daxpedda_vsprintf/
lib.rs

1//! Convert C format strings to Rust.
2
3extern crate libc;
4
5use libc::size_t;
6use std::iter::repeat;
7use std::io::Error;
8use std::os::raw::*;
9
10const INITIAL_BUFFER_SIZE: usize = 512;
11
12/// The result of a vsprintf call.
13pub type Result<T> = ::std::result::Result<T, Error>;
14
15/// Prints a format string into a Rust string.
16pub unsafe fn vsprintf<V>(format: *const c_char,
17                          va_list: *mut V) -> Result<String> {
18    vsprintf_raw(format, va_list).map(|bytes| {
19        String::from_utf8(bytes).expect("vsprintf result is not valid utf-8")
20    })
21}
22
23/// Prints a format string into a list of raw bytes that form
24/// a null-terminated C string.
25pub unsafe fn vsprintf_raw<V>(format: *const c_char,
26                              va_list: *mut V) -> Result<Vec<u8>> {
27    let list_ptr = va_list  as *mut c_void;
28
29    let mut buffer = Vec::new();
30    buffer.extend([0u8; INITIAL_BUFFER_SIZE].iter().cloned());
31
32    loop {
33        let character_count = vsnprintf_wrapper(
34            buffer.as_mut_ptr(), buffer.len(), format, list_ptr
35        );
36
37        // Check for errors.
38        if character_count == -1 {
39            // C does not require vsprintf to set errno, but POSIX does.
40            //
41            // Default handling will just generate an 'unknown' IO error
42            // if no errno is set.
43            return Err(Error::last_os_error());
44        } else {
45            assert!(character_count >= 0);
46            let character_count = character_count as usize;
47
48            let current_max = buffer.len() - 1;
49
50            // Check if we had enough room in the buffer to fit everything.
51            if character_count > current_max {
52                let extra_space_required = character_count - current_max;
53
54                // Reserve enough space and try again.
55                buffer.extend(repeat(0).take(extra_space_required as usize));
56                continue;
57            } else { // We fit everything into the buffer.
58                // Truncate the buffer up until the null terminator.
59                buffer = buffer.into_iter()
60                               .take_while(|&b| b != 0)
61                               .collect();
62                break;
63            }
64        }
65    }
66
67    Ok(buffer)
68}
69
70extern {
71    fn vsnprintf_wrapper(buffer: *mut u8,
72                         size: size_t,
73                         format: *const c_char,
74                         va_list: *mut c_void) -> libc::c_int;
75}
daxpedda_vsprintf/lib.rs

daxpedda_vsprintf/
lib.rs
