Remove emulation of FD_CLOEXEC/O_NONBLOCK

Rather than using the native implementation of these constants
on supported platforms, the native implementation was instead
emulated. This was also hidden from the user even though this
could result in data races and the functionality being broken.

Native functionality is, however, not support on macos/ios.
Rather than enable this emulation solely for this platform, it
should be removed as this is a dangerous abstraction.

3 files changed, 88 insertions, 98 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 39f78ddd..8189dd20 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -51,6 +51,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#892](https://github.com/nix-rust/nix/pull/892))
 - Remove `IFF_NOTRAILERS` on OpenBSD, as it has been removed in OpenBSD 6.3
   ([#893](https://github.com/nix-rust/nix/pull/893))
+- Emulation of `FD_CLOEXEC` and `O_NONBLOCK` was removed from `socket()`, `accept4()`, and
+  `socketpair()`.
+  ([#907](https://github.com/nix-rust/nix/pull/907))
 
 ### Fixed
 - Fixed possible panics when using `SigAction::flags` on Linux
@@ -68,6 +71,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#872](https://github.com/nix-rust/nix/pull/872))
 - Removed `sys::aio::lio_listio`.  Use `sys::aio::LioCb::listio` instead.
   ([#872](https://github.com/nix-rust/nix/pull/872))
+- Removed emulated `accept4()` from macos, ios, and netbsd targets
+  ([#907](https://github.com/nix-rust/nix/pull/907))
 
 ## [0.10.0] 2018-01-26
 
diff --git a/src/sys/socket/mod.rs b/src/sys/socket/mod.rs
index fcb79af9..b46fa8b0 100644
--- a/src/sys/socket/mod.rs
+++ b/src/sys/socket/mod.rs
@@ -3,7 +3,6 @@
 //! [Further reading](http://man7.org/linux/man-pages/man7/socket.7.html)
 use {Error, Result};
 use errno::Errno;
-use features;
 use libc::{self, c_void, c_int, socklen_t, size_t};
 use std::{fmt, mem, ptr, slice};
 use std::os::unix::io::RawFd;
@@ -692,42 +691,20 @@ pub fn recvmsg<'a, T>(fd: RawFd, iov: &[IoVec<&mut [u8]>], cmsg_buffer: Option<&
 ///
 /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/socket.html)
 pub fn socket<T: Into<Option<SockProtocol>>>(domain: AddressFamily, ty: SockType, flags: SockFlag, protocol: T) -> Result<RawFd> {
-    let mut ty = ty as c_int;
     let protocol = match protocol.into() {
         None => 0,
         Some(p) => p as c_int,
     };
-    let feat_atomic = features::socket_atomic_cloexec();
-
-    if feat_atomic {
-        ty |= flags.bits();
-    }
-
-    // TODO: Check the kernel version
-    let res = try!(Errno::result(unsafe { libc::socket(domain as c_int, ty, protocol) }));
-
-    #[cfg(any(target_os = "android",
-              target_os = "dragonfly",
-              target_os = "freebsd",
-              target_os = "linux",
-              target_os = "netbsd",
-              target_os = "openbsd"))]
-    {
-        use fcntl::{fcntl, FdFlag, OFlag};
-        use fcntl::FcntlArg::{F_SETFD, F_SETFL};
 
-        if !feat_atomic {
-            if flags.contains(SockFlag::SOCK_CLOEXEC) {
-                try!(fcntl(res, F_SETFD(FdFlag::FD_CLOEXEC)));
-            }
+    // SockFlags are usually embedded into `ty`, but we don't do that in `nix` because it's a
+    // little easier to understand by separating it out. So we have to merge these bitfields
+    // here.
+    let mut ty = ty as c_int;
+    ty |= flags.bits();
 
-            if flags.contains(SockFlag::SOCK_NONBLOCK) {
-                try!(fcntl(res, F_SETFL(OFlag::O_NONBLOCK)));
-            }
-        }
-    }
+    let res = unsafe { libc::socket(domain as c_int, ty, protocol) };
 
-    Ok(res)
+    Errno::result(res)
 }
 
 /// Create a pair of connected sockets
@@ -735,44 +712,22 @@ pub fn socket<T: Into<Option<SockProtocol>>>(domain: AddressFamily, ty: SockType
 /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/socketpair.html)
 pub fn socketpair<T: Into<Option<SockProtocol>>>(domain: AddressFamily, ty: SockType, protocol: T,
                   flags: SockFlag) -> Result<(RawFd, RawFd)> {
-    let mut ty = ty as c_int;
     let protocol = match protocol.into() {
         None => 0,
         Some(p) => p as c_int,
     };
-    let feat_atomic = features::socket_atomic_cloexec();
 
-    if feat_atomic {
-        ty |= flags.bits();
-    }
+    // SockFlags are usually embedded into `ty`, but we don't do that in `nix` because it's a
+    // little easier to understand by separating it out. So we have to merge these bitfields
+    // here.
+    let mut ty = ty as c_int;
+    ty |= flags.bits();
+
     let mut fds = [-1, -1];
-    let res = unsafe {
-        libc::socketpair(domain as c_int, ty, protocol, fds.as_mut_ptr())
-    };
-    try!(Errno::result(res));
-
-    #[cfg(any(target_os = "android",
-              target_os = "dragonfly",
-              target_os = "freebsd",
-              target_os = "linux",
-              target_os = "netbsd",
-              target_os = "openbsd"))]
-    {
-        use fcntl::{fcntl, FdFlag, OFlag};
-        use fcntl::FcntlArg::{F_SETFD, F_SETFL};
 
-        if !feat_atomic {
-            if flags.contains(SockFlag::SOCK_CLOEXEC) {
-                try!(fcntl(fds[0], F_SETFD(FdFlag::FD_CLOEXEC)));
-                try!(fcntl(fds[1], F_SETFD(FdFlag::FD_CLOEXEC)));
-            }
+    let res = unsafe { libc::socketpair(domain as c_int, ty, protocol, fds.as_mut_ptr()) };
+    Errno::result(res)?;
 
-            if flags.contains(SockFlag::SOCK_NONBLOCK) {
-                try!(fcntl(fds[0], F_SETFL(OFlag::O_NONBLOCK)));
-                try!(fcntl(fds[1], F_SETFL(OFlag::O_NONBLOCK)));
-            }
-        }
-    }
     Ok((fds[0], fds[1]))
 }
 
@@ -809,46 +764,14 @@ pub fn accept(sockfd: RawFd) -> Result<RawFd> {
 /// Accept a connection on a socket
 ///
 /// [Further reading](http://man7.org/linux/man-pages/man2/accept.2.html)
+#[cfg(any(target_os = "android",
+          target_os = "freebsd",
+          target_os = "linux",
+          target_os = "openbsd"))]
 pub fn accept4(sockfd: RawFd, flags: SockFlag) -> Result<RawFd> {
-    accept4_polyfill(sockfd, flags)
-}
-
-#[inline]
-fn accept4_polyfill(sockfd: RawFd, flags: SockFlag) -> Result<RawFd> {
-    let res = try!(Errno::result(unsafe { libc::accept(sockfd, ptr::null_mut(), ptr::null_mut()) }));
-
-    #[cfg(any(target_os = "android",
-              target_os = "dragonfly",
-              target_os = "freebsd",
-              target_os = "linux",
-              target_os = "netbsd",
-              target_os = "openbsd"))]
-    {
-        use fcntl::{fcntl, FdFlag, OFlag};
-        use fcntl::FcntlArg::{F_SETFD, F_SETFL};
-
-        if flags.contains(SockFlag::SOCK_CLOEXEC) {
-            try!(fcntl(res, F_SETFD(FdFlag::FD_CLOEXEC)));
-        }
-
-        if flags.contains(SockFlag::SOCK_NONBLOCK) {
-            try!(fcntl(res, F_SETFL(OFlag::O_NONBLOCK)));
-        }
-    }
-
-    // Disable unused variable warning on some platforms
-    #[cfg(not(any(target_os = "android",
-                  target_os = "dragonfly",
-                  target_os = "freebsd",
-                  target_os = "linux",
-                  target_os = "netbsd",
-                  target_os = "openbsd")))]
-    {
-        let _ = flags;
-    }
+    let res = unsafe { libc::accept4(sockfd, ptr::null_mut(), ptr::null_mut(), flags.bits()) };
 
-
-    Ok(res)
+    Errno::result(res)
 }
 
 /// Initiate a connection on a socket
diff --git a/test/sys/test_socket.rs b/test/sys/test_socket.rs
index a997fbca..5d57ac17 100644
--- a/test/sys/test_socket.rs
+++ b/test/sys/test_socket.rs
@@ -255,3 +255,65 @@ pub fn test_syscontrol() {
     // requires root privileges
     // connect(fd, &sockaddr).expect("connect failed");
 }
+
+/// Test non-blocking mode on new sockets via SockFlag::O_NONBLOCK
+#[cfg(any(target_os = "android",
+          target_os = "dragonfly",
+          target_os = "freebsd",
+          target_os = "linux",
+          target_os = "netbsd",
+          target_os = "openbsd"))]
+#[test]
+pub fn test_sockflag_nonblock() {
+    use libc;
+    use nix::fcntl::{fcntl};
+    use nix::fcntl::FcntlArg::{F_GETFL};
+    use nix::sys::socket::{socket, AddressFamily, SockType, SockFlag};
+
+    /* first, try without SockFlag::SOCK_NONBLOCK */
+    let sock = socket(AddressFamily::Unix, SockType::Stream, SockFlag::empty(), None)
+                 .expect("socket failed");
+
+    let fcntl_res = fcntl(sock, F_GETFL).expect("fcntl failed");
+
+    assert!(fcntl_res & libc::O_NONBLOCK == 0);
+
+    /* next, try with SockFlag::SOCK_NONBLOCK */
+    let sock = socket(AddressFamily::Unix, SockType::Stream, SockFlag::SOCK_NONBLOCK, None)
+                 .expect("socket failed");
+
+    let fcntl_res = fcntl(sock, F_GETFL).expect("fcntl failed");
+
+    assert!(fcntl_res & libc::O_NONBLOCK == libc::O_NONBLOCK);
+}
+
+/// Test close-on-exec on new sockets via SockFlag::SOCK_CLOEXEC
+#[cfg(any(target_os = "android",
+          target_os = "dragonfly",
+          target_os = "freebsd",
+          target_os = "linux",
+          target_os = "netbsd",
+          target_os = "openbsd"))]
+#[test]
+pub fn test_sockflag_cloexec() {
+    use libc;
+    use nix::fcntl::{fcntl};
+    use nix::fcntl::FcntlArg::{F_GETFD};
+    use nix::sys::socket::{socket, AddressFamily, SockType, SockFlag};
+
+    /* first, test without SockFlag::SOCK_CLOEXEC */
+    let sock = socket(AddressFamily::Unix, SockType::Stream, SockFlag::empty(), None)
+                 .expect("socket failed");
+
+    let fcntl_res = fcntl(sock, F_GETFD).expect("fcntl failed");
+
+    assert!(fcntl_res & libc::FD_CLOEXEC == 0);
+
+    /* next, test without SockFlag::SOCK_CLOEXEC */
+    let sock = socket(AddressFamily::Unix, SockType::Stream, SockFlag::SOCK_CLOEXEC, None)
+                 .expect("socket failed");
+
+    let fcntl_res = fcntl(sock, F_GETFD).expect("fcntl failed");
+
+    assert!(fcntl_res & libc::FD_CLOEXEC == libc::FD_CLOEXEC);
+}