std: Clean up process spawn impl on unix

* De-indent quite a bit by removing usage of FnOnce closures
* Clearly separate code for the parent/child after the fork
* Use `fs2::{File, OpenOptions}` instead of calling `open` manually
* Use RAII to close I/O objects wherever possible
* Remove loop for closing all file descriptors, all our own ones are now
  `CLOEXEC` by default so they cannot be inherited

Author: alexcrichton

src/libstd/process.rs

@@ -340,7 +340,7 @@ fn setup_io(io: &StdioImp, fd: libc::c_int, readable: bool)
             (Some(AnonPipe::from_fd(fd)), None)
         }
         Piped => {
-            let (reader, writer) = try!(unsafe { pipe2::anon_pipe() });
+            let (reader, writer) = try!(pipe2::anon_pipe());
             if readable {
                 (Some(reader), Some(writer))
             } else {

src/libstd/sys/unix/c.rs

@@ -159,6 +159,8 @@ extern {
     pub fn utimes(filename: *const libc::c_char,
                   times: *const libc::timeval) -> libc::c_int;
     pub fn gai_strerror(errcode: libc::c_int) -> *const libc::c_char;
+    pub fn setgroups(ngroups: libc::c_int,
+                     ptr: *const libc::c_void) -> libc::c_int;
 }
 
 #[cfg(any(target_os = "macos", target_os = "ios"))]

src/libstd/sys/unix/fs2.rs

@@ -205,13 +205,17 @@ impl OpenOptions {
 
 impl File {
     pub fn open(path: &Path, opts: &OpenOptions) -> io::Result<File> {
+        let path = try!(cstr(path));
+        File::open_c(&path, opts)
+    }
+
+    pub fn open_c(path: &CStr, opts: &OpenOptions) -> io::Result<File> {
         let flags = opts.flags | match (opts.read, opts.write) {
             (true, true) => libc::O_RDWR,
             (false, true) => libc::O_WRONLY,
             (true, false) |
             (false, false) => libc::O_RDONLY,
         };
-        let path = try!(cstr(path));
         let fd = try!(cvt_r(|| unsafe {
             libc::open(path.as_ptr(), flags, opts.mode)
         }));
@@ -220,6 +224,8 @@ impl File {
         Ok(File(fd))
     }
 
+    pub fn into_fd(self) -> FileDesc { self.0 }
+
     pub fn file_attr(&self) -> io::Result<FileAttr> {
         let mut stat: libc::stat = unsafe { mem::zeroed() };
         try!(cvt(unsafe { libc::fstat(self.0.raw(), &mut stat) }));

src/libstd/sys/unix/pipe2.rs

@@ -20,11 +20,10 @@ use libc;
 
 pub struct AnonPipe(FileDesc);
 
-pub unsafe fn anon_pipe() -> io::Result<(AnonPipe, AnonPipe)> {
+pub fn anon_pipe() -> io::Result<(AnonPipe, AnonPipe)> {
     let mut fds = [0; 2];
-    if libc::pipe(fds.as_mut_ptr()) == 0 {
-        Ok((AnonPipe::from_fd(fds[0]),
-            AnonPipe::from_fd(fds[1])))
+    if unsafe { libc::pipe(fds.as_mut_ptr()) == 0 } {
+        Ok((AnonPipe::from_fd(fds[0]), AnonPipe::from_fd(fds[1])))
     } else {
         Err(io::Error::last_os_error())
     }
@@ -45,7 +44,7 @@ impl AnonPipe {
         self.0.write(buf)
     }
 
-    pub fn raw(&self) -> libc::c_int {
-        self.0.raw()
+    pub fn into_fd(self) -> FileDesc {
+        self.0
     }
 }