Impl of a subsystem flag in "deno compile" for background process in Windows

[hironichu]

Hello fellow denodevs

I was wondering if it was possible to run a compiled deno binary in background on windows, after some research and discussion on the official Deno Discord, I found that yes indeed it was.

So I made an implementation that works, only change the subsystem to "Windows" (because I don't think it would be useful to add more but we never know)

(I am new to Rust, you can probably do a better implementation !)

let mut standalone_bin = final_bin;
  #[cfg(windows)]
  {
    use byteorder::{ReadBytesExt, LittleEndian, WriteBytesExt};
    // This is just for adding support for Windows background process into compiled binaries
    // By default the Deno.exe binary is set to Console,
    // while this implementation may be junky it works
    if subsystem == "windows" {
        let mut reader = std::io::Cursor::new(&mut standalone_bin);
        // We Read until the PE Pointer
        reader.seek(SeekFrom::Start(0x3C))?;
        let pe_header_start = reader.read_u32::<LittleEndian>()?;
        //We go 92 bytes further to reach the Subsysem field
        let subsys_offset = pe_header_start + 92;
        reader.seek(SeekFrom::Start(subsys_offset as u64))?;
        let subsys = reader.read_u16::<LittleEndian>()?;
        //can be tweaked to add more subsytems
        if subsys != 0x2 {
            reader.seek(SeekFrom::Start(subsys_offset as u64))?;
            reader.write_u16::<LittleEndian>(0x2)?;
        }
    }
}

This is added at the end of the write_standalone_binary function, which also now has the subsystem param, that contains the value set in the flag deno compile -A -s windows app.ts

I made this so it can works with multiple options 🤷‍♂️ but it is not really useful.

This implementation can be useful for app that uses Webview (best example i have), I have been trying to work with Wry from the Tauri project, in order to implement Deno bindings for a personal project, with this it can run on windows in background and can display a Browser (or any really) window without showing up a new CMD.

I found the solution in this thread #11638