sausage/vfs/src/mounts.rs

//! Resolves virtual paths before routing them to mounted layers.
use crate::*;
use std::{collections::BTreeMap, io::ErrorKind as E};
struct Mount {
    layer: Arc<dyn Layer>,
    readonly: bool,
}
/// A per-process mount namespace. Mount the root before use.
#[derive(Default)]
pub struct Mounts {
    mounts: BTreeMap<String, Mount>,
}
impl Mounts {
    /// Add or replace a mount. Read-only mounts reject every mutation.
    pub fn mount(&mut self, path: &str, layer: Arc<dyn Layer>, readonly: bool) {
        self.mounts
            .insert(resolve("/", path), Mount { layer, readonly });
    }
    pub(crate) async fn metadata_file(&self, path: &str, follow: bool) -> Result<Arc<dyn File>> {
        let (m, p) = self.route(path, true)?;
        m.layer
            .open(
                &p,
                Open {
                    follow,
                    ..Open::default()
                },
            )
            .await
    }
    fn route(&self, path: &str, write: bool) -> Result<(&Mount, String)> {
        let path = resolve("/", path);
        let (base, m) = self
            .mounts
            .iter()
            .filter(|(p, _)| p.as_str() == "/" || path == **p || path.starts_with(&format!("{p}/")))
            .max_by_key(|(p, _)| p.len())
            .ok_or_else(|| error(E::NotFound))?;
        if write && m.readonly {
            return Err(error(E::ReadOnlyFilesystem));
        }
        let rest = if base == "/" {
            path
        } else {
            path[base.len()..].into()
        };
        Ok((m, if rest.is_empty() { "/".into() } else { rest }))
    }
}
#[async_trait]
impl Layer for Mounts {
    async fn stat(&self, path: &str, follow: bool) -> Result<Stat> {
        let (m, p) = self.route(path, false)?;
        m.layer.stat(&p, follow).await
    }
    async fn readlink(&self, path: &str) -> Result<String> {
        let (m, p) = self.route(path, false)?;
        m.layer.readlink(&p).await
    }
    async fn list(&self, path: &str) -> Result<Vec<Entry>> {
        let path = resolve("/", path);
        let (m, p) = self.route(&path, false)?;
        let mut entries = m.layer.list(&p).await?;
        let prefix = if path == "/" {
            "/".into()
        } else {
            format!("{path}/")
        };
        for mount in self.mounts.keys() {
            if let Some(rest) = mount.strip_prefix(&prefix)
                && !rest.is_empty()
            {
                let name = rest.split('/').next().unwrap();
                entries.retain(|e| e.name != name);
                entries.push(Entry {
                    name: name.into(),
                    directory: true,
                    symlink: false,
                });
            }
        }
        entries.sort_by(|a, b| a.name.cmp(&b.name));
        Ok(entries)
    }
    async fn open(&self, path: &str, options: Open) -> Result<Arc<dyn File>> {
        let (m, p) = self.route(path, options.write || options.create || options.truncate)?;
        let file = m.layer.open(&p, options).await?;
        if m.readonly {
            Ok(Arc::new(crate::readonly::Readonly(file)))
        } else {
            Ok(file)
        }
    }
    async fn mkdir(&self, path: &str) -> Result<()> {
        let (m, p) = self.route(path, true)?;
        m.layer.mkdir(&p).await
    }
    async fn remove_file(&self, path: &str) -> Result<()> {
        let (m, p) = self.route(path, true)?;
        m.layer.remove_file(&p).await
    }
    async fn remove_dir(&self, path: &str) -> Result<()> {
        let (m, p) = self.route(path, true)?;
        m.layer.remove_dir(&p).await
    }
    async fn rename(&self, from: &str, to: &str) -> Result<()> {
        let (a, p) = self.route(from, true)?;
        let (b, q) = self.route(to, true)?;
        if !std::ptr::eq(a, b) {
            return Err(error(E::CrossesDevices));
        }
        a.layer.rename(&p, &q).await
    }
}