Hi Copilot! What's the best way to check what OS and display server is in use from Rust?

I'd like to be able to tell:

- Running as a plain teletypewriter with no terminal emulation (like when being piped to another script)
- Running as a videoterminal (that accepts VT100 sequences, etc)
- Has a GUI server available (yes/no)
- OS: Linux/Win/Mac/iOS/Android/etc...
- Display server: Is there a running X10 or X11 server? Is there a running Wayland server? I do *not* want to use `XDG_SESSION_ID` as it requires a display manager to be running, nor to use anything that requires loginctl/systemd/running external commands. I just want to check if the server's available.

Could you let me know what crate can do this, or if there isn't one, let me know how to do it myself? Thank you!



Great questions! Here’s a breakdown for each of your requirements, along with Rust ecosystem advice and how to implement them yourself if there’s no crate:

---

### 1. **Detecting if running as a teletypewriter (no terminal emulation)**

- **Check if stdin/stdout is a TTY (terminal):**
    - If not, you're piped or redirected.
    - Use the [`atty`](https://crates.io/crates/atty) crate:
        ```rust
        if atty::is(atty::Stream::Stdout) {
            // Is a terminal (could be VT100 or other terminal)
        } else {
            // Not a terminal (likely piped or file redirected)
        }
        ```
    - **No terminal emulation**: If not a TTY, you're in a plain pipe or file.

---

### 2. **Detecting videoterminal (VT100 etc.)**

- If `atty::is(atty::Stream::Stdout)` returns true, check the `TERM` environment variable for "xterm", "linux", "vt100", etc.
    ```rust
    if let Ok(term) = std::env::var("TERM") {
        if term.contains("xterm") || term.contains("vt") || term == "linux" {
            // Likely a VT-style terminal
        }
    }
    ```
- There’s no foolproof way, but this is the standard approach.

---

### 3. **Detecting if a GUI server is available**

- **X11**: Check if `DISPLAY` env var is set.
- **Wayland**: Check if `WAYLAND_DISPLAY` env var is set.
- If either is set, a GUI server is probably available.
    ```rust
    let gui_available = std::env::var("DISPLAY").is_ok() || std::env::var("WAYLAND_DISPLAY").is_ok();
    ```
- **Caveat:** This only means the variables are set—it doesn't guarantee a connection is possible, but that's the portable, non-systemd way.

---

### 4. **Detecting the OS**

- Use [`std::env::consts::OS`](https://doc.rust-lang.org/std/env/consts/constant.OS.html):
    ```rust
    println!("Running on: {}", std::env::consts::OS);
    // Output: linux, macos, windows, ios, android, etc.
    ```

---

### 5. **Detecting display server (X10/X11/Wayland) without loginctl/systemd**

- **X10** is quite rare; if `DISPLAY` is set, likely X11 (or Xorg).
- **Wayland**: If `WAYLAND_DISPLAY` is set, likely Wayland.
    ```rust
    let display_server = if std::env::var("WAYLAND_DISPLAY").is_ok() {
        "wayland"
    } else if std::env::var("DISPLAY").is_ok() {
        "x11"
    } else {
        "none"
    };
    ```
- **Do not use `XDG_SESSION_ID` or `loginctl`.**
- **No crate** currently gives more detail without native bindings or external commands.

---

## Summary Table

| Requirement            | Crate/Method          | Code Snippet or Approach                                             |
|------------------------|-----------------------|-----------------------------------------------------------------------|
| TTY/teletypewriter     | [`atty`]              | `atty::is(atty::Stream::Stdout)`                                     |
| VT100/terminal         | [`atty`]+`TERM` env   | `std::env::var("TERM")`                                              |
| GUI server available   | None, env check       | `DISPLAY` or `WAYLAND_DISPLAY` env                                   |
| OS type                | Built-in              | `std::env::consts::OS`                                               |
| Display server         | None, env check       | `WAYLAND_DISPLAY` (Wayland), `DISPLAY` (X11), else none              |

---

## No comprehensive crate exists for all of these together

- **[`atty`](https://crates.io/crates/atty)** is the de facto for TTY detection.
- For display server, all Rust GUI toolkits do the manual env-var method first, **unless** you want to use something like [`x11rb`](https://crates.io/crates/x11rb) to try to actually connect to the X server—which is overkill for just detection.

---

## Example: All Together

```rust
use atty::Stream;

fn main() {
    let is_tty = atty::is(Stream::Stdout);
    let term = std::env::var("TERM").unwrap_or_default();
    let is_terminal = is_tty && (term.contains("xterm") || term.contains("vt") || term == "linux");
    let gui_available = std::env::var("DISPLAY").is_ok() || std::env::var("WAYLAND_DISPLAY").is_ok();
    let os = std::env::consts::OS;
    let display_server = if std::env::var("WAYLAND_DISPLAY").is_ok() {
        "wayland"
    } else if std::env::var("DISPLAY").is_ok() {
        "x11"
    } else {
        "none"
    };

    println!("is_tty: {is_tty}");
    println!("is_terminal: {is_terminal}");
    println!("gui_available: {gui_available}");
    println!("os: {os}");
    println!("display_server: {display_server}");
}
```

---

### **Summary**

- There is **no single crate** that does all this out-of-the-box.
- Use `atty` for TTY detection, built-in Rust for OS, and manual env checks for GUI/display server.
- If you want to actually **test connection** to X11/Wayland, you’ll need to use a crate like [`x11rb`](https://crates.io/crates/x11rb) or [`wayland-client`](https://crates.io/crates/wayland-client), but for mere presence, the above is the best portable approach.

Let me know if you want more code, examples, or want to probe the display servers more deeply!
