Merge #817

817: Implement nix wrapper for libc::signal r=asomers a=rgardner

This implements `nix::sys::signal::signal` and adds corresponding documentation and tests.

Closes #476

Co-authored-by: Robert Gardner <[email protected]>

Author: bors[bot]

CHANGELOG.md

@@ -15,6 +15,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#997](https://github.com/nix-rust/nix/pull/997))
 - Added `ptrace::{getregs, setregs}`.
   ([#1010](https://github.com/nix-rust/nix/pull/1010))
+- Added `nix::sys::signal::signal`.
+  ([#817](https://github.com/nix-rust/nix/pull/817))
 
 ### Changed
 ### Fixed

src/errno.rs

@@ -107,6 +107,10 @@ impl ErrnoSentinel for *mut c_void {
     fn sentinel() -> Self { (-1 as isize) as *mut c_void }
 }
 
+impl ErrnoSentinel for libc::sighandler_t {
+    fn sentinel() -> Self { libc::SIG_ERR }
+}
+
 impl error::Error for Errno {
     fn description(&self) -> &str {
         self.desc()

src/sys/signal.rs

@@ -542,6 +542,79 @@ pub unsafe fn sigaction(signal: Signal, sigaction: &SigAction) -> Result<SigActi
     Errno::result(res).map(|_| SigAction { sigaction: oldact })
 }
 
+/// Signal management (see [signal(3p)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/signal.html))
+///
+/// Installs `handler` for the given `signal`, returning the previous signal
+/// handler. `signal` should only be used following another call to `signal` or
+/// if the current handler is the default. The return value of `signal` is
+/// undefined after setting the handler with [`sigaction`][SigActionFn].
+///
+/// # Safety
+///
+/// If the pointer to the previous signal handler is invalid, undefined
+/// behavior could be invoked when casting it back to a [`SigAction`][SigActionStruct].
+///
+/// # Examples
+///
+/// Ignore `SIGINT`:
+///
+/// ```no_run
+/// # use nix::sys::signal::{self, Signal, SigHandler};
+/// unsafe { signal::signal(Signal::SIGINT, SigHandler::SigIgn) }.unwrap();
+/// ```
+///
+/// Use a signal handler to set a flag variable:
+///
+/// ```no_run
+/// # #[macro_use] extern crate lazy_static;
+/// # extern crate libc;
+/// # extern crate nix;
+/// # use std::sync::atomic::{AtomicBool, Ordering};
+/// # use nix::sys::signal::{self, Signal, SigHandler};
+/// lazy_static! {
+///    static ref SIGNALED: AtomicBool = AtomicBool::new(false);
+/// }
+///
+/// extern fn handle_sigint(signal: libc::c_int) {
+///     let signal = Signal::from_c_int(signal).unwrap();
+///     SIGNALED.store(signal == Signal::SIGINT, Ordering::Relaxed);
+/// }
+///
+/// fn main() {
+///     let handler = SigHandler::Handler(handle_sigint);
+///     unsafe { signal::signal(Signal::SIGINT, handler) }.unwrap();
+/// }
+/// ```
+///
+/// # Errors
+///
+/// Returns [`Error::UnsupportedOperation`] if `handler` is
+/// [`SigAction`][SigActionStruct]. Use [`sigaction`][SigActionFn] instead.
+///
+/// `signal` also returns any error from `libc::signal`, such as when an attempt
+/// is made to catch a signal that cannot be caught or to ignore a signal that
+/// cannot be ignored.
+///
+/// [`Error::UnsupportedOperation`]: ../../enum.Error.html#variant.UnsupportedOperation
+/// [SigActionStruct]: struct.SigAction.html
+/// [sigactionFn]: fn.sigaction.html
+pub unsafe fn signal(signal: Signal, handler: SigHandler) -> Result<SigHandler> {
+    let signal = signal as libc::c_int;
+    let res = match handler {
+        SigHandler::SigDfl => libc::signal(signal, libc::SIG_DFL),
+        SigHandler::SigIgn => libc::signal(signal, libc::SIG_IGN),
+        SigHandler::Handler(handler) => libc::signal(signal, handler as libc::sighandler_t),
+        SigHandler::SigAction(_) => return Err(Error::UnsupportedOperation),
+    };
+    Errno::result(res).map(|oldhandler| {
+        match oldhandler {
+            libc::SIG_DFL => SigHandler::SigDfl,
+            libc::SIG_IGN => SigHandler::SigIgn,
+            f => SigHandler::Handler(mem::transmute(f)),
+        }
+    })
+}
+
 /// Manages the signal mask (set of blocked signals) for the calling thread.
 ///
 /// If the `set` parameter is `Some(..)`, then the signal mask will be updated with the signal set.

test/sys/test_signal.rs

@@ -1,5 +1,8 @@
-use nix::unistd::*;
+use libc;
+use nix::Error;
 use nix::sys::signal::*;
+use nix::unistd::*;
+use std::sync::atomic::{AtomicBool, Ordering};
 
 #[test]
 fn test_kill_none() {
@@ -60,3 +63,36 @@ fn test_sigprocmask() {
     sigprocmask(SigmaskHow::SIG_UNBLOCK, Some(&signal_set), None)
         .expect("expect to be able to block signals");
 }
+
+lazy_static! {
+    static ref SIGNALED: AtomicBool = AtomicBool::new(false);
+}
+
+extern fn test_sigaction_handler(signal: libc::c_int) {
+    let signal = Signal::from_c_int(signal).unwrap();
+    SIGNALED.store(signal == Signal::SIGINT, Ordering::Relaxed);
+}
+
+extern fn test_sigaction_action(_: libc::c_int, _: *mut libc::siginfo_t, _: *mut libc::c_void) {
+}
+
+#[test]
+fn test_signal() {
+    let _m = ::SIGNAL_MTX.lock().expect("Mutex got poisoned by another test");
+
+    unsafe { signal(Signal::SIGINT, SigHandler::SigIgn) }.unwrap();
+    raise(Signal::SIGINT).unwrap();
+    assert_eq!(unsafe { signal(Signal::SIGINT, SigHandler::SigDfl) }.unwrap(), SigHandler::SigIgn);
+
+    let handler = SigHandler::Handler(test_sigaction_handler);
+    assert_eq!(unsafe { signal(Signal::SIGINT, handler) }.unwrap(), SigHandler::SigDfl);
+    raise(Signal::SIGINT).unwrap();
+    assert!(SIGNALED.load(Ordering::Relaxed));
+    assert_eq!(unsafe { signal(Signal::SIGINT, SigHandler::SigDfl) }.unwrap(), handler);
+
+    let action_handler = SigHandler::SigAction(test_sigaction_action);
+    assert_eq!(unsafe { signal(Signal::SIGINT, action_handler) }.unwrap_err(), Error::UnsupportedOperation);
+
+    // Restore default signal handler
+    unsafe { signal(Signal::SIGINT, SigHandler::SigDfl) }.unwrap();
+}