Existing tests for Read, Write, and Seek traits

paulyoung · March 15, 2022, 4:18am

I’ve provided implementations of the Read, Write, and Seek traits and would like to test that they work as expected.

It seems likely that this has already been codified in an abstract sense somewhere in a test suite or testing crate, but I haven’t been able to find anything yet.

Does such a thing exist?

Michael-F-Bryan · March 15, 2022, 5:10am

I don't think such a test suite exists because there is no standardized definition for Read, Write, and Seek. For example, some Read+Write+Seek implementations can have their data modified behind their back (e.g. std::fs::File), while this is statically prevented in other implementations (e.g. std::fs::Cursor).

I think the best example you'll find of a "well behaved" implementation are the std::io::Cursor tests.

github.com

rust-lang/rust/blob/master/library/std/src/io/cursor/tests.rs

use crate::io::prelude::*;
use crate::io::{Cursor, IoSlice, IoSliceMut, SeekFrom};

#[test]
fn test_vec_writer() {
    let mut writer = Vec::new();
    assert_eq!(writer.write(&[0]).unwrap(), 1);
    assert_eq!(writer.write(&[1, 2, 3]).unwrap(), 3);
    assert_eq!(writer.write(&[4, 5, 6, 7]).unwrap(), 4);
    assert_eq!(
        writer
            .write_vectored(&[IoSlice::new(&[]), IoSlice::new(&[8, 9]), IoSlice::new(&[10])],)
            .unwrap(),
        3
    );
    let b: &[_] = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
    assert_eq!(writer, b);
}

#[test]

This file has been truncated. show original

paulyoung · April 4, 2022, 11:12pm

@Michael-F-Bryan thanks for this.

I created my own version of these tests and ran into something unexpected; the assertion on the result of write_vectored fails because only 2 bytes are written when 3 are expected. &[10] doesn't get written for some reason.

Since write_vectored is a provided method, I'm not sure where to start.

Doing the equivalent with write appears to work, and IoSlice::new(&[8, 9, 10]) also works.

paulyoung · April 5, 2022, 12:06am

According to this, the behavior is expected:

github.com/rust-lang/rust

std::io::Write::write_vectored() to io::stdout() does not produce all expected lines.

opened 03:55AM - 09 Jan 20 UTC

closed 01:46PM - 09 Jan 20 UTC

rustyconover

T-libs-api C-bug

When trying to write an array of 8192 IoSlices consisting of "1" followed by "\n…" only the first character is written on Mac OS X. ```rust use std::io; use std::io::prelude::*; use std::io::IoSlice; fn main() { let mut write_array: Vec<IoSlice> = Vec::new(); for _ in 1..1024 * 4 { write_array.push(IoSlice::new(b"1")); write_array.push(IoSlice::new(b"\n")); } io::stdout().write_vectored(&write_array).unwrap(); io::stdout().flush().unwrap(); } ``` Output: ``` 1 ``` Just one byte is written: ``` ./target/debug/vector-bug | wc 0 1 1 ``` I expected 4096 pairs of `"1\n"` to be written. ## Meta ``` $ rustc --version --verbose rustc 1.40.0 (73528e339 2019-12-16) binary: rustc commit-hash: 73528e339aae0f17a15ffa49a8ac608f50c6cf14 commit-date: 2019-12-16 host: x86_64-apple-darwin release: 1.40.0 LLVM version: 9.0 ```

paulyoung · April 5, 2022, 12:11am

The docs say this as well.

system · July 4, 2022, 12:12am

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Existing tests for Read, Write, and Seek traits

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