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//! The file-related utilities.
//!
//! # Examples
//!
//! ```no_run
//! use std::io;
//!
//! use blake3::file::hash_path_maybe_mmap;
//!
//! fn main() -> io::Result<()> {
//! let args: Vec<_> = std::env::args_os().collect();
//! assert_eq!(args.len(), 2);
//! let path = &args[1];
//! let mut hasher = blake3::Hasher::new();
//! hash_path_maybe_mmap(&mut hasher, path)?;
//! println!("{}", hasher.finalize());
//! Ok(())
//! }
//! ```
use std::{fs::File, io, path::Path};
/// Mmap a file, if it looks like a good idea. Return None in cases where we
/// know mmap will fail, or if the file is short enough that mmapping isn't
/// worth it. However, if we do try to mmap and it fails, return the error.
pub fn maybe_memmap_file(file: &File) -> io::Result<Option<memmap2::Mmap>> {
let metadata = file.metadata()?;
let file_size = metadata.len();
#[allow(clippy::if_same_then_else)]
if !metadata.is_file() {
// Not a real file.
Ok(None)
} else if file_size > isize::max_value() as u64 {
// Too long to safely map.
// https://github.com/danburkert/memmap-rs/issues/69
Ok(None)
} else if file_size == 0 {
// Mapping an empty file currently fails.
// https://github.com/danburkert/memmap-rs/issues/72
Ok(None)
} else if file_size < 16 * 1024 {
// Mapping small files is not worth it.
Ok(None)
} else {
// Explicitly set the length of the memory map, so that filesystem
// changes can't race to violate the invariants we just checked.
let map = unsafe {
memmap2::MmapOptions::new()
.len(file_size as usize)
.map(file)?
};
Ok(Some(map))
}
}
/// Hash a file fast.
///
/// It may use mmap if the file is big enough. If not, it will read the whole file into a buffer.
pub fn hash_path_maybe_mmap(hasher: &mut crate::Hasher, path: impl AsRef<Path>) -> io::Result<()> {
let file = File::open(path.as_ref())?;
if let Some(mmap) = maybe_memmap_file(&file)? {
hasher.update_rayon(&mmap);
} else {
crate::copy_wide(&file, hasher)?;
}
Ok(())
}
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