53 lines
1.8 KiB
Rust
53 lines
1.8 KiB
Rust
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//! Interface for injecting I/O-related functionality into tvix-eval.
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//!
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//! The Nix language contains several builtins (e.g. `builtins.readDir`), as
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//! well as language feature (e.g. string-"coercion" of paths) that interact
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//! with the filesystem.
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//!
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//! The language evaluator implemented by this crate does not depend on any
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//! particular filesystem interaction model. Instead, this module provides a
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//! trait that can be implemented by tvix-eval callers to provide the
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//! functionality they desire.
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//!
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//! In theory this can be used to implement "mocked" filesystem interactions, or
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//! interaction with remote filesystems, etc.
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//!
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//! In the context of Nix builds, callers also use this interface to determine
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//! how store paths are opened and so on.
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use std::path::PathBuf;
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use crate::errors::ErrorKind;
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/// Defines how filesystem interaction occurs inside of tvix-eval.
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pub trait EvalIO {
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/// Read the file at the specified path to a string.
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fn read_to_string(&self, path: PathBuf) -> Result<String, ErrorKind>;
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}
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/// Implementation of [`EvalIO`] that simply uses the equivalent
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/// standard library functions, i.e. does local file-IO.
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struct StdIO;
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impl EvalIO for StdIO {
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fn read_to_string(&self, path: PathBuf) -> Result<String, ErrorKind> {
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let path: PathBuf = path.into();
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std::fs::read_to_string(&path).map_err(|e| ErrorKind::IO {
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path: Some(path),
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error: std::rc::Rc::new(e),
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})
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}
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}
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/// Dummy implementation of [`EvalIO`], can be used in contexts where
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/// IO is not available but code should "pretend" that it is.
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struct DummyIO;
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impl EvalIO for DummyIO {
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fn read_to_string(&self, _: PathBuf) -> Result<String, ErrorKind> {
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Err(ErrorKind::NotImplemented(
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"I/O methods are not implemented in DummyIO",
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))
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}
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}
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