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//! A crate that holds a logging implementation that logs to standard error and //! standard out. It uses standard error for all regular messages and standard //! out for requests. //! //! This crate provides only a logging implementation. To do actual logging use //! the [`log`] crate and it's various macros. //! //! //! # Setting severity //! //! You can use various environment variables to change the severity (log level) //! of the messages to actually log and which to ignore. //! //! `LOG` and `LOG_LEVEL` can be used to set the severity to a specific value, //! see the [`log`]'s package `LevelFilter` type for available values. //! //! ```bash //! # In your shell of choose: //! //! # Set the log severity to only print log message with info severity or //! # higher, trace and debug messages won't be printed anymore. //! $ LOG=info ./my_binary //! //! # Set the log severity to only print log message with warning severity or //! # higher, informational (or lower severity) messages won't be printed //! # anymore. //! $ LOG=warn ./my_binary //! ``` //! //! Alternatively setting the `TRACE` variable (e.g. `TRACE=1`) sets the //! severity to the trace, meaning it will log everything. Setting `DEBUG` will //! set the severity to debug. //! //! ```bash //! # In your shell of choose: //! //! # Enables trace logging. //! $ TRACE=1 ./my_binary //! //! # Enables debug logging. //! $ DEBUG=1 ./my_binary //! ``` //! //! If none of these environment variables are found it will default to an //! information severity. //! //! //! # Logging requests //! //! To log requests a special target is provided: [`REQUEST_TARGET`] and a //! special macro: [`request`]. This will cause the message to be logged to //! standard out, rather then standard error. This allows for separate //! processing of error messages and request logs. //! //! ``` //! use std_logger::request; //! //! # fn main() { //! request!("Got a request!"); //! # } //! ``` //! //! //! # Limiting logging targets //! //! Sometimes it's useful to only log messages related to a specific target, for //! example when debugging a single function you might want only see messages //! from the module the function is in. This can be achieved by using the //! `LOG_TARGET` environment variable. //! //! ```bash //! # In your shell of choose: //! //! # Only log messages from your crate. //! $ LOG_TARGET=my_crate ./my_binary //! //! # Only log messages from the `my_module` module in your crate. //! $ LOG_TARGET=my_crate::my_module ./my_binary //! //! # Multiple log targets are also supported by separating the values by a //! # comma. //! $ LOG_TARGET=my_crate::my_module,my_crate::my_other_module ./my_binary //! //! # Very useful in combination with trace severity to get all messages you //! # want, but filter out the message you don't need. //! $ LOG_LEVEL=trace LOG_TARGET=my_crate::my_module ./my_binary //! ``` //! //! Note that [requests] are always logged. //! //! [requests]: index.html#logging-requests //! //! //! # Format //! //! For regular messages, printed to standard error, the following format is //! used: //! //! ```text //! timestamp [LOG_LEVEL] target: message //! //! For example: //! //! 2018-03-24T13:48:28.820588Z [ERROR] my_module: my error message //! ``` //! //! For requests, logged using the [`REQUEST_TARGET`] target or the [`request`] //! macro and printed to standard out, the following format is used: //! //! ```text //! timestamp [REQUEST]: message //! //! For example: //! //! 2018-03-24T13:30:28.820588Z [REQUEST]: my request message //! ``` //! //! Note: the timestamp is not printed when the *timestamp* feature is not //! enabled, this feature is enabled by default, see [Timestamp feature] below. //! //! //! # Crate features //! //! This crate has two features, both of which are enabled by default, //! *timestamp* and *log-panic*. //! //! //! ## Timestamp feature //! //! The *timestamp* feature adds a timestamp in front of every message. It uses //! the format defined in [`RFC3339`] with 6 digit nanosecond precision, e.g. //! `2018-03-24T13:48:48.063934Z`. This means that the timestamp is **always** //! logged in UTC. //! //! //! ## Log-panic feature //! //! The *log-panic* feature will log all panics using the `error` severity, //! rather then using the default panic handler. It will log the panic message //! as well as the location and a backtrace, see the log output below for an //! example (this example doesn't include a timestamp). //! //! ```log //! [ERROR] panic: thread 'main' panicked at 'oops': examples/panic.rs:24 //! stack backtrace: //! 0: 0x106ba8f74 - backtrace::backtrace::trace<closure> //! at backtrace-0.3.2/src/backtrace/mod.rs:42 //! 1: 0x106ba49af - backtrace::capture::Backtrace::new::h54d7cfa8f40c5b43 //! at backtrace-0.3.2/src/capture.rs:64 //! 2: 0x106b9f4e6 - log_panics::init::{{closure}} //! at log-panics-1.2.0/src/lib.rs:52 //! 3: 0x106bc6951 - std::panicking::rust_panic_with_hook::h6c19f9ba35264287 //! at src/libstd/panicking.rs:612 //! 4: 0x106b93146 - std::panicking::begin_panic<&str> //! at src/libstd/panicking.rs:572 //! 5: 0x106b93bf1 - panic::main //! at examples/panic.rs:24 //! 6: 0x106bc751c - __rust_maybe_catch_panic //! at src/libpanic_unwind/lib.rs:98 //! 7: 0x106bc6c08 - std::rt::lang_start::h6f338c4ae2d58bbe //! at src/libstd/rt.rs:61 //! 8: 0x106b93c29 - main //! ``` //! //! If the *timestamp* feature is enable the first line of the message will be //! prefixed with a timestamp as described in the [Timestamp feature]. //! //! //! # Example //! //! ``` //! # use std::time::Duration; //! # //! use log::info; //! use std_logger::request; //! //! fn main() { //! // First thing we need to do is initialise the logger before anything //! // else. //! std_logger::init(); //! //! // Now we can start logging! //! info!("Our application started!"); //! //! // Do useful stuff, like starting a HTTP server. //! # log_handler(Request { url: "/some_page".to_owned(), status: 200, //! # response_time: Duration::from_millis(100) }); //! } //! //! # struct Request { //! # url: String, //! # status: u16, //! # response_time: Duration, //! # } //! # //! /// This our example request handler, just pretend it gets called with a //! /// request. //! fn log_handler(req: Request) { //! // This will be logged to standard out, rather then standard error. //! request!("url = {}, status = {}, response_time = {:?}", //! req.url, req.status, req.response_time); //! } //! ``` //! //! [`REQUEST_TARGET`]: constant.REQUEST_TARGET.html //! [`log`]: https://crates.io/crates/log //! [`RFC3339`]: https://tools.ietf.org/html/rfc3339 //! [Timestamp feature]: #timestamp-feature #![warn(missing_debug_implementations, missing_docs, unused_results)] use std::cell::RefCell; use std::env; use std::io::{self, Write}; use log::{LevelFilter, Log, Metadata, Record, SetLoggerError}; mod format; #[cfg(test)] mod tests; /// Target for logging requests. /// /// The [`request`] macro provides a convenient way to log requests, it better /// to use that. /// /// See the [crate level documentation] for more. /// /// [crate level documentation]: index.html#logging-requests pub const REQUEST_TARGET: &str = "request"; /// Logs a request. /// /// This uses [info] level severity and the [`REQUEST_TARGET`] target to log a /// request. See the [crate level documentation] for more. /// /// [info]: log::Level::Info /// [crate level documentation]: index.html#logging-requests #[macro_export] macro_rules! request { ($($arg:tt)*) => ( log::log!(target: $crate::REQUEST_TARGET, log::Level::Info, $($arg)*); ) } /// Initialise the logger. /// /// See the [crate level documentation] for more. /// /// [crate level documentation]: index.html /// /// # Panics /// /// This will panic if the logger fails to initialise. Use [`try_init`] if you /// want to handle the error yourself. pub fn init() { try_init().unwrap_or_else(|err| panic!("failed to initialise the logger: {}", err)); } /// Try to initialise the logger. /// /// Unlike [`init`] this doesn't panic when the logger fails to initialise. See /// the [crate level documentation] for more. /// /// [`init`]: fn.init.html /// [crate level documentation]: index.html pub fn try_init() -> Result<(), SetLoggerError> { let filter = get_max_level(); let targets = get_log_targets(); let logger = Logger { filter, targets }; log::set_boxed_logger(Box::new(logger))?; log::set_max_level(filter); #[cfg(feature = "log-panic")] log_panics::init(); Ok(()) } /// Get the maximum log level based on the environment. fn get_max_level() -> LevelFilter { for var in &["LOG", "LOG_LEVEL"] { if let Ok(level) = env::var(var) { if let Ok(level) = level.parse() { return level; } } } if env::var("TRACE").is_ok() { LevelFilter::Trace } else if env::var("DEBUG").is_ok() { LevelFilter::Debug } else { LevelFilter::Info } } /// Get the targets to log, if any. fn get_log_targets() -> Targets { match env::var("LOG_TARGET") { Ok(ref targets) if !targets.is_empty() => { Targets::Only(targets.split(',').map(|target| target.to_owned()).collect()) } _ => Targets::All, } } /// Our `Log` implementation. struct Logger { /// The filter used to determine what messages to log. filter: LevelFilter, /// What logging targets to log. targets: Targets, } #[derive(Debug, Eq, PartialEq)] enum Targets { /// Log all targets. All, /// Only log certain targets. Only(Vec<String>), } impl Targets { /// Returns `true` if the `target` should be logged. fn should_log(&self, target: &str) -> bool { if target == REQUEST_TARGET { // Always log requests. true } else if let Targets::Only(targets) = self { // Log all targets that start with an allowed target. This way we // can just use `LOG_TARGET=my_crate`, rather then // `LOG_TARGET=my_crate::module1,my_crate::module2` etc. targets .iter() .any(|log_target| target.starts_with(log_target)) } else { // All targets should be logged. true } } } impl Log for Logger { fn enabled(&self, metadata: &Metadata) -> bool { self.filter >= metadata.level() && self.targets.should_log(metadata.target()) } fn log(&self, record: &Record) { if self.enabled(record.metadata()) { log(record); } } fn flush(&self) { // Can't handle the errors here and we likely can't log them either // because that also goes through std out/err, so we can't do much here. let _ = stdout().flush(); let _ = stderr().flush(); } } /// The actual logging of a record. fn log(record: &Record) { // Thread local buffer for logging. This way we only lock standard out/error // for a single write call and don't create half written logs. thread_local! { static BUF: RefCell<Vec<u8>> = RefCell::new(Vec::with_capacity(1024)); } BUF.with(|buf| { let mut buf = buf.borrow_mut(); buf.clear(); format::record(&mut buf, record); match record.target() { REQUEST_TARGET => write_once(stdout(), &buf), _ => write_once(stderr(), &buf), } .unwrap_or_else(log_failure); }); } /// Write the entire `buf`fer into the `output` or return an error. #[inline(always)] fn write_once<W>(mut output: W, buf: &[u8]) -> io::Result<()> where W: Write, { output.write(buf).and_then(|written| { if written != buf.len() { // Not completely correct when going by the name alone, but it's the // closest we can get to a descriptive error. Err(io::ErrorKind::WriteZero.into()) } else { Ok(()) } }) } /// The function that gets called when we're unable to print a message. #[inline(never)] #[cold] fn log_failure(err: io::Error) { panic!("unexpected error logging message: {}", err) } // Functions to get standard out/error, which are stubbed in testing. Even // though the return type of the functions are different we only need them both // to implement `io::Write`. #[cfg(test)] use self::test_instruments::{stderr, stdout, LOG_OUTPUT, LOG_OUTPUT_INDEX}; #[cfg(not(test))] use std::io::{stderr, stdout}; // The testing variant of the functions. #[cfg(test)] mod test_instruments { use std::io::{self, Write}; use std::ptr::null_mut; use std::sync::atomic::{AtomicUsize, Ordering}; // TODO: replace `LOG_OUTPUT` with type `[Option<Vec<u8>>; 10]`, once the // `drop_types_in_const` feature is stable, that would make all of this a // bit safer. /// Maximum number of logs we can hold. const LOG_OUTPUT_MAX: usize = 10; /// The output of the log macros, **if this is not null it must point to /// valid memory**. pub static mut LOG_OUTPUT: *mut [Option<Vec<u8>>; LOG_OUTPUT_MAX] = null_mut(); /// Increase to get a position in the `LOG_OUTPUT` array. pub static LOG_OUTPUT_INDEX: AtomicUsize = AtomicUsize::new(0); /// Simple wrapper around a `Vec<u8>` which adds itself to `LOG_OUTPUT` when /// dropped. pub struct LogOutput { /// Must always be something, until it's dropped. inner: Option<Vec<u8>>, } impl Write for LogOutput { fn write(&mut self, buf: &[u8]) -> io::Result<usize> { self.inner.as_mut().unwrap().write(buf) } fn flush(&mut self) -> io::Result<()> { self.inner.as_mut().unwrap().flush() } } impl Drop for LogOutput { fn drop(&mut self) { let output = self.inner.take().unwrap(); let index = LOG_OUTPUT_INDEX.fetch_add(1, Ordering::SeqCst); if index >= LOG_OUTPUT_MAX { panic!("too many logs written, increase the size of `LOG_OUTPUT`"); } unsafe { if let Some(log_output) = LOG_OUTPUT.as_mut() { log_output[index] = Some(output); } else { panic!("LOG_OUTPUT is not set, this is required in testing"); } } } } #[inline(always)] pub fn stdout() -> LogOutput { LogOutput { inner: Some(Vec::new()), } } #[inline(always)] pub fn stderr() -> LogOutput { LogOutput { inner: Some(Vec::new()), } } }