small_c_string.rs - source
Description: Source of the Rust file `library/std/src/sys/helpers/small_c_string.rs`.

#
std/sys/helpers/
small_c_string.rs

    1use crate::ffi::{CStr, CString};
    2use crate::mem::MaybeUninit;
    3use crate::path::Path;
    4use crate::{io, ptr, slice};
    5
    6// Make sure to stay under 4096 so the compiler doesn't insert a probe frame:
    7// https://docs.rs/compiler_builtins/latest/compiler_builtins/probestack/index.html
    8#[cfg(not(target_os = "espidf"))]
    9const MAX_STACK_ALLOCATION: usize = 384;
    10#[cfg(target_os = "espidf")]
    11const MAX_STACK_ALLOCATION: usize = 32;
    12
    13const NUL_ERR: io::Error =
    14    io::const_error!(io::ErrorKind::InvalidInput, "file name contained an unexpected NUL byte");
    15
    16#[inline]
    17pub fn run_path_with_cstr<T>(path: &Path, f: &dyn Fn(&CStr) -> io::Result<T>) -> io::Result<T> {
    18    run_with_cstr(path.as_os_str().as_encoded_bytes(), f)
    19}
    20
    21#[inline]
    22pub fn run_with_cstr<T>(bytes: &[u8], f: &dyn Fn(&CStr) -> io::Result<T>) -> io::Result<T> {
    23    // Dispatch and dyn erase the closure type to prevent mono bloat.
    24    // See https://github.com/rust-lang/rust/pull/121101.
    25    if bytes.len() >= MAX_STACK_ALLOCATION {
    26        run_with_cstr_allocating(bytes, f)
    27    } else {
    28        unsafe { run_with_cstr_stack(bytes, f) }
    29    }
    30}
    31
    32/// # Safety
    33///
    34/// `bytes` must have a length less than `MAX_STACK_ALLOCATION`.
    35unsafe fn run_with_cstr_stack<T>(
    36    bytes: &[u8],
    37    f: &dyn Fn(&CStr) -> io::Result<T>,
    38) -> io::Result<T> {
    39    let mut buf = MaybeUninit::<[u8; MAX_STACK_ALLOCATION]>::uninit();
    40    let buf_ptr = buf.as_mut_ptr() as *mut u8;
    41
    42    unsafe {
    43        ptr::copy_nonoverlapping(bytes.as_ptr(), buf_ptr, bytes.len());
    44        buf_ptr.add(bytes.len()).write(0);
    45    }
    46
    47    match CStr::from_bytes_with_nul(unsafe { slice::from_raw_parts(buf_ptr, bytes.len() + 1) }) {
    48        Ok(s) => f(s),
    49        Err(_) => Err(NUL_ERR),
    50    }
    51}
    52
    53#[cold]
    54#[inline(never)]
    55fn run_with_cstr_allocating<T>(bytes: &[u8], f: &dyn Fn(&CStr) -> io::Result<T>) -> io::Result<T> {
    56    match CString::new(bytes) {
    57        Ok(s) => f(&s),
    58        Err(_) => Err(NUL_ERR),
    59    }
    60}