Added libstd::io::fs::access()

src/libstd/io/fs.rs

@@ -70,6 +70,8 @@ use vec::Vec;
 use sys::fs as fs_imp;
 use sys_common;
 
+pub use libc::{F_OK,R_OK,W_OK,X_OK};
+
 /// Unconstrained file access type that exposes read and write operations
 ///
 /// Can be constructed via `File::open()`, `File::create()`, and
@@ -326,6 +328,36 @@ pub fn lstat(path: &Path) -> IoResult<FileStat> {
                format!("{}; path={}", e, path.display()))
 }
 
+/// Given a path and access mode, checks whether the calling process can access
+/// the path and perform the requested operations.
+/// Mode can either be F_OK to check for existence or a bitwise OR of one or
+/// more of R_OK, W_OK, and X_OK to test for read, write and execute access
+/// respectively.
+///
+/// # Example
+///
+/// ```rust
+/// use std::io::fs;
+/// use std::io::fs::{R_OK,W_OK,X_OK};
+///
+/// let p = Path::new("/some/file/path.txt");
+/// match fs::access(&p, R_OK|W_OK|X_OK) {
+///     Err(e) => { /* handle error */ }
+///     _ => { /* ... */ }
+/// }
+/// ```
+///
+/// # Error
+///
+/// This function will return an error if the user is not allowed to
+/// perform the requested operations on the file.
+pub fn access(path: &Path, amode: i32) -> IoResult<()> {
+    fs_imp::access(path, amode)
+           .update_err("couldn't access path", |e|
+               format!("{}; path={}; amode={}", e, path.display(), amode))
+
+}
+
 /// Rename a file or directory to a new name.
 ///
 /// # Example

src/libstd/sys/unix/fs.rs

@@ -25,6 +25,7 @@ use sys::retry;
 use sys_common::{keep_going, eof, mkerr_libc};
 
 pub use path::PosixPath as Path;
+pub use libc::{F_OK,R_OK,W_OK,X_OK};
 
 pub type fd_t = libc::c_int;
 
@@ -349,6 +350,11 @@ pub fn lstat(p: &Path) -> IoResult<FileStat> {
     }
 }
 
+pub fn access(p: &Path, a: i32) -> IoResult<()> {
+    let p = p.to_c_str();
+    mkerr_libc(unsafe { libc::access(p.as_ptr(), a) })
+}
+
 pub fn utime(p: &Path, atime: u64, mtime: u64) -> IoResult<()> {
     let p = p.to_c_str();
     let buf = libc::utimbuf {

src/libstd/sys/windows/fs.rs

@@ -30,6 +30,8 @@ use io::{IoResult, IoError, FileStat, SeekStyle, Seek, Writer, Reader};
 use io::{Read, Truncate, SeekCur, SeekSet, ReadWrite, SeekEnd, Append};
 
 pub use path::WindowsPath as Path;
+pub use libc::{F_OK,R_OK,W_OK,X_OK};
+
 pub type fd_t = libc::c_int;
 
 pub struct FileDesc {
@@ -448,6 +450,11 @@ pub fn lstat(_p: &Path) -> IoResult<FileStat> {
     Err(super::unimpl())
 }
 
+pub fn access(p: &Path, a: i32) -> IoResult<()> {
+    let p = p.to_c_str();
+    mkerr_libc(unsafe { libc::access(p.as_ptr(), a) })
+}
+
 pub fn utime(p: &Path, atime: u64, mtime: u64) -> IoResult<()> {
     let mut buf = libc::utimbuf {
         actime: atime as libc::time64_t,