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lib.rs
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//! `bkt` (pronounced "bucket") is a library for caching subprocess executions. It enables reuse of
//! expensive invocations across separate processes and supports synchronous and asynchronous
//! refreshing, TTLs, and other functionality. `bkt` is also a standalone binary for use by shell
//! scripts and other languages, see <https://github.com/dimo414/bkt> for binary details.
//!
//! ```no_run
//! # fn do_something(_: &str) {}
//! # fn main() -> anyhow::Result<()> {
//! # use std::time::Duration;
//! let bkt = bkt::Bkt::in_tmp()?;
//! let expensive_cmd = bkt::CommandDesc::new(["wget", "https://example.com"]);
//! let (result, age) = bkt.retrieve(&expensive_cmd, Duration::from_secs(3600))?;
//! do_something(result.stdout_utf8());
//! # Ok(()) }
//! ```
#![warn(missing_docs)]
use std::collections::{BTreeMap, BTreeSet};
use std::convert::{TryFrom, TryInto};
use std::ffi::{OsString, OsStr};
use std::fs::{File, OpenOptions};
use std::hash::{Hash, Hasher};
use std::io::{self, BufReader, ErrorKind, BufWriter, Write, Read};
use std::path::{PathBuf, Path};
use std::time::{Duration, SystemTime};
use anyhow::{anyhow, Context, Error, Result};
use serde::{Serialize, Deserialize};
use serde::de::DeserializeOwned;
use base64::{Engine as _, engine::general_purpose};
#[cfg(feature="debug")]
macro_rules! debug_msg {
($($arg:tt)*) => { eprintln!("bkt: {}", format!($($arg)*)) }
}
#[cfg(not(feature="debug"))]
macro_rules! debug_msg {
($($arg:tt)*) => { }
}
/// Returns the modtime of the given path. Returns Ok(None) if the file is not found, and
/// otherwise returns an error if the modtime cannot be determined.
fn modtime(path: &Path) -> Result<Option<SystemTime>> {
let metadata = std::fs::metadata(path);
match metadata {
Ok(metadata) => {
Ok(Some(metadata.modified().context("Modtime is not supported")?))
},
Err(ref err) => {
match err.kind() {
ErrorKind::NotFound => Ok(None),
_ => { metadata?; unreachable!() },
}
}
}
}
/// A stateless description of a command to be executed and cached. It consists of a command line
/// invocation and additional metadata about how the command should be cached which are configured
/// via the `with_*` methods. Instances can be persisted and reused.
///
/// Calling any of these methods changes how the invocation's cache key will be constructed,
/// therefore two invocations with different metadata configured will be cached separately. This
/// allows - for example - commands that interact with the current working directory to be cached
/// dependent on the working directory even if the command line arguments are equal.
///
/// # Examples
///
/// ```
/// let cmd = bkt::CommandDesc::new(["echo", "Hello World!"]);
/// let with_cwd = bkt::CommandDesc::new(["ls"]).with_cwd();
/// let with_env = bkt::CommandDesc::new(["date"]).with_env("TZ");
/// ```
#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize, Deserialize)]
pub struct CommandDesc {
args: Vec<OsString>,
use_cwd: bool,
envs: BTreeSet<OsString>,
mod_files: BTreeSet<PathBuf>,
persist_failures: bool,
}
impl CommandDesc {
/// Constructs a CommandDesc instance for the given command line.
///
/// ```
/// let cmd = bkt::CommandDesc::new(["echo", "Hello World!"]);
/// ```
pub fn new<I, S>(command: I) -> Self where I: IntoIterator<Item=S>, S: Into<OsString> {
let ret = CommandDesc {
args: command.into_iter().map(Into::into).collect(),
use_cwd: false,
envs: BTreeSet::new(),
mod_files: BTreeSet::new(),
persist_failures: true,
};
assert!(!ret.args.is_empty(), "Command cannot be empty");
ret
}
/// Specifies that the current process' working directory should be included in the cache key.
/// Commands that depend on the working directory (e.g. `ls` or `git status`) should call this
/// in order to cache executions in different working directories separately.
///
/// # Examples
///
/// ```
/// let cmd = bkt::CommandDesc::new(["pwd"]).with_cwd();
/// ```
pub fn with_cwd(mut self) -> Self {
self.use_cwd = true;
self
}
/// Specifies that the given environment variable should be included in the cache key. Commands
/// that depend on the values of certain environment variables (e.g. `LANG`, `PATH`, or `TZ`)
/// should call this in order to cache such executions separately. Although it's possible to
/// pass `PWD` here calling [`with_cwd()`] is generally recommended instead for clarity and
/// consistency with subprocesses that don't read this environment variable.
///
/// Note: If the given variable name is not found in the current process' environment at
/// execution time the variable is _not_ included in the cache key, and the execution will be
/// cached as if the environment variable had not been specified at all.
///
/// [`with_cwd()`]: CommandDesc::with_cwd
///
/// # Examples
///
/// ```
/// let cmd = bkt::CommandDesc::new(["date"]).with_env("TZ");
/// ```
pub fn with_env<K>(mut self, key: K) -> Self where K: AsRef<OsStr> {
self.envs.insert(key.as_ref().into());
self
}
/// Specifies that the given environment variables should be included in the cache key. Commands
/// that depend on the values of certain environment variables (e.g. `LANG`, `PATH`, or `TZ`)
/// should call this in order to cache such executions separately. Although it's possible to
/// pass `PWD` here calling [`with_cwd()`] is generally recommended instead for clarity and
/// consistency with subprocesses that don't read this environment variable.
///
/// Note: If a given variable name is not found in the current process' environment at execution
/// time that variable is _not_ included in the cache key, and the execution will be cached as
/// if the environment variable had not been specified at all.
///
/// [`with_cwd()`]: CommandDesc::with_cwd
///
/// # Examples
///
/// ```
/// let cmd = bkt::CommandDesc::new(["date"]).with_envs(["LANG", "TZ"]);
/// ```
pub fn with_envs<I, E>(mut self, envs: I) -> Self where
I: IntoIterator<Item=E>,
E: AsRef<OsStr>,
{
self.envs.extend(envs.into_iter().map(|e| e.as_ref().into()));
self
}
/// Specifies that the modification time of the given file should be included in the cache key,
/// causing cached commands to be invalidated if the file is modified in the future. Commands
/// that depend on the contents of certain files should call this in order to invalidate the
/// cache when the file changes.
///
/// It is recommended to pass absolute paths when this is used along with [`with_cwd()`] or
/// [`CommandState::with_working_dir()`] to avoid any ambiguity in how relative paths are
/// resolved.
///
/// Note: If the given path is not found at execution time the file is _not_ included in the
/// cache key, and the execution will be cached as if the file had not been specified at all.
///
/// [`with_cwd()`]: CommandDesc::with_cwd
///
/// # Examples
///
/// ```
/// let cmd = bkt::CommandDesc::new(["..."]).with_modtime("/etc/passwd");
/// ```
pub fn with_modtime<P>(mut self, file: P) -> Self where P: AsRef<Path> {
self.mod_files.insert(file.as_ref().into());
self
}
/// Specifies that the modification time of the given files should be included in the cache key,
/// causing cached commands to be invalidated if the files are modified in the future. Commands
/// that depend on the contents of certain files should call this in order to invalidate the
/// cache when the files change.
///
/// It is recommended to pass absolute paths when this is used along with [`with_cwd()`] or
/// [`CommandState::with_working_dir()`] to avoid any ambiguity in how relative paths are
/// resolved.
///
/// Note: If a given path is not found at execution time that file is _not_ included in the
/// cache key, and the execution will be cached as if the file had not been specified at all.
///
/// [`with_cwd()`]: CommandDesc::with_cwd
///
/// # Examples
///
/// ```
/// let cmd = bkt::CommandDesc::new(["..."]).with_modtimes(["/etc/passwd", "/etc/group"]);
/// ```
pub fn with_modtimes<I, P>(mut self, files: I) -> Self where
I: IntoIterator<Item=P>,
P: AsRef<Path>, {
self.mod_files.extend(files.into_iter().map(|f| f.as_ref().into()));
self
}
/// Specifies this command should only be cached if it succeeds - i.e. it returns a zero exit
/// code. Commands that return a non-zero exit code will not be cached, and therefore will be
/// rerun on each invocation (until they succeed).
///
/// **WARNING:** use this option with caution. Discarding invocations that fail can overload
/// downstream resources that were protected by the caching layer limiting QPS. For example,
/// if a website is rejecting a fraction of requests to shed load and then clients start
/// sending _more_ requests when their attempts fail the website could be taken down outright by
/// the added load. In other words, using this option can lead to accidental DDoSes.
///
/// ```
/// let cmd = bkt::CommandDesc::new(["grep", "foo", "/var/log/syslog"]).with_discard_failures(true);
/// ```
pub fn with_discard_failures(mut self, discard_failures: bool) -> Self {
// Invert the boolean so it's not a double negative at usage sites
self.persist_failures = !discard_failures;
self
}
/// Constructs a [`CommandState`] instance, capturing application state that will be used in the
/// cache key, such as the current working directory and any specified environment variables.
/// The `CommandState` can also be further customized to change how the subprocess is invoked.
///
/// Most callers should be able to pass a `CommandDesc` directly to a [`Bkt`] instance without
/// needing to construct a separate `CommandState` first.
///
/// Example:
///
/// ```no_run
/// # fn main() -> anyhow::Result<()> {
/// # use std::time::Duration;
/// let bkt = bkt::Bkt::in_tmp()?;
/// let cmd = bkt::CommandDesc::new(["foo", "bar"]).capture_state()?.with_env("FOO", "BAR");
/// let (result, age) = bkt.retrieve(cmd, Duration::from_secs(3600))?;
/// # Ok(()) }
/// ```
pub fn capture_state(&self) -> Result<CommandState> {
let cwd = if self.use_cwd {
Some(std::env::current_dir()?)
} else {
None
};
let envs = self.envs.iter()
.flat_map(|e| std::env::var_os(e).map(|v| (e.clone(), v)))
.collect();
let modtimes = self.mod_files.iter()
.map(|f| modtime(f).map(|m| (f, m)))
.collect::<Result<Vec<_>>>()?.into_iter()
.flat_map(|(f, m)| m.map(|m| (f.clone(), m)))
.collect();
let state = CommandState { args: self.args.clone(), cwd, envs, modtimes, persist_failures: self.persist_failures };
debug_msg!("state: {}", state.debug_info());
Ok(state)
}
}
/// The stateful sibling of [`CommandDesc`] which represents a command to be executed and cached
/// along with environment state (e.g. the current working directory) at the time the `CommandState`
/// instance is constructed. It consists of a command line invocation and application state
/// determining how the command should be cached and executed. Additional `with_*` methods are
/// provided on this type for further modifying how the subprocess will be executed.
///
/// Calling any of these methods changes how the invocation's cache key will be constructed,
/// therefore two invocations with different configured state will be cached separately, in the same
/// manner as the `with_*` methods on `CommandDesc`.
///
/// # Examples
///
/// ```
/// # fn main() -> anyhow::Result<()> {
/// let cmd = bkt::CommandDesc::new(["echo", "Hello World!"]).capture_state();
/// let with_custom_wd = bkt::CommandDesc::new(["ls"]).capture_state()?.with_working_dir("/");
/// let with_env = bkt::CommandDesc::new(["date"]).capture_state()?.with_env("TZ", "UTC");
/// # Ok(()) }
/// ```
#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize, Deserialize)]
pub struct CommandState {
// TODO Borrow<Vec<OsString>> or Cow<Vec<OsString>> might be better, need to validate
// serialization. Or maybe just make it &Vec<OsString> and add a lifetime to CommandState?
args: Vec<OsString>,
cwd: Option<PathBuf>,
envs: BTreeMap<OsString, OsString>,
modtimes: BTreeMap<PathBuf, SystemTime>,
persist_failures: bool,
}
impl CommandState {
/// Sets the working directory the command should be run from, and causes this working directory
/// to be included in the cache key. If unset the working directory will be inherited from the
/// current process' and will _not_ be used to differentiate invocations in separate working
/// directories.
///
/// ```
/// # fn main() -> anyhow::Result<()> {
/// let cmd = bkt::CommandDesc::new(["pwd"]);
/// let state = cmd.capture_state()?.with_working_dir("/tmp");
/// # Ok(()) }
/// ```
pub fn with_working_dir<P: AsRef<Path>>(mut self, cwd: P) -> Self {
self.cwd = Some(cwd.as_ref().into());
self
}
/// Adds the given key/value pair to the environment the command should be run from, and causes
/// this pair to be included in the cache key.
///
/// ```
/// # fn main() -> anyhow::Result<()> {
/// let cmd = bkt::CommandDesc::new(["pwd"]);
/// let state = cmd.capture_state()?.with_env("FOO", "bar");
/// # Ok(()) }
/// ```
pub fn with_env<K, V>(mut self, key: K, value: V) -> Self
where K: AsRef<OsStr>, V: AsRef<OsStr> {
self.envs.insert(key.as_ref().into(), value.as_ref().into());
self
}
/// Adds the given key/value pairs to the environment the command should be run from, and causes
/// these pair to be included in the cache key.
///
/// ```
/// # fn main() -> anyhow::Result<()> {
/// use std::env;
/// use std::collections::HashMap;
///
/// let important_envs : HashMap<String, String> =
/// env::vars().filter(|&(ref k, _)|
/// k == "TERM" || k == "TZ" || k == "LANG" || k == "PATH"
/// ).collect();
/// let cmd = bkt::CommandDesc::new(["..."]);
/// let state = cmd.capture_state()?.with_envs(&important_envs);
/// # Ok(()) }
/// ```
pub fn with_envs<I, K, V>(mut self, envs: I) -> Self
where
I: IntoIterator<Item=(K, V)>,
K: AsRef<OsStr>,
V: AsRef<OsStr>,
{
for (ref key, ref val) in envs {
self.envs.insert(key.as_ref().into(), val.as_ref().into());
}
self
}
/// Format's the CommandState's metadata (information read from the system rather than provided
/// by the caller) for diagnostic purposes.
#[cfg(feature="debug")]
fn debug_info(&self) -> String {
fn to_timestamp(time: &SystemTime) -> u128 {
time.duration_since(SystemTime::UNIX_EPOCH).expect("Precedes epoch").as_micros()
}
let mut parts = Vec::new();
if let Some(ref cwd) = self.cwd {
parts.push(format!("cwd:{}", cwd.to_string_lossy()));
}
if !self.envs.is_empty() {
parts.push(self.envs.iter()
.map(|(k, v)| format!("{}={}", k.to_string_lossy(), v.to_string_lossy()))
.collect::<Vec<_>>().join(","));
}
if !self.modtimes.is_empty() {
parts.push(self.modtimes.iter()
.map(|(p, m)| format!("{}:{}", p.to_string_lossy(), to_timestamp(m)))
.collect::<Vec<_>>().join(" "));
}
parts.join(" | ")
}
}
impl TryFrom<&CommandDesc> for CommandState {
type Error = anyhow::Error;
fn try_from(desc: &CommandDesc) -> Result<Self> {
desc.capture_state()
}
}
impl From<&CommandState> for std::process::Command {
fn from(cmd: &CommandState) -> Self {
let mut command = std::process::Command::new(&cmd.args[0]);
command.args(&cmd.args[1..]);
if let Some(cwd) = &cmd.cwd {
command.current_dir(cwd);
}
if !cmd.envs.is_empty() {
command.envs(&cmd.envs);
}
command
}
}
impl CacheKey for CommandState {
fn debug_label(&self) -> Option<String> {
Some(self.args.iter()
.map(|a| a.to_string_lossy()).collect::<Vec<_>>().join("-")
.chars()
.map(|c| if c.is_whitespace() { '_' } else { c })
.filter(|&c| c.is_alphanumeric() || c == '-' || c == '_')
.take(100).collect())
}
}
#[cfg(test)]
mod cmd_tests {
use super::*;
#[test]
fn debug_label() {
let cmd = CommandDesc::new(["foo", "bar", "b&r _- a"]);
assert_eq!(CommandState::try_from(&cmd).unwrap().debug_label(), Some("foo-bar-br__-_a".into()));
}
#[test]
fn collisions() {
std::env::set_var("FOO", "BAR");
let commands = [
CommandDesc::new(["foo"]),
CommandDesc::new(["foo", "bar"]),
CommandDesc::new(["foo", "b", "ar"]),
CommandDesc::new(["foo", "b ar"]),
CommandDesc::new(["foo"]).with_cwd(),
CommandDesc::new(["foo"]).with_env("FOO"),
CommandDesc::new(["foo"]).with_cwd().with_env("FOO"),
];
// https://old.reddit.com/r/rust/comments/2koptu/best_way_to_visit_all_pairs_in_a_vec/clnhxr5/
let mut iter = commands.iter();
for a in &commands {
iter.next();
for b in iter.clone() {
assert_ne!(
CommandState::try_from(a).unwrap().cache_key(),
CommandState::try_from(b).unwrap().cache_key(),
"{:?} and {:?} have equivalent hashes", a, b);
}
}
}
}
/// The outputs of a cached invocation of a [`CommandDesc`], akin to [`std::process::Output`].
#[derive(Serialize, Deserialize, Debug, Eq, PartialEq)]
pub struct Invocation {
stdout: Vec<u8>,
stderr: Vec<u8>,
exit_code: i32,
runtime: Duration,
}
impl Invocation {
/// The data that the process wrote to stdout.
pub fn stdout(&self) -> &[u8] { &self.stdout }
/// Helper to view stdout as a UTF-8 string. Use [`from_utf8`](std::str::from_utf8) directly if
/// you need to handle output that may not be UTF-8.
pub fn stdout_utf8(&self) -> &str {
std::str::from_utf8(&self.stdout).expect("stdout not valid UTF-8")
}
/// The data that the process wrote to stderr.
pub fn stderr(&self) -> &[u8] { &self.stderr }
/// Helper to view stderr as a UTF-8 string. Use [`from_utf8`](std::str::from_utf8) directly if
/// you need to handle output that may not be UTF-8.
pub fn stderr_utf8(&self) -> &str {
std::str::from_utf8(&self.stderr).expect("stderr not valid UTF-8")
}
/// The exit code of the program, or 126 if the program terminated without an exit status.
/// See [`ExitStatus::code()`](std::process::ExitStatus::code()). This is subject to change to
/// better support other termination states.
pub fn exit_code(&self) -> i32 { self.exit_code }
/// The time the process took to complete.
pub fn runtime(&self) -> Duration { self.runtime }
}
/// A file-lock mechanism that holds a lock by atomically creating a file in the given directory,
/// and deleting the file upon being dropped. Callers should beware that dropping is not guaranteed
/// (e.g. if the program panics). When a conflicting lock file is found its age (mtime) is checked
/// to detect stale locks leaked by a separate process that failed to properly drop its lock.
#[derive(Debug)]
struct FileLock {
lock_file: PathBuf,
}
impl FileLock {
fn try_acquire<P: AsRef<Path>>(lock_dir: P, name: &str, consider_stale: Duration) -> Result<Option<Self>> {
let lock_file = lock_dir.as_ref().join(name).with_extension("lock");
match OpenOptions::new().create_new(true).write(true).open(&lock_file) {
Ok(mut lock) => {
write!(lock, "{}", std::process::id())?;
Ok(Some(FileLock{ lock_file }))
},
Err(io) => {
match io.kind() {
ErrorKind::AlreadyExists => {
if let Ok(lock_metadata) = std::fs::metadata(&lock_file) {
if let Ok(age) = lock_metadata.modified()?.elapsed() {
if age > consider_stale {
return Err(Error::msg(format!(
"Lock {} held by PID {} appears stale and may need to be deleted manually.",
lock_file.display(),
std::fs::read_to_string(&lock_file).unwrap_or_else(|_| "unknown".into()))));
}
}
}
Ok(None)
},
_ => { Err(Error::new(io)) }
}
},
}
}
}
impl Drop for FileLock {
fn drop(&mut self) {
if let Err(e) = std::fs::remove_file(&self.lock_file) {
eprintln!("Failed to delete lockfile {}, may need to be deleted manually. Reason: {:?}",
self.lock_file.display(), e);
}
}
}
#[cfg(test)]
mod file_lock_tests {
use super::*;
use test_dir::{TestDir, DirBuilder};
#[test]
fn locks() {
let dir = TestDir::temp();
let lock = FileLock::try_acquire(dir.root(), "test", Duration::from_secs(100)).unwrap();
let lock = lock.expect("Could not take lock");
assert!(dir.path("test.lock").exists());
std::mem::drop(lock);
assert!(!dir.path("test.lock").exists());
}
#[test]
fn already_locked() {
let dir = TestDir::temp();
let lock = FileLock::try_acquire(dir.root(), "test", Duration::from_secs(100)).unwrap();
let lock = lock.expect("Could not take lock");
let attempt = FileLock::try_acquire(dir.root(), "test", Duration::from_secs(100)).unwrap();
assert!(attempt.is_none());
std::mem::drop(lock);
let attempt = FileLock::try_acquire(dir.root(), "test", Duration::from_secs(100)).unwrap();
assert!(attempt.is_some());
}
}
/// Trait allowing a type to be used as a cache key. It would be nice to blanket-implement
/// this for all types that implement the dependent traits, but without a way for specific
/// impls to opt-out of the blanket that would prevent customizing the debug_label().
/// Specialization might resolve that issue, in the meantime it's fine since Cache is a
/// private type anyways.
trait CacheKey: std::fmt::Debug+Hash+PartialEq {
/// Label is added to the cache key when run with the debug feature, useful for diagnostics.
fn debug_label(&self) -> Option<String> { None }
/// Generates a string sufficiently unique to describe the key; typically just the hex encoding
/// of the key's hash code. Most impls should not need to override this.
fn cache_key(&self) -> String {
// The hash_map::DefaultHasher is somewhat underspecified, but it notes that "hashes should
// not be relied upon over releases", which implies it is stable across multiple
// invocations of the same build.... See cache_tests::stable_hash.
let mut s = std::collections::hash_map::DefaultHasher::new();
self.hash(&mut s);
let hash = s.finish();
if cfg!(feature = "debug") {
if let Some(label) = self.debug_label() {
if !label.is_empty() {
return format!("{}_{:016X}", label, hash);
}
}
}
format!("{:016X}", hash)
}
}
/// Container for serialized key/value pairs.
#[derive(Serialize, Deserialize)]
struct CacheEntry<K, V> {
key: K,
value: V,
}
// See https://doc.rust-lang.org/std/fs/fn.soft_link.html
#[cfg(windows)]
fn symlink<P: AsRef<Path>, Q: AsRef<Path>>(original: P, link: Q) -> Result<()> {
std::os::windows::fs::symlink_file(original, link)
.context("Windows prevents most programs from creating symlinks; see https://github.com/dimo414/bkt/issues/3")
}
#[cfg(unix)]
use std::os::unix::fs::symlink;
/// A file-system-backed cache for mapping keys (i.e. `CommandDesc`) to values (i.e. `Invocation`)
/// for a given duration.
// TODO make this a trait so we can swap out impls, such as an in-memory cache or SQLite-backed
#[derive(Clone, Debug)]
struct Cache {
cache_dir: PathBuf,
scope: Option<String>,
}
impl Cache {
fn new<P: AsRef<Path>>(cache_dir: P) -> Self {
Cache{ cache_dir: cache_dir.as_ref().into(), scope: None }
}
fn scoped(mut self, scope: String) -> Self {
assert!(self.scope.is_none());
self.scope = Some(scope);
self
}
#[cfg(not(feature = "debug"))]
fn serialize<W, T>(writer: W, value: &T) -> Result<()>
where W: io::Write, T: Serialize + ?Sized {
Ok(bincode::serialize_into(writer, value)?)
}
#[cfg(feature = "debug")]
fn serialize<W, T>(writer: W, value: &T) -> Result<()>
where W: io::Write, T: Serialize + ?Sized {
Ok(serde_json::to_writer_pretty(writer, value)?)
}
#[cfg(not(feature = "debug"))]
fn deserialize<R, T>(reader: R) -> Result<T>
where R: std::io::Read, T: DeserializeOwned {
Ok(bincode::deserialize_from(reader)?)
}
#[cfg(feature = "debug")]
fn deserialize<R, T>(reader: R) -> Result<T>
where R: std::io::Read, T: DeserializeOwned {
Ok(serde_json::from_reader(reader)?)
}
fn key_dir(&self) -> PathBuf {
self.cache_dir.join("keys")
}
fn key_path(&self, key: &str) -> PathBuf {
let file = match &self.scope {
Some(scope) => format!("{}.{}", general_purpose::STANDARD_NO_PAD.encode(scope), key),
None => key.into(),
};
self.key_dir().join(file)
}
fn data_dir(&self) -> PathBuf {
self.cache_dir.join("data")
}
/// Looks up the given key in the cache, returning the associated value and its age
/// if the data is found and is newer than the max_age.
fn lookup<K, V>(&self, key: &K, max_age: Duration) -> Result<Option<(V, SystemTime)>>
where K: CacheKey+DeserializeOwned, V: DeserializeOwned {
let path = self.key_path(&key.cache_key());
let file = File::open(&path);
if let Err(ref e) = file {
if e.kind() == ErrorKind::NotFound {
debug_msg!("lookup {} not found", path.display());
return Ok(None);
}
}
// Missing file is OK; other errors get propagated to the caller
let reader = BufReader::new(file.context("Failed to access cache file")?);
// TODO consider returning OK(None) if deserialization fails, which could happen if
// different types hashed to the same key
let found: CacheEntry<K, V> = Cache::deserialize(reader)?;
// Discard data that is too old
let mtime = std::fs::metadata(&path)?.modified()?;
let elapsed = mtime.elapsed().unwrap_or(Duration::MAX);
if elapsed > max_age {
debug_msg!("lookup {} expired", path.display());
return match std::fs::remove_file(&path) {
Ok(_) => Ok(None),
Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(None),
Err(e) => Err(e)
}.context("Failed to remove expired data")
}
// Ignore false-positive hits that happened to collide with the hash code
if &found.key != key {
debug_msg!("lookup {} hash collision", path.display());
return Ok(None);
}
debug_msg!("lookup {} found", path.display());
Ok(Some((found.value, mtime)))
}
fn seconds_ceiling(duration: Duration) -> u64 {
duration.as_secs() + if duration.subsec_nanos() != 0 { 1 } else { 0 }
}
// https://rust-lang-nursery.github.io/rust-cookbook/algorithms/randomness.html#create-random-passwords-from-a-set-of-alphanumeric-characters
fn rand_filename(dir: &Path, label: &str) -> PathBuf {
use rand::{thread_rng, Rng};
use rand::distributions::Alphanumeric;
let rand_str: String = thread_rng().sample_iter(Alphanumeric).take(16).map(char::from).collect();
dir.join(format!("{}.{}", label, rand_str))
}
/// Write the given key/value pair to the cache, persisting it for at least the given TTL.
///
/// Note: This method takes references to the key and value because they are serialized
/// externally, therefore consuming either parameter is unhelpful. An in-memory implementation
/// would need to do an internal `.clone()` which is at odds with
/// [`C-CALLER-CONTROL`](https://rust-lang.github.io/api-guidelines/flexibility.html) but Cache
/// is intended for serialization use cases so some overhead in the in-memory case may be
/// acceptable.
// TODO C-INTERMEDIATE suggests emulating HashMap::insert and returning any existing value in
// the cache, though it would be expensive to construct this so perhaps should be a callback
fn store<K, V>(&self, key: &K, value: &V, ttl: Duration) -> Result<()>
where K: CacheKey+Serialize, V: Serialize {
assert!(!ttl.is_zero(), "ttl cannot be zero");
let ttl_dir = self.data_dir().join(Cache::seconds_ceiling(ttl).to_string());
std::fs::create_dir_all(&ttl_dir)?;
std::fs::create_dir_all(self.key_dir())?;
let data_path = Cache::rand_filename(&ttl_dir, "data");
// Note: this will fail if filename collides, could retry in a loop if that happens
let file = OpenOptions::new().create_new(true).write(true).open(&data_path)?;
let entry = CacheEntry{ key, value };
Cache::serialize(BufWriter::new(&file), &entry).context("Serialization failed")?;
debug_msg!("store data {}", data_path.display());
// The target needs to be canonicalized as we're creating the link in a subdirectory, but I'd somewhat prefer
// to fix it to be correctly relative to the link's location. Probably not worth the trouble though.
let data_path = data_path.canonicalize()?;
// Roundabout approach to an atomic symlink replacement
// https://github.com/dimo414/bash-cache/issues/26
let tmp_symlink = Cache::rand_filename(&self.key_dir(), "tmp-symlink");
// Note: this call will fail if the tmp_symlink filename collides, could retry in a loop if that happens.
symlink(data_path, &tmp_symlink)?;
let key_path = self.key_path(&entry.key.cache_key());
debug_msg!("store key {}", key_path.display());
std::fs::rename(&tmp_symlink, key_path)?;
Ok(())
}
fn cleanup(&self) -> Result<()> {
fn delete_stale_file(file: &Path, ttl: Duration) -> Result<()> {
let age = std::fs::metadata(file)?.modified()?.elapsed().unwrap_or(Duration::MAX);
if age > ttl {
std::fs::remove_file(file)?;
}
Ok(())
}
// if try_acquire fails, e.g. because the directory does not exist, there's nothing to clean up
if let Ok(Some(_lock)) = FileLock::try_acquire(&self.cache_dir, "cleanup", Duration::from_secs(60*10)) {
// Don't bother if cleanup has been attempted recently
let last_attempt_file = self.cache_dir.join("last_cleanup");
if let Ok(metadata) = last_attempt_file.metadata() {
if metadata.modified()?.elapsed().unwrap_or(Duration::MAX) < Duration::from_secs(30) {
debug_msg!("cleanup skip recent");
return Ok(());
}
}
File::create(&last_attempt_file)?; // resets mtime if already exists
// First delete stale data files
debug_msg!("cleanup data {}", &self.data_dir().display());
if let Ok(data_dir_iter) = std::fs::read_dir(self.data_dir()) {
for entry in data_dir_iter {
let ttl_dir = entry?.path();
let ttl = Duration::from_secs(
ttl_dir.file_name().and_then(|s| s.to_str()).and_then(|s| s.parse().ok())
.ok_or_else(|| Error::msg(format!("Invalid ttl directory {}", ttl_dir.display())))?);
for entry in std::fs::read_dir(&ttl_dir)? {
let file = entry?.path();
// Disregard errors on individual files; typically due to concurrent deletion
// or other changes we don't care about.
let _ = delete_stale_file(&file, ttl);
}
}
}
// Then delete broken symlinks
debug_msg!("cleanup keys {}", &self.key_dir().display());
if let Ok(key_dir_iter) = std::fs::read_dir(self.key_dir()) {
for entry in key_dir_iter {
let symlink = entry?.path();
// This reads as if we're deleting files that no longer exist, but what it really
// means is "if the symlink is broken, try to delete _the symlink_." It would also
// try to delete a symlink that happened to be deleted concurrently, but this is
// harmless since we ignore the error.
// std::fs::symlink_metadata() could be used to check that the symlink itself exists
// if needed, but this could still have false-positives due to a TOCTOU race.
if !symlink.exists() {
let _ = std::fs::remove_file(symlink);
}
}
}
}
Ok(())
}
}
#[cfg(test)]
mod cache_tests {
use super::*;
use test_dir::{TestDir, DirBuilder};
impl CacheKey for i32 {}
impl CacheKey for String {
fn debug_label(&self) -> Option<String> {
Some(self.clone())
}
}
fn modtime<P: AsRef<Path>>(path: P) -> SystemTime {
std::fs::metadata(&path).expect("No metadata").modified().expect("No modtime")
}
fn make_dir_stale<P: AsRef<Path>>(dir: P, age: Duration) -> Result<()> {
let desired_time = SystemTime::now() - age;
let stale_time = filetime::FileTime::from_system_time(desired_time);
for entry in std::fs::read_dir(dir)? {
let path = entry?.path();
let last_modified = modtime(&path);
if path.is_file() && last_modified > desired_time {
filetime::set_file_mtime(&path, stale_time)?;
} else if path.is_dir() {
make_dir_stale(&path, age)?;
}
}
Ok(())
}
fn dir_contents<P: AsRef<Path>>(dir: P) -> Vec<String> {
fn contents(dir: &Path, ret: &mut Vec<PathBuf>) -> Result<()> {
for entry in std::fs::read_dir(dir)? {
let path = entry?.path();
if path.is_dir() {
contents(&path, ret)?;
} else {
ret.push(path);
}
}
Ok(())
}
let mut paths = vec![];
contents(dir.as_ref(), &mut paths).unwrap();
paths.iter().map(|p| p.strip_prefix(dir.as_ref()).unwrap().display().to_string()).collect()
}
// Sanity-checking that cache_key's behavior is stable over time. This test may need to be
// updated when changing Rust versions / editions.
#[test]
fn stable_hash() {
assert_eq!(100.cache_key(), "7D208C81E8236995");
if cfg!(feature = "debug") {
assert_eq!("FooBar".to_string().cache_key(), "FooBar_2C8878C07E3ADA57");
} else {
assert_eq!("FooBar".to_string().cache_key(), "2C8878C07E3ADA57");
}
}
#[test]
fn cache() {
let dir = TestDir::temp();
let key = "foo".to_string();
let val = "A".to_string();
let cache = Cache::new(dir.root());
let absent = cache.lookup::<_, String>(&key, Duration::from_secs(100)).unwrap();
assert!(absent.is_none());
cache.store(&key, &val, Duration::from_secs(100)).unwrap();
let present = cache.lookup::<_, String>(&key, Duration::from_secs(100)).unwrap();
assert_eq!(present.unwrap().0, val);
}
#[test]
fn lookup_ttls() {
let dir = TestDir::temp();
let key = "foo".to_string();
let val = "A".to_string();
let cache = Cache::new(dir.root());
cache.store(&key, &val, Duration::from_secs(5)).unwrap(); // store duration doesn't affect lookups
make_dir_stale(dir.root(), Duration::from_secs(15)).unwrap();
// data is still present until a cleanup iteration runs, or a lookup() invalidates it
let present = cache.lookup::<_, String>(&key, Duration::from_secs(20)).unwrap();
assert_eq!(present.unwrap().0, "A");
// lookup() finds stale data, deletes it
let absent = cache.lookup::<_, String>(&key, Duration::from_secs(10)).unwrap();
assert!(absent.is_none());
// now data is gone, even though this lookup() would have accepted it
let absent = cache.lookup::<_, String>(&key, Duration::from_secs(20)).unwrap();
assert!(absent.is_none());
}
#[test]
fn scoped() {
let dir = TestDir::temp();
let key = "foo".to_string();
let val_a = "A".to_string();
let val_b = "B".to_string();
let cache = Cache::new(dir.root());
let cache_scoped = Cache::new(dir.root()).scoped("scope".into());
cache.store(&key, &val_a, Duration::from_secs(100)).unwrap();
cache_scoped.store(&key, &val_b, Duration::from_secs(100)).unwrap();
let present = cache.lookup::<_, String>(&key, Duration::from_secs(20)).unwrap();
assert_eq!(present.unwrap().0, val_a);
let present_scoped = cache_scoped.lookup::<_, String>(&key, Duration::from_secs(20)).unwrap();
assert_eq!(present_scoped.unwrap().0, val_b);
}
#[test]
fn scopes_support_special_chars() {
let dir = TestDir::temp();
let key = "foo".to_string();
let val_a = "A".to_string();
let val_b = "B".to_string();
let cache = Cache::new(dir.root());
let cache_scoped = Cache::new(dir.root()).scoped("/scope/with/path/separators".into());
cache.store(&key, &val_a, Duration::from_secs(100)).unwrap();
cache_scoped.store(&key, &val_b, Duration::from_secs(100)).unwrap();
let present = cache.lookup::<_, String>(&key, Duration::from_secs(20)).unwrap();
assert_eq!(present.unwrap().0, val_a);
let present_scoped = cache_scoped.lookup::<_, String>(&key, Duration::from_secs(20)).unwrap();
assert_eq!(present_scoped.unwrap().0, val_b);
}
#[test]
fn cleanup() {
let dir = TestDir::temp();
let key = "foo".to_string();
let val = "A".to_string();
let cache = Cache::new(dir.root());
cache.store(&key, &val, Duration::from_secs(5)).unwrap();
make_dir_stale(dir.root(), Duration::from_secs(10)).unwrap();
cache.cleanup().unwrap();
assert_eq!(dir_contents(dir.root()), ["last_cleanup"]); // keys and data dirs are now empty
let absent = cache.lookup::<_, String>(&key, Duration::from_secs(20)).unwrap();
assert!(absent.is_none());
}
}
/// Holds information about the cache status of a given command.
#[derive(Debug, Copy, Clone)]
pub enum CacheStatus {
/// Command was found in the cache. Contains the time the returned invocation was cached.
Hit(SystemTime),
/// Command was not found in the cache and was executed. Contains the execution time of the
/// subprocess.
Miss(Duration),
}
#[cfg(test)]
impl CacheStatus {
// Note these functions are intentionally not public for now. They're only currently needed to
// make assertions shorter, and should be able to be removed once assert_matches #82775 is
// stable. Can be made public if other use-cases arise.
fn is_hit(&self) -> bool { match self { CacheStatus::Hit(_) => true, CacheStatus::Miss(_) => false, } }
fn is_miss(&self) -> bool { match self { CacheStatus::Hit(_) => false, CacheStatus::Miss(_) => true, } }
}
/// This struct is the main API entry point for the `bkt` library, allowing callers to invoke and
/// cache subprocesses for later reuse.
///
/// Example:
///
/// ```no_run
/// # fn main() -> anyhow::Result<()> {
/// # use std::time::Duration;
/// let bkt = bkt::Bkt::in_tmp()?;