sausage/host/src/world.rs

//! A world directory and the one virtual root that host code and guests share.
//!
//! Layout of a world directory:
//! - `world/`: the virtual root `/` that every guest sees. Agents change everything in it.
//! - `host/`: host state outside the sandbox (harness storage, later the vault). No guest sees it.
use sausage_vfs::{Generated, Host, Layer, Memory, Mounts, Process};
use std::{
    os::unix::fs::PermissionsExt,
    path::{Path, PathBuf},
    sync::Arc,
};

/// An open world. `root` is the filesystem every guest sees as `/`; host code (the harness's file
/// tools) reads and writes through the same layer, so both always see the same files.
pub struct World {
    pub root: Arc<dyn Layer>,
    /// The host state folder, `<dir>/host`.
    pub host_dir: PathBuf,
    /// Live process metadata shared with the process table.
    pub processes: crate::process::Processes,
}

fn copy_tree(source: &Path, destination: &Path) -> std::io::Result<()> {
    std::fs::create_dir_all(destination)?;
    let mut permissions = std::fs::metadata(destination)?.permissions();
    permissions.set_mode(permissions.mode() | 0o200);
    std::fs::set_permissions(destination, permissions)?;
    for entry in std::fs::read_dir(source)? {
        let entry = entry?;
        let target = destination.join(entry.file_name());
        if entry.file_type()?.is_dir() {
            copy_tree(&entry.path(), &target)?;
        } else {
            std::fs::copy(entry.path(), &target)?;
            let mut permissions = std::fs::metadata(&target)?.permissions();
            permissions.set_mode(permissions.mode() | 0o200);
            std::fs::set_permissions(&target, permissions)?;
        }
    }
    Ok(())
}

impl World {
    /// Open (and create if missing) the world directory `dir`, including `/proc` and `/run` mounts.
    pub fn open(dir: &Path) -> anyhow::Result<Self> {
        Self::open_with_userland(dir, None)
    }

    /// Copy an optional bundle into a new world. Existing worlds retain their programs.
    pub fn open_with_userland(dir: &Path, userland: Option<&Path>) -> anyhow::Result<Self> {
        let root_dir = dir.join("world");
        let host_dir = dir.join("host");
        let fresh = !root_dir.exists();
        std::fs::create_dir_all(root_dir.join("usr/local/bin"))?;
        if fresh && let Some(bundle) = userland {
            for folder in ["bin", "src"] {
                copy_tree(&bundle.join(folder), &root_dir.join(folder))?;
            }
        }
        std::fs::create_dir_all(&host_dir)?;
        let mut mounts = Mounts::default();
        mounts.mount(
            "/",
            Arc::new(Host::new(&root_dir, Process::default())?),
            false,
        );
        let processes: crate::process::Processes =
            Arc::new(std::sync::Mutex::new(Default::default()));
        let snapshot = processes.clone();
        let mut proc = Generated::default();
        proc.insert("/processes", move || {
            let mut text = String::from("PID\tPPID\tSTATE\tCWD\tCONVERSATION\tARGV\n");
            for (pid, info) in snapshot.lock().unwrap().iter() {
                text.push_str(&format!(
                    "{pid}\t{}\t{}\t{}\t{}\t{}\n",
                    info.parent,
                    info.state,
                    info.cwd,
                    info.conversation.as_deref().unwrap_or("-"),
                    info.argv.join(" ")
                ));
            }
            Ok(text.into_bytes())
        });
        mounts.mount("/proc", Arc::new(proc), true);
        mounts.mount("/run", Arc::new(Memory::default()), false);
        let root: Arc<dyn Layer> = Arc::new(mounts);
        Ok(World {
            root,
            host_dir,
            processes,
        })
    }
}

#[cfg(test)]
#[test]
fn readonly_bundle_copies_are_writable() -> std::io::Result<()> {
    use std::fs;
    let bundle = tempfile::tempdir()?;
    let world = tempfile::tempdir()?;
    for (name, mode) in [("bin/tool.wasm", 0o555), ("src/lib.rs", 0o444)] {
        let path = bundle.path().join(name);
        fs::create_dir_all(path.parent().unwrap())?;
        fs::write(&path, b"original")?;
        fs::set_permissions(path, fs::Permissions::from_mode(mode))?;
    }
    for path in [bundle.path().join("bin"), bundle.path().join("src"), bundle.path().to_owned(), world.path().to_owned()] {
        fs::set_permissions(path, fs::Permissions::from_mode(0o555))?;
    }
    let result = copy_tree(bundle.path(), world.path());
    // Restore source directories so the temporary directory can remove its files.
    for path in [bundle.path(), &bundle.path().join("bin"), &bundle.path().join("src")] {
        fs::set_permissions(path, fs::Permissions::from_mode(0o755))?;
    }
    result?;
    assert_eq!(fs::metadata(world.path())?.permissions().mode() & 0o777, 0o755);
    for (name, mode) in [("bin/tool.wasm", 0o555), ("src/lib.rs", 0o444)] {
        let source = bundle.path().join(name);
        let target = world.path().join(name);
        assert_eq!(fs::metadata(&source)?.permissions().mode() & 0o777, mode);
        assert_eq!(fs::metadata(&target)?.permissions().mode() & 0o777, mode | 0o200);
        fs::write(&target, b"changed")?;
        assert_eq!(fs::read(source)?, b"original");
    }
    fs::write(world.path().join("bin/added.wasm"), b"new")?;
    fs::write(world.path().join("src/added.rs"), b"new")?;
    Ok(())
}