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//! Free space on the volume that holds a path.
//!
//! [`free_bytes`] asks the OS directly: `statvfs(3)` on unix, `GetDiskFreeSpaceExW` on Windows. No
//! child process is started (an app that shells out to `df -k` pays for a process and parses text
//! that changes between platforms).
use std::io;
use std::path::Path;
/// Bytes available to the calling user on the volume that holds `path`.
///
/// `path` must exist (on unix it is handed to `statvfs`, which needs an existing entry; on Windows
/// any existing path on the volume works). This is the space the user may write, which can be
/// less than the volume's total free space when the filesystem reserves blocks for root or quotas
/// apply. Other platforms return [`io::ErrorKind::Unsupported`].
#[cfg(unix)]
#[allow(clippy::unnecessary_cast)]
pub fn free_bytes(path: &Path) -> io::Result<u64> {
use std::ffi::CString;
use std::os::unix::ffi::OsStrExt;
let c_path = CString::new(path.as_os_str().as_bytes())
.map_err(|_| io::Error::new(io::ErrorKind::InvalidInput, "path contains a NUL byte"))?;
// SAFETY: `statvfs` is plain old data; every field is an integer, so all-zero is a valid value
// that the call then overwrites on success.
let mut stat: libc::statvfs = unsafe { std::mem::zeroed() };
// SAFETY: `c_path` is a valid NUL-terminated string that outlives the call, and `stat` is a
// valid out-parameter.
let rc = unsafe { libc::statvfs(c_path.as_ptr(), &mut stat) };
if rc != 0 {
return Err(io::Error::last_os_error());
}
// `f_bavail` counts fragment-size blocks available to unprivileged users.
Ok((stat.f_bavail as u64).saturating_mul(stat.f_frsize as u64))
}
/// Bytes available to the calling user on the volume that holds `path` (`GetDiskFreeSpaceExW`).
#[cfg(windows)]
pub fn free_bytes(path: &Path) -> io::Result<u64> {
use std::os::windows::ffi::OsStrExt;
#[link(name = "kernel32")]
unsafe extern "system" {
fn GetDiskFreeSpaceExW(
directory: *const u16,
free_to_caller: *mut u64,
total: *mut u64,
total_free: *mut u64,
) -> i32;
}
let wide: Vec<u16> = path
.as_os_str()
.encode_wide()
.chain(std::iter::once(0))
.collect();
let mut free_to_caller: u64 = 0;
// SAFETY: `wide` is NUL-terminated and outlives the call; the optional out-parameters are
// null, which the API accepts; `free_to_caller` is a valid out-parameter.
let ok = unsafe {
GetDiskFreeSpaceExW(
wide.as_ptr(),
&mut free_to_caller,
std::ptr::null_mut(),
std::ptr::null_mut(),
)
};
if ok == 0 {
return Err(io::Error::last_os_error());
}
Ok(free_to_caller)
}
/// Other platforms have no free-space query in this crate.
#[cfg(not(any(unix, windows)))]
pub fn free_bytes(_path: &Path) -> io::Result<u64> {
Err(io::Error::new(
io::ErrorKind::Unsupported,
"free_bytes is implemented for unix and Windows",
))
}