std/sys/pal/common/
small_c_string.rs

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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}
std/sys/pal/common/small_c_string.rs

std/sys/pal/common/
small_c_string.rs
