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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 smol_str::SmolStr;
use std::{
io,
path::{Path, PathBuf},
};
/// Types of files as represented by `builtins.readDir` in Nix.
#[derive(Debug)]
pub enum FileType {
Directory,
Regular,
Symlink,
Unknown,
}
/// Defines how filesystem interaction occurs inside of tvix-eval.
pub trait EvalIO {
/// Verify whether the file at the specified path exists.
fn path_exists(&mut self, path: PathBuf) -> Result<bool, io::Error>;
/// Read the file at the specified path to a string.
fn read_to_string(&mut self, path: PathBuf) -> Result<String, io::Error>;
/// Read the directory at the specified path and return the names
/// of its entries associated with their [`FileType`].
fn read_dir(&mut self, path: PathBuf) -> Result<Vec<(SmolStr, FileType)>, io::Error>;
/// 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 primarily used in the context of things like coercing
/// a local path to a string, or builtins like `path`.
fn import_path(&mut self, path: &Path) -> Result<PathBuf, io::Error>;
/// Returns the root of the store directory, if such a thing
/// exists in the evaluation context.
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;
#[cfg(feature = "impure")]
impl EvalIO for StdIO {
fn path_exists(&mut self, path: PathBuf) -> Result<bool, io::Error> {
path.try_exists()
}
fn read_to_string(&mut self, path: PathBuf) -> Result<String, io::Error> {
std::fs::read_to_string(&path)
}
fn read_dir(&mut self, path: PathBuf) -> Result<Vec<(SmolStr, FileType)>, io::Error> {
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((SmolStr::new(entry.file_name().to_string_lossy()), val));
}
Ok(result)
}
// this is a no-op for `std::io`, as the user can already refer to
// the path directly
fn import_path(&mut self, path: &Path) -> Result<PathBuf, io::Error> {
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(&mut self, _: PathBuf) -> Result<bool, io::Error> {
Err(io::Error::new(
io::ErrorKind::Unsupported,
"I/O methods are not implemented in DummyIO",
))
}
fn read_to_string(&mut self, _: PathBuf) -> Result<String, io::Error> {
Err(io::Error::new(
io::ErrorKind::Unsupported,
"I/O methods are not implemented in DummyIO",
))
}
fn read_dir(&mut self, _: PathBuf) -> Result<Vec<(SmolStr, FileType)>, io::Error> {
Err(io::Error::new(
io::ErrorKind::Unsupported,
"I/O methods are not implemented in DummyIO",
))
}
fn import_path(&mut self, _: &Path) -> Result<PathBuf, io::Error> {
Err(io::Error::new(
io::ErrorKind::Unsupported,
"I/O methods are not implemented in DummyIO",
))
}
}
|
