library/std/src/io/copy/tests.rs

use crate::cmp::{max, min};
use crate::collections::VecDeque;
use crate::io;
use crate::io::*;

#[test]
fn copy_copies() {
    let mut r = repeat(0).take(4);
    let mut w = sink();
    assert_eq!(copy(&mut r, &mut w).unwrap(), 4);

    let mut r = repeat(0).take(1 << 17);
    assert_eq!(copy(&mut r as &mut dyn Read, &mut w as &mut dyn Write).unwrap(), 1 << 17);
}

struct ShortReader {
    cap: usize,
    read_size: usize,
    observed_buffer: usize,
}

impl Read for ShortReader {
    fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
        let bytes = min(self.cap, self.read_size).min(buf.len());
        self.cap -= bytes;
        self.observed_buffer = max(self.observed_buffer, buf.len());
        Ok(bytes)
    }
}

struct WriteObserver {
    observed_buffer: usize,
}

impl Write for WriteObserver {
    fn write(&mut self, buf: &[u8]) -> Result<usize> {
        self.observed_buffer = max(self.observed_buffer, buf.len());
        Ok(buf.len())
    }

    fn flush(&mut self) -> Result<()> {
        Ok(())
    }
}

#[test]
fn copy_specializes_bufwriter() {
    let cap = 117 * 1024;
    let buf_sz = 16 * 1024;
    let mut r = ShortReader { cap, observed_buffer: 0, read_size: 1337 };
    let mut w = BufWriter::with_capacity(buf_sz, WriteObserver { observed_buffer: 0 });
    assert_eq!(
        copy(&mut r, &mut w).unwrap(),
        cap as u64,
        "expected the whole capacity to be copied"
    );
    assert_eq!(r.observed_buffer, buf_sz, "expected a large buffer to be provided to the reader");
    assert!(w.get_mut().observed_buffer > DEFAULT_BUF_SIZE, "expected coalesced writes");
}

#[test]
fn copy_specializes_bufreader() {
    let mut source = vec![0; 768 * 1024];
    source[1] = 42;
    let mut buffered = BufReader::with_capacity(256 * 1024, Cursor::new(&mut source));

    let mut sink = Vec::new();
    assert_eq!(crate::io::copy(&mut buffered, &mut sink).unwrap(), source.len() as u64);
    assert_eq!(source.as_slice(), sink.as_slice());

    let buf_sz = 71 * 1024;
    assert!(buf_sz > DEFAULT_BUF_SIZE, "test precondition");

    let mut buffered = BufReader::with_capacity(buf_sz, Cursor::new(&mut source));
    let mut sink = WriteObserver { observed_buffer: 0 };
    assert_eq!(crate::io::copy(&mut buffered, &mut sink).unwrap(), source.len() as u64);
    assert_eq!(
        sink.observed_buffer, buf_sz,
        "expected a large buffer to be provided to the writer"
    );
}

#[test]
fn copy_specializes_to_vec() {
    let cap = DEFAULT_BUF_SIZE * 10;
    let mut source = ShortReader { cap, observed_buffer: 0, read_size: DEFAULT_BUF_SIZE };
    let mut sink = Vec::new();
    let copied = io::copy(&mut source, &mut sink).unwrap();
    assert_eq!(cap as u64, copied);
    assert_eq!(sink.len() as u64, copied);
    assert!(
        source.observed_buffer > DEFAULT_BUF_SIZE,
        "expected a large buffer to be provided to the reader, got {}",
        source.observed_buffer
    );
}

#[test]
fn copy_specializes_from_vecdeque() {
    let mut source = VecDeque::with_capacity(100 * 1024);
    for _ in 0..20 * 1024 {
        source.push_front(0);
    }
    for _ in 0..20 * 1024 {
        source.push_back(0);
    }
    let mut sink = WriteObserver { observed_buffer: 0 };
    assert_eq!(40 * 1024u64, io::copy(&mut source, &mut sink).unwrap());
    assert_eq!(20 * 1024, sink.observed_buffer);
}

#[test]
fn copy_specializes_from_slice() {
    let mut source = [1; 60 * 1024].as_slice();
    let mut sink = WriteObserver { observed_buffer: 0 };
    assert_eq!(60 * 1024u64, io::copy(&mut source, &mut sink).unwrap());
    assert_eq!(60 * 1024, sink.observed_buffer);
}

#[cfg(unix)]
mod io_benches {
    use test::Bencher;

    use crate::fs::{File, OpenOptions};
    use crate::io::BufReader;
    use crate::io::prelude::*;

    #[bench]
    #[cfg_attr(target_os = "emscripten", ignore)] // no /dev
    fn bench_copy_buf_reader(b: &mut Bencher) {
        let mut file_in = File::open("/dev/zero").expect("opening /dev/zero failed");
        // use dyn to avoid specializations unrelated to readbuf
        let dyn_in = &mut file_in as &mut dyn Read;
        let mut reader = BufReader::with_capacity(256 * 1024, dyn_in.take(0));
        let mut writer =
            OpenOptions::new().write(true).open("/dev/null").expect("opening /dev/null failed");

        const BYTES: u64 = 1024 * 1024;

        b.bytes = BYTES;

        b.iter(|| {
            reader.get_mut().set_limit(BYTES);
            crate::io::copy(&mut reader, &mut writer).unwrap()
        });
    }
}