Incorrect content-length header in reply to HEAD request when chunked transfer enconding is used

[mdickopp]

Bug Report

This is a followup to #730. Unfortunately, I found a case in which it still does not work correctly.

Version

axum main branch, commit 16ee83a

Platform

Debian Linux 12 (“bookworm”)
Linux feynman 5.15.0-3-amd64 #1 SMP Debian 5.15.15-1 (2022-01-18) x86_64 GNU/Linux
rustc 1.58.1 (db9d1b20b 2022-01-20)

Description

The content-length header in the reply to a simple HEAD request is set to 0 if the corresponding GET request uses transfer-encoding: chunked.

Steps to reproduce

Run the example program (which uses tower-http v0.2.1):

use axum::{routing::get, Router};
use tower_http::compression::{predicate::SizeAbove, CompressionLayer};

#[tokio::main]
async fn main() {
    let app = Router::new()
        .route("/", get(|| async { "Hello, World!" }))
        .layer(CompressionLayer::new().compress_when(SizeAbove::new(0)));
    axum::Server::bind(&"0.0.0.0:3000".parse().unwrap())
        .serve(app.into_make_service())
        .await
        .unwrap();
}

Send a HTTP/1.1 HEAD request for /. Set the accept-encoding request header to gzip. I used the the following command on the Linux command line:

printf 'HEAD / HTTP/1.1\r\naccept-encoding: gzip\r\n\r\n' | nc 127.0.0.1 3000

Observed behavior

The output contains the line:

content-length: 0

Expected behavior

The output contains no content-length header.

Note the response to the corresponding GET request uses chunked transfer encoding. Its headers look like this:

HTTP/1.1 200 OK
content-type: text/plain; charset=utf-8
content-encoding: gzip
transfer-encoding: chunked
date: Sun, 06 Feb 2022 16:03:44 GMT