Struct rev_buf_reader::RevBufReader

pub struct RevBufReader<R> { /* fields omitted */ }

RevBufReader is a struct similar to std::io::BufReader, which adds buffering to any reader. But unlike BufReader, RevBufReader reads a data stream from the end to the start. The order of the bytes, however, remains the same. For example, when using RevBufReader to read a text file, we can read the same lines as we would by using BufReader, but starting from the last line until we get to the first one.

In order to able to read a data stream in reverse order, it must implement both std::io::Read and std::io::Seek.

Examples

use rev_buf_reader::RevBufReader;
use std::io::prelude::*;
use std::fs::File;

fn main() -> std::io::Result<()> {
    let f = File::open("log.txt")?;
    let mut reader = RevBufReader::new(f);

    let mut line = String::new();
    let len = reader.read_line(&mut line)?;
    println!("Last line is {} bytes long", len);
    Ok(())
}

Methods

impl<R: Read + Seek> RevBufReader<R>

Important traits for RevBufReader<R>

impl<R: Read + Seek> Read for RevBufReader<R>

pub fn new(inner: R) -> RevBufReader<R>

Creates a new RevBufReader with a default buffer capacity. The default is currently 8 KB, but may change in the future.

Examples

use rev_buf_reader::RevBufReader;
use std::fs::File;

fn main() -> std::io::Result<()> {
    let f = File::open("log.txt")?;
    let reader = RevBufReader::new(f);
    Ok(())
}

Important traits for RevBufReader<R>

impl<R: Read + Seek> Read for RevBufReader<R>

pub fn with_capacity(cap: usize, inner: R) -> RevBufReader<R>

Creates a new RevBufReader with the specified buffer capacity.

Examples

Creating a buffer with ten bytes of capacity:

use rev_buf_reader::RevBufReader;
use std::fs::File;

fn main() -> std::io::Result<()> {
    let f = File::open("log.txt")?;
    let reader = RevBufReader::with_capacity(10, f);
    Ok(())
}

impl<R: Read> RevBufReader<R>

pub fn get_ref(&self) -> &R

Gets a reference to the underlying reader.

It is inadvisable to directly read from the underlying reader.

Examples

use rev_buf_reader::RevBufReader;
use std::fs::File;

fn main() -> std::io::Result<()> {
    let f1 = File::open("log.txt")?;
    let reader = RevBufReader::new(f1);

    let f2 = reader.get_ref();
    Ok(())
}

pub fn get_mut(&mut self) -> &mut R

Gets a mutable reference to the underlying reader.

It is inadvisable to directly read from the underlying reader.

Examples

use rev_buf_reader::RevBufReader;
use std::fs::File;

fn main() -> std::io::Result<()> {
    let f1 = File::open("log.txt")?;
    let mut reader = RevBufReader::new(f1);

    let f2 = reader.get_mut();
    Ok(())
}

pub fn buffer(&self) -> &[u8]

Returns a reference to the internally buffered data.

Unlike fill_buf, this will not attempt to fill the buffer if it is empty.

Examples

use rev_buf_reader::RevBufReader;
use std::io::BufRead;
use std::fs::File;

fn main() -> std::io::Result<()> {
    let f = File::open("log.txt")?;
    let mut reader = RevBufReader::new(f);
    assert!(reader.buffer().is_empty());

    if reader.fill_buf()?.len() > 0 {
        assert!(!reader.buffer().is_empty());
    }
    Ok(())
}

pub fn into_inner(self) -> R

Unwraps this RevBufReader, returning the underlying reader.

Note that any leftover data in the internal buffer is lost.

Examples

use rev_buf_reader::RevBufReader;
use std::fs::File;

fn main() -> std::io::Result<()> {
    let f1 = File::open("log.txt")?;
    let reader = RevBufReader::new(f1);

    let f2 = reader.into_inner();
    Ok(())
}

impl<R: Seek> RevBufReader<R>

pub fn seek_relative(&mut self, offset: i64) -> Result<()>

Seeks relative to the current position. If the new position lies within the buffer, the buffer will not be flushed, allowing for more efficient seeks. This method does not return the location of the underlying reader, so the caller must track this information themselves if it is required.

Trait Implementations

impl<R> Debug for RevBufReader<R> where
    R: Debug, 

fn fmt(&self, fmt: &mut Formatter) -> Result

Formats the value using the given formatter.

impl<R: Read + Seek> BufRead for RevBufReader<R>

fn fill_buf(&mut self) -> Result<&[u8]>

Returns the contents of the internal buffer, filling it with more data from the inner reader if it is empty.

fn consume(&mut self, amt: usize)

Tells this buffer that amt bytes have been consumed from the buffer, so they should no longer be returned in calls to read.

fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize>

Read all bytes into buf until the delimiter byte or EOF is reached.

fn read_line(&mut self, buf: &mut String) -> Result<usize>

Read all bytes until a newline (the 0xA byte) is reached, and append them to the provided buffer.

fn split(self, byte: u8) -> Split<Self>

Returns an iterator over the contents of this reader split on the byte byte.

fn lines(self) -> Lines<Self>

Returns an iterator over the lines of this reader.

impl<R: Read + Seek> Read for RevBufReader<R>

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

Pull some bytes from this source into the specified buffer, returning how many bytes were read.

fn read_vectored(&mut self, bufs: &mut [IoVecMut]) -> Result<usize, Error>

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

Like read, except that it reads into a slice of buffers.

unsafe fn initializer(&self) -> Initializer

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

Determines if this Reader can work with buffers of uninitialized memory.

fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize, Error>

Read all bytes until EOF in this source, placing them into buf.

fn read_to_string(&mut self, buf: &mut String) -> Result<usize, Error>

Read all bytes until EOF in this source, appending them to buf.

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

Read the exact number of bytes required to fill buf.

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

Creates a "by reference" adaptor for this instance of Read.

fn bytes(self) -> Bytes<Self>

Transforms this Read instance to an [Iterator] over its bytes.

fn chain<R>(self, next: R) -> Chain<Self, R> where
    R: Read, 

Creates an adaptor which will chain this stream with another.

fn take(self, limit: u64) -> Take<Self>

Creates an adaptor which will read at most limit bytes from it.

impl<R: Seek> Seek for RevBufReader<R>

fn seek(&mut self, pos: SeekFrom) -> Result<u64>

Seek to an offset, in bytes, in the underlying reader.

The position used for seeking with SeekFrom::Current(_) is the position the underlying reader would be at if the RevBufReader had no internal buffer.

Seeking always discards the internal buffer, even if the seek position would otherwise fall within it. This guarantees that calling .into_inner() immediately after a seek yields the underlying reader at the same position.

To seek without discarding the internal buffer, use RevBufReader::seek_relative.

See std::io::Seek for more details.

Note: In the edge case where you're seeking with SeekFrom::Current(n) where n minus the internal buffer length overflows an i64, two seeks will be performed instead of one. If the second seek returns Err, the underlying reader will be left at the same position it would have if you called seek with SeekFrom::Current(0).