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//! Code to watch configuration files for any changes.
use std::collections::HashSet;
use std::path::{Path, PathBuf};
use std::sync::mpsc::{channel as std_channel, Sender};
use std::sync::Weak;
use std::time::Duration;
use anyhow::Context;
use arti_client::config::Reconfigure;
use arti_client::TorClient;
use notify::Watcher;
use tor_config::{sources::FoundConfigFiles, ConfigurationSource, ConfigurationSources};
use tor_rtcompat::Runtime;
use tracing::{debug, error, info, warn};
use crate::{ArtiCombinedConfig, ArtiConfig};
/// How long to wait after an event got received, before we try to process it.
const DEBOUNCE_INTERVAL: Duration = Duration::from_secs(1);
/// Event possibly triggering a configuration reload
#[derive(Debug)]
enum Event {
/// SIGHUP has been received.
#[cfg(target_family = "unix")]
SigHup,
/// Some files may have been modified.
FileChanged,
/// Some filesystem events may have been missed.
Rescan,
}
/// An object that can be reconfigured when our configuration changes.
///
/// We use this trait so that we can represent abstract modules in our
/// application, and pass the configuration to each of them.
//
// TODO: It is very likely we will want to refactor this even further once we
// have a notion of what our modules truly are.
#[cfg_attr(feature = "experimental-api", visibility::make(pub))]
pub(crate) trait ReconfigurableModule: Send + Sync {
/// Try to reconfigure this module according to a newly loaded configuration.
///
/// By convention, this should only return fatal errors; any such error
/// should cause the program to exit. For other cases, we should just warn.
//
// TODO: This should probably take "how: Reconfigure" as an argument, and
// pass it down as appropriate. See issue #1156.
fn reconfigure(&self, new: &ArtiCombinedConfig) -> anyhow::Result<()>;
}
/// Launch a thread to reload our configuration files.
///
/// If current configuration requires it, watch for changes in `sources`
/// and try to reload our configuration. On unix platforms, also watch
/// for SIGHUP and reload configuration then.
///
/// The modules are `Weak` references to prevent this background task
/// from keeping them alive.
#[cfg_attr(feature = "experimental-api", visibility::make(pub))]
pub(crate) fn watch_for_config_changes<R: Runtime>(
#[cfg_attr(not(target_family = "unix"), allow(unused_variables))]
runtime: &R,
sources: ConfigurationSources,
config: &ArtiConfig,
modules: Vec<Weak<dyn ReconfigurableModule>>,
) -> anyhow::Result<()> {
let watch_file = config.application().watch_configuration;
let (tx, rx) = std_channel();
let mut watcher = if watch_file {
// If watching, we must reload the config once right away, because
// we have set up the watcher *after* loading the config.
// ignore send error, rx can't be disconnected if we are here
let _ = tx.send(Event::Rescan);
let mut watcher = FileWatcher::builder();
watcher.prepare(&sources)?;
Some(watcher.start_watching(tx.clone())?)
} else {
None
};
#[cfg(target_family = "unix")]
{
use futures::task::SpawnExt;
use futures::StreamExt;
use crate::process::sighup_stream;
let mut sighup_stream = sighup_stream()?;
let tx = tx.clone();
runtime.spawn(async move {
while let Some(()) = sighup_stream.next().await {
info!("Received SIGHUP");
if tx.send(Event::SigHup).is_err() {
warn!("Failed to reload configuration");
break;
}
}
})?;
}
#[allow(clippy::cognitive_complexity)]
std::thread::spawn(move || {
// TODO: If someday we make this facility available outside of the
// `arti` application, we probably don't want to have this thread own
// the FileWatcher.
debug!("Entering FS event loop");
let mut iife = || -> Result<(), anyhow::Error> {
while let Ok(event) = rx.recv() {
// we are in a dedicated thread, it's safe to thread::sleep.
std::thread::sleep(DEBOUNCE_INTERVAL);
while let Ok(_ignore) = rx.try_recv() {
// Discard other events, so that we only reload once.
//
// We can afford to treat both error cases from try_recv [Empty
// and Disconnected] as meaning that we've discarded other
// events: if we're disconnected, we'll notice it when we next
// call recv() in the outer loop.
}
debug!("Config reload event {:?}: reloading configuration.", event);
let found_files = if watcher.is_some() {
let mut new_watcher = FileWatcher::builder();
let found_files = new_watcher
.prepare(&sources)
.context("FS watch: failed to rescan config and re-establish watch")?;
let new_watcher = new_watcher
.start_watching(tx.clone())
.context("FS watch: failed to rescan config and re-establish watch")?;
watcher = Some(new_watcher);
found_files
} else {
sources
.scan()
.context("FS watch: failed to rescan config")?
};
match reconfigure(found_files, &modules) {
Ok(watch) => {
info!("Successfully reloaded configuration.");
if watch && watcher.is_none() {
info!("Starting watching over configuration.");
// If watching, we must reload the config once right away, because
// we have set up the watcher *after* loading the config.
// ignore send error, rx can't be disconnected if we are here
let _ = tx.send(Event::Rescan);
let mut new_watcher = FileWatcher::builder();
let _found_files = new_watcher.prepare(&sources).context(
"FS watch: failed to rescan config and re-establish watch: {}",
)?;
let new_watcher = new_watcher.start_watching(tx.clone()).context(
"FS watch: failed to rescan config and re-establish watch: {}",
)?;
watcher = Some(new_watcher);
} else if !watch && watcher.is_some() {
info!("Stopped watching over configuration.");
watcher = None;
}
}
// TODO: warn_report does not work on anyhow::Error.
Err(e) => warn!("Couldn't reload configuration: {}", tor_error::Report(e)),
}
}
Ok(())
};
match iife() {
Ok(()) => debug!("Thread exiting"),
// TODO: warn_report does not work on anyhow::Error.
Err(e) => error!("Config reload thread exiting: {}", tor_error::Report(e)),
}
});
// Dropping the thread handle here means that we don't get any special
// notification about a panic. TODO: We should change that at some point in
// the future.
Ok(())
}
impl<R: Runtime> ReconfigurableModule for TorClient<R> {
fn reconfigure(&self, new: &ArtiCombinedConfig) -> anyhow::Result<()> {
TorClient::reconfigure(self, &new.1, Reconfigure::WarnOnFailures)?;
Ok(())
}
}
/// Internal type to represent the Arti application as a `ReconfigurableModule`.
pub(crate) struct Application {
/// The configuration that Arti had at startup.
///
/// We use this to check whether the user is asking for any impermissible
/// transitions.
original_config: ArtiConfig,
}
impl Application {
/// Construct a new `Application` to receive configuration changes for the
/// arti application.
pub(crate) fn new(cfg: ArtiConfig) -> Self {
Self {
original_config: cfg,
}
}
}
impl ReconfigurableModule for Application {
// TODO: This should probably take "how: Reconfigure" as an argument, and
// pass it down as appropriate. See issue #1156.
#[allow(clippy::cognitive_complexity)]
fn reconfigure(&self, new: &ArtiCombinedConfig) -> anyhow::Result<()> {
let original = &self.original_config;
let config = &new.0;
if config.proxy() != original.proxy() {
warn!("Can't (yet) reconfigure proxy settings while arti is running.");
}
if config.logging() != original.logging() {
warn!("Can't (yet) reconfigure logging settings while arti is running.");
}
if config.application().permit_debugging && !original.application().permit_debugging {
warn!("Cannot disable application hardening when it has already been enabled.");
}
// Note that this is the only config transition we actually perform so far.
if !config.application().permit_debugging {
#[cfg(feature = "harden")]
crate::process::enable_process_hardening()?;
}
Ok(())
}
}
/// Reload the configuration files, apply the runtime configuration, and
/// reconfigure the client as much as we can.
///
/// Return true if we should be watching for configuration changes.
//
// TODO: This should probably take "how: Reconfigure" as an argument, and
// pass it down as appropriate. See issue #1156.
fn reconfigure(
found_files: FoundConfigFiles<'_>,
reconfigurable: &[Weak<dyn ReconfigurableModule>],
) -> anyhow::Result<bool> {
let _ = reconfigurable;
let config = found_files.load()?;
let config = tor_config::resolve::<ArtiCombinedConfig>(config)?;
// Filter out the modules that have been dropped
let reconfigurable = reconfigurable.iter().flat_map(Weak::upgrade);
// If there are no more modules, we should exit.
let mut has_modules = false;
for module in reconfigurable {
has_modules = true;
module.reconfigure(&config)?;
}
Ok(has_modules && config.0.application().watch_configuration)
}
/// A wrapper around `notify::RecommendedWatcher` to watch a set of parent
/// directories in order to learn about changes in some specific files that they
/// contain.
///
/// The wrapper contains the `Watcher` and also the channel for receiving events.
///
/// The `Watcher` implementation in `notify` has a weakness: it gives sensible
/// results when you're watching directories, but if you start watching
/// non-directory files, it won't notice when those files get replaced. That's
/// a problem for users who want to change their configuration atomically by
/// making new files and then moving them into place over the old ones.
///
/// For more background on the issues with `notify`, see
/// <https://github.com/notify-rs/notify/issues/165> and
/// <https://github.com/notify-rs/notify/pull/166>.
///
/// TODO: Someday we might want to make this code exported someplace. If we do,
/// we should test it, and improve its API a lot. Right now, the caller needs
/// to mess around with `std::sync::mpsc` and filter out the events they want
/// using `FileWatcher::event_matched`.
struct FileWatcher {
/// An underlying `notify` watcher that tells us about directory changes.
// this field is kept only so the watcher is not dropped
_watcher: notify::RecommendedWatcher,
}
impl FileWatcher {
/// Create a `FileWatcherBuilder`
fn builder() -> FileWatcherBuilder {
FileWatcherBuilder::new()
}
}
/// Builder used to configure a [`FileWatcher`] before it starts watching for changes.
struct FileWatcherBuilder {
/// The list of directories that we're currently watching.
watching_dirs: HashSet<PathBuf>,
/// The list of files we actually care about.
watching_files: HashSet<PathBuf>,
}
impl FileWatcherBuilder {
/// Create a `FileWatcherBuilder`
fn new() -> Self {
FileWatcherBuilder {
watching_dirs: HashSet::new(),
watching_files: HashSet::new(),
}
}
/// Find the configuration files and prepare the watcher
fn prepare<'a>(
&mut self,
sources: &'a ConfigurationSources,
) -> anyhow::Result<FoundConfigFiles<'a>> {
let sources = sources.scan()?;
for source in sources.iter() {
match source {
ConfigurationSource::Dir(dir) => self.watch_dir(dir)?,
ConfigurationSource::File(file) => self.watch_file(file)?,
ConfigurationSource::Verbatim(_) => {}
}
}
Ok(sources)
}
/// Add a single file (not a directory) to the list of things to watch.
///
/// Idempotent: does nothing if we're already watching that file.
fn watch_file<P: AsRef<Path>>(&mut self, path: P) -> anyhow::Result<()> {
self.watch_just_parents(path.as_ref())?;
Ok(())
}
/// Add a directory (but not any subdirs) to the list of things to watch.
///
/// Idempotent.
fn watch_dir<P: AsRef<Path>>(&mut self, path: P) -> anyhow::Result<()> {
let path = self.watch_just_parents(path.as_ref())?;
self.watch_just_abs_dir(&path);
Ok(())
}
/// Add the parents of `path` to the list of things to watch.
///
/// Returns the absolute path of `path`.
///
/// Idempotent.
fn watch_just_parents(&mut self, path: &Path) -> anyhow::Result<PathBuf> {
// Make the path absolute (without necessarily making it canonical).
//
// We do this because `notify` reports all of its events in terms of
// absolute paths, so if we were to tell it to watch a directory by its
// relative path, we'd get reports about the absolute paths of the files
// in that directory.
let cwd = std::env::current_dir()?;
let path = cwd.join(path);
debug_assert!(path.is_absolute());
// See what directory we should watch in order to watch this file.
let watch_target = match path.parent() {
// The file has a parent, so watch that.
Some(parent) => parent,
// The file has no parent. Given that it's absolute, that means
// that we're looking at the root directory. There's nowhere to go
// "up" from there.
None => path.as_ref(),
};
self.watch_just_abs_dir(watch_target);
// Note this file as one that we're watching, so that we can see changes
// to it later on.
self.watching_files.insert(path.clone());
Ok(path)
}
/// Add just this (absolute) directory to the list of things to watch.
///
/// Does not watch any of the parents.
///
/// Idempotent.
fn watch_just_abs_dir(&mut self, watch_target: &Path) {
self.watching_dirs.insert(watch_target.into());
}
/// Build a `FileWatcher` and start sending events to `tx`.
///
/// For the watching to be reliably effective (race-free), the config must be read
/// *after* this point, using the `FoundConfigFiles` returned by `prepare`.
fn start_watching(self, tx: Sender<Event>) -> anyhow::Result<FileWatcher> {
let event_sender = move |event: notify::Result<notify::Event>| {
let watching = |f| self.watching_files.contains(f);
// filter events we don't want and map to event code
let event = match event {
Ok(event) => {
if event.need_rescan() {
Some(Event::Rescan)
} else if event.paths.iter().any(watching) {
Some(Event::FileChanged)
} else {
None
}
}
Err(error) => {
if error.paths.iter().any(watching) {
Some(Event::FileChanged)
} else {
None
}
}
};
if let Some(event) = event {
let _ = tx.send(event);
};
};
let mut watcher = notify::RecommendedWatcher::new(event_sender, notify::Config::default())?;
for dir in self.watching_dirs {
watcher.watch(&dir, notify::RecursiveMode::NonRecursive)?;
}
Ok(FileWatcher { _watcher: watcher })
}
}