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to PaaS I/O in the Rust Track

Published at Oct 12 2019 · 0 comments
Instructions
Test suite
Solution

Report network IO statistics.

You are writing a PaaS, and you need a way to bill customers based on network and filesystem usage.

Create a wrapper for network connections and files that can report IO statistics. The wrapper must report:

  • The total number of bytes read/written.
  • The total number of read/write operations.

Abstraction over Networks and Files

Network and file operations are implemented in terms of the io::Read and io::Write traits. It will therefore be necessary to implement those traits for your types.

Rust Installation

Refer to the exercism help page for Rust installation and learning resources.

Writing the Code

Execute the tests with:

$ cargo test

All but the first test have been ignored. After you get the first test to pass, open the tests source file which is located in the tests directory and remove the #[ignore] flag from the next test and get the tests to pass again. Each separate test is a function with #[test] flag above it. Continue, until you pass every test.

If you wish to run all ignored tests without editing the tests source file, use:

$ cargo test -- --ignored

To run a specific test, for example some_test, you can use:

$ cargo test some_test

If the specific test is ignored use:

$ cargo test some_test -- --ignored

To learn more about Rust tests refer to the online test documentation

Make sure to read the Modules chapter if you haven't already, it will help you with organizing your files.

Further improvements

After you have solved the exercise, please consider using the additional utilities, described in the installation guide, to further refine your final solution.

To format your solution, inside the solution directory use

cargo fmt

To see, if your solution contains some common ineffective use cases, inside the solution directory use

cargo clippy --all-targets

Submitting the solution

Generally you should submit all files in which you implemented your solution (src/lib.rs in most cases). If you are using any external crates, please consider submitting the Cargo.toml file. This will make the review process faster and clearer.

Feedback, Issues, Pull Requests

The exercism/rust repository on GitHub is the home for all of the Rust exercises. If you have feedback about an exercise, or want to help implement new exercises, head over there and create an issue. Members of the rust track team are happy to help!

If you want to know more about Exercism, take a look at the contribution guide.

Source

Brian Matsuo https://github.com/bmatsuo

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

paasio.rs

use paasio;

/// test a few read scenarios
macro_rules! test_read {
    ($(#[$attr:meta])* $modname:ident ($input:expr, $len:expr)) => {
        mod $modname {
            use std::io::{Read, BufReader};
            use paasio::*;

            const CHUNK_SIZE: usize = 2;

            $(#[$attr])*
            #[test]
            fn test_read_passthrough() {
                let data = $input;
                let size = $len(&data);
                let mut reader = ReadStats::new(data);

                let mut buffer = Vec::with_capacity(size);
                let qty_read = reader.read_to_end(&mut buffer);

                assert!(qty_read.is_ok());
                assert_eq!(size, qty_read.unwrap());
                assert_eq!(size, buffer.len());
                // 2: first to read all the data, second to check that
                // there wasn't any more pending data which simply didn't
                // fit into the existing buffer
                assert_eq!(2, reader.reads());
                assert_eq!(size, reader.bytes_through());
            }

            $(#[$attr])*
            #[test]
            fn test_read_chunks() {
                let data = $input;
                let size = $len(&data);
                let mut reader = ReadStats::new(data);

                let mut buffer = [0_u8; CHUNK_SIZE];
                let mut chunks_read = 0;
                while reader.read(&mut buffer[..]).unwrap_or_else(|_| panic!("read failed at chunk {}", chunks_read+1)) > 0 {
                    chunks_read += 1;
                }

                assert_eq!(size / CHUNK_SIZE + std::cmp::min(1, size % CHUNK_SIZE), chunks_read);
                // we read once more than the number of chunks, because the final
                // read returns 0 new bytes
                assert_eq!(1+chunks_read, reader.reads());
                assert_eq!(size, reader.bytes_through());
            }

            $(#[$attr])*
            #[test]
            fn test_read_buffered_chunks() {
                let data = $input;
                let size = $len(&data);
                let mut reader = BufReader::new(ReadStats::new(data));

                let mut buffer = [0_u8; CHUNK_SIZE];
                let mut chunks_read = 0;
                while reader.read(&mut buffer[..]).unwrap_or_else(|_| panic!("read failed at chunk {}", chunks_read+1)) > 0 {
                    chunks_read += 1;
                }

                assert_eq!(size / CHUNK_SIZE + std::cmp::min(1, size % CHUNK_SIZE), chunks_read);
                // the BufReader should smooth out the reads, collecting into
                // a buffer and performing only two read operations:
                // the first collects everything into the buffer,
                // and the second ensures that no data remains
                assert_eq!(2, reader.get_ref().reads());
                assert_eq!(size, reader.get_ref().bytes_through());
            }
        }
    };
}

/// test a few write scenarios
macro_rules! test_write {
    ($(#[$attr:meta])* $modname:ident ($input:expr, $len:expr)) => {
        mod $modname {
            use std::io::{self, Write, BufWriter};
            use paasio::*;

            const CHUNK_SIZE: usize = 2;
            $(#[$attr])*
            #[test]
            fn test_write_passthrough() {
                let data = $input;
                let size = $len(&data);
                let mut writer = WriteStats::new(Vec::with_capacity(size));
                let written = writer.write(data);
                assert!(written.is_ok());
                assert_eq!(size, written.unwrap());
                assert_eq!(size, writer.bytes_through());
                assert_eq!(1, writer.writes());
                assert_eq!(data, writer.get_ref().as_slice());
            }

            $(#[$attr])*
            #[test]
            fn test_sink_oneshot() {
                let data = $input;
                let size = $len(&data);
                let mut writer = WriteStats::new(io::sink());
                let written = writer.write(data);
                assert!(written.is_ok());
                assert_eq!(size, written.unwrap());
                assert_eq!(size, writer.bytes_through());
                assert_eq!(1, writer.writes());
            }

            $(#[$attr])*
            #[test]
            fn test_sink_windowed() {
                let data = $input;
                let size = $len(&data);
                let mut writer = WriteStats::new(io::sink());

                let mut chunk_count = 0;
                for chunk in data.chunks(CHUNK_SIZE) {
                    chunk_count += 1;
                    let written = writer.write(chunk);
                    assert!(written.is_ok());
                    assert_eq!(CHUNK_SIZE, written.unwrap());
                }
                assert_eq!(size, writer.bytes_through());
                assert_eq!(chunk_count, writer.writes());
            }

            $(#[$attr])*
            #[test]
            fn test_sink_buffered_windowed() {
                let data = $input;
                let size = $len(&data);
                let mut writer = BufWriter::new(WriteStats::new(io::sink()));

                for chunk in data.chunks(CHUNK_SIZE) {
                    let written = writer.write(chunk);
                    assert!(written.is_ok());
                    assert_eq!(CHUNK_SIZE, written.unwrap());
                }
                // at this point, nothing should have yet been passed through to
                // our writer
                assert_eq!(0, writer.get_ref().bytes_through());
                assert_eq!(0, writer.get_ref().writes());

                // after flushing, everything should pass through in one go
                assert!(writer.flush().is_ok());
                assert_eq!(size, writer.get_ref().bytes_through());
                assert_eq!(1, writer.get_ref().writes());
            }
        }
    };
}

#[test]
fn test_create_stats() {
    let mut data: Vec<u8> = Vec::new();
    let _ = paasio::ReadStats::new(data.as_slice());
    let _ = paasio::WriteStats::new(data.as_mut_slice());
}

test_read!(#[ignore] read_string (
    "Twas brillig, and the slithy toves/Did gyre and gimble in the wabe:/All mimsy were the borogoves,/And the mome raths outgrabe.".as_bytes(),
    |d: &[u8]| d.len()
));
test_write!(#[ignore] write_string (
    "Beware the Jabberwock, my son!/The jaws that bite, the claws that catch!/Beware the Jubjub bird, and shun/The frumious Bandersnatch!".as_bytes(),
    |d: &[u8]| d.len()
));

test_read!(#[ignore]
read_byte_literal(
    &[1_u8, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144][..],
    |d: &[u8]| d.len()
));
test_write!(#[ignore]
write_byte_literal(
    &[2_u8, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61,][..],
    |d: &[u8]| d.len()
));

test_read!(#[ignore]
read_file(
    ::std::fs::File::open("README.md").expect("readme must be present"),
    |f: &::std::fs::File| f.metadata().expect("metadata must be present").len() as usize
));

#[test]
#[ignore]
fn read_stats_by_ref_returns_wrapped_reader() {
    use paasio::ReadStats;

    let input =
        "Why, sometimes I've believed as many as six impossible things before breakfast".as_bytes();
    let reader = ReadStats::new(input);
    assert_eq!(reader.get_ref(), &input);
}
use std::io::{Read, Result, Write};

pub struct ReadStats<R> {
    reference: R,
    bytes: usize,
    count: usize,
}

impl<R: Read> ReadStats<R> {
    pub fn new(wrapped: R) -> ReadStats<R> {
        Self {
            reference: wrapped,
            bytes: 0,
            count: 0,
        }
    }

    pub fn get_ref(&self) -> &R {
        &self.reference
    }

    pub fn bytes_through(&self) -> usize {
        self.bytes
    }

    pub fn reads(&self) -> usize {
        self.count
    }
}

impl<R: Read> Read for ReadStats<R> {
    fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
        let bytes = self.reference.read(buf)?;
        self.bytes += bytes;
        self.count += 1;
        Ok(bytes)
    }
}

pub struct WriteStats<W> {
    reference: W,
    bytes: usize,
    count: usize,
}

impl<W: Write> WriteStats<W> {
    pub fn new(wrapped: W) -> WriteStats<W> {
        Self {
            reference: wrapped,
            bytes: 0,
            count: 0,
        }
    }

    pub fn get_ref(&self) -> &W {
        &self.reference
    }

    pub fn bytes_through(&self) -> usize {
        self.bytes
    }

    pub fn writes(&self) -> usize {
        self.count
    }
}

impl<W: Write> Write for WriteStats<W> {
    fn write(&mut self, buf: &[u8]) -> Result<usize> {
        let bytes = self.reference.write(buf)?;
        self.bytes += bytes;
        self.count += 1;
        Ok(bytes)
    }

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

What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that you could read more about to improve your understanding?