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.

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

Into	Function	Notes
`&CStr`	`UnixString::as_c_str`	Available through `AsRef` as well
`&Path`	`UnixString::as_path`	Available through `AsRef` as well
`&str`	`UnixString::as_str`	Fails if the bytes of the `UnixString` aren't valid UTF-8
`&[u8]`	`UnixString::as_bytes`	Returns the bytes of the `UnixString` without the null terminator
`&[u8]`	`UnixString::as_bytes_with_nul`	Returns the bytes of the `UnixString` with the null terminator
`&OsStr`	`UnixString::as_os_str`	Available through `AsRef` as well

Creating an UnixString

From	Potential failure	Trait impl	Function
`CString`	Infallible	From	`UnixString::from_cstring`
`PathBuf`	Fails if contains an interior zero byte	TryFrom	`UnixString::from_pathbuf`
`String`	Fails if contains an interior zero byte	TryFrom	`UnixString::from_string`
`Vec<u8>`	Fails if contains an interior zero byte	TryFrom	`UnixString::from_bytes`
`OsString`	Fails if contains an interior zero byte	Text	`UnixString::from_os_string`

Converting from an UnixString

Into	Function	Notes
`CString`	`UnixString::into_cstring`
`PathBuf`	`UnixString::into_pathbuf`
`OsString`	`UnixString::from_os_string`
`String`	`UnixString::into_string`	Fails if the `UnixString`'s bytes are not valid UTF-8
`String`	`UnixString::into_string_lossy`
`String`	`UnixString::to_string_lossy`	Non-moving version of `UnixString::into_string_lossy`
`String`	`UnixString::into_string_unchecked`	Unsafe: creates a String without checking if the bytes are valid UTF-8
`Vec<u8>`	`UnixString::into_bytes`	Returns the bytes of the `UnixString` without the null terminator
`Vec<u8>`	`UnixString::into_bytes_with_nul`	Returns the bytes of the `UnixString` with the null terminator

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

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

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(())
}

unixstring 0.2.3