std: Avoid the WSA_FLAG_NO_HANDLE_INHERIT option

This was added after Windows 7 SP1, so it's not always available. Instead use
the `SetHandleInformation` function to flag a socket as not inheritable. This is
not atomic with respect to creating new processes, but it mirrors what Unix does
with respect to possibly using the atomic option in the future.

Closes #26543

src/libstd/sys/windows/c.rs

@@ -64,6 +64,8 @@
 pub const STD_OUTPUT_HANDLE: libc::DWORD = -11i32 as libc::DWORD;
 pub const STD_ERROR_HANDLE: libc::DWORD = -12i32 as libc::DWORD;
 
+pub const HANDLE_FLAG_INHERIT: libc::DWORD = 0x00000001;
+
 #[repr(C)]
 #[cfg(target_arch = "x86")]
 pub struct WSADATA {
@@ -408,6 +410,9 @@ pub fn WaitForSingleObject(hHandle: libc::HANDLE,
     pub fn GetUserProfileDirectoryW(hToken: libc::HANDLE,
                                     lpProfileDir: libc::LPCWSTR,
                                     lpcchSize: *mut libc::DWORD) -> libc::BOOL;
+    pub fn SetHandleInformation(hObject: libc::HANDLE,
+                                dwMask: libc::DWORD,
+                                dwFlags: libc::DWORD) -> libc::BOOL;
 }
 
 // Functions that aren't available on Windows XP, but we still use them and just

src/libstd/sys/windows/net.rs

@@ -82,26 +82,31 @@ pub fn new(addr: &SocketAddr, ty: c_int) -> io::Result<Socket> {
             SocketAddr::V4(..) => libc::AF_INET,
             SocketAddr::V6(..) => libc::AF_INET6,
         };
-        let socket = unsafe {
-            c::WSASocketW(fam, ty, 0, 0 as *mut _, 0,
-                          c::WSA_FLAG_OVERLAPPED | c::WSA_FLAG_NO_HANDLE_INHERIT)
-        };
-        match socket {
-            INVALID_SOCKET => Err(last_error()),
-            n => Ok(Socket(n)),
-        }
+        let socket = try!(unsafe {
+            match c::WSASocketW(fam, ty, 0, 0 as *mut _, 0,
+                                c::WSA_FLAG_OVERLAPPED) {
+                INVALID_SOCKET => Err(last_error()),
+                n => Ok(Socket(n)),
+            }
+        });
+        try!(socket.set_no_inherit());
+        Ok(socket)
     }
 
     pub fn accept(&self, storage: *mut libc::sockaddr,
                   len: *mut libc::socklen_t) -> io::Result<Socket> {
-        match unsafe { libc::accept(self.0, storage, len) } {
-            INVALID_SOCKET => Err(last_error()),
-            n => Ok(Socket(n)),
-        }
+        let socket = try!(unsafe {
+            match libc::accept(self.0, storage, len) {
+                INVALID_SOCKET => Err(last_error()),
+                n => Ok(Socket(n)),
+            }
+        });
+        try!(socket.set_no_inherit());
+        Ok(socket)
     }
 
     pub fn duplicate(&self) -> io::Result<Socket> {
-        unsafe {
+        let socket = try!(unsafe {
             let mut info: c::WSAPROTOCOL_INFO = mem::zeroed();
             try!(cvt(c::WSADuplicateSocketW(self.0,
                                             c::GetCurrentProcessId(),
@@ -110,12 +115,13 @@ pub fn duplicate(&self) -> io::Result<Socket> {
                                 info.iSocketType,
                                 info.iProtocol,
                                 &mut info, 0,
-                                c::WSA_FLAG_OVERLAPPED |
-                                    c::WSA_FLAG_NO_HANDLE_INHERIT) {
+                                c::WSA_FLAG_OVERLAPPED) {
                 INVALID_SOCKET => Err(last_error()),
                 n => Ok(Socket(n)),
             }
-        }
+        });
+        try!(socket.set_no_inherit());
+        Ok(socket)
     }
 
     pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
@@ -156,6 +162,13 @@ pub fn timeout(&self, kind: libc::c_int) -> io::Result<Option<Duration>> {
             Ok(Some(Duration::new(secs as u64, nsec as u32)))
         }
     }
+
+    fn set_no_inherit(&self) -> io::Result<()> {
+        sys::cvt(unsafe {
+            c::SetHandleInformation(self.0 as libc::HANDLE,
+                                    c::HANDLE_FLAG_INHERIT, 0)
+        }).map(|_| ())
+    }
 }
 
 impl Drop for Socket {