{header, Request};
use axum::routing::post;
use axum::Router;
use std::io::Write;
use tower::ServiceExt;
use tower_http::{decompression::RequestDecompressionLayer, limit::RequestBodyLimitLayer};

const MIB: usize = 1 << 20;

// 10 MiB 的零，压成 gzip
fn bomb() -> Vec<u8> {
  let mut e = flate2::write::GzEncoder::new(Vec::new(), flate2::Compression::best());
  e.write_all(&vec![0u8; 10 * MIB]).unwrap();
  e.finish().unwrap()
}

fn routes() -> Router {
  Router::new().route("/", post(|body: Bytes| async move { format!("handler got {} bytes", body.len()) }))
}

async fn send(name: &str, app: Router, gz: &[u8]) {
  let req = Request::post("/")
    .header(header::CONTENT_ENCODING, "gzip")
    .header(header::CONTENT_LENGTH, gz.len())
    .body(Body::from(gz.to_vec()))
    .unwrap();
  let res = app.oneshot(req).await.unwrap();
  let status = res.status();
  let body = axum::body::to_bytes(res.into_body(), usize::MAX).await.unwrap();
  println!("{name:<44} {status} {}", String::from_utf8_lossy(&body));
}

#[tokio::main(flavor = "current_thread")]
async fn main() {
  let gz = bomb();
  println!("gzip body: {} bytes on the wire, {} bytes inflated", gz.len(), 10 * MIB);
  // axum：最后一个 .layer 在最外层
  send(
    "disable, decompression, limit (limit outer)",
    routes().layer(DefaultBodyLimit::disable()).layer(RequestDecompressionLayer::new()).layer(RequestBodyLimitLayer::new(MIB)),
    &gz,
  )
  .await;
  send(
    "disable, limit, decompression (limit inner)",
    routes().layer(DefaultBodyLimit::disable()).layer(RequestBodyLimitLayer::new(MIB)).layer(RequestDecompressionLayer::new()),
    &gz,
  )
  .await;
  send(
    "default 2 MiB, decompression, limit",
    routes().layer(RequestDecompressionLayer::new()).layer(RequestBodyLimitLayer::new(MIB)),
    &gz,
  )
  .await;
}

gzip body: 10208 bytes on the wire, 10485760 bytes inflated
disable, decompression, limit (limit outer)  200 OK handler got 10485760 bytes
disable, limit, decompression (limit inner)  413 Payload Too Large Failed to buffer the request body: length limit exceeded
default 2 MiB, decompression, limit          413 Payload Too Large Failed to buffer the request body: length limit exceeded