Struct CountWrite

pub struct CountWrite<W> { /* private fields */ }

A wrapper for std::io::Write (and other optional Write implementations) that counts the total number of bytes written successfully.

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

use count_write::CountWrite;

let vec = vec![]; // note that Vec<u8> : Write
let cw = CountWrite::from(vec);
let mut bw = BufWriter::new(cw);
write!(bw, "abc")?;
assert_eq!(bw.into_inner()?.count(), 3);

If the inner writer does not successfully write all bytes, only the successfully written bytes are counted. (This does not affect users who always use write_all, write!, etc.)

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

use count_write::CountWrite;;

/// A dummy struct that only accepts half of the input into a Vec.
struct OnlyHalf;

impl Write for OnlyHalf {
    fn write(&mut self, buf: &[u8]) -> Result<usize> {
    dbg!(buf);
        Ok((buf.len() + 1) / 2)
    }

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

let mut cw = CountWrite::from(OnlyHalf);
write!(cw, "abc")?; // Here, we keep retrying writing into the writer
assert_eq!(cw.count(), 3);

let mut cw = CountWrite::from(OnlyHalf);
cw.write(b"abc")?; // Here, we only write to the writer once and do not retry
assert_eq!(cw.count(), 2);

Implementations

impl<W> CountWrite<W>

pub fn count(&self) -> u64

Returns the number of bytes successfull written so far

pub fn into_inner(self) -> W

Extracts the inner writer, discarding this wrapper

Trait Implementations

impl<W> From<W> for CountWrite<W>

fn from(inner: W) -> Self

Converts to this type from the input type.

impl<W: Write> Write for CountWrite<W>

fn write(&mut self, buf: &[u8]) -> Result<usize, Error>

Writes a buffer into this writer, returning how many bytes were written.

fn flush(&mut self) -> Result<(), Error>

Flushes this output stream, ensuring that all intermediately buffered contents reach their destination.

fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize, Error>

Like write, except that it writes from a slice of buffers.

fn is_write_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (can_vector)

Determines if this Writer has an efficient write_vectored implementation.

fn write_all(&mut self, buf: &[u8]) -> Result<(), Error>

Attempts to write an entire buffer into this writer.

fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<(), Error>

🔬This is a nightly-only experimental API. (write_all_vectored)

Attempts to write multiple buffers into this writer.

fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<(), Error>

Writes a formatted string into this writer, returning any error encountered.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Creates a “by reference” adapter for this instance of Write.