Add a truncate(2) wrapper

CHANGELOG.md

@@ -21,6 +21,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - Added `AF_UNSPEC` wrapper to `AddressFamily` ([#948](https://github.com/nix-rust/nix/pull/948))
 - Added the `mode_t` public alias within `sys::stat`.
   ([#954](https://github.com/nix-rust/nix/pull/954))
+- Added a `truncate` wrapper.
+  ([#956](https://github.com/nix-rust/nix/pull/956))
 
 ### Changed
 - Increased required Rust version to 1.22.1/

src/unistd.rs

@@ -986,6 +986,20 @@ fn pipe2_setflags(fd1: RawFd, fd2: RawFd, flags: OFlag) -> Result<()> {
     }
 }
 
+/// Truncate a file to a specified length
+///
+/// See also
+/// [truncate(2)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/truncate.html)
+pub fn truncate<P: ?Sized + NixPath>(path: &P, len: off_t) -> Result<()> {
+    let res = try!(path.with_nix_path(|cstr| {
+        unsafe {
+            libc::truncate(cstr.as_ptr(), len)
+        }
+    }));
+
+    Errno::result(res).map(drop)
+}
+
 /// Truncate a file to a specified length
 ///
 /// See also

test/test_unistd.rs

@@ -6,7 +6,7 @@ use nix::sys::wait::*;
 use nix::sys::stat::{self, Mode, SFlag};
 use std::{env, iter};
 use std::ffi::CString;
-use std::fs::File;
+use std::fs::{self, File};
 use std::io::Write;
 use std::os::unix::prelude::*;
 use tempfile::{self, tempfile};
@@ -390,6 +390,42 @@ fn test_pipe2() {
     assert!(f1.contains(FdFlag::FD_CLOEXEC));
 }
 
+#[test]
+fn test_truncate() {
+    let tempdir = tempfile::tempdir().unwrap();
+    let path = tempdir.path().join("file");
+
+    {
+        let mut tmp = File::create(&path).unwrap();
+        const CONTENTS: &[u8] = b"12345678";
+        tmp.write_all(CONTENTS).unwrap();
+    }
+
+    truncate(&path, 4).unwrap();
+
+    let metadata = fs::metadata(&path).unwrap();
+    assert_eq!(4, metadata.len());
+}
+
+#[test]
+fn test_ftruncate() {
+    let tempdir = tempfile::tempdir().unwrap();
+    let path = tempdir.path().join("file");
+
+    let tmpfd = {
+        let mut tmp = File::create(&path).unwrap();
+        const CONTENTS: &[u8] = b"12345678";
+        tmp.write_all(CONTENTS).unwrap();
+        tmp.into_raw_fd()
+    };
+
+    ftruncate(tmpfd, 2).unwrap();
+    close(tmpfd).unwrap();
+
+    let metadata = fs::metadata(&path).unwrap();
+    assert_eq!(2, metadata.len());
+}
+
 // Used in `test_alarm`.
 static mut ALARM_CALLED: bool = false;