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86 lines
2.6 KiB
Rust
86 lines
2.6 KiB
Rust
use std::io::{self, Read};
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use std::iter::FromIterator;
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pub struct ReadableSlices<A> {
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inner: Vec<A>,
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pos: u64,
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}
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impl<A> FromIterator<A> for ReadableSlices<A> {
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fn from_iter<T: IntoIterator<Item = A>>(iter: T) -> Self {
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ReadableSlices { inner: iter.into_iter().collect(), pos: 0 }
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}
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}
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impl<A: AsRef<[u8]>> Read for ReadableSlices<A> {
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fn read(&mut self, mut buf: &mut [u8]) -> io::Result<usize> {
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let original_buf_len = buf.len();
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// We explore the list of slices to find the one where we must start reading.
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let mut pos = self.pos;
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let index = match self
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.inner
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.iter()
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.map(|s| s.as_ref().len() as u64)
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.position(|size| pos.checked_sub(size).map(|p| pos = p).is_none())
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{
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Some(index) => index,
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None => return Ok(0),
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};
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let mut inner_pos = pos as usize;
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for slice in &self.inner[index..] {
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let slice = &slice.as_ref()[inner_pos..];
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if buf.len() > slice.len() {
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// We must exhaust the current slice and go to the next one there is not enough here.
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buf[..slice.len()].copy_from_slice(slice);
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buf = &mut buf[slice.len()..];
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inner_pos = 0;
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} else {
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// There is enough in this slice to fill the remaining bytes of the buffer.
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// Let's break just after filling it.
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buf.copy_from_slice(&slice[..buf.len()]);
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buf = &mut [];
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break;
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}
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}
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let written = original_buf_len - buf.len();
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self.pos += written as u64;
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Ok(written)
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}
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}
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#[cfg(test)]
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mod test {
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use std::io::Read;
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use super::ReadableSlices;
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#[test]
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fn basic() {
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let data: Vec<_> = (0..100).collect();
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let splits: Vec<_> = data.chunks(3).collect();
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let mut rdslices: ReadableSlices<_> = splits.into_iter().collect();
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let mut output = Vec::new();
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let length = rdslices.read_to_end(&mut output).unwrap();
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assert_eq!(length, data.len());
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assert_eq!(output, data);
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}
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#[test]
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fn small_reads() {
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let data: Vec<_> = (0..u8::MAX).collect();
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let splits: Vec<_> = data.chunks(27).collect();
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let mut rdslices: ReadableSlices<_> = splits.into_iter().collect();
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let buffer = &mut [0; 45];
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let length = rdslices.read(buffer).unwrap();
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let expected: Vec<_> = (0..buffer.len() as u8).collect();
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assert_eq!(length, buffer.len());
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assert_eq!(buffer, &expected[..]);
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}
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}
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