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| 1 | +//! See [`HtmlWithLimit`]. |
| 2 | +
|
| 3 | +use std::fmt::Write; |
| 4 | +use std::ops::ControlFlow; |
| 5 | + |
| 6 | +use crate::html::escape::Escape; |
| 7 | + |
| 8 | +/// A buffer that allows generating HTML with a length limit. |
| 9 | +/// |
| 10 | +/// This buffer ensures that: |
| 11 | +/// |
| 12 | +/// * all tags are closed, |
| 13 | +/// * tags are closed in the reverse order of when they were opened (i.e., the correct HTML order), |
| 14 | +/// * no tags are left empty (e.g., `<em></em>`) due to the length limit being reached, |
| 15 | +/// * all text is escaped. |
| 16 | +#[derive(Debug)] |
| 17 | +pub(super) struct HtmlWithLimit { |
| 18 | + buf: String, |
| 19 | + len: usize, |
| 20 | + limit: usize, |
| 21 | + /// A list of tags that have been requested to be opened via [`Self::open_tag()`] |
| 22 | + /// but have not actually been pushed to `buf` yet. This ensures that tags are not |
| 23 | + /// left empty (e.g., `<em></em>`) due to the length limit being reached. |
| 24 | + queued_tags: Vec<&'static str>, |
| 25 | + /// A list of all tags that have been opened but not yet closed. |
| 26 | + unclosed_tags: Vec<&'static str>, |
| 27 | +} |
| 28 | + |
| 29 | +impl HtmlWithLimit { |
| 30 | + /// Create a new buffer, with a limit of `length_limit`. |
| 31 | + pub(super) fn new(length_limit: usize) -> Self { |
| 32 | + let buf = if length_limit > 1000 { |
| 33 | + // If the length limit is really large, don't preallocate tons of memory. |
| 34 | + String::new() |
| 35 | + } else { |
| 36 | + // The length limit is actually a good heuristic for initial allocation size. |
| 37 | + // Measurements showed that using it as the initial capacity ended up using less memory |
| 38 | + // than `String::new`. |
| 39 | + // See https://github.com/rust-lang/rust/pull/88173#discussion_r692531631 for more. |
| 40 | + String::with_capacity(length_limit) |
| 41 | + }; |
| 42 | + Self { |
| 43 | + buf, |
| 44 | + len: 0, |
| 45 | + limit: length_limit, |
| 46 | + unclosed_tags: Vec::new(), |
| 47 | + queued_tags: Vec::new(), |
| 48 | + } |
| 49 | + } |
| 50 | + |
| 51 | + /// Finish using the buffer and get the written output. |
| 52 | + /// This function will close all unclosed tags for you. |
| 53 | + pub(super) fn finish(mut self) -> String { |
| 54 | + self.close_all_tags(); |
| 55 | + self.buf |
| 56 | + } |
| 57 | + |
| 58 | + /// Write some plain text to the buffer, escaping as needed. |
| 59 | + /// |
| 60 | + /// This function skips writing the text if the length limit was reached |
| 61 | + /// and returns [`ControlFlow::Break`]. |
| 62 | + pub(super) fn push(&mut self, text: &str) -> ControlFlow<(), ()> { |
| 63 | + if self.len + text.len() > self.limit { |
| 64 | + return ControlFlow::BREAK; |
| 65 | + } |
| 66 | + |
| 67 | + self.flush_queue(); |
| 68 | + write!(self.buf, "{}", Escape(text)).unwrap(); |
| 69 | + self.len += text.len(); |
| 70 | + |
| 71 | + ControlFlow::CONTINUE |
| 72 | + } |
| 73 | + |
| 74 | + /// Open an HTML tag. |
| 75 | + /// |
| 76 | + /// **Note:** HTML attributes have not yet been implemented. |
| 77 | + /// This function will panic if called with a non-alphabetic `tag_name`. |
| 78 | + pub(super) fn open_tag(&mut self, tag_name: &'static str) { |
| 79 | + assert!( |
| 80 | + tag_name.chars().all(|c| ('a'..='z').contains(&c)), |
| 81 | + "tag_name contained non-alphabetic chars: {:?}", |
| 82 | + tag_name |
| 83 | + ); |
| 84 | + self.queued_tags.push(tag_name); |
| 85 | + } |
| 86 | + |
| 87 | + /// Close the most recently opened HTML tag. |
| 88 | + pub(super) fn close_tag(&mut self) { |
| 89 | + match self.unclosed_tags.pop() { |
| 90 | + // Close the most recently opened tag. |
| 91 | + Some(tag_name) => write!(self.buf, "</{}>", tag_name).unwrap(), |
| 92 | + // There are valid cases where `close_tag()` is called without |
| 93 | + // there being any tags to close. For example, this occurs when |
| 94 | + // a tag is opened after the length limit is exceeded; |
| 95 | + // `flush_queue()` will never be called, and thus, the tag will |
| 96 | + // not end up being added to `unclosed_tags`. |
| 97 | + None => {} |
| 98 | + } |
| 99 | + } |
| 100 | + |
| 101 | + /// Write all queued tags and add them to the `unclosed_tags` list. |
| 102 | + fn flush_queue(&mut self) { |
| 103 | + for tag_name in self.queued_tags.drain(..) { |
| 104 | + write!(self.buf, "<{}>", tag_name).unwrap(); |
| 105 | + |
| 106 | + self.unclosed_tags.push(tag_name); |
| 107 | + } |
| 108 | + } |
| 109 | + |
| 110 | + /// Close all unclosed tags. |
| 111 | + fn close_all_tags(&mut self) { |
| 112 | + while !self.unclosed_tags.is_empty() { |
| 113 | + self.close_tag(); |
| 114 | + } |
| 115 | + } |
| 116 | +} |
| 117 | + |
| 118 | +#[cfg(test)] |
| 119 | +mod tests; |
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