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use std::io::{Error, ErrorKind, Read, Result, Seek, SeekFrom, Write};
pub struct IoCursor<Io> {
io: Io,
cursor: u64,
bounds: (u64, u64),
}
impl<Io: Seek> IoCursor<Io> {
pub fn new(mut io: Io, start: u64, end: u64) -> Result<Self> {
let cursor = io.seek(SeekFrom::Start(start))?;
Ok(Self {
io,
cursor,
bounds: (cursor, end),
})
}
}
impl<Io: Read> Read for IoCursor<Io> {
fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
let upper = buf.len().min((self.bounds.1 - self.cursor) as usize);
let bytes = self.io.read(&mut buf[..upper])?;
self.cursor += bytes as u64;
Ok(bytes)
}
}
impl<Io: Write> Write for IoCursor<Io> {
fn write(&mut self, buf: &[u8]) -> Result<usize> {
let upper = buf.len().min((self.bounds.1 - self.cursor) as usize);
let bytes = self.io.write(&buf[..upper])?;
self.cursor += bytes as u64;
Ok(bytes)
}
#[inline]
fn flush(&mut self) -> Result<()> {
self.io.flush()
}
}
impl<Io: Seek> Seek for IoCursor<Io> {
fn seek(&mut self, pos: SeekFrom) -> Result<u64> {
self.cursor = match pos {
SeekFrom::Start(0) => return Ok(self.cursor - self.bounds.0),
SeekFrom::Start(offset) => self.bounds.0.checked_add(offset),
SeekFrom::End(offset) => self.bounds.1.checked_add_signed(offset),
SeekFrom::Current(offset) => self.cursor.checked_add_signed(offset),
}
.filter(|v| *v >= self.bounds.0)
.ok_or(Error::new(
ErrorKind::InvalidInput,
"Invalid seek to a negative or overflowing position",
))?
.min(self.bounds.1);
Ok(self.io.seek(SeekFrom::Start(self.cursor))? - self.bounds.0)
}
}
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