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use std::io;
use std::io::Read;
/// Retry `read` if it read short, to check we're at the end of the file.
///
/// `read` is allowed to return fewer bytes than requested, even if
/// we're not at the end of the file.
///
/// `read_exact` has undefined behaviour if we hit the end of the file
/// while reading. It will return an error, but won't necessarily have
/// put the lost bytes into the buffer.
///
/// `read_many` will only return a short read if the underlying reader
/// returns `0`, indicating an end of file condition.
pub trait ReadMany {
/// Try quite hard to fill `buf` with bytes.
///
/// Give up if the underlying reader returns an end-of-file
/// condition or error only, not if it's just a bit lazy.
///
/// Errors from the underlying reader will be returned as-is.
fn read_many(&mut self, buf: &mut [u8]) -> io::Result<usize>;
}
impl<T: Read> ReadMany for T {
fn read_many(&mut self, buf: &mut [u8]) -> io::Result<usize> {
let mut pos = 0;
while pos < buf.len() {
match self.read(&mut buf[pos..]) {
Ok(0) => break,
Ok(read) => pos += read,
Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
Err(e) => return Err(e),
}
}
Ok(pos)
}
}
#[cfg(test)]
mod tests {
use crate::many::ReadMany;
use crate::short::ShortRead;
use std::io;
#[test]
fn short_read() {
let mut naughty =
ShortRead::new(io::Cursor::new(b"1234567890"), vec![2, 1, 4, 5].into_iter());
let mut buf = [0u8; 3];
assert_eq!(3, naughty.read_many(&mut buf).unwrap());
assert_eq!(b"123", &buf);
let mut buf = [0u8; 12];
assert_eq!(7, naughty.read_many(&mut buf).unwrap());
assert_eq!(b"4567890", &buf[..7]);
}
#[test]
fn interrupted_read() {
let mut take_a_break = ShortRead::new(io::Cursor::new(b"12345"), vec![2, 0, 3].into_iter());
let mut buf = [0u8; 5];
assert_eq!(5, take_a_break.read_many(&mut buf).unwrap());
assert_eq!(b"12345", &buf);
}
}