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