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#![doc(html_root_url = "https://docs.rs/reopen/0.2.0/reopen/")] #![warn(missing_docs)] //! A tiny `Read`/`Write` wrapper that can reopen the underlying IO object. //! //! The main motivation is integration of logging with logrotate. Usually, when //! logrotate wants to rotate log files, it moves the current log file to a new //! place and creates a new empty file. However, for the new messages to appear in //! the new file, a running program needs to close and reopen the file. This is //! most often signalled by SIGHUP. //! //! # Examples //! //! This allows reopening the IO object used inside the logging drain at runtime. //! //! ```rust //! extern crate libc; //! #[macro_use] //! extern crate log; //! extern crate reopen; //! extern crate simple_logging; //! //! use std::fs::{File, OpenOptions}; //! use std::io::Error; //! //! use reopen::Reopen; //! //! fn open() -> Result<File, Error> { //! OpenOptions::new() //! .create(true) //! .write(true) //! .append(true) //! .open("/dev/null") //! } //! //! fn main() -> Result<(), Error> { //! let file = Reopen::new(Box::new(&open))?; //! // Must be called before any threads are started //! unsafe { file.handle().register_signal(libc::SIGHUP).unwrap() }; //! simple_logging::log_to(file, log::LevelFilter::Debug); //! info!("Hey, it's logging"); //! Ok(()) //! } //! ``` //! //! Note that this solution is a bit hacky and probably solves only the most common use case. //! //! If you find another use case for it, I'd like to hear about it. extern crate libc; use std::io::{Error, Read, Write}; #[cfg(unix)] use std::mem; #[cfg(unix)] use std::ptr; use std::sync::atomic::{AtomicBool, Ordering}; use std::sync::Arc; /// A handle to signal a companion [`Reopen`](struct.Reopen.html) object to do a reopen on its next /// operation. #[derive(Clone, Debug)] pub struct Handle(Arc<AtomicBool>); static mut GLOBAL_HANDLE: Option<Handle> = None; #[cfg(unix)] extern "C" fn handler(_: libc::c_int, _: *mut libc::siginfo_t, _: *mut libc::c_void) { let handle = unsafe { GLOBAL_HANDLE.as_ref().unwrap().clone() }; handle.reopen(); } impl Handle { /// Signals the companion [`Reopen`](struct.Reopen.html) object to do a reopen on its next /// operation. pub fn reopen(&self) { self.0.store(true, Ordering::Relaxed); } /// Creates a useless handle, not paired to anything. /// /// Note that this useless handle can be added to a new [`Reopen`](struct.Reopen.html) with the /// [`with_handle`](struct.Reopen.html#method.with_handle) and becomes useful. pub fn stub() -> Self { Handle(Arc::new(AtomicBool::new(true))) } #[cfg(unix)] /// Installs a signal handler to invoke the reopening when a certain signal comes. /// /// # Notes /// /// * This *replaces* any other signal with the given signal number. It's not really possible /// to reopen multiple things with a single signal in this simple way. If you need that, call /// `reopen` manually. /// * There's only one global handle, so no matter how many signals you want to use, it still /// won't handle multiple reopen instances. If you need that, you can either handle signals /// yourself or open a pull request (I'm not against doing it properly, I just didn't need it /// yet). /// * And yes, this function is an ugly hack. /// * This may be called only before you start any additional threads ‒ best way to place it at /// the start of the `main` function. If any threads are running and accessing the reopen /// object (eg. logging), it invokes undefined behaviour. pub unsafe fn register_signal(&self, signal: libc::c_int) -> Result<(), Error> { let mut new: libc::sigaction = mem::zeroed(); new.sa_sigaction = handler as usize; #[cfg(target_os = "android")] fn flags() -> libc::c_ulong { (libc::SA_RESTART as libc::c_ulong) | libc::SA_SIGINFO | (libc::SA_NOCLDSTOP as libc::c_ulong) } #[cfg(not(target_os = "android"))] fn flags() -> libc::c_int { libc::SA_RESTART | libc::SA_SIGINFO | libc::SA_NOCLDSTOP } new.sa_flags = flags(); // Insert it first, so it is ready once we install the signal handler let mut original = Some(self.clone()); mem::swap(&mut original, &mut GLOBAL_HANDLE); if libc::sigaction(signal, &new, ptr::null_mut()) == 0 { Ok(()) } else { // Return it back to the original if the signal handler failed, whatever it was. That // is not very useful likely, but probably more expected. mem::swap(&mut original, &mut GLOBAL_HANDLE); Err(Error::last_os_error()) } } } /// A `Read`/`Write` proxy that can reopen the underlying object. /// /// It is constructed with a function that can open a new instance of the object. If it is signaled /// to reopen it (though [`handle`](#method.handle)), it drops the old instance and uses the /// function to create a new one at the next IO operation. /// /// # Error handling /// /// The reopening is performed lazily, on the first operation done to the object. Opening a new /// instance can fail with an error. If this happens, the error is returned as part of the /// operation being performed ‒ therefore, you can get an error like `File not found` while /// performing `read`. /// /// If an error happens, the operation is aborted. Next time an operation is performed, another /// attempt to open the object is made (which in turn can fail again). pub struct Reopen<FD> { signal: Arc<AtomicBool>, constructor: Box<Fn() -> Result<FD, Error> + Send>, fd: Option<FD>, } impl<FD> Reopen<FD> { /// Creates a new instance. pub fn new(constructor: Box<Fn() -> Result<FD, Error> + Send>) -> Result<Self, Error> { Self::with_handle(Handle::stub(), constructor) } /// Creates a new instance from the given handle. /// /// This might come useful if you want to create the handle beforehand with /// [`Handle::stub`](struct.Handle.html#method.stub) (eg. in /// [`lazy_static`](https://docs.rs/lazy_static)). /// Note that using the same handle for multiple `Reopen`s will not work as expected (the first /// one to be used resets the signal and the others don't reopen). /// /// # Examples /// /// ``` /// # use reopen::*; /// // Something that implements `Write`, for example. /// struct Writer; /// /// let handle = Handle::stub(); /// let reopen = Reopen::with_handle(handle.clone(), Box::new(|| Ok(Writer))); /// /// handle.reopen(); /// ``` pub fn with_handle( handle: Handle, constructor: Box<Fn() -> Result<FD, Error> + Send>, ) -> Result<Self, Error> { let fd = constructor()?; Ok(Self { signal: handle.0, constructor, fd: Some(fd), }) } /// Returns a handle to signal this `Reopen` to perform the reopening. pub fn handle(&self) -> Handle { Handle(Arc::clone(&self.signal)) } fn check(&mut self) -> Result<&mut FD, Error> { if self.signal.swap(false, Ordering::Relaxed) { self.fd.take(); } if self.fd.is_none() { self.fd = Some((self.constructor)()?); } Ok(self.fd.as_mut().unwrap()) } } impl<FD: Read> Read for Reopen<FD> { fn read(&mut self, buf: &mut [u8]) -> Result<usize, Error> { self.check().and_then(|fd| fd.read(buf)) } } impl<FD: Write> Write for Reopen<FD> { fn write(&mut self, buf: &[u8]) -> Result<usize, Error> { self.check().and_then(|fd| fd.write(buf)) } fn flush(&mut self) -> Result<(), Error> { self.check().and_then(Write::flush) } }