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use std::io; use std::error::Error; use std::cmp; const DAFAULT_BUF_SIZE: usize = 8 * 1024; #[derive(Debug)] pub struct RollBuf<R> { inner: R, buf: Vec<u8>, pos: usize, end: usize, aux: Vec<u8>, is_rolled: bool, max_cap: usize, } impl<R: io::Read> RollBuf<R> { pub fn new(inner: R) -> RollBuf<R> { Self::with_capacity(DAFAULT_BUF_SIZE, inner) } pub fn with_capacity(cap: usize, inner: R) -> RollBuf<R> { RollBuf { inner , buf: vec![0; cap], pos: 0, end: 0, aux: vec![0; cap], is_rolled: false, max_cap: 1 << 24, } } #[inline] pub fn capacity(&self) -> usize { self.buf.len() } #[inline] pub fn end_position(&self) -> usize { self.end } pub fn fill_buf(&mut self) -> Result<bool, Box<Error>> { if self.pos >= self.end { debug_assert!(self.pos == self.end); self.end = self.inner.read(&mut self.buf)?; self.pos = 0; } if self.is_rolled { self.end += self.inner.read(&mut self.buf[self.end..])?; self.is_rolled = false; } let is_full = self.buf.len() == self.end; Ok(is_full) } pub fn consume(&mut self, n: usize) { self.pos = cmp::min(self.pos + n, self.end); } pub fn roll(&mut self) { if self.pos > 0 { self.aux.clear(); self.aux.extend_from_slice(&self.buf[self.pos..self.end]); let new_end = self.aux.len(); self.buf[0..new_end].copy_from_slice(&self.aux); self.pos = 0; self.end = new_end; } else { let old_len = self.buf.len(); let reserved = cmp::min(old_len, self.max_cap - old_len); self.buf.reserve(reserved); self.buf.extend((0..reserved).map(|_| 0)); } self.is_rolled = true; } pub fn contents(&self) -> &[u8] { &self.buf[self.pos..self.end] } pub fn is_full(&self) -> bool { self.buf.len() == self.end } } #[cfg(test)] mod tests { use super::{RollBuf}; #[test] fn test_rollbuf_no_extend() { let inner: &[u8] = &[1, 2, 3, 4, 5, 6, 7]; let mut b = RollBuf::with_capacity(3, inner); struct TestCase { consume: usize, roll: bool, want: (Vec<u8>, bool), } let test_cases = vec![ TestCase { consume: 2, roll: false, want: (vec![1, 2, 3], true) }, TestCase { consume: 2, roll: false, want: (vec![3], true) }, TestCase { consume: 1, roll: false, want: (vec![4, 5, 6], true) }, TestCase { consume: 2, roll: true, want: (vec![6, 7], false) }, TestCase { consume: 2, roll: false, want: (vec![], false) }, ]; for t in test_cases { b.consume(t.consume); if t.roll { b.roll(); } let is_full = b.fill_buf().unwrap(); let contents = b.contents(); assert_eq!((contents, is_full), (t.want.0.as_slice(), t.want.1)); } } #[test] fn test_rollbuf_extend() { let inner: &[u8] = &[1, 2, 3, 4, 5, 6, 7]; let mut b = RollBuf::with_capacity(3, inner); struct TestCase { consume: usize, roll: bool, want: (Vec<u8>, bool), } let test_cases = vec![ TestCase { consume: 2, roll: false, want: (vec![1, 2, 3], true) }, TestCase { consume: 0, roll: true, want: (vec![1, 2, 3, 4, 5, 6], true) }, TestCase { consume: 4, roll: false, want: (vec![5, 6], true) }, TestCase { consume: 2, roll: true, want: (vec![7], false) }, TestCase { consume: 2, roll: false, want: (vec![], false) }, ]; for t in test_cases { b.consume(t.consume); if t.roll { b.roll(); } let is_full = b.fill_buf().unwrap(); let contents = b.contents(); assert_eq!((contents, is_full), (t.want.0.as_slice(), t.want.1)); } } }