Support for no-change of parameters of setresuid and setresgid

CHANGELOG.md

@@ -13,6 +13,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#972](https://github.com/nix-rust/nix/pull/972))
 - Added `symlinkat` wrapper.
   ([#997](https://github.com/nix-rust/nix/pull/997))
+- Support for no-change of parameters of `setresuid` and `setresgid` wrapper
+  ([#1009](https://github.com/nix-rust/nix/pull/1009))
 
 ### Changed
 ### Fixed

src/unistd.rs

@@ -2286,8 +2286,11 @@ mod setres {
     ///
     /// Err is returned if the user doesn't have permission to set this UID.
     #[inline]
-    pub fn setresuid(ruid: Uid, euid: Uid, suid: Uid) -> Result<()> {
-        let res = unsafe { libc::setresuid(ruid.into(), euid.into(), suid.into()) };
+    pub fn setresuid(ruid: Option<Uid>, euid: Option<Uid>, suid: Option<Uid>) -> Result<()> {
+        let ruid = ruid.map(Into::into).unwrap_or((0 as libc::uid_t).wrapping_sub(1));
+        let euid = euid.map(Into::into).unwrap_or((0 as libc::uid_t).wrapping_sub(1));
+        let suid = suid.map(Into::into).unwrap_or((0 as libc::uid_t).wrapping_sub(1));
+        let res = unsafe { libc::setresuid(ruid, euid, suid) };
 
         Errno::result(res).map(drop)
     }
@@ -2302,8 +2305,11 @@ mod setres {
     ///
     /// Err is returned if the user doesn't have permission to set this GID.
     #[inline]
-    pub fn setresgid(rgid: Gid, egid: Gid, sgid: Gid) -> Result<()> {
-        let res = unsafe { libc::setresgid(rgid.into(), egid.into(), sgid.into()) };
+    pub fn setresgid(rgid: Option<Gid>, egid: Option<Gid>, sgid: Option<Gid>) -> Result<()> {
+        let rgid = rgid.map(Into::into).unwrap_or((0 as libc::gid_t).wrapping_sub(1));
+        let egid = egid.map(Into::into).unwrap_or((0 as libc::gid_t).wrapping_sub(1));
+        let sgid = sgid.map(Into::into).unwrap_or((0 as libc::gid_t).wrapping_sub(1));
+        let res = unsafe { libc::setresgid(rgid, egid, sgid) };
 
         Errno::result(res).map(drop)
     }

test/test_unistd.rs

@@ -570,3 +570,19 @@ fn test_symlinkat() {
         target
     );
 }
+
+#[cfg(any(target_os = "android", target_os = "freebsd",
+target_os = "linux", target_os = "openbsd"))]
+#[test]
+fn test_setresuid() {
+    setresuid(Some(getuid()), Some(getuid()), Some(getuid())).unwrap();
+    assert_eq!(geteuid(), getuid());
+}
+
+#[cfg(any(target_os = "android", target_os = "freebsd",
+target_os = "linux", target_os = "openbsd"))]
+#[test]
+fn test_setresgid() {
+    setresgid(Some(getgid()), Some(getgid()), Some(getgid())).unwrap();
+    assert_eq!(getegid(), getgid());
+}