Auto merge of #416 - philippkeller:master, r=posborne

add unistd::getcwd and unistd::mkdir

As a (late) followup of [this withdrawn PR](rust-lang/libc#326) I have added getcwd (wrapper around `libc::getcwd`) and mkdir (wrapper around `libc::mkdir`) and added testing.

A few notes:

 - I'm new to rust so I would appreciate some pair of eyes testing the code, plus I'm open for revision of code or general remarks about my coding style
 - I have run the tests both on OSX as on Linux (Ubuntu)
 - I've run `clippy` to see if my code is well formatted, however clippy issues many warnings about the project. I think I didn't add any more warnings
 - the methods in unistd are not documented so I also left out the documentation of `getcwd` and `mkdir`, although I think it'd probably be good to add some documentation, especially some example code how to use the methods
 - the base idea of `getcwd` is [taken from std](https://github.com/rust-lang/rust/blob/1.9.0/src/libstd/sys/unix/os.rs#L95-L119), should I mention that somewhere?

src/unistd.rs

@@ -3,11 +3,14 @@
 use {Errno, Error, Result, NixPath};
 use fcntl::{fcntl, OFlag, O_NONBLOCK, O_CLOEXEC, FD_CLOEXEC};
 use fcntl::FcntlArg::{F_SETFD, F_SETFL};
-use libc::{self, c_char, c_void, c_int, c_uint, size_t, pid_t, off_t, uid_t, gid_t};
+use libc::{self, c_char, c_void, c_int, c_uint, size_t, pid_t, off_t, uid_t, gid_t, mode_t};
 use std::mem;
-use std::ffi::CString;
+use std::ffi::{CString, CStr, OsString};
+use std::os::unix::ffi::OsStringExt;
+use std::path::PathBuf;
 use std::os::unix::io::RawFd;
 use void::Void;
+use sys::stat::Mode;
 
 #[cfg(any(target_os = "linux", target_os = "android"))]
 pub use self::linux::*;
@@ -111,6 +114,100 @@ pub fn chdir<P: ?Sized + NixPath>(path: &P) -> Result<()> {
     Errno::result(res).map(drop)
 }
 
+/// Creates new directory `path` with access rights `mode`.
+///
+/// # Errors
+///
+/// There are several situations where mkdir might fail:
+///
+/// - current user has insufficient rights in the parent directory
+/// - the path already exists
+/// - the path name is too long (longer than `PATH_MAX`, usually 4096 on linux, 1024 on OS X)
+///
+/// For a full list consult 
+/// [man mkdir(2)](http://man7.org/linux/man-pages/man2/mkdir.2.html#ERRORS)
+///
+/// # Example
+///
+/// ```rust
+/// extern crate tempdir;
+/// extern crate nix;
+///
+/// use nix::unistd;
+/// use nix::sys::stat;
+/// use tempdir::TempDir;
+///
+/// fn main() {
+///     let mut tmp_dir = TempDir::new("test_mkdir").unwrap().into_path();
+///     tmp_dir.push("new_dir");
+///
+///     // create new directory and give read, write and execute rights to the owner
+///     match unistd::mkdir(&tmp_dir, stat::S_IRWXU) {
+///        Ok(_) => println!("created {:?}", tmp_dir),
+///        Err(err) => println!("Error creating directory: {}", err),
+///     }
+/// }
+/// ```
+#[inline]
+pub fn mkdir<P: ?Sized + NixPath>(path: &P, mode: Mode) -> Result<()> {
+    let res = try!(path.with_nix_path(|cstr| {
+        unsafe { libc::mkdir(cstr.as_ptr(), mode.bits() as mode_t) }
+    }));
+
+    Errno::result(res).map(drop)
+}
+
+/// Returns the current directory as a PathBuf
+///
+/// Err is returned if the current user doesn't have the permission to read or search a component
+/// of the current path.
+///
+/// # Example
+///
+/// ```rust
+/// extern crate nix;
+///
+/// use nix::unistd;
+///
+/// fn main() {
+///     // assume that we are allowed to get current directory
+///     let dir = unistd::getcwd().unwrap();
+///     println!("The current directory is {:?}", dir);
+/// }
+/// ```
+#[inline]
+pub fn getcwd() -> Result<PathBuf> {
+    let mut buf = Vec::with_capacity(512);
+    loop {
+        unsafe {
+            let ptr = buf.as_mut_ptr() as *mut libc::c_char;
+
+            // The buffer must be large enough to store the absolute pathname plus
+            // a terminating null byte, or else null is returned.
+            // To safely handle this we start with a reasonable size (512 bytes)
+            // and double the buffer size upon every error
+            if !libc::getcwd(ptr, buf.capacity()).is_null() {
+                let len = CStr::from_ptr(buf.as_ptr() as *const libc::c_char).to_bytes().len();
+                buf.set_len(len);
+                buf.shrink_to_fit();
+                return Ok(PathBuf::from(OsString::from_vec(buf)));
+            } else {
+                let error = Errno::last();
+                // ERANGE means buffer was too small to store directory name
+                if error != Errno::ERANGE {
+                    return Err(Error::Sys(error));
+                }
+            }
+
+            // Trigger the internal buffer resizing logic of `Vec` by requiring
+            // more space than the current capacity.
+            let cap = buf.capacity();
+            buf.set_len(cap);
+            buf.reserve(1);
+        }
+    }
+}
+
 #[inline]
 pub fn chown<P: ?Sized + NixPath>(path: &P, owner: Option<uid_t>, group: Option<gid_t>) -> Result<()> {
     let res = try!(path.with_nix_path(|cstr| {

test/test_unistd.rs

@@ -1,54 +1,57 @@
+extern crate tempdir;
+
 use nix::unistd::*;
 use nix::unistd::ForkResult::*;
 use nix::sys::wait::*;
+use nix::sys::stat;
+use std::iter;
 use std::ffi::CString;
-
 use std::io::{Write, Read};
+use std::os::unix::prelude::*;
+use std::env::current_dir;
 use tempfile::tempfile;
+use tempdir::TempDir;
 use libc::off_t;
-use std::os::unix::prelude::*;
-
-
 
 #[test]
 fn test_fork_and_waitpid() {
     let pid = fork();
     match pid {
-      Ok(Child) => {} // ignore child here
-      Ok(Parent { child }) => {
-          // assert that child was created and pid > 0
-          assert!(child > 0);
-          let wait_status = waitpid(child, None);
-          match wait_status {
-              // assert that waitpid returned correct status and the pid is the one of the child
-              Ok(WaitStatus::Exited(pid_t, _)) =>  assert!(pid_t == child),
-
-              // panic, must never happen
-              Ok(_) => panic!("Child still alive, should never happen"),
-
-              // panic, waitpid should never fail
-              Err(_) => panic!("Error: waitpid Failed")
-          }
-
-      },
-      // panic, fork should never fail unless there is a serious problem with the OS
-      Err(_) => panic!("Error: Fork Failed")
+        Ok(Child) => {} // ignore child here
+        Ok(Parent { child }) => {
+            // assert that child was created and pid > 0
+            assert!(child > 0);
+            let wait_status = waitpid(child, None);
+            match wait_status {
+                // assert that waitpid returned correct status and the pid is the one of the child
+                Ok(WaitStatus::Exited(pid_t, _)) =>  assert!(pid_t == child),
+
+                // panic, must never happen
+                Ok(_) => panic!("Child still alive, should never happen"),
+
+                // panic, waitpid should never fail
+                Err(_) => panic!("Error: waitpid Failed")
+            }
+
+        },
+        // panic, fork should never fail unless there is a serious problem with the OS
+        Err(_) => panic!("Error: Fork Failed")
     }
 }
 
 #[test]
 fn test_wait() {
     let pid = fork();
     match pid {
-      Ok(Child) => {} // ignore child here
-      Ok(Parent { child }) => {
-          let wait_status = wait();
-
-          // just assert that (any) one child returns with WaitStatus::Exited
-          assert_eq!(wait_status, Ok(WaitStatus::Exited(child, 0)));
-      },
-      // panic, fork should never fail unless there is a serious problem with the OS
-      Err(_) => panic!("Error: Fork Failed")
+        Ok(Child) => {} // ignore child here
+        Ok(Parent { child }) => {
+            let wait_status = wait();
+
+            // just assert that (any) one child returns with WaitStatus::Exited
+            assert_eq!(wait_status, Ok(WaitStatus::Exited(child, 0)));
+        },
+        // panic, fork should never fail unless there is a serious problem with the OS
+        Err(_) => panic!("Error: Fork Failed")
     }
 }
 
@@ -119,6 +122,24 @@ macro_rules! execve_test_factory(
     )
 );
 
+#[test]
+fn test_getcwd() {
+    let mut tmp_dir = TempDir::new("test_getcwd").unwrap().into_path();
+    assert!(chdir(tmp_dir.as_path()).is_ok());
+    assert_eq!(getcwd().unwrap(), current_dir().unwrap());
+
+    // make path 500 chars longer so that buffer doubling in getcwd kicks in.
+    // Note: One path cannot be longer than 255 bytes (NAME_MAX)
+    // whole path cannot be longer than PATH_MAX (usually 4096 on linux, 1024 on macos)
+    for _ in 0..5 {
+        let newdir = iter::repeat("a").take(100).collect::<String>();
+        tmp_dir.push(newdir);
+        assert!(mkdir(tmp_dir.as_path(), stat::S_IRWXU).is_ok());
+    }
+    assert!(chdir(tmp_dir.as_path()).is_ok());
+    assert_eq!(getcwd().unwrap(), current_dir().unwrap());
+}
+
 #[test]
 fn test_lseek() {
     const CONTENTS: &'static [u8] = b"abcdef123456";
@@ -129,10 +150,10 @@ fn test_lseek() {
     lseek(tmp.as_raw_fd(), offset, Whence::SeekSet).unwrap();
 
     let mut buf = String::new();
-     tmp.read_to_string(&mut buf).unwrap();
-     assert_eq!(b"f123456", buf.as_bytes());
+    tmp.read_to_string(&mut buf).unwrap();
+    assert_eq!(b"f123456", buf.as_bytes());
 
-     close(tmp.as_raw_fd()).unwrap();
+    close(tmp.as_raw_fd()).unwrap();
 }
 
 #[cfg(any(target_os = "linux", target_os = "android"))]