Add getresuid() and getresgid() to unistd

CHANGELOG.md

@@ -5,6 +5,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 ## [Unreleased] - ReleaseDate
 ### Added
+- Added `getresuid` and `getresgid`
+  (#[1430](https://github.com/nix-rust/nix/pull/1430))
 - Added TIMESTAMPNS support for linux
   (#[1402](https://github.com/nix-rust/nix/pull/1402))
 - Added `sendfile64` (#[1439](https://github.com/nix-rust/nix/pull/1439))

src/unistd.rs

@@ -29,6 +29,9 @@ pub use self::pivot_root::*;
           target_os = "linux", target_os = "openbsd"))]
 pub use self::setres::*;
 
+#[cfg(any(target_os = "android", target_os = "linux"))]
+pub use self::getres::*;
+
 /// User identifier
 ///
 /// Newtype pattern around `uid_t` (which is just alias). It prevents bugs caused by accidentally
@@ -2516,6 +2519,67 @@ mod setres {
     }
 }
 
+#[cfg(any(target_os = "android", target_os = "linux"))]
+mod getres {
+    use crate::Result;
+    use crate::errno::Errno;
+    use super::{Uid, Gid};
+
+    /// Real, effective and saved user IDs.
+    #[derive(Debug, Copy, Clone, Eq, PartialEq)]
+    pub struct ResUid {
+        pub real: Uid,
+        pub effective: Uid,
+        pub saved: Uid
+    }
+
+    /// Real, effective and saved group IDs.
+    #[derive(Debug, Copy, Clone, Eq, PartialEq)]
+    pub struct ResGid {
+        pub real: Gid,
+        pub effective: Gid,
+        pub saved: Gid
+    }
+
+    /// Gets the real, effective, and saved user IDs.
+    ///
+    /// ([see getresuid(2)](http://man7.org/linux/man-pages/man2/getresuid.2.html))
+    ///
+    /// #Returns
+    ///
+    /// - `Ok((Uid, Uid, Uid))`: tuple of real, effective and saved uids on success.
+    /// - `Err(x)`: libc error code on failure.
+    ///
+    #[inline]
+    pub fn getresuid() -> Result<ResUid> {
+        let mut ruid = libc::uid_t::max_value();
+        let mut euid = libc::uid_t::max_value();
+        let mut suid = libc::uid_t::max_value();
+        let res = unsafe { libc::getresuid(&mut ruid, &mut euid, &mut suid) };
+
+        Errno::result(res).map(|_| ResUid{ real: Uid(ruid), effective: Uid(euid), saved: Uid(suid) })
+    }
+
+    /// Gets the real, effective, and saved group IDs.
+    ///
+    /// ([see getresgid(2)](http://man7.org/linux/man-pages/man2/getresgid.2.html))
+    ///
+    /// #Returns
+    ///
+    /// - `Ok((Gid, Gid, Gid))`: tuple of real, effective and saved gids on success.
+    /// - `Err(x)`: libc error code on failure.
+    ///
+    #[inline]
+    pub fn getresgid() -> Result<ResGid> {
+        let mut rgid = libc::gid_t::max_value();
+        let mut egid = libc::gid_t::max_value();
+        let mut sgid = libc::gid_t::max_value();
+        let res = unsafe { libc::getresgid(&mut rgid, &mut egid, &mut sgid) };
+
+        Errno::result(res).map(|_| ResGid { real: Gid(rgid), effective: Gid(egid), saved: Gid(sgid) } )
+    }
+}
+
 libc_bitflags!{
     /// Options for access()
     pub struct AccessFlags : c_int {

test/test_unistd.rs

@@ -624,6 +624,25 @@ fn test_sysconf_unsupported() {
     assert!(open_max.expect("sysconf failed").is_none())
 }
 
+
+#[cfg(any(target_os = "android", target_os = "linux"))]
+#[test]
+fn test_getresuid() {
+    let resuids = getresuid().unwrap();
+    assert!(resuids.real.as_raw() != libc::uid_t::max_value());
+    assert!(resuids.effective.as_raw() != libc::uid_t::max_value());
+    assert!(resuids.saved.as_raw() != libc::uid_t::max_value());
+}
+
+#[cfg(any(target_os = "android", target_os = "linux"))]
+#[test]
+fn test_getresgid() {
+    let resgids = getresgid().unwrap();
+    assert!(resgids.real.as_raw() != libc::gid_t::max_value());
+    assert!(resgids.effective.as_raw() != libc::gid_t::max_value());
+    assert!(resgids.saved.as_raw() != libc::gid_t::max_value());
+}
+
 // Test that we can create a pair of pipes.  No need to verify that they pass
 // data; that's the domain of the OS, not nix.
 #[test]