unixstring

UnixString is an FFI-friendly null-terminated byte string that may be constructed from a String, a CString, a PathBuf, an OsString or a collection of bytes.

An UnixString can then be converted into a slice of CStr, Path or OsStr in infallible and zero-cost operations.

Why?

UnixString aims to be useful in any scenario where you'd like to use FFI (specially with C) on Unix systems. If you have a PathBuf, for example, you can send that data to a libc function, such as stat, but you'd have to first allocate a CString (or something analogous) to do so.

The same is true with OsString and String because these three types are allowed to have internal zero bytes and are not null-terminated.

A UnixString is very close to what a CString is but with increased flexibility and usability. A CString cannot be changed or increased after instantited, while UnixString is growable through its push and push_bytes methods, somewhat similar to OsString.

A CString also does not have direct reference conversions to anything but &[u8] or &CStr, while UnixString has those and more (described below).

Obtaining references from an UnixString

Creating an UnixString

Converting from an UnixString

All of the above are also available through .into().

Examples

Creating an UnixString with bytes received through FFI

use libc::{c_char, getcwd};
use unixstring::UnixString;

fn main() {
    const PATH_SIZ: usize = 1024;
    let mut buf: [c_char; 1024] = [0; 1024];

    let ptr = &mut buf as *mut c_char;

    unsafe { getcwd(ptr, PATH_SIZ) };

    if ptr.is_null() {
        panic!("getcwd failed");
    }

    let unix_string = unsafe { UnixString::from_ptr(ptr as *const c_char) };

    assert_eq!(unix_string.as_path(), std::env::current_dir().unwrap())
}

Using an UnixString to send bytes through FFI

use std::{convert::TryFrom, env};

use unixstring::UnixString;

fn stat(path: &UnixString) -> std::io::Result<libc::stat> {
    // Safety: The all-zero byte-pattern is a valid `struct stat`
    let mut stat_buf = unsafe { std::mem::zeroed() };

    if -1 == unsafe { libc::lstat(path.as_ptr(), &mut stat_buf) } {
        let io_err = std::io::Error::last_os_error();
        Err(io_err)
    } else {
        Ok(stat_buf)
    }
}


fn main() -> std::io::Result<()>{
    for arg in env::args_os().map(UnixString::try_from).flatten() {
        let stat = stat(&arg)?;
        
        let size = stat.st_size;

        println!("{} occupies {} bytes.", arg.as_path().display(), size);
    }

    Ok(())
}