1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314
//! A [`log::Log`] implementation which dynamically reloads inner loggers.
//!
//! [`ReloadLog`] wraps an inner logger and provides a [`ReloadHandle`] to
//! dynamically replace or modify the inner logger.
//!
//! This allows programs to dynamically change the log level or log target at
//! runtime.
#![deny(warnings, clippy::all, missing_docs)]
#![forbid(unsafe_code)]
use std::sync::{Arc, RwLock, Weak};
use log::Log;
use thiserror::Error;
/// Filter an underlying logger by a given max level.
///
/// Only forward log events whose log level is smaller or equal than the
/// configured level to the underlying logger.
#[derive(Debug)]
pub struct LevelFilter<T> {
level: log::Level,
logger: T,
}
impl<T> LevelFilter<T> {
/// Create a new level filter with the given max `level` around the given `logger`.
pub fn new(level: log::Level, logger: T) -> Self {
Self { level, logger }
}
/// Get the current log level.
pub fn level(&self) -> log::Level {
self.level
}
/// Change the maximum log level.
pub fn set_level(&mut self, level: log::Level) {
self.level = level;
}
fn level_passes(&self, metadata: &log::Metadata) -> bool {
metadata.level() <= self.level
}
/// Get a reference to the inner unfiltered logger.
pub fn inner(&self) -> &T {
&self.logger
}
/// Replace the inner logger.
pub fn set_inner(&mut self, logger: T) {
self.logger = logger;
}
}
impl<T: Log> log::Log for LevelFilter<T> {
/// Wether this logger is enabled.
///
/// Return `true` if the log level in `metadata` is less then the level of
/// the given `metadata`, and the underlying logger is enabled.
fn enabled(&self, metadata: &log::Metadata) -> bool {
self.level_passes(metadata) && self.logger.enabled(metadata)
}
/// Forward a log `record` to the underlying logger if it passes the level filter.
fn log(&self, record: &log::Record) {
if self.level_passes(record.metadata()) {
self.logger.log(record)
}
}
/// Flush the underlying logger.
fn flush(&self) {
self.logger.flush();
}
}
/// A logger which can dynamically reload an inner logger.
///
/// This enables applications to dyanmically change e.g. the log output or
/// log level.
#[derive(Debug)]
pub struct ReloadLog<T> {
underlying: Arc<RwLock<T>>,
}
impl<T> ReloadLog<T> {
/// Create a new reloadable logger over the given `logger`.
pub fn new(logger: T) -> Self {
Self {
underlying: Arc::new(RwLock::new(logger)),
}
}
/// Obtain a handle to reload or modify the inner logger.
pub fn handle(&self) -> ReloadHandle<T> {
ReloadHandle {
underlying: Arc::downgrade(&self.underlying),
}
}
}
impl<T: Log> Log for ReloadLog<T> {
/// Whether the underlying logger is enabled.
///
/// Always return `false` if the [`RwLock`] protecting the inner logger is poisoned,
/// because we can't trust that the inner logger is valid if a panic occurred
/// while it was modified, so we indicate that this logger shouldn't be used at all.
fn enabled(&self, metadata: &log::Metadata) -> bool {
self.underlying
.read()
.map_or(false, |l| l.enabled(metadata))
}
/// Log the given `record` with the inner logger.
///
/// If the [`RwLock`] protecting the inner logger is poisoned do nothing,
/// because we can't trust that the inner logger is valid if a panic occurred
/// while it was modified. The `record` is likely lost in this case.
fn log(&self, record: &log::Record) {
// We can't reasonably do anything if the lock is poisoned so we ignore the result
let _ = self.underlying.read().map(|l| l.log(record));
}
/// Flush the inner logger
///
/// If the [`RwLock`] protecting the inner logger is poisoned do nothing,
/// because we can't trust that the inner logger is valid if a panic occurred
/// while it was modified.
fn flush(&self) {
// We can't reasonably do anything if the lock is poisoned so we ignore the result
let _ = self.underlying.read().map(|l| l.flush());
}
}
/// An error which occurred while reloading the logger.
#[derive(Debug, Clone, Copy, Error)]
pub enum ReloadError {
/// The logger referenced by the reload handle was dropped meanwhile.
#[error("Referenced logger was dropped")]
Gone,
/// The lock protecting the inner logger referenced by the reload is poisoned.
///
/// Note that this is an error because we currently can't recover from a
/// poisoned [`RwLock`] in stable rust, as [`RwLock::clear_poison`] is still
/// experimental.
///
/// Once this method stabilizes reloading can simply overwrite any poisoned
/// data and clear the poison flag to resume logging. At this point this
/// error condition will be removed.
///
/// See <https://github.com/rust-lang/rust/issues/96469> for stabilization of
/// [`RwLock::clear_poison`].
#[error("Lock poisoned")]
Poisoned,
}
/// A handle to reload a logger inside a [`ReloadLog`].
#[derive(Debug, Clone)]
pub struct ReloadHandle<T> {
underlying: Weak<RwLock<T>>,
}
impl<T> ReloadHandle<T> {
/// Replace the inner logger.
///
/// This replaces the inner logger of the referenced [`ReloadLog`] with the given `logger`.
pub fn replace(&self, logger: T) -> Result<(), ReloadError> {
let lock = self.underlying.upgrade().ok_or(ReloadError::Gone)?;
// TODO: Overwrite and clear poison, once clear_poison() is stabilized
// See https://github.com/rust-lang/rust/issues/96469
let mut guard = lock.write().map_err(|_| ReloadError::Poisoned)?;
*guard = logger;
Ok(())
}
/// Modify the inner logger.
///
/// Call the given function with a mutable reference to the logger. Note that
/// a lock is held while invoking `f`, so no log messages will be processed
/// until `f` returns.
///
/// If `f` panics this lock gets poisoned which effectively disables the logger.
pub fn modify<F>(&self, f: F) -> Result<(), ReloadError>
where
F: FnOnce(&mut T),
{
let lock = self.underlying.upgrade().ok_or(ReloadError::Gone)?;
// TODO: Overwrite and clear poison, once clear_poison() is stabilized
// See https://github.com/rust-lang/rust/issues/96469
let mut guard = lock.write().map_err(|_| ReloadError::Poisoned)?;
f(&mut *guard);
Ok(())
}
}
#[cfg(test)]
mod tests {
use crate::{LevelFilter, ReloadLog};
use log::{Log, Record};
use similar_asserts::assert_eq;
use std::sync::{Arc, Mutex};
struct CollectMessages {
messages: Mutex<Vec<String>>,
}
impl CollectMessages {
fn new() -> Self {
Self {
messages: Mutex::new(Vec::new()),
}
}
}
impl Log for CollectMessages {
fn enabled(&self, _metadata: &log::Metadata) -> bool {
true
}
fn log(&self, record: &log::Record) {
let mut guard = self.messages.try_lock().unwrap();
guard.push(format!("{}", record.args()));
}
fn flush(&self) {}
}
#[test]
fn sanity_check_log_level_ordering() {
use log::Level;
assert!(Level::Error <= Level::Warn);
assert!(Level::Warn <= Level::Warn);
assert!(Level::Debug >= Level::Warn);
}
#[test]
fn level_filter() {
let collect_logs = Arc::new(CollectMessages::new());
let mut filter = LevelFilter::new(log::Level::Warn, collect_logs.clone());
for level in log::Level::iter() {
filter.log(
&Record::builder()
.level(level)
.args(format_args!("{level}"))
.build(),
);
}
let mut messages = collect_logs.messages.try_lock().unwrap();
assert_eq!(*messages, vec!["ERROR", "WARN"]);
messages.clear();
drop(messages);
filter.set_level(log::Level::Debug);
for level in log::Level::iter() {
filter.log(
&Record::builder()
.level(level)
.args(format_args!("{level}"))
.build(),
);
}
let messages = collect_logs.messages.try_lock().unwrap();
assert_eq!(*messages, &["ERROR", "WARN", "INFO", "DEBUG"]);
}
#[test]
fn reloadlog_replace() {
let collect_logs_1 = Arc::new(CollectMessages::new());
let collect_logs_2 = Arc::new(CollectMessages::new());
let reload_log = ReloadLog::new(collect_logs_1.clone());
let reload_handle = reload_log.handle();
reload_log.log(&Record::builder().args(format_args!("Message 1")).build());
reload_handle.replace(collect_logs_2.clone()).unwrap();
reload_log.log(&Record::builder().args(format_args!("Message 2")).build());
let messages_1 = collect_logs_1.messages.try_lock().unwrap();
let messages_2 = collect_logs_2.messages.try_lock().unwrap();
assert_eq!(*messages_1, &["Message 1"]);
assert_eq!(*messages_2, &["Message 2"]);
}
#[test]
fn reloadlog_modify() {
let collect_logs = Arc::new(CollectMessages::new());
let reload_log = ReloadLog::new(collect_logs.clone());
let reload_handle = reload_log.handle();
reload_log.log(&Record::builder().args(format_args!("Message 1")).build());
let messages = collect_logs.messages.try_lock().unwrap();
assert_eq!(*messages, &["Message 1"]);
drop(messages);
// Clear the message store through the reload handle.
reload_handle
.modify(|l| l.messages.try_lock().unwrap().clear())
.unwrap();
// At this point the first message doesn't appear anymore.
reload_log.log(&Record::builder().args(format_args!("Message 2")).build());
let messages = collect_logs.messages.try_lock().unwrap();
assert_eq!(*messages, &["Message 2"]);
}
}