raylib_wasm/util/
small_c_string.rs

1//! `run_with_cstr` function extracted from Rust standard library
2
3use std::{ptr, slice};
4use std::mem::MaybeUninit;
5use std::ffi::{CStr, CString};
6
7// Make sure to stay under 4096 so the compiler doesn't insert a probe frame:
8// https://docs.rs/compiler_builtins/latest/compiler_builtins/probestack/index.html
9#[cfg(not(target_os = "espidf"))]
10const MAX_STACK_ALLOCATION: usize = 384;
11#[cfg(target_os = "espidf")]
12const MAX_STACK_ALLOCATION: usize = 32;
13
14#[inline]
15pub fn run_with_cstr<R>(bytes: &[u8], f: impl FnOnce(&CStr) -> R) -> R {
16    // Dispatch and dyn erase the closure type to prevent mono bloat.
17    // See https://github.com/rust-lang/rust/pull/121101.
18    if bytes.len() >= MAX_STACK_ALLOCATION {
19        run_with_cstr_allocating(bytes, f)
20    } else {
21        unsafe { run_with_cstr_stack(bytes, f) }
22    }
23}
24
25/// # Safety
26///
27/// `bytes` must have a length less than `MAX_STACK_ALLOCATION`.
28#[inline]
29unsafe fn run_with_cstr_stack<R>(
30    bytes: &[u8],
31    f: impl FnOnce(&CStr) -> R,
32) -> R {
33    let mut buf = MaybeUninit::<[u8; MAX_STACK_ALLOCATION]>::uninit();
34    let buf_ptr = buf.as_mut_ptr() as *mut u8;
35
36    unsafe {
37        ptr::copy_nonoverlapping(bytes.as_ptr(), buf_ptr, bytes.len());
38        buf_ptr.add(bytes.len()).write(0);
39    }
40
41    match CStr::from_bytes_with_nul(unsafe { slice::from_raw_parts(buf_ptr, bytes.len() + 1) }) {
42        Ok(s) => f(s),
43        Err(_) => panic!("file name contained an unexpected NUL byte")
44    }
45}
46
47#[inline]
48fn run_with_cstr_allocating<R>(bytes: &[u8], f: impl FnOnce(&CStr) -> R) -> R {
49    match CString::new(bytes) {
50        Ok(s) => f(&s),
51        Err(_) => panic!("file name contained an unexpected NUL byte")
52    }
53}
raylib_wasm/util/small_c_string.rs

raylib_wasm/util/
small_c_string.rs
