unistd: Add conversion from User to libc::passwd

Add From<User> for libc::passwd trait implementation to convert
a User into a libc::passwd

Implementation consumes the User struct, giving ownership over
the internal members to the libc::passwd struct

Add the User::gecos field to 64-bit Android builds, since it is
supported by libc::passwd for those builds

Author: orvij

CHANGELOG.md

@@ -8,16 +8,23 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 - Added `TimeSpec::from_duration` and `TimeSpec::from_timespec`
   (#[1465](https://github.com/nix-rust/nix/pull/1465))
-
 - Added `IPV6_V6ONLY` sockopt.
   (#[1470](https://github.com/nix-rust/nix/pull/1470))
+- Added `impl From<User> for libc::passwd` trait implementation to convert a `User`
+  into a `libc::passwd`. Consumes the `User` struct to give ownership over
+  the member pointers.
+  (#[1471](https://github.com/nix-rust/nix/pull/1471))
 - Added `pthread_kill`.
   (#[1472](https://github.com/nix-rust/nix/pull/1472))
 
 ### Changed
 
 - `FdSet::{contains, highest, fds}` no longer require a mutable reference.
   (#[1464](https://github.com/nix-rust/nix/pull/1464))
+- `User::gecos` and corresponding `libc::passwd::pw_gecos` are supported on
+  64-bit Android, change conditional compilation to include the field in
+  64-bit Android builds
+  (#[1471](https://github.com/nix-rust/nix/pull/1471))
 
 ### Fixed
 

src/unistd.rs

@@ -2629,7 +2629,7 @@ pub struct User {
     /// Group ID
     pub gid: Gid,
     /// User information
-    #[cfg(not(target_os = "android"))]
+    #[cfg(not(all(target_os = "android", target_pointer_width = "32")))]
     pub gecos: CString,
     /// Home directory
     pub dir: PathBuf,
@@ -2665,7 +2665,7 @@ impl From<&libc::passwd> for User {
             User {
                 name: CStr::from_ptr((*pw).pw_name).to_string_lossy().into_owned(),
                 passwd: CString::new(CStr::from_ptr((*pw).pw_passwd).to_bytes()).unwrap(),
-                #[cfg(not(target_os = "android"))]
+                #[cfg(not(all(target_os = "android", target_pointer_width = "32")))]
                 gecos: CString::new(CStr::from_ptr((*pw).pw_gecos).to_bytes()).unwrap(),
                 dir: PathBuf::from(OsStr::from_bytes(CStr::from_ptr((*pw).pw_dir).to_bytes())),
                 shell: PathBuf::from(OsStr::from_bytes(CStr::from_ptr((*pw).pw_shell).to_bytes())),
@@ -2694,6 +2694,58 @@ impl From<&libc::passwd> for User {
     }
 }
 
+#[cfg(not(target_os = "redox"))] // RedoxFS does not support passwd
+impl From<User> for libc::passwd {
+    fn from(u: User) -> Self {
+        let name = match CString::new(u.name) {
+            Ok(n) => n.into_raw(),
+            Err(_) => CString::new("").unwrap().into_raw(),
+        };
+        let dir = match u.dir.into_os_string().into_string() {
+            Ok(s) => CString::new(s.as_str()).unwrap().into_raw(),
+            Err(_) => CString::new("").unwrap().into_raw(),
+        };
+        let shell = match u.shell.into_os_string().into_string() {
+            Ok(s) => CString::new(s.as_str()).unwrap().into_raw(),
+            Err(_) => CString::new("").unwrap().into_raw(),
+        };
+        Self {
+            pw_name: name,
+            pw_passwd: u.passwd.into_raw(),
+            #[cfg(not(all(target_os = "android", target_pointer_width = "32")))]
+            pw_gecos: u.gecos.into_raw(),
+            pw_dir: dir,
+            pw_shell: shell,
+            pw_uid: u.uid.0,
+            pw_gid: u.gid.0,
+            #[cfg(not(any(target_os = "android",
+                          target_os = "fuchsia",
+                          target_os = "illumos",
+                          target_os = "linux",
+                          target_os = "solaris")))]
+            pw_class: u.class.into_raw(),
+            #[cfg(not(any(target_os = "android",
+                          target_os = "fuchsia",
+                          target_os = "illumos",
+                          target_os = "linux",
+                          target_os = "solaris")))]
+            pw_change: u.change,
+            #[cfg(not(any(target_os = "android",
+                          target_os = "fuchsia",
+                          target_os = "illumos",
+                          target_os = "linux",
+                          target_os = "solaris")))]
+            pw_expire: u.expire,
+            #[cfg(target_os = "illumos")]
+            pw_age: CString::new("").unwrap().into_raw(),
+            #[cfg(target_os = "illumos")]
+            pw_comment: CString::new("").unwrap().into_raw(),
+            #[cfg(target_os = "freebsd")]
+            pw_fields: 0,
+        }
+    }
+}
+
 #[cfg(not(target_os = "redox"))] // RedoxFS does not support passwd
 impl User {
     fn from_anything<F>(f: F) -> Result<Option<Self>>

test/test_unistd.rs

@@ -1025,6 +1025,14 @@ fn test_access_file_exists() {
     assert!(access(&path, AccessFlags::R_OK | AccessFlags::W_OK).is_ok());
 }
 
+#[test]
+fn test_user_into_passwd() {
+    // get the UID of the "nobody" user
+    let nobody = User::from_name("nobody").unwrap().unwrap();
+    let pwd: libc::passwd = nobody.into();
+    let _: User = (&pwd).into();
+}
+
 /// Tests setting the filesystem UID with `setfsuid`.
 #[cfg(any(target_os = "linux", target_os = "android"))]
 #[test]