partial-io 0.5.4

// Copyright (c) The partial-io Contributors
// SPDX-License-Identifier: MIT

//! An example of a buggy buffered writer that does not handle
//! `io::ErrorKind::Interrupted` properly.

#![allow(dead_code)]

use std::io::{self, Write};

/// A buffered writer whose `write` method is faulty.
pub struct BuggyWrite<W> {
    inner: W,
    buf: Vec<u8>,
    offset: usize,
}

impl<W: Write> BuggyWrite<W> {
    pub fn new(inner: W) -> Self {
        BuggyWrite {
            inner,
            buf: Vec::with_capacity(256),
            offset: 0,
        }
    }

    fn write_from_offset(&mut self) -> io::Result<()> {
        while self.offset < self.buf.len() {
            self.offset += self.inner.write(&self.buf[self.offset..])?;
        }
        Ok(())
    }

    fn reset_buffer(&mut self) {
        unsafe {
            self.buf.set_len(0);
        }
        self.offset = 0;
    }

    pub fn into_inner(self) -> W {
        self.inner
    }
}

impl<W: Write> Write for BuggyWrite<W> {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        // Write out anything that is currently in the internal buffer.
        if self.offset < self.buf.len() {
            self.write_from_offset()?;
        }

        // Reset the internal buffer.
        self.reset_buffer();

        // Read from the provided buffer.
        self.buf.extend_from_slice(buf);

        // BUG: it is incorrect to call write immediately because if it fails,
        // we'd have read some bytes from the buffer without telling the caller
        // how many.
        // XXX: To fix the bug, comment out the next line.
        self.write_from_offset()?;
        Ok(self.buf.len())
    }

    fn flush(&mut self) -> io::Result<()> {
        // Flush out any data that can be flushed out.
        while self.offset < self.buf.len() {
            self.write_from_offset()?;
        }

        // If that succeeded, reset the internal buffer.
        self.reset_buffer();

        // Flush the inner writer
        self.inner.flush()
    }
}

fn main() {
    check::check_write_is_buggy();
}

mod check {
    use super::*;
    use once_cell::sync::Lazy;
    use partial_io::{PartialOp, PartialWrite};

    // These strings have been chosen to be around the default size for
    // quickcheck (100). With significantly smaller or larger inputs, the
    // results might not be as good.
    pub(crate) static HELLO_STR: Lazy<Vec<u8>> = Lazy::new(|| "Hello".repeat(50).into_bytes());
    pub(crate) static WORLD_STR: Lazy<Vec<u8>> = Lazy::new(|| "World".repeat(40).into_bytes());

    pub fn check_write_is_buggy() {
        let partial = vec![
            PartialOp::Err(io::ErrorKind::Interrupted),
            PartialOp::Unlimited,
        ];
        let (hello_res, world_res, flush_res, inner) = buggy_write_internal(partial);
        assert_eq!(hello_res.unwrap_err().kind(), io::ErrorKind::Interrupted);
        assert_eq!(world_res.unwrap(), 5 * 40);
        flush_res.unwrap();

        // Note that inner has both "Hello" and "World" in it, even though according
        // to what the API returned it should only have had "World" in it.
        let mut expected = Vec::new();
        expected.extend_from_slice(&HELLO_STR);
        expected.extend_from_slice(&WORLD_STR);
        assert_eq!(inner, expected);
    }

    pub(crate) fn buggy_write_internal<I>(
        partial_iter: I,
    ) -> (
        io::Result<usize>,
        io::Result<usize>,
        io::Result<()>,
        Vec<u8>,
    )
    where
        I: IntoIterator<Item = PartialOp> + 'static,
        I::IntoIter: Send,
    {
        let inner = Vec::new();
        let partial_writer = PartialWrite::new(inner, partial_iter);

        let mut buggy_write = BuggyWrite::new(partial_writer);

        // Try writing a couple of things into it.
        let hello_res = buggy_write.write(&HELLO_STR);
        let world_res = buggy_write.write(&WORLD_STR);

        // Flush the contents to make sure nothing remains in the internal buffer.
        let flush_res = buggy_write.flush();

        let inner = buggy_write.into_inner().into_inner();

        (hello_res, world_res, flush_res, inner)
    }
}

#[cfg(test)]
mod tests {
    //! Tests to demonstrate how to use partial-io to catch bugs in `buggy_write`.
    use super::*;
    use partial_io::{
        proptest_types::{interrupted_strategy, partial_op_strategy},
        quickcheck_types::{GenInterrupted, PartialWithErrors},
    };
    use proptest::{collection::vec, prelude::*};
    use quickcheck::{quickcheck, TestResult};

    /// Test that BuggyWrite is actually buggy.
    #[test]
    fn test_check_write_is_buggy() {
        check::check_write_is_buggy();
    }

    /// Test that quickcheck catches buggy writes.
    ///
    /// To run this test and see it fail, run this example with `--ignored`. To fix the bug, see the
    /// section of this file marked "// BUG:".
    #[test]
    #[ignore]
    fn test_quickcheck_buggy_write() {
        quickcheck(quickcheck_buggy_write2 as fn(PartialWithErrors<GenInterrupted>) -> TestResult);
    }

    fn quickcheck_buggy_write2(partial: PartialWithErrors<GenInterrupted>) -> TestResult {
        let (hello_res, world_res, flush_res, inner) = check::buggy_write_internal(partial);
        // If flush_res failed then we can't really do anything since we don't know
        // how much was written internally. Otherwise hello_res and world_res should
        // work.
        if flush_res.is_err() {
            return TestResult::discard();
        }

        let mut expected = Vec::new();
        if hello_res.is_ok() {
            expected.extend_from_slice(&check::HELLO_STR);
        }
        if world_res.is_ok() {
            expected.extend_from_slice(&check::WORLD_STR);
        }
        assert_eq!(inner, expected);
        TestResult::passed()
    }

    proptest! {
        /// Test that proptest catches buggy writes.
        ///
        /// To run this test and see it fail, run this example with `--ignored`. To
        /// fix the bug, see the section of this file marked "// BUG:".
        #[test]
        #[ignore]
        fn test_proptest_buggy_write(ops in vec(partial_op_strategy(interrupted_strategy(), 128), 0..128)) {
            let (hello_res, world_res, flush_res, inner) = check::buggy_write_internal(ops);

            // If flush_res failed then we can't really do anything since we don't know
            // how much was written internally. Otherwise hello_res and world_res should
            // work.
            prop_assume!(flush_res.is_ok(), "if flush failed, we don't know what was written");

            let mut expected = Vec::new();
            if hello_res.is_ok() {
                expected.extend_from_slice(&check::HELLO_STR);
            }
            if world_res.is_ok() {
                expected.extend_from_slice(&check::WORLD_STR);
            }
            prop_assert_eq!(inner, expected, "actual value matches expected");
        }
    }
}