phoxal-model 0.52.0

//! Canonical logical asset identities, and validated access to the assets
//! compiled into a runtime bundle.
//!
//! The resolver lives here rather than in the `phoxal` facade because it is not
//! participant-authoring surface: the supervisor serves declared assets itself
//! (organization#978), and `phoxal-cli` deliberately does not depend on the
//! facade. Fencing that both ends must agree on belongs in the model both ends
//! already share.

use std::collections::BTreeMap;
use std::path::{Component, Path, PathBuf};

use serde::{Deserialize, Serialize};

use crate::ModelError;

/// A normalized, forward-slash logical asset identifier.
#[derive(Clone, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct AssetId(String);

impl AssetId {
    /// Validate and construct a logical asset identifier.
    pub fn new(value: impl Into<String>) -> Result<Self, ModelError> {
        let value = value.into();
        if value.is_empty()
            || value.starts_with('/')
            || value.contains('\\')
            || value
                .split('/')
                .any(|segment| segment.is_empty() || matches!(segment, "." | ".."))
        {
            return Err(ModelError::Invalid(format!(
                "invalid logical asset id '{value}'"
            )));
        }
        Ok(Self(value))
    }

    /// The normalized forward-slash representation.
    #[must_use]
    pub fn as_str(&self) -> &str {
        &self.0
    }
}

impl Serialize for AssetId {
    fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
        serializer.serialize_str(self.as_str())
    }
}

impl<'de> Deserialize<'de> for AssetId {
    fn deserialize<D: serde::Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
        Self::new(String::deserialize(deserializer)?).map_err(serde::de::Error::custom)
    }
}

/// A failure reading the compiled asset tree.
#[derive(Debug, thiserror::Error)]
pub enum AssetError {
    /// The tree, or a request against it, violated the fencing rules.
    #[error("{0}")]
    Rejected(String),
    /// The filesystem refused the operation.
    #[error("asset filesystem failure: {0}")]
    Io(#[from] std::io::Error),
}

impl From<ModelError> for AssetError {
    fn from(error: ModelError) -> Self {
        AssetError::Rejected(error.to_string())
    }
}

/// Read-only resolver for the declared assets below `<bundle>/assets`.
///
/// Discovery is the fence: the tree is walked once, every entry validated into
/// an [`AssetId`], and only that map is ever consulted afterwards. A request
/// therefore cannot reach `robot.json`, participant binaries, undeclared files,
/// or anything outside the asset root - not because a request is inspected for
/// traversal, but because no path outside the map is reachable at all.
#[derive(Clone, Debug, Default)]
pub struct AssetResolver {
    paths: BTreeMap<AssetId, PathBuf>,
}

impl AssetResolver {
    /// Walk `root` and validate every entry into the declared set.
    ///
    /// A missing root is an empty set, not an error: a bundle may legitimately
    /// declare no assets.
    pub fn discover(root: PathBuf) -> Result<Self, AssetError> {
        if !root.exists() {
            return Ok(Self::default());
        }
        let canonical_root = std::fs::canonicalize(&root).map_err(|error| {
            AssetError::Rejected(format!(
                "failed to resolve compiled asset root {}: {error}",
                root.display()
            ))
        })?;
        let mut paths = BTreeMap::new();
        discover_assets(&canonical_root, &canonical_root, &mut paths)?;
        Ok(Self { paths })
    }

    /// Read a declared asset.
    pub fn read(&self, id: &AssetId) -> Result<Vec<u8>, AssetError> {
        Ok(std::fs::read(self.path(id)?)?)
    }

    /// Open a declared asset.
    pub fn open(&self, id: &AssetId) -> Result<std::fs::File, AssetError> {
        Ok(std::fs::File::open(self.path(id)?)?)
    }

    /// Resolve a declared asset without permitting traversal or symlink escape.
    pub fn path(&self, id: &AssetId) -> Result<&Path, AssetError> {
        self.paths
            .get(id)
            .map(PathBuf::as_path)
            .ok_or_else(|| AssetError::Rejected(format!("undeclared asset '{}'", id.as_str())))
    }

    /// The validated logical identifiers available in this bundle.
    pub fn ids(&self) -> impl ExactSizeIterator<Item = &AssetId> {
        self.paths.keys()
    }
}

fn discover_assets(
    root: &Path,
    directory: &Path,
    paths: &mut BTreeMap<AssetId, PathBuf>,
) -> Result<(), AssetError> {
    let mut entries = std::fs::read_dir(directory)?.collect::<std::io::Result<Vec<_>>>()?;
    entries.sort_by_key(std::fs::DirEntry::file_name);
    for entry in entries {
        let source = entry.path();
        let metadata = std::fs::symlink_metadata(&source)?;
        if metadata.file_type().is_symlink() {
            return Err(AssetError::Rejected(format!(
                "compiled asset tree contains forbidden symlink {}",
                source.display()
            )));
        }
        if metadata.is_dir() {
            discover_assets(root, &source, paths)?;
            continue;
        }
        if !metadata.is_file() {
            return Err(AssetError::Rejected(format!(
                "compiled asset tree contains unsupported entry {}",
                source.display()
            )));
        }
        let relative = source.strip_prefix(root).map_err(|_| {
            AssetError::Rejected(format!("compiled asset escaped root: {}", source.display()))
        })?;
        if relative
            .components()
            .any(|component| !matches!(component, Component::Normal(_)))
        {
            return Err(AssetError::Rejected(format!(
                "compiled asset path is not normalized: {}",
                relative.display()
            )));
        }
        let logical = relative
            .components()
            .map(|component| {
                component.as_os_str().to_str().ok_or_else(|| {
                    AssetError::Rejected(format!(
                        "compiled asset path is not UTF-8: {}",
                        relative.display()
                    ))
                })
            })
            .collect::<Result<Vec<_>, AssetError>>()?
            .join("/");
        let id = AssetId::new(logical)?;
        if paths.insert(id.clone(), source).is_some() {
            return Err(AssetError::Rejected(format!(
                "duplicate compiled asset '{}'",
                id.as_str()
            )));
        }
    }
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn validates_normalized_ids() {
        for invalid in ["", "/a", "../a", "a/../b", "a\\b", "a//b"] {
            assert!(AssetId::new(invalid).is_err(), "{invalid}");
        }
        assert_eq!(
            AssetId::new("meshes/base.stl").unwrap().as_str(),
            "meshes/base.stl"
        );
    }

    #[test]
    fn a_missing_root_is_an_empty_set_not_a_failure() {
        let resolver = AssetResolver::discover(PathBuf::from("/nonexistent/assets"))
            .expect("a bundle may declare no assets");
        assert_eq!(resolver.ids().len(), 0);
    }

    #[test]
    fn only_discovered_assets_are_reachable() {
        let root = tempfile::tempdir().expect("temp dir");
        let assets = root.path().join("assets");
        std::fs::create_dir_all(assets.join("meshes")).unwrap();
        std::fs::write(assets.join("meshes/base.stl"), b"mesh").unwrap();
        // A sibling of the asset root, exactly like `robot.json` and `bin/` in a
        // real bundle: reachable on disk, never through the resolver.
        std::fs::write(root.path().join("robot.json"), b"secret").unwrap();

        let resolver = AssetResolver::discover(assets).expect("discovery succeeds");
        assert_eq!(resolver.ids().len(), 1);
        assert_eq!(
            resolver
                .read(&AssetId::new("meshes/base.stl").unwrap())
                .unwrap(),
            b"mesh"
        );
        // Nothing outside the declared set resolves, and the fencing does not
        // depend on inspecting the request: these ids simply are not keys.
        for undeclared in ["robot.json", "meshes/other.stl", "bin/phoxal-service-drive"] {
            let id = AssetId::new(undeclared).expect("a syntactically valid id");
            assert!(resolver.path(&id).is_err(), "{undeclared}");
        }
    }

    #[test]
    fn a_symlink_in_the_tree_is_refused_outright() {
        let root = tempfile::tempdir().expect("temp dir");
        let assets = root.path().join("assets");
        std::fs::create_dir_all(&assets).unwrap();
        let outside = root.path().join("outside.txt");
        std::fs::write(&outside, b"outside").unwrap();
        std::os::unix::fs::symlink(&outside, assets.join("link.txt")).unwrap();

        let error = AssetResolver::discover(assets).expect_err("a symlink must fail discovery");
        assert!(error.to_string().contains("forbidden symlink"), "{error}");
    }
}