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//! Interface for injecting I/O-related functionality into tvix-eval.
//!
//! The Nix language contains several builtins (e.g. `builtins.readDir`), as
//! well as language feature (e.g. string-"coercion" of paths) that interact
//! with the filesystem.
//!
//! The language evaluator implemented by this crate does not depend on any
//! particular filesystem interaction model. Instead, this module provides a
//! trait that can be implemented by tvix-eval callers to provide the
//! functionality they desire.
//!
//! In theory this can be used to implement "mocked" filesystem interactions, or
//! interaction with remote filesystems, etc.
//!
//! In the context of Nix builds, callers also use this interface to determine
//! how store paths are opened and so on.
use std::{
fs::File,
io,
path::{Path, PathBuf},
};
#[cfg(target_family = "unix")]
use std::os::unix::ffi::OsStringExt;
/// Types of files as represented by `builtins.readDir` in Nix.
#[derive(Debug)]
pub enum FileType {
Directory,
Regular,
Symlink,
Unknown,
}
/// Represents all possible filesystem interactions that exist in the Nix
/// language, and that need to be executed somehow.
///
/// This trait is specifically *only* concerned with what is visible on the
/// level of the language. All internal implementation details are not part of
/// this trait.
pub trait EvalIO {
/// Verify whether the file at the specified path exists.
///
/// This is used for the following language evaluation cases:
///
/// * checking whether a file added to the `NIX_PATH` actually exists when
/// it is referenced in `<...>` brackets.
/// * `builtins.pathExists :: path -> bool`
fn path_exists(&self, path: &Path) -> io::Result<bool>;
/// Open the file at the specified path to a `io::Read`.
fn open(&self, path: &Path) -> io::Result<Box<dyn io::Read>>;
/// Read the directory at the specified path and return the names
/// of its entries associated with their [`FileType`].
///
/// This is used for the following language evaluation cases:
///
/// * `builtins.readDir :: path -> attrs<filename, filetype>`
fn read_dir(&self, path: &Path) -> io::Result<Vec<(bytes::Bytes, FileType)>>;
/// Import the given path. What this means depends on the implementation,
/// for example for a `std::io`-based implementation this might be a no-op,
/// while for a Tvix store this might be a copy of the given files to the
/// store.
///
/// This is used for the following language evaluation cases:
///
/// * string coercion of path literals (e.g. `/foo/bar`), which are expected
/// to return a path
/// * `builtins.toJSON` on a path literal, also expected to return a path
fn import_path(&self, path: &Path) -> io::Result<PathBuf>;
/// Returns the root of the store directory, if such a thing
/// exists in the evaluation context.
///
/// This is used for the following language evaluation cases:
///
/// * `builtins.storeDir :: string`
fn store_dir(&self) -> Option<String> {
None
}
}
/// Implementation of [`EvalIO`] that simply uses the equivalent
/// standard library functions, i.e. does local file-IO.
#[cfg(feature = "impure")]
pub struct StdIO;
// TODO: we might want to make this whole impl to be target_family = "unix".
#[cfg(feature = "impure")]
impl EvalIO for StdIO {
fn path_exists(&self, path: &Path) -> io::Result<bool> {
path.try_exists()
}
fn open(&self, path: &Path) -> io::Result<Box<dyn io::Read>> {
Ok(Box::new(File::open(path)?))
}
fn read_dir(&self, path: &Path) -> io::Result<Vec<(bytes::Bytes, FileType)>> {
let mut result = vec![];
for entry in path.read_dir()? {
let entry = entry?;
let file_type = entry.metadata()?.file_type();
let val = if file_type.is_dir() {
FileType::Directory
} else if file_type.is_file() {
FileType::Regular
} else if file_type.is_symlink() {
FileType::Symlink
} else {
FileType::Unknown
};
result.push((entry.file_name().into_vec().into(), val))
}
Ok(result)
}
// this is a no-op for `std::io`, as the user can already refer to
// the path directly
fn import_path(&self, path: &Path) -> io::Result<PathBuf> {
Ok(path.to_path_buf())
}
}
/// Dummy implementation of [`EvalIO`], can be used in contexts where
/// IO is not available but code should "pretend" that it is.
pub struct DummyIO;
impl EvalIO for DummyIO {
fn path_exists(&self, _: &Path) -> io::Result<bool> {
Err(io::Error::new(
io::ErrorKind::Unsupported,
"I/O methods are not implemented in DummyIO",
))
}
fn open(&self, _: &Path) -> io::Result<Box<dyn io::Read>> {
Err(io::Error::new(
io::ErrorKind::Unsupported,
"I/O methods are not implemented in DummyIO",
))
}
fn read_dir(&self, _: &Path) -> io::Result<Vec<(bytes::Bytes, FileType)>> {
Err(io::Error::new(
io::ErrorKind::Unsupported,
"I/O methods are not implemented in DummyIO",
))
}
fn import_path(&self, _: &Path) -> io::Result<PathBuf> {
Err(io::Error::new(
io::ErrorKind::Unsupported,
"I/O methods are not implemented in DummyIO",
))
}
}
|
