Native Messaging - Rust

host.json

{
    "name": "pingpong",
    "description": "Native messaging host example",
    "path": "path/to/release_executable",
    "type": "stdio",
    "allowed_origins": [
      "chrome-extension://extension_id/"
    ]
  }

main.js

var start;

/*
On a click on the browser action, send the app a message.
*/
chrome.browserAction.onClicked.addListener(() => {
    console.log('Sending: ping')
    start = performance.now();
    chrome.runtime.sendNativeMessage("pingpong", {text: "ping"}, onResponse);
});

function onResponse(res) {
    let end = performance.now();
    console.log(`Received: ${res.msg}, Took: ${end - start} ms`);
}

main.rs

use std::io::{self, Read, Write};

fn main() {
    read_input().unwrap();
    write_output("{\"msg\":\"pang\"}").unwrap();
}

pub fn read_input() -> io::Result<Vec<u8>> {
    let mut instream = io::stdin();
    let mut length = [0; 4];
    instream.read(&mut length)?;
    let mut buffer = vec![0; u32::from_ne_bytes(length) as usize];
    instream.read_exact(&mut buffer)?;
    Ok(buffer)
}

pub fn write_output(msg: &str) -> io::Result<()> {
    let mut outstream = io::stdout();
    let len = msg.len();
    if len > 1024 * 1024 {
        panic!("Message was too large, length: {}", len)
    }
    outstream.write(&len.to_ne_bytes())?;
    outstream.write_all(msg.as_bytes())?;
    outstream.flush()?;
    Ok(())
}

manifest.json

{
    "name": "Native Messaging Example",
    "version": "1.0",
    "manifest_version": 2,
    "description": "Send a message to a native application.",
    "background": {
        "scripts": ["main.js"]
    },
    "browser_action": {
        "default_icon": "message.svg"
    },
    "permissions": [
      "nativeMessaging"
    ]
  }

On Chromium 129

The sender sent an invalid JSON message; message ignored.

{message: 'Error when communicating with the native messaging host.'}

How to echo the input?