C-string manipulation and management

This modules provides the basic methods for creating and manipulating null-terminated strings for use with FFI calls (back to C). Most C APIs require that the string being passed to them is null-terminated, and by default rust's string types are not null terminated.

The other problem with translating Rust strings to C strings is that Rust strings can validly contain a null-byte in the middle of the string (0 is a valid unicode codepoint). This means that not all Rust strings can actually be translated to C strings.

Creation of a C string

A C string is managed through the CString type defined in this module. It "owns" the internal buffer of characters and will automatically deallocate the buffer when the string is dropped. The ToCStr trait is implemented for &str and &[u8], but the conversions can fail due to some of the limitations explained above.

This also means that currently whenever a C string is created, an allocation must be performed to place the data elsewhere (the lifetime of the C string is not tied to the lifetime of the original string/data buffer). If C strings are heavily used in applications, then caching may be advisable to prevent unnecessary amounts of allocations.

An example of creating and using a C string would be:

use std::libc;
extern {
    fn puts(s: *libc::c_char);
}

let my_string = "Hello, world!";

// Allocate the C string with an explicit local that owns the string. The
// `c_buffer` pointer will be deallocated when `my_c_string` goes out of scope.
let my_c_string = my_string.to_c_str();
my_c_string.with_ref(|c_buffer| {
    unsafe { puts(c_buffer); }
});

// Don't save off the allocation of the C string, the `c_buffer` will be
// deallocated when this block returns!
my_string.with_c_str(|c_buffer| {
    unsafe { puts(c_buffer); }
});