ffsync 1.1.0

Chunk-level file synchronization for big files and fast links
Documentation 
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use std::fs::File;
use std::io;

/// Trait for positional I/O (reading/writing at an offset without moving cursor)
pub trait FileExt {
    fn read_at(&self, buf: &mut [u8], offset: u64) -> io::Result<usize>;
    fn write_at(&self, buf: &[u8], offset: u64) -> io::Result<usize>;
}

// Unix Implementation (uses pread/pwrite)
#[cfg(unix)]
impl FileExt for File {
    fn read_at(&self, buf: &mut [u8], offset: u64) -> io::Result<usize> {
        std::os::unix::fs::FileExt::read_at(self, buf, offset)
    }

    fn write_at(&self, buf: &[u8], offset: u64) -> io::Result<usize> {
        std::os::unix::fs::FileExt::write_at(self, buf, offset)
    }
}

// Windows Implementation (uses Seek+Write atomically or Overlapped I/O internally)
#[cfg(windows)]
impl FileExt for File {
    fn read_at(&self, buf: &mut [u8], offset: u64) -> io::Result<usize> {
        std::os::windows::fs::FileExt::seek_read(self, buf, offset)
    }

    fn write_at(&self, buf: &[u8], offset: u64) -> io::Result<usize> {
        std::os::windows::fs::FileExt::seek_write(self, buf, offset)
    }
}