Rework handling general entity references (&entity;)
#766
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,76 +1,207 @@ | ||
| //! This example demonstrate how custom entities can be extracted from the DOCTYPE, | ||
| //! and later use to: | ||
| //! - insert new pieces of document (particular case - insert only textual content) | ||
| //! - decode attribute values | ||
| //! | ||
| //! NB: this example is deliberately kept simple: | ||
| //! * it assumes that the XML file is UTF-8 encoded (custom_entities must only contain UTF-8 data) | ||
| //! * it only handles internal entities; | ||
| //! * the regex in this example is simple but brittle; | ||
| //! * it does not support the use of entities in entity declaration. | ||
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| use std::borrow::Cow; | ||
| use std::collections::{HashMap, VecDeque}; | ||
| use std::str::from_utf8; | ||
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| use quick_xml::encoding::Decoder; | ||
| use quick_xml::errors::Error; | ||
| use quick_xml::escape::EscapeError; | ||
| use quick_xml::events::{BytesEnd, BytesStart, BytesText, Event}; | ||
| use quick_xml::name::QName; | ||
| use quick_xml::reader::Reader; | ||
| use regex::bytes::Regex; | ||
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| use pretty_assertions::assert_eq; | ||
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| struct MyReader<'i> { | ||
|
There was a problem hiding this comment. You mentioned a future PR that would implement this functionality on There was a problem hiding this comment. My point just being that the current example as-is is a bit much to expect people to implement or copy and paste, and I just want to check my understanding that it's not a long-term solution. There was a problem hiding this comment. I have not really decided yet whether to leave this example as it is to demonstrate how the reader stack can be implemented if for some reason the standard solution does not work, or rewrite it to a new API. If it remains as it is, then there will be a mention of the standard way |
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| /// Stack of readers, the first element is the initial reader, the other are | ||
| /// readers created for each resolved entity | ||
| readers: VecDeque<Reader<&'i [u8]>>, | ||
| /// Map of captured internal _parsed general entities_. _Parsed_ means that | ||
| /// value of the entity is parsed by XML reader | ||
| entities: HashMap<&'i [u8], &'i [u8]>, | ||
| /// In this example we use simple regular expression to capture entities from DTD. | ||
| /// In real application you should use DTD parser. | ||
| entity_re: Regex, | ||
| } | ||
| impl<'i> MyReader<'i> { | ||
| fn new(input: &'i str) -> Result<Self, regex::Error> { | ||
| let mut reader = Reader::from_str(input); | ||
| reader.config_mut().trim_text(true); | ||
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| let mut readers = VecDeque::new(); | ||
| readers.push_back(reader); | ||
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| // Capture "name" and "content" from such string: | ||
| // <!ENTITY name "content" > | ||
| let entity_re = Regex::new(r#"<!ENTITY\s+([^ \t\r\n]+)\s+"([^"]*)"\s*>"#)?; | ||
| Ok(Self { | ||
| readers, | ||
| entities: HashMap::new(), | ||
| entity_re, | ||
| }) | ||
| } | ||
| fn read_event(&mut self) -> Result<Event<'i>, Error> { | ||
| loop { | ||
| if let Some(mut reader) = self.readers.pop_back() { | ||
| match dbg!(reader.read_event())? { | ||
| // Capture defined entities from the DTD inside document and skip that event | ||
| Event::DocType(e) => { | ||
| self.readers.push_back(reader); | ||
| self.capture(e); | ||
| continue; | ||
| } | ||
| // When entity is referenced, create new reader with the same settings as | ||
| // the current reader have and push it to the top of stack. Then try to | ||
| // read next event from it (on next iteration) | ||
| Event::GeneralRef(e) => { | ||
| if let Some(ch) = e.resolve_char_ref()? { | ||
| self.readers.push_back(reader); | ||
| return Ok(Event::Text(BytesText::from_escaped(ch.to_string()))); | ||
| } | ||
| let mut r = Reader::from_reader(self.resolve(&e)?); | ||
| *r.config_mut() = reader.config().clone(); | ||
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| self.readers.push_back(reader); | ||
| self.readers.push_back(r); | ||
| continue; | ||
| } | ||
| // When reader is exhausted, do not return it to the stack | ||
| Event::Eof => continue, | ||
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| // Return all other events to caller | ||
| e => { | ||
| self.readers.push_back(reader); | ||
| return Ok(e); | ||
| } | ||
| } | ||
| } | ||
| return Ok(Event::Eof); | ||
| } | ||
| } | ||
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| /// In this example we use simple regular expression to capture entities from DTD. | ||
| /// In real application you should use DTD parser | ||
| fn capture(&mut self, doctype: BytesText<'i>) { | ||
| let doctype = match doctype.into_inner() { | ||
| Cow::Borrowed(doctype) => doctype, | ||
| Cow::Owned(_) => unreachable!("We are sure that event will be borrowed"), | ||
| }; | ||
| for cap in self.entity_re.captures_iter(doctype) { | ||
| self.entities.insert( | ||
| cap.get(1).unwrap().as_bytes(), | ||
| cap.get(2).unwrap().as_bytes(), | ||
| ); | ||
| } | ||
| } | ||
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| fn resolve(&self, entity: &[u8]) -> Result<&'i [u8], EscapeError> { | ||
| match self.entities.get(entity) { | ||
| Some(replacement) => Ok(replacement), | ||
| None => Err(EscapeError::UnrecognizedEntity( | ||
| 0..0, | ||
| String::from_utf8_lossy(entity).into_owned(), | ||
| )), | ||
| } | ||
| } | ||
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| fn get_entity(&self, entity: &str) -> Option<&'i str> { | ||
| self.entities | ||
| .get(entity.as_bytes()) | ||
| // SAFETY: We are sure that slices are correct UTF-8 because we get | ||
| // them from rust string | ||
| .map(|value| from_utf8(value).unwrap()) | ||
| } | ||
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| fn decoder(&self) -> Decoder { | ||
| self.readers.back().unwrap().decoder() | ||
| } | ||
| } | ||
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| fn main() -> Result<(), Box<dyn std::error::Error>> { | ||
| let mut reader = MyReader::new( | ||
| r#" | ||
| <!DOCTYPE test [ | ||
| <!ENTITY text "hello world" > | ||
| <!ENTITY element1 "<dtd attr = 'Message: &text;'/>" > | ||
| <!ENTITY element2 "<a>&element1;</a>" > | ||
| ]> | ||
| <test label="Message: &text;">'&element2;'</test> | ||
| "#, | ||
| )?; | ||
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| let event = reader.read_event()?; | ||
| assert_eq!( | ||
| event, | ||
| Event::Start(BytesStart::from_content( | ||
| r#"test label="Message: &text;""#, | ||
| 4 | ||
| )) | ||
| ); | ||
| if let Event::Start(e) = event { | ||
| let mut attrs = e.attributes(); | ||
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| let label = attrs.next().unwrap()?; | ||
| assert_eq!(label.key, QName(b"label")); | ||
| assert_eq!( | ||
| label.decode_and_unescape_value_with(reader.decoder(), |ent| reader.get_entity(ent))?, | ||
| "Message: hello world" | ||
| ); | ||
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| assert_eq!(attrs.next(), None); | ||
| } | ||
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| // This is decoded decimal character reference ' | ||
| assert_eq!( | ||
| reader.read_event()?, | ||
| Event::Text(BytesText::from_escaped("'")) | ||
| ); | ||
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| //-------------------------------------------------------------------------- | ||
| // This part was inserted into original document from entity defined in DTD | ||
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| assert_eq!(reader.read_event()?, Event::Start(BytesStart::new("a"))); | ||
| let event = reader.read_event()?; | ||
| assert_eq!( | ||
| event, | ||
| Event::Empty(BytesStart::from_content( | ||
| r#"dtd attr = 'Message: &text;'"#, | ||
| 3 | ||
| )) | ||
| ); | ||
| if let Event::Start(e) = event { | ||
| let mut attrs = e.attributes(); | ||
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| let attr = attrs.next().unwrap()?; | ||
| assert_eq!(attr.key, QName(b"attr")); | ||
| assert_eq!( | ||
| attr.decode_and_unescape_value_with(reader.decoder(), |ent| reader.get_entity(ent))?, | ||
| "Message: hello world" | ||
| ); | ||
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| assert_eq!(attrs.next(), None); | ||
| } | ||
| assert_eq!(reader.read_event()?, Event::End(BytesEnd::new("a"))); | ||
| //-------------------------------------------------------------------------- | ||
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| // This is decoded hexadecimal character reference ' | ||
| assert_eq!( | ||
| reader.read_event()?, | ||
| Event::Text(BytesText::from_escaped("'")) | ||
| ); | ||
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| assert_eq!(reader.read_event()?, Event::End(BytesEnd::new("test"))); | ||
| assert_eq!(reader.read_event()?, Event::Eof); | ||
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| Ok(()) | ||
| } | ||
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Which applications?
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I meant case from #719 here