flex-page 2.1.0

Database storage system
Documentation 
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use std::os;

#[cfg(target_family = "unix")]
pub use os::unix::fs::FileExt;

#[cfg(target_family = "wasm")]
pub use os::wasi::fs::FileExt;

#[cfg(target_family = "windows")]
pub trait FileExt {
    fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize>;
    fn write_at(&self, buf: &[u8], offset: u64) -> Result<usize>;

    fn read_exact_at(&self, mut buf: &mut [u8], mut offset: u64) -> Result<()> {
        while !buf.is_empty() {
            match self.read_at(buf, offset) {
                Ok(0) => break,
                Ok(n) => {
                    let tmp = buf;
                    buf = &mut tmp[n..];
                    offset += n as u64;
                }
                Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
                Err(e) => return Err(e),
            }
        }
        if !buf.is_empty() {
            Err(Error::new(
                ErrorKind::UnexpectedEof,
                "failed to fill whole buffer",
            ))
        } else {
            Ok(())
        }
    }

    fn write_all_at(&self, mut buf: &[u8], mut offset: u64) -> Result<()> {
        while !buf.is_empty() {
            match self.write_at(buf, offset) {
                Ok(0) => {
                    return Err(Error::new(
                        ErrorKind::WriteZero,
                        "failed to write whole buffer",
                    ));
                }
                Ok(n) => {
                    buf = &buf[n..];
                    offset += n as u64
                }
                Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
                Err(e) => return Err(e),
            }
        }
        Ok(())
    }
}

#[cfg(target_family = "windows")]
use std::{
    fs::File,
    io::{Error, ErrorKind, Result},
};

#[cfg(target_family = "windows")]
impl FileExt for File {
    #[inline]
    fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize> {
        os::windows::fs::FileExt::seek_read(self, buf, offset)
    }

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