Add a access(2) wrapper

CHANGELOG.md

@@ -22,6 +22,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - Added `nix::unistd:seteuid` and `nix::unistd::setegid` for those platforms that do
   not support `setresuid` nor `setresgid` respectively.
   ([#1044](https://github.com/nix-rust/nix/pull/1044))
+- Added a `access` wrapper
+  ([#1045](https://github.com/nix-rust/nix/pull/1045))
 
 ### Changed
 - `PollFd` event flags renamed to `PollFlags` ([#1024](https://github.com/nix-rust/nix/pull/1024/))

src/unistd.rs

@@ -2334,3 +2334,28 @@ mod setres {
         Errno::result(res).map(drop)
     }
 }
+
+libc_bitflags!{
+    /// Options for access()
+    pub struct AccessFlags : c_int {
+        /// Test for existence of file.
+        F_OK;
+        /// Test for read permission.
+        R_OK;
+        /// Test for write permission.
+        W_OK;
+        /// Test for execute (search) permission.
+        X_OK;
+    }
+}
+
+/// Checks the file named by `path` for accessibility according to the flags given by `amode`
+/// See [access(2)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/access.html)
+pub fn access<P: ?Sized + NixPath>(path: &P, amode: AccessFlags) -> Result<()> {
+    let res = path.with_nix_path(|cstr| {
+        unsafe {
+            libc::access(cstr.as_ptr(), amode.bits)
+        }
+    })?;
+    Errno::result(res).map(drop)
+}

test/test_unistd.rs

@@ -4,6 +4,7 @@ use nix::unistd::ForkResult::*;
 use nix::sys::signal::{SaFlags, SigAction, SigHandler, SigSet, Signal, sigaction};
 use nix::sys::wait::*;
 use nix::sys::stat::{self, Mode, SFlag};
+use nix::errno::Errno;
 use std::{env, iter};
 use std::ffi::CString;
 use std::fs::{self, File};
@@ -574,3 +575,19 @@ fn test_symlinkat() {
         target
     );
 }
+
+#[test]
+fn test_access_not_existing() {
+    let tempdir = tempfile::tempdir().unwrap();
+    let dir = tempdir.path().join("does_not_exist.txt");
+    assert_eq!(access(&dir, AccessFlags::F_OK).err().unwrap().as_errno().unwrap(),
+               Errno::ENOENT);
+}
+
+#[test]
+fn test_access_file_exists() {
+    let tempdir = tempfile::tempdir().unwrap();
+    let path  = tempdir.path().join("does_exist.txt");
+    let _file = File::create(path.clone()).unwrap();
+    assert!(access(&path, AccessFlags::R_OK | AccessFlags::W_OK).is_ok());
+}