Change API for providing custom entities

Instead of providing unescaping functions with an entity mapping
via a data structure, instead provide a closure which maps the entity
with replacement text.

Author: dralley

Changelog.md

@@ -109,6 +109,8 @@
   |`read_event_unbuffered`  |`read_event`
   |`read_to_end_unbuffered` |`read_to_end`
 - [#412]: Change `read_to_end*` and `read_text_into` to accept `QName` instead of `AsRef<[u8]>`
+- [#415]: Changed custom entity unescaping API to accept closures rather than a mapping of entity to
+  replacement text. This avoids needing to allocate a map and provides the user with more flexibility.
 
 - [#416]: `BytesStart::to_borrowed` renamed to `BytesStart::borrow`, the same method
   added to all events
@@ -136,6 +138,7 @@
 [#403]: https://github.com/tafia/quick-xml/pull/403
 [#407]: https://github.com/tafia/quick-xml/pull/407
 [#412]: https://github.com/tafia/quick-xml/pull/412
+[#415]: https://github.com/tafia/quick-xml/pull/415
 [#416]: https://github.com/tafia/quick-xml/pull/416
 
 ## 0.23.0 -- 2022-05-08

examples/custom_entities.rs

@@ -7,10 +7,11 @@
 //! * the regex in this example is simple but brittle;
 //! * it does not support the use of entities in entity declaration.
 
+use std::collections::HashMap;
+
 use quick_xml::events::Event;
 use quick_xml::Reader;
 use regex::bytes::Regex;
-use std::collections::HashMap;
 
 const DATA: &str = r#"
 
@@ -27,35 +28,41 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     reader.trim_text(true);
 
     let mut buf = Vec::new();
-    let mut custom_entities = HashMap::new();
+    let mut custom_entities: HashMap<Vec<u8>, String> = HashMap::new();
     let entity_re = Regex::new(r#"<!ENTITY\s+([^ \t\r\n]+)\s+"([^"]*)"\s*>"#)?;
 
     loop {
         match reader.read_event_into(&mut buf) {
             Ok(Event::DocType(ref e)) => {
                 for cap in entity_re.captures_iter(&e) {
-                    custom_entities.insert(cap[1].to_vec(), cap[2].to_vec());
+                    custom_entities.insert(
+                        cap[1].to_vec(),
+                        reader.decoder().decode(&cap[2])?.into_owned(),
+                    );
                 }
             }
             Ok(Event::Start(ref e)) => match e.name().as_ref() {
-                b"test" => println!(
-                    "attributes values: {:?}",
-                    e.attributes()
-                        .map(|a| a
-                            .unwrap()
-                            .unescape_and_decode_value_with_custom_entities(
-                                &reader,
-                                &custom_entities
-                            )
-                            .unwrap())
-                        .collect::<Vec<_>>()
-                ),
+                b"test" => {
+                    let attributes = e
+                        .attributes()
+                        .map(|a| {
+                            a.unwrap()
+                                .unescape_and_decode_value_with_custom_entities(&reader, |ent| {
+                                    custom_entities.get(ent).map(|s| s.as_str())
+                                })
+                                .unwrap()
+                        })
+                        .collect::<Vec<_>>();
+                    println!("attributes values: {:?}", attributes);
+                }
                 _ => (),
             },
             Ok(Event::Text(ref e)) => {
                 println!(
                     "text value: {}",
-                    e.unescape_and_decode_with_custom_entities(&reader, &custom_entities)
+                    e.unescape_and_decode_with_custom_entities(&reader, |ent| custom_entities
+                        .get(ent)
+                        .map(|s| s.as_str()))
                         .unwrap()
                 );
             }

src/escapei.rs

@@ -2,7 +2,6 @@
 
 use memchr;
 use std::borrow::Cow;
-use std::collections::HashMap;
 use std::ops::Range;
 
 #[cfg(test)]
@@ -66,31 +65,15 @@ impl std::error::Error for EscapeError {}
 /// Escapes a `&[u8]` and replaces all xml special characters (<, >, &, ', ") with their
 /// corresponding xml escaped value.
 pub fn escape(raw: &[u8]) -> Cow<[u8]> {
-    #[inline]
-    fn to_escape(b: u8) -> bool {
-        match b {
-            b'<' | b'>' | b'\'' | b'&' | b'"' => true,
-            _ => false,
-        }
-    }
-
-    _escape(raw, to_escape)
+    _escape(raw, |ch| matches!(ch, b'<' | b'>' | b'&' | b'\'' | b'\"'))
 }
 
 /// Should only be used for escaping text content. In xml text content, it is allowed
 /// (though not recommended) to leave the quote special characters " and ' unescaped.
 /// This function escapes a `&[u8]` and replaces xml special characters (<, >, &) with
 /// their corresponding xml escaped value, but does not escape quote characters.
 pub fn partial_escape(raw: &[u8]) -> Cow<[u8]> {
-    #[inline]
-    fn to_escape(b: u8) -> bool {
-        match b {
-            b'<' | b'>' | b'&' => true,
-            _ => false,
-        }
-    }
-
-    _escape(raw, to_escape)
+    _escape(raw, |ch| matches!(ch, b'<' | b'>' | b'&'))
 }
 
 /// Escapes a `&[u8]` and replaces a subset of xml special characters (<, >, &, ', ") with their
@@ -130,32 +113,23 @@ fn _escape<F: Fn(u8) -> bool>(raw: &[u8], escape_chars: F) -> Cow<[u8]> {
 /// Unescape a `&[u8]` and replaces all xml escaped characters ('&...;') into their corresponding
 /// value
 pub fn unescape(raw: &[u8]) -> Result<Cow<[u8]>, EscapeError> {
-    do_unescape(raw, None)
-}
-
-/// Unescape a `&[u8]` and replaces all xml escaped characters ('&...;') into their corresponding
-/// value, using a dictionnary of custom entities.
-///
-/// # Pre-condition
-///
-/// The keys and values of `custom_entities`, if any, must be valid UTF-8.
-pub fn unescape_with<'a>(
-    raw: &'a [u8],
-    custom_entities: &HashMap<Vec<u8>, Vec<u8>>,
-) -> Result<Cow<'a, [u8]>, EscapeError> {
-    do_unescape(raw, Some(custom_entities))
+    unescape_with(raw, |_| None)
 }
 
 /// Unescape a `&[u8]` and replaces all xml escaped characters ('&...;') into their corresponding
-/// value, using an optional dictionary of custom entities.
+/// value, using a resolver function for custom entities.
 ///
 /// # Pre-condition
 ///
-/// The keys and values of `custom_entities`, if any, must be valid UTF-8.
-pub fn do_unescape<'a>(
-    raw: &'a [u8],
-    custom_entities: Option<&HashMap<Vec<u8>, Vec<u8>>>,
-) -> Result<Cow<'a, [u8]>, EscapeError> {
+/// The implementation of `resolve_entity` is expected to operate over UTF-8 inputs.
+pub fn unescape_with<'input, 'entity, F>(
+    raw: &'input [u8],
+    resolve_entity: F,
+) -> Result<Cow<'input, [u8]>, EscapeError>
+where
+    // the lifetime of the output comes from a capture or is `'static`
+    F: Fn(&[u8]) -> Option<&'entity str>,
+{
     let mut unescaped = None;
     let mut last_end = 0;
     let mut iter = memchr::memchr2_iter(b'&', b';', raw);
@@ -171,12 +145,14 @@ pub fn do_unescape<'a>(
 
                 // search for character correctness
                 let pat = &raw[start + 1..end];
-                if let Some(s) = named_entity(pat) {
-                    unescaped.extend_from_slice(s.as_bytes());
-                } else if pat.starts_with(b"#") {
-                    push_utf8(unescaped, parse_number(&pat[1..], start..end)?);
-                } else if let Some(value) = custom_entities.and_then(|hm| hm.get(pat)) {
-                    unescaped.extend_from_slice(&value);
+                if pat.starts_with(b"#") {
+                    let entity = &pat[1..]; // starts after the #
+                    let codepoint = parse_number(entity, start..end)?;
+                    push_utf8(unescaped, codepoint);
+                } else if let Some(value) = named_entity(pat) {
+                    unescaped.extend_from_slice(value.as_bytes());
+                } else if let Some(value) = resolve_entity(pat) {
+                    unescaped.extend_from_slice(value.as_bytes());
                 } else {
                     return Err(EscapeError::UnrecognizedSymbol(
                         start + 1..end,
@@ -1740,18 +1716,20 @@ fn test_unescape() {
 
 #[test]
 fn test_unescape_with() {
-    let custom_entities = vec![(b"foo".to_vec(), b"BAR".to_vec())]
-        .into_iter()
-        .collect();
-    assert_eq!(&*unescape_with(b"test", &custom_entities).unwrap(), b"test");
+    let custom_entities = |ent: &[u8]| match ent {
+        b"foo" => Some("BAR"),
+        _ => None,
+    };
+
+    assert_eq!(&*unescape_with(b"test", custom_entities).unwrap(), b"test");
     assert_eq!(
-        &*unescape_with(b"&lt;test&gt;", &custom_entities).unwrap(),
+        &*unescape_with(b"&lt;test&gt;", custom_entities).unwrap(),
         b"<test>"
     );
-    assert_eq!(&*unescape_with(b"&#x30;", &custom_entities).unwrap(), b"0");
-    assert_eq!(&*unescape_with(b"&#48;", &custom_entities).unwrap(), b"0");
-    assert_eq!(&*unescape_with(b"&foo;", &custom_entities).unwrap(), b"BAR");
-    assert!(unescape_with(b"&fop;", &custom_entities).is_err());
+    assert_eq!(&*unescape_with(b"&#x30;", custom_entities).unwrap(), b"0");
+    assert_eq!(&*unescape_with(b"&#48;", custom_entities).unwrap(), b"0");
+    assert_eq!(&*unescape_with(b"&foo;", custom_entities).unwrap(), b"BAR");
+    assert!(unescape_with(b"&fop;", custom_entities).is_err());
 }
 
 #[test]

src/events/attributes.rs

@@ -3,13 +3,13 @@
 //! Provides an iterator over attributes key/value pairs
 
 use crate::errors::{Error, Result as XmlResult};
-use crate::escape::{do_unescape, escape};
+use crate::escape::{escape, unescape_with};
 use crate::name::QName;
 use crate::reader::{is_whitespace, Reader};
 use crate::utils::{write_byte_string, write_cow_string, Bytes};
 use std::fmt::{self, Debug, Display, Formatter};
 use std::iter::FusedIterator;
-use std::{borrow::Cow, collections::HashMap, ops::Range};
+use std::{borrow::Cow, ops::Range};
 
 /// A struct representing a key/value XML attribute.
 ///
@@ -39,7 +39,7 @@ impl<'a> Attribute<'a> {
     ///
     /// See also [`unescaped_value_with_custom_entities()`](Self::unescaped_value_with_custom_entities)
     pub fn unescaped_value(&self) -> XmlResult<Cow<[u8]>> {
-        self.make_unescaped_value(None)
+        self.unescaped_value_with_custom_entities(|_| None)
     }
 
     /// Returns the unescaped value, using custom entities.
@@ -55,18 +55,11 @@ impl<'a> Attribute<'a> {
     /// # Pre-condition
     ///
     /// The keys and values of `custom_entities`, if any, must be valid UTF-8.
-    pub fn unescaped_value_with_custom_entities(
-        &self,
-        custom_entities: &HashMap<Vec<u8>, Vec<u8>>,
-    ) -> XmlResult<Cow<[u8]>> {
-        self.make_unescaped_value(Some(custom_entities))
-    }
-
-    fn make_unescaped_value(
-        &self,
-        custom_entities: Option<&HashMap<Vec<u8>, Vec<u8>>>,
-    ) -> XmlResult<Cow<[u8]>> {
-        do_unescape(&*self.value, custom_entities).map_err(Error::EscapeError)
+    pub fn unescaped_value_with_custom_entities<'s, 'entity>(
+        &'s self,
+        resolve_entity: impl Fn(&[u8]) -> Option<&'entity str>,
+    ) -> XmlResult<Cow<'s, [u8]>> {
+        unescape_with(&*self.value, resolve_entity).map_err(Error::EscapeError)
     }
 
     /// Decode then unescapes the value
@@ -80,7 +73,7 @@ impl<'a> Attribute<'a> {
     /// [`unescaped_value()`]: Self::unescaped_value
     /// [`Reader::decoder().decode()`]: crate::reader::Decoder::decode
     pub fn unescape_and_decode_value<B>(&self, reader: &Reader<B>) -> XmlResult<String> {
-        self.do_unescape_and_decode_value(reader, None)
+        self.unescape_and_decode_value_with_custom_entities(reader, |_| None)
     }
 
     /// Decode then unescapes the value with custom entities
@@ -97,23 +90,13 @@ impl<'a> Attribute<'a> {
     /// # Pre-condition
     ///
     /// The keys and values of `custom_entities`, if any, must be valid UTF-8.
-    pub fn unescape_and_decode_value_with_custom_entities<B>(
+    pub fn unescape_and_decode_value_with_custom_entities<'entity, B>(
         &self,
         reader: &Reader<B>,
-        custom_entities: &HashMap<Vec<u8>, Vec<u8>>,
-    ) -> XmlResult<String> {
-        self.do_unescape_and_decode_value(reader, Some(custom_entities))
-    }
-
-    /// The keys and values of `custom_entities`, if any, must be valid UTF-8.
-    fn do_unescape_and_decode_value<B>(
-        &self,
-        reader: &Reader<B>,
-        custom_entities: Option<&HashMap<Vec<u8>, Vec<u8>>>,
+        resolve_entity: impl Fn(&[u8]) -> Option<&'entity str>,
     ) -> XmlResult<String> {
         let decoded = reader.decoder().decode(&*self.value)?;
-
-        let unescaped = do_unescape(decoded.as_bytes(), custom_entities)?;
+        let unescaped = unescape_with(decoded.as_bytes(), resolve_entity)?;
         Ok(String::from_utf8(unescaped.into_owned())?)
     }
 }