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article_scraper/src/full_text_parser/readability/mod.rs
2023-03-26 11:31:59 +02:00

711 lines
30 KiB
Rust

mod state;
#[cfg(test)]
mod tests;
use std::cmp::Ordering;
use libxml::tree::{Document, Node};
use self::state::State;
use super::error::FullTextParserError;
use crate::{constants, util::Util};
pub struct Readability;
impl Readability {
pub fn extract_body(
document: Document,
root: &mut Node,
title: Option<&str>,
) -> Result<bool, FullTextParserError> {
let mut state = State::default();
let mut document = document;
let mut attempts: Vec<(Node, usize, Document)> = Vec::new();
let document_cache = document
.dup()
.map_err(|()| FullTextParserError::Readability)?;
loop {
let mut elements_to_score = Vec::new();
let mut node: Option<Node> = document.clone().get_root_element();
while let Some(node_ref) = node.as_mut() {
let tag_name = node_ref.get_name().to_uppercase();
if tag_name == "TEXT" && node_ref.get_content().trim().is_empty() {
node = Util::next_node(node_ref, true);
continue;
}
let match_string = node_ref
.get_class_names()
.iter()
.fold(String::new(), |a, b| format!("{a} {b}"));
let match_string = match node_ref.get_property("id") {
Some(id) => format!("{match_string} {id}"),
None => match_string,
};
if !Util::is_probably_visible(node_ref) {
node = Util::remove_and_next(node_ref);
continue;
}
if Self::check_byline(node_ref, &match_string, &mut state) {
node = Util::remove_and_next(node_ref);
continue;
}
if state.should_remove_title_header
&& Self::header_duplicates_title(node_ref, title)
{
state.should_remove_title_header = false;
node = Util::remove_and_next(node_ref);
continue;
}
// Remove unlikely candidates
if state.strip_unlikely {
if constants::UNLIELY_CANDIDATES.is_match(&match_string)
&& !constants::OKAY_MAYBE_ITS_A_CANDIDATE.is_match(&match_string)
&& !Util::has_ancestor_tag(
node_ref,
"table",
None,
None::<fn(&Node) -> bool>,
)
&& !Util::has_ancestor_tag(
node_ref,
"code",
None,
None::<fn(&Node) -> bool>,
)
&& tag_name != "BODY"
&& tag_name != "A"
{
node = Util::remove_and_next(node_ref);
continue;
}
if let Some(role) = node_ref.get_attribute("role") {
if constants::UNLIKELY_ROLES.contains(&role.as_str()) {
node = Util::remove_and_next(node_ref);
continue;
}
}
}
// Remove DIV, SECTION, and HEADER nodes without any content(e.g. text, image, video, or iframe).
if (tag_name == "DIV"
|| tag_name == "SECTION"
|| tag_name == "HEADER"
|| tag_name == "H1"
|| tag_name == "H2"
|| tag_name == "H3"
|| tag_name == "H4"
|| tag_name == "H5"
|| tag_name == "H6")
&& Util::is_element_without_content(node_ref)
{
node = Util::remove_and_next(node_ref);
continue;
}
if constants::DEFAULT_TAGS_TO_SCORE.contains(&tag_name.as_str()) {
elements_to_score.push(node_ref.clone());
}
// Turn all divs that don't have children block level elements into p's
if tag_name == "DIV" {
// Put phrasing content into paragraphs.
let mut p: Option<Node> = None;
for mut child in node_ref.get_child_nodes().into_iter() {
if Util::is_phrasing_content(&child) {
if let Some(p) = p.as_mut() {
child.unlink();
p.add_child(&mut child).map_err(|error| {
log::error!("{error}");
FullTextParserError::Readability
})?;
} else if !Util::is_whitespace(&child) {
let mut new_node = Node::new("p", None, &document)
.map_err(|()| FullTextParserError::Readability)?;
let mut old_node = node_ref
.replace_child_node(new_node.clone(), child)
.map_err(|error| {
log::error!("{error}");
FullTextParserError::Readability
})?;
new_node.add_child(&mut old_node).map_err(|error| {
log::error!("{error}");
FullTextParserError::Readability
})?;
p.replace(new_node);
}
} else if p.is_some() {
if let Some(p) = p.as_mut() {
for mut r_node in p.get_child_nodes().into_iter().rev() {
if Util::is_whitespace(&r_node) {
r_node.unlink();
continue;
}
break;
}
}
_ = p.take();
}
}
// Sites like http://mobile.slate.com encloses each paragraph with a DIV
// element. DIVs with only a P element inside and no text content can be
// safely converted into plain P elements to avoid confusing the scoring
// algorithm with DIVs with are, in practice, paragraphs.
if Util::has_single_tag_inside_element(node_ref, "P")
&& Util::get_link_density(node_ref) < 0.25
{
if let Some(new_node) = node_ref.get_first_element_child() {
if let Some(mut parent) = node_ref.get_parent() {
parent
.replace_child_node(new_node.clone(), node_ref.clone())
.map_err(|error| {
log::error!("{error}");
FullTextParserError::Readability
})?;
node = Util::next_node(&new_node, false);
elements_to_score.push(new_node.clone());
continue;
}
}
} else if !Util::has_child_block_element(node_ref)
&& node_ref.set_name("P").is_ok()
{
elements_to_score.push(node_ref.clone());
}
}
node = Util::next_node(node_ref, false);
}
let mut candidates = Vec::new();
// Loop through all paragraphs, and assign a score to them based on how content-y they look.
// Then add their score to their parent node.
// A score is determined by things like number of commas, class names, etc. Maybe eventually link density.
for element_to_score in elements_to_score.drain(..) {
if element_to_score.get_parent().is_none() {
continue;
}
let inner_text = Util::get_inner_text(&element_to_score, true);
let inner_text_len = inner_text.len();
// If this paragraph is less than 25 characters, don't even count it.
if inner_text_len < 25 {
continue;
}
// Exclude nodes with no ancestor.
let ancestors = Util::get_node_ancestors(&element_to_score, Some(5));
if ancestors.is_empty() {
continue;
}
let mut content_score = 0.0;
// Add a point for the paragraph itself as a base.
content_score += 1.0;
// Add points for any commas within this paragraph.
content_score += inner_text.split(',').count() as f64;
// For every 100 characters in this paragraph, add another point. Up to 3 points.
content_score += f64::min(f64::floor(inner_text.len() as f64 / 100.0), 3.0);
// Initialize and score ancestors.
for (level, mut ancestor) in ancestors.into_iter().enumerate() {
let tag_name = ancestor.get_name().to_uppercase();
if ancestor.get_parent().is_none() || tag_name == "HTML" {
continue;
}
if Self::get_content_score(&ancestor).is_none() {
Self::initialize_node(&mut ancestor, &state)?;
candidates.push(ancestor.clone());
}
// Node score divider:
// - parent: 1 (no division)
// - grandparent: 2
// - great grandparent+: ancestor level * 3
let score_divider = if level == 0 {
1.0
} else if level == 1 {
2.0
} else {
level as f64 * 3.0
};
if let Some(score) = Self::get_content_score(&ancestor) {
let add_score = content_score / score_divider;
let new_score = score + add_score;
log::debug!(
"{}: {score} + {add_score} = {new_score}",
ancestor.get_name()
);
Self::set_content_score(&mut ancestor, new_score)?;
}
}
}
// After we've calculated scores, loop through all of the possible
// candidate nodes we found and find the one with the highest score.
for candidate in candidates.iter_mut() {
// Scale the final candidates score based on link density. Good content
// should have a relatively small link density (5% or less) and be mostly
// unaffected by this operation.
if let Some(content_score) = Self::get_content_score(candidate) {
let candidate_score = content_score * (1.0 - Util::get_link_density(candidate));
Self::set_content_score(candidate, candidate_score)?;
}
}
candidates.sort_by(|a, b| {
if let (Some(a), Some(b)) = (Self::get_content_score(a), Self::get_content_score(b))
{
b.partial_cmp(&a).unwrap_or(Ordering::Equal)
} else {
Ordering::Equal
}
});
let top_candidates = candidates.into_iter().take(5).collect::<Vec<_>>();
for candidate in top_candidates.iter() {
log::debug!(
"candidate: {} {:?}",
candidate.get_name(),
candidate.get_attributes()
);
}
let mut needed_to_create_top_candidate = false;
let mut top_candidate = top_candidates.first().cloned().unwrap_or_else(|| {
// If we still have no top candidate, just use the body as a last resort.
// We also have to copy the body node so it is something we can modify.
let mut root = document.get_root_element().expect("doc should have root");
if let Some(body) = root
.get_child_elements()
.into_iter()
.find(|n| n.get_name().to_uppercase() == "BODY")
{
root = body;
}
let mut new_top_candidate =
Node::new("DIV", None, &document).expect("can't create new node");
for mut child in root.get_child_elements().drain(..) {
child.unlink();
new_top_candidate.add_child(&mut child).unwrap();
}
root.add_child(&mut new_top_candidate).unwrap();
Self::initialize_node(&mut new_top_candidate, &state)
.expect("init should not fail");
needed_to_create_top_candidate = true;
new_top_candidate
});
// Util::serialize_node(&top_candidate, "top_candidate.html");
let mut alternative_candidate_ancestors = Vec::new();
// Find a better top candidate node if it contains (at least three) nodes which belong to `topCandidates` array
// and whose scores are quite closed with current `topCandidate` node.
if let Some(top_score) = Self::get_content_score(&top_candidate) {
for candidate in top_candidates.iter().skip(1) {
let score = Self::get_content_score(candidate).unwrap_or(0.0);
if score / top_score >= 0.75 {
alternative_candidate_ancestors
.push(Util::get_node_ancestors(candidate, None));
}
}
}
if alternative_candidate_ancestors.len() >= constants::MINIMUM_TOPCANDIDATES {
let mut parent_of_top_candidate = top_candidate.get_parent();
while let Some(parent) = &parent_of_top_candidate {
if parent.get_name().to_uppercase() == "BODY" {
break;
}
let mut lists_containing_this_ancestor = 0;
let tmp = usize::min(
alternative_candidate_ancestors.len(),
constants::MINIMUM_TOPCANDIDATES,
);
for ancestors in alternative_candidate_ancestors.iter().take(tmp) {
lists_containing_this_ancestor +=
ancestors.iter().filter(|n| n == &parent).count();
}
if lists_containing_this_ancestor >= constants::MINIMUM_TOPCANDIDATES {
top_candidate = parent.clone();
break;
}
parent_of_top_candidate = parent_of_top_candidate.and_then(|n| n.get_parent());
}
}
if Self::get_content_score(&top_candidate).is_none() {
Self::initialize_node(&mut top_candidate, &state)?;
}
//Util::serialize_node(&top_candidate, "new_top_candidate.html");
// Because of our bonus system, parents of candidates might have scores
// themselves. They get half of the node. There won't be nodes with higher
// scores than our topCandidate, but if we see the score going *up* in the first
// few steps up the tree, that's a decent sign that there might be more content
// lurking in other places that we want to unify in. The sibling stuff
// below does some of that - but only if we've looked high enough up the DOM
// tree.
let mut parent_of_top_candidate = top_candidate.get_parent();
let mut last_score = Self::get_content_score(&top_candidate).unwrap_or(0.0);
// The scores shouldn't get too low.
let score_threshold = last_score / 3.0;
while parent_of_top_candidate.is_some()
&& !Util::has_tag_name(parent_of_top_candidate.as_ref(), "BODY")
{
if parent_of_top_candidate
.as_ref()
.map(|n| Self::get_content_score(n).is_none())
.unwrap_or(false)
{
parent_of_top_candidate = parent_of_top_candidate.and_then(|n| n.get_parent());
continue;
}
let parent_score = parent_of_top_candidate
.as_ref()
.and_then(Self::get_content_score)
.unwrap_or(0.0);
if parent_score < score_threshold {
break;
}
if parent_score > last_score {
// Alright! We found a better parent to use.
if let Some(parent) = parent_of_top_candidate {
top_candidate = parent;
}
break;
}
last_score = parent_of_top_candidate
.as_ref()
.and_then(Self::get_content_score)
.unwrap_or(0.0);
parent_of_top_candidate = parent_of_top_candidate.and_then(|n| n.get_parent());
}
// If the top candidate is the only child, use parent instead. This will help sibling
// joining logic when adjacent content is actually located in parent's sibling node.
parent_of_top_candidate = top_candidate.get_parent();
while !Util::has_tag_name(parent_of_top_candidate.as_ref(), "BODY")
&& parent_of_top_candidate
.as_ref()
.map(|n| n.get_child_elements().len() == 1)
.unwrap_or(false)
{
top_candidate = parent_of_top_candidate.ok_or(FullTextParserError::Readability)?;
parent_of_top_candidate = top_candidate.get_parent();
}
if Self::get_content_score(&top_candidate).is_none() {
Self::initialize_node(&mut top_candidate, &state)?;
}
// Now that we have the top candidate, look through its siblings for content
// that might also be related. Things like preambles, content split by ads
// that we removed, etc.
let mut article_content =
Node::new("DIV", None, &document).map_err(|()| FullTextParserError::Readability)?;
let sibling_score_threshold = f64::max(
10.0,
Self::get_content_score(&top_candidate).unwrap_or(0.0) * 0.2,
);
// Keep potential top candidate's parent node to try to get text direction of it later.
parent_of_top_candidate = top_candidate.get_parent();
let siblings = parent_of_top_candidate
.as_ref()
.map(|n| n.get_child_elements());
if let Some(mut siblings) = siblings {
for mut sibling in siblings.drain(..) {
let mut append = false;
let score = Self::get_content_score(&sibling).unwrap_or(0.0);
log::debug!(
"Looking at sibling node: {} ({:?}) with score {score}",
sibling.get_name(),
sibling.get_attribute("class")
);
if top_candidate == sibling {
append = true;
} else {
let mut content_bonus = 0.0;
// Give a bonus if sibling nodes and top candidates have the example same classname
let sibling_classes = sibling.get_class_names();
let tc_classes = top_candidate.get_class_names();
if !tc_classes.is_empty()
&& !sibling_classes.is_empty()
&& sibling_classes
.iter()
.all(|class| tc_classes.contains(class))
{
content_bonus +=
Self::get_content_score(&top_candidate).unwrap_or(0.0) * 0.2;
}
if score + content_bonus >= sibling_score_threshold {
append = true;
} else if sibling.get_name().to_uppercase() == "P" {
let link_density = Util::get_link_density(&sibling);
let node_content = Util::get_inner_text(&sibling, false);
let node_length = node_content.len();
if node_length > 80
&& (link_density < 0.25
|| (node_length > 0
&& link_density == 0.0
&& constants::SIBLING_CONTENT.is_match(&node_content)))
{
append = true;
}
}
}
if append {
log::debug!(
"Appending node: {} ({:?})",
sibling.get_name(),
sibling.get_attribute("class")
);
if !constants::ALTER_TO_DIV_EXCEPTIONS
.contains(sibling.get_name().to_uppercase().as_str())
{
// We have a node that isn't a common block level element, like a form or td tag.
// Turn it into a div so it doesn't get filtered out later by accident.
log::debug!(
"Altering sibling: {} ({:?})",
sibling.get_name(),
sibling.get_attribute("class")
);
sibling.set_name("DIV").map_err(|error| {
log::error!("{error}");
FullTextParserError::Readability
})?;
}
sibling.unlink();
article_content.add_child(&mut sibling).map_err(|error| {
log::error!("{error}");
FullTextParserError::Readability
})?;
}
}
}
if state.clean_conditionally {
crate::FullTextParser::post_process_page(&mut article_content)?;
}
if needed_to_create_top_candidate {
// We already created a fake div thing, and there wouldn't have been any siblings left
// for the previous loop, so there's no point trying to create a new div, and then
// move all the children over. Just assign IDs and class names here. No need to append
// because that already happened anyway.
top_candidate
.set_property("id", "readability-page-1")
.map_err(|error| {
log::error!("{error}");
FullTextParserError::Readability
})?;
} else {
let mut div = Node::new("DIV", None, &document)
.map_err(|()| FullTextParserError::Readability)?;
div.set_property("id", "readability-page-1")
.map_err(|error| {
log::error!("{error}");
FullTextParserError::Readability
})?;
for mut child in article_content.get_child_nodes() {
child.unlink();
div.add_child(&mut child).map_err(|error| {
log::error!("{error}");
FullTextParserError::Readability
})?;
}
article_content.add_child(&mut div).map_err(|error| {
log::error!("{error}");
FullTextParserError::Readability
})?;
}
let mut parse_successful = true;
// Now that we've gone through the full algorithm, check to see if
// we got any meaningful content. If we didn't, we may need to re-run
// grabArticle with different flags set. This gives us a higher likelihood of
// finding the content, and the sieve approach gives us a higher likelihood of
// finding the -right- content.
let text = Util::get_inner_text(&article_content, true);
let text_length = text.len();
//Util::serialize_node(&article_content, "debug.html");
if text_length < constants::DEFAULT_CHAR_THRESHOLD {
parse_successful = false;
if state.strip_unlikely {
state.strip_unlikely = false;
attempts.push((article_content, text_length, document));
} else if state.weigh_classes {
state.weigh_classes = false;
attempts.push((article_content, text_length, document));
} else if state.clean_conditionally {
state.clean_conditionally = false;
attempts.push((article_content, text_length, document));
} else {
attempts.push((article_content, text_length, document));
// No luck after removing flags, just return the longest text we found during the different loops
attempts.sort_by(|(_, size_a, _), (_, size_b, _)| size_a.cmp(size_b));
// But first check if we actually have something
if let Some((best_attempt, _len, _document)) = attempts.pop() {
for mut child in best_attempt.get_child_nodes() {
child.unlink();
root.add_child(&mut child).map_err(|error| {
log::error!("{error}");
FullTextParserError::Readability
})?;
}
parse_successful = true;
}
return Ok(parse_successful);
}
document = document_cache
.dup()
.map_err(|()| FullTextParserError::Readability)?;
} else {
for mut child in article_content.get_child_nodes() {
child.unlink();
root.add_child(&mut child).map_err(|error| {
log::error!("{error}");
FullTextParserError::Readability
})?;
}
return Ok(parse_successful);
}
}
}
fn get_content_score(node: &Node) -> Option<f64> {
node.get_attribute(constants::SCORE_ATTR)
.and_then(|a| a.parse::<f64>().ok())
}
fn set_content_score(node: &mut Node, score: f64) -> Result<(), FullTextParserError> {
node.set_attribute(constants::SCORE_ATTR, &score.to_string())
.map_err(|err| {
log::error!("failed to set content score: {err}");
FullTextParserError::Readability
})
}
fn check_byline(node: &Node, matchstring: &str, state: &mut State) -> bool {
if state.byline.is_some() {
return false;
}
let rel = node
.get_attribute("rel")
.map(|rel| rel == "author")
.unwrap_or(false);
let itemprop = node
.get_attribute("itemprop")
.map(|prop| prop.contains("author"))
.unwrap_or(false);
let content = node.get_content();
if rel
|| itemprop
|| constants::BYLINE.is_match(matchstring) && Self::is_valid_byline(&content)
{
state.byline = Some(content.trim().into());
true
} else {
false
}
}
// Check whether the input string could be a byline.
// This verifies that the input length is less than 100 chars.
fn is_valid_byline(line: &str) -> bool {
let len = line.trim().len();
len > 0 && len < 100
}
// Check if this node is an H1 or H2 element whose content is mostly
// the same as the article title.
fn header_duplicates_title(node: &Node, title: Option<&str>) -> bool {
let name = node.get_name().to_lowercase();
if name != "h1" && name != "h2" {
return false;
}
let heading = Util::get_inner_text(node, false);
if let Some(title) = title {
Util::text_similarity(&heading, title) > 0.75
} else {
false
}
}
// Initialize a node with the readability object. Also checks the
// className/id for special names to add to its score.
fn initialize_node(node: &mut Node, state: &State) -> Result<(), FullTextParserError> {
let score = match node.get_name().to_uppercase().as_str() {
"DIV" => 5,
"PRE" | "TD" | "BLOCKQUITE" => 3,
"ADDRESS" | "OL" | "UL" | "DL" | "DD" | "DT" | "LI" | "FORM" => -3,
"H1" | "H2" | "H3" | "H4" | "H5" | "H6" | "TH" => -5,
_ => 0,
};
let class_weight = if state.weigh_classes {
Util::get_class_weight(node)
} else {
0
};
let score = score + class_weight;
Self::set_content_score(node, score as f64)?;
Ok(())
}
}