markup5ever/util/buffer_queue.rs
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// Copyright 2014-2017 The html5ever Project Developers. See the
// COPYRIGHT file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! The `BufferQueue` struct and helper types.
//!
//! This type is designed for the efficient parsing of string data, especially where many
//! significant characters are from the ascii range 0-63. This includes, for example, important
//! characters in xml/html parsing.
//!
//! Good and predictable performance is achieved by avoiding allocation where possible (a.k.a. zero
//! copy).
//!
//! [`BufferQueue`]: struct.BufferQueue.html
use std::{cell::RefCell, collections::VecDeque, mem};
use tendril::StrTendril;
pub use self::SetResult::{FromSet, NotFromSet};
use crate::util::smallcharset::SmallCharSet;
/// Result from [`pop_except_from`] containing either a character from a [`SmallCharSet`], or a
/// string buffer of characters not from the set.
///
/// [`pop_except_from`]: struct.BufferQueue.html#method.pop_except_from
/// [`SmallCharSet`]: ../struct.SmallCharSet.html
#[derive(PartialEq, Eq, Debug)]
pub enum SetResult {
/// A character from the `SmallCharSet`.
FromSet(char),
/// A string buffer containing no characters from the `SmallCharSet`.
NotFromSet(StrTendril),
}
/// A queue of owned string buffers, which supports incrementally consuming characters.
///
/// Internally it uses [`VecDeque`] and has the same complexity properties.
///
/// [`VecDeque`]: https://doc.rust-lang.org/std/collections/struct.VecDeque.html
#[derive(Debug)]
pub struct BufferQueue {
/// Buffers to process.
buffers: RefCell<VecDeque<StrTendril>>,
}
impl Default for BufferQueue {
/// Create an empty BufferQueue.
#[inline]
fn default() -> Self {
Self {
buffers: RefCell::new(VecDeque::with_capacity(16)),
}
}
}
impl BufferQueue {
/// Returns whether the queue is empty.
#[inline]
pub fn is_empty(&self) -> bool {
self.buffers.borrow().is_empty()
}
/// Get the buffer at the beginning of the queue.
#[inline]
pub fn pop_front(&self) -> Option<StrTendril> {
self.buffers.borrow_mut().pop_front()
}
/// Add a buffer to the beginning of the queue.
///
/// If the buffer is empty, it will be skipped.
pub fn push_front(&self, buf: StrTendril) {
if buf.len32() == 0 {
return;
}
self.buffers.borrow_mut().push_front(buf);
}
/// Add a buffer to the end of the queue.
///
/// If the buffer is empty, it will be skipped.
pub fn push_back(&self, buf: StrTendril) {
if buf.len32() == 0 {
return;
}
self.buffers.borrow_mut().push_back(buf);
}
/// Look at the next available character without removing it, if the queue is not empty.
pub fn peek(&self) -> Option<char> {
debug_assert!(
!self.buffers.borrow().iter().any(|el| el.len32() == 0),
"invariant \"all buffers in the queue are non-empty\" failed"
);
self.buffers
.borrow()
.front()
.map(|b| b.chars().next().unwrap())
}
/// Pops and returns either a single character from the given set, or
/// a buffer of characters none of which are in the set.
///
/// # Examples
///
/// ```
/// # #[macro_use] extern crate markup5ever;
/// # #[macro_use] extern crate tendril;
/// # fn main() {
/// use markup5ever::buffer_queue::{BufferQueue, SetResult};
///
/// let mut queue = BufferQueue::default();
/// queue.push_back(format_tendril!(r#"<some_tag attr="text">SomeText</some_tag>"#));
/// let set = small_char_set!(b'<' b'>' b' ' b'=' b'"' b'/');
/// let tag = format_tendril!("some_tag");
/// let attr = format_tendril!("attr");
/// let attr_val = format_tendril!("text");
/// assert_eq!(queue.pop_except_from(set), Some(SetResult::FromSet('<')));
/// assert_eq!(queue.pop_except_from(set), Some(SetResult::NotFromSet(tag)));
/// assert_eq!(queue.pop_except_from(set), Some(SetResult::FromSet(' ')));
/// assert_eq!(queue.pop_except_from(set), Some(SetResult::NotFromSet(attr)));
/// assert_eq!(queue.pop_except_from(set), Some(SetResult::FromSet('=')));
/// assert_eq!(queue.pop_except_from(set), Some(SetResult::FromSet('"')));
/// assert_eq!(queue.pop_except_from(set), Some(SetResult::NotFromSet(attr_val)));
/// // ...
/// # }
/// ```
pub fn pop_except_from(&self, set: SmallCharSet) -> Option<SetResult> {
let (result, now_empty) = match self.buffers.borrow_mut().front_mut() {
None => (None, false),
Some(buf) => {
let n = set.nonmember_prefix_len(buf);
if n > 0 {
let out;
unsafe {
out = buf.unsafe_subtendril(0, n);
buf.unsafe_pop_front(n);
}
(Some(NotFromSet(out)), buf.is_empty())
} else {
let c = buf.pop_front_char().expect("empty buffer in queue");
(Some(FromSet(c)), buf.is_empty())
}
},
};
// Unborrow self for this part.
if now_empty {
self.buffers.borrow_mut().pop_front();
}
result
}
/// Consume bytes matching the pattern, using a custom comparison function `eq`.
///
/// Returns `Some(true)` if there is a match, `Some(false)` if there is no match, or `None` if
/// it wasn't possible to know (more data is needed).
///
/// The custom comparison function is used elsewhere to compare ascii-case-insensitively.
///
/// # Examples
///
/// ```
/// # extern crate markup5ever;
/// # #[macro_use] extern crate tendril;
/// # fn main() {
/// use markup5ever::buffer_queue::BufferQueue;
///
/// let mut queue = BufferQueue::default();
/// queue.push_back(format_tendril!("testtext"));
/// let test_str = "test";
/// assert_eq!(queue.eat("test", |&a, &b| a == b), Some(true));
/// assert_eq!(queue.eat("text", |&a, &b| a == b), Some(true));
/// assert!(queue.is_empty());
/// # }
/// ```
pub fn eat<F: Fn(&u8, &u8) -> bool>(&self, pat: &str, eq: F) -> Option<bool> {
let mut buffers_exhausted = 0;
let mut consumed_from_last = 0;
self.buffers.borrow().front()?;
for pattern_byte in pat.bytes() {
if buffers_exhausted >= self.buffers.borrow().len() {
return None;
}
let buf = &self.buffers.borrow()[buffers_exhausted];
if !eq(&buf.as_bytes()[consumed_from_last], &pattern_byte) {
return Some(false);
}
consumed_from_last += 1;
if consumed_from_last >= buf.len() {
buffers_exhausted += 1;
consumed_from_last = 0;
}
}
// We have a match. Commit changes to the BufferQueue.
for _ in 0..buffers_exhausted {
self.buffers.borrow_mut().pop_front();
}
match self.buffers.borrow_mut().front_mut() {
None => assert_eq!(consumed_from_last, 0),
Some(ref mut buf) => buf.pop_front(consumed_from_last as u32),
}
Some(true)
}
/// Get the next character if one is available, removing it from the queue.
///
/// This function manages the buffers, removing them as they become empty.
pub fn next(&self) -> Option<char> {
let (result, now_empty) = match self.buffers.borrow_mut().front_mut() {
None => (None, false),
Some(buf) => {
let c = buf.pop_front_char().expect("empty buffer in queue");
(Some(c), buf.is_empty())
},
};
if now_empty {
self.buffers.borrow_mut().pop_front();
}
result
}
pub fn replace_with(&self, other: BufferQueue) {
let _ = mem::replace(&mut *self.buffers.borrow_mut(), other.buffers.take());
}
pub fn swap_with(&self, other: &BufferQueue) {
mem::swap(
&mut *self.buffers.borrow_mut(),
&mut *other.buffers.borrow_mut(),
);
}
}
#[cfg(test)]
#[allow(non_snake_case)]
mod test {
use tendril::SliceExt;
use super::BufferQueue;
use super::SetResult::{FromSet, NotFromSet};
#[test]
fn smoke_test() {
let bq = BufferQueue::default();
assert_eq!(bq.peek(), None);
assert_eq!(bq.next(), None);
bq.push_back("abc".to_tendril());
assert_eq!(bq.peek(), Some('a'));
assert_eq!(bq.next(), Some('a'));
assert_eq!(bq.peek(), Some('b'));
assert_eq!(bq.peek(), Some('b'));
assert_eq!(bq.next(), Some('b'));
assert_eq!(bq.peek(), Some('c'));
assert_eq!(bq.next(), Some('c'));
assert_eq!(bq.peek(), None);
assert_eq!(bq.next(), None);
}
#[test]
fn can_unconsume() {
let bq = BufferQueue::default();
bq.push_back("abc".to_tendril());
assert_eq!(bq.next(), Some('a'));
bq.push_front("xy".to_tendril());
assert_eq!(bq.next(), Some('x'));
assert_eq!(bq.next(), Some('y'));
assert_eq!(bq.next(), Some('b'));
assert_eq!(bq.next(), Some('c'));
assert_eq!(bq.next(), None);
}
#[test]
fn can_pop_except_set() {
let bq = BufferQueue::default();
bq.push_back("abc&def".to_tendril());
let pop = || bq.pop_except_from(small_char_set!('&'));
assert_eq!(pop(), Some(NotFromSet("abc".to_tendril())));
assert_eq!(pop(), Some(FromSet('&')));
assert_eq!(pop(), Some(NotFromSet("def".to_tendril())));
assert_eq!(pop(), None);
}
#[test]
fn can_eat() {
// This is not very comprehensive. We rely on the tokenizer
// integration tests for more thorough testing with many
// different input buffer splits.
let bq = BufferQueue::default();
bq.push_back("a".to_tendril());
bq.push_back("bc".to_tendril());
assert_eq!(bq.eat("abcd", u8::eq_ignore_ascii_case), None);
assert_eq!(bq.eat("ax", u8::eq_ignore_ascii_case), Some(false));
assert_eq!(bq.eat("ab", u8::eq_ignore_ascii_case), Some(true));
assert_eq!(bq.next(), Some('c'));
assert_eq!(bq.next(), None);
}
}