Silly program that replaces a string in a MPV process.

_hello_proc_mem.rs

use std::io::{Read, Write, Seek, SeekFrom};
use std::fs::OpenOptions;
use std::ffi::OsString;
use std::error::Error;
use procfs::process::*;

fn main() -> Result<(), Box<dyn Error>> {
    for proc in all_processes()?.filter_map(|p| p.ok()) {
        match scan(proc) {
            Ok(true) => return Ok(()),
            _ => {}
        }
    }
    eprintln!("no mpv process found");
    Ok(())
}

fn scan(proc: Process) -> Result<bool, Box<dyn Error>> {
    let s = "Waikyō".as_bytes();
    let r = b"WARIOOO";
    assert_eq!(s.len(), r.len());
    Ok(if proc.exe()?.file_name() == Some(&OsString::from("mpv")) {
        dbg!(&proc);
        let mem_path = format!("/proc/{}/mem", proc.pid);
        let mut mem = OpenOptions::new().read(true).write(true).open(&mem_path).unwrap();
        let maps = proc.maps()?;
        for map in maps {
            match map.pathname {
                MMapPath::Heap | MMapPath::Anonymous => {
                    mem.seek(SeekFrom::Start(map.address.0)).unwrap();
                    assert_eq!(map.address.1 % 0x1000, 0);
                    let mut buf = (map.address.0..map.address.1).map(|_| 0).collect::<Vec<_>>();
                    mem.read_exact(&mut buf).unwrap();
                    for (i, w) in buf.windows(s.len()).enumerate() {
                        if w == s {
                            mem.seek(SeekFrom::Start(map.address.0 + i as u64)).unwrap();
                            mem.write_all(r).unwrap();
                            dbg!(i, map);
                            return Ok(true)
                        }
                    }
                }
                _ => {}
            }
        }
        true
    } else {
        false
    })
}

Cargo.toml

[package]
name = "hello_world"
version = "0.1.0"
edition = "2021"

[dependencies.procfs]
version = "0.13"