diff options
Diffstat (limited to 'tvix/nix-compat/src/nar/listing/mod.rs')
-rw-r--r-- | tvix/nix-compat/src/nar/listing/mod.rs | 128 |
1 files changed, 128 insertions, 0 deletions
diff --git a/tvix/nix-compat/src/nar/listing/mod.rs b/tvix/nix-compat/src/nar/listing/mod.rs new file mode 100644 index 000000000000..5a9a3b4d3613 --- /dev/null +++ b/tvix/nix-compat/src/nar/listing/mod.rs @@ -0,0 +1,128 @@ +//! Parser for the Nix archive listing format, aka .ls. +//! +//! LS files are produced by the C++ Nix implementation via `write-nar-listing=1` query parameter +//! passed to a store implementation when transferring store paths. +//! +//! Listing files contains metadata about a file and its offset in the corresponding NAR. +//! +//! NOTE: LS entries does not offer any integrity field to validate the retrieved file at the provided +//! offset. Validating the contents is the caller's responsibility. + +use std::{ + collections::HashMap, + path::{Component, Path}, +}; + +use serde::Deserialize; + +#[cfg(test)] +mod test; + +#[derive(Debug, thiserror::Error)] +pub enum ListingError { + // TODO: add an enum of what component was problematic + // reusing `std::path::Component` is not possible as it contains a lifetime. + /// An unsupported path component can be: + /// - either a Windows prefix (`C:\\`, `\\share\\`) + /// - either a parent directory (`..`) + /// - either a root directory (`/`) + #[error("unsupported path component")] + UnsupportedPathComponent, + #[error("invalid encoding for entry component")] + InvalidEncoding, +} + +#[derive(Debug, Deserialize)] +#[serde(tag = "type", rename_all = "lowercase")] +pub enum ListingEntry { + Regular { + size: u64, + #[serde(default)] + executable: bool, + #[serde(rename = "narOffset")] + nar_offset: u64, + }, + Directory { + // It's tempting to think that the key should be a `Vec<u8>` + // but Nix does not support that and will fail to emit a listing version 1 for any non-UTF8 + // encodeable string. + entries: HashMap<String, ListingEntry>, + }, + Symlink { + target: String, + }, +} + +impl ListingEntry { + /// Given a relative path without `..` component, this will locate, relative to this entry, a + /// deeper entry. + /// + /// If the path is invalid, a listing error [`ListingError`] will be returned. + /// If the entry cannot be found, `None` will be returned. + pub fn locate<P: AsRef<Path>>(&self, path: P) -> Result<Option<&ListingEntry>, ListingError> { + // We perform a simple DFS on the components of the path + // while rejecting dangerous components, e.g. `..` or `/` + // Files and symlinks are *leaves*, i.e. we return them + let mut cur = self; + for component in path.as_ref().components() { + match component { + Component::CurDir => continue, + Component::RootDir | Component::Prefix(_) | Component::ParentDir => { + return Err(ListingError::UnsupportedPathComponent) + } + Component::Normal(file_or_dir_name) => { + if let Self::Directory { entries } = cur { + // As Nix cannot encode non-UTF8 components in the listing (see comment on + // the `Directory` enum variant), invalid encodings path components are + // errors. + let entry_name = file_or_dir_name + .to_str() + .ok_or(ListingError::InvalidEncoding)?; + + if let Some(new_entry) = entries.get(entry_name) { + cur = new_entry; + } else { + return Ok(None); + } + } else { + return Ok(None); + } + } + } + } + + // By construction, we found the node that corresponds to the path traversal. + Ok(Some(cur)) + } +} + +#[derive(Debug)] +pub struct ListingVersion<const V: u8>; + +#[derive(Debug, thiserror::Error)] +#[error("Invalid version: {0}")] +struct ListingVersionError(u8); + +impl<'de, const V: u8> Deserialize<'de> for ListingVersion<V> { + fn deserialize<D>(deserializer: D) -> Result<Self, D::Error> + where + D: serde::Deserializer<'de>, + { + let value = u8::deserialize(deserializer)?; + if value == V { + Ok(ListingVersion::<V>) + } else { + Err(serde::de::Error::custom(ListingVersionError(value))) + } + } +} + +#[derive(Debug, Deserialize)] +#[serde(untagged)] +#[non_exhaustive] +pub enum Listing { + V1 { + root: ListingEntry, + version: ListingVersion<1>, + }, +} |